| 1. |
- Ibron, Christian, et al.
(författare)
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Numerical simulation of a mixed-mode reaction front in a PPC engine
- 2021. - 4
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38, s. 5703-5711
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Konferensbidrag (refereegranskat)abstract
- The ignition process, mode of combustion and reaction front propagation in a partially premixed combustion (PPC) engine running with a primary reference fuel (87 vol% iso-octane, 13 vol% n-heptane) were investigated numerically in a large eddy simulation (LES). A one-equation sub-grid scale model coupled to the partially stirred reactor model and a finite rate chemical model were used in LES. Different combustion modes, ignition front propagation, premixed flame and non-premixed flame, were observed simultaneously. Displacement speed of CO iso-surface propagation described the transition of premixed auto-ignition to non-premixed flame. High temporal resolution optical data of CH2O and chemiluminescence were compared with simulated results. A high-speed ignition front was found to expand through fuel-rich mixture and stabilize around stoichiometry in a non-premixed flame while lean premixed combustion occurs in the spray wake at a much slower pace. A good qualitative agreement of the distribution of chemiluminescence and CH2O formation and destruction indicated that the simulation approach sufficiently captures the driving physics of mixed-mode combustion in PPC engines. The transition from auto-ignition to flame occurs over a period of several crank angles and the reaction front propagation can be captured using the described model.
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| 2. |
- Lundgren, Marcus Olof, et al.
(författare)
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Effects of Post-Injections Strategies on UHC and CO at Gasoline PPC Conditions in a Heavy-Duty Optical Engine
- 2017
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; 2017:March
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Tidskriftsartikel (refereegranskat)abstract
- Gasoline partially premixed combustion (PPC) has shown potential in terms of high efficiency with low emissions of oxides of nitrogen (NOx) and soot. Despite these benefits, emissions of unburned hydrocarbons (UHC) and carbon monoxide (CO) are the main shortcomings of the concept. These are caused, among other things, by overlean zones near the injector tip and injector dribble. Previous diesel low temperature combustion (LTC) research has demonstrated post injections to be an effective strategy to mitigate these emissions. The main objective of this work is to investigate the impact of post injections on CO and UHC emissions in a quiescent (non-swirling) combustion system. A blend of primary reference fuels, PRF87, having properties similar to US pump gasoline was used at PPC conditions in a heavy duty optical engine. The start of the main injection was maintained constant. Dwell and mass repartition between the main and post injections were varied to evaluate their effect. All points were run at 7 bar IMEPg. High-speed imaging of the natural combustion luminescence was performed together with measurements of performance and engine out emissions. Results show reduction in both CO and UHC with close coupled injections. A large close coupled post injection show the largest reduction in UHC. Analysis show that a post injection prior to combustion reduces the dribble and increases the recirculation in the downstream region of the fuel jet, hence reaching more of the UHC in the area near the injector. General observations show that the partition of fuel between the injections have the largest impact on the CO while the dwell time affects UHC emissions. Injector dribble seems to be a significant contributor to the UHC emissions.
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| 3. |
- Lundgren, Marcus, et al.
(författare)
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Optical study on combustion transition from HCCI to PPC with gasoline compression ignition in a HD engine
- 2016. - April
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Ingår i: SAE 2016 World Congress and Exhibition. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. ; 2016-April
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Konferensbidrag (refereegranskat)abstract
- The partially premixed combustion (PPC) concept has shown high efficiency with low soot emissions. However, the in-cylinder phenomena are still to be explained and evaluated for further progress in the research. This work studies the start of combustion process during a transition from homogenous charge compression ignition (HCCI) to PPC. The process is visualized using a heavy-duty, non-swirling engine modified for optical access. High speed video was used to capture the natural luminosity of the combustion. The fuel used was PRF87. Single and double injection strategies were used at a load kept to the moderate level of 7.5 bar IMEPg. Single injections were swept from early HCCI to retarded PPC conditions whilst running a cycle to cycle temperature sweep, to capture the effect of injection timing and temperature differences simultaneously. Results show that retarded injections show less cycle-to-cycle variation due to temperature variations. Advanced in-bowl injections show a stochastic behavior in the location of the first combustion, due to large variations in local fuel rich zones. For the double injection case the main injection cools the bulk temperature and hence delays the start of combustion before igniting in the fuel rich zones.
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| 4. |
- Wang, Zhenkan, et al.
(författare)
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Simultaneous 36 kHz PLIF/chemiluminescence imaging of fuel, CH2O and combustion in a PPC engine
- 2019
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:4, s. 4751-4758
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Tidskriftsartikel (refereegranskat)abstract
- The requirements on high efficiency and low emissions of internal combustion engines (ICEs) raise the research focus on advanced combustion concepts, e.g., premixed-charge compression ignition (PCCI), partially premixed compression ignition (PPCI), reactivity controlled compression ignition (RCCI), partially premixed combustion (PPC), gasoline compression ignition (GCI) etc. In the present study, an optically accessible engine is operated in PPC mode, featuring compression ignition of a diluted, stratified charge of gasoline-like fuel injected directly into the cylinder. A high-speed, high-power burst-mode laser system in combination with a high-speed CMOS camera is employed for diagnostics of the autoignition process which is critical for the combustion phasing and efficiency of the engine. To the authors' best knowledge, this work demonstrates for the first time the application of the burst-system for simultaneous fuel tracer planar laser induced fluorescence (PLIF) and chemiluminescence imaging in an optical engine, at 36 kHz repetition rate. In addition, high-speed formaldehyde PLIF and chemiluminescence imaging are employed for investigation of autoignition events with a high temporal resolution (5 frames/CAD). The development of autoignition together with fuel or CH2O distribution are simultaneously visualized using a large number of consecutive images. Prior to the onset of combustion the majority of both fuel and CH2O are located in the recirculation zone, where the first autoignition also occurs. The ability to record, in excess of 100 PLIF images, in a single cycle brings unique possibilities to follow the in-cylinder processes without the averaging effects caused by cycle-to-cycle variations.
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| 5. |
- Wang, Zhenkan, et al.
(författare)
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Ultra-High Speed Fuel Tracer PLIF Imaging in a Heavy-Duty Optical PPC Engine
- 2018
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; 2018-April
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Tidskriftsartikel (refereegranskat)abstract
- In order to meet the requirements in the stringent emission regulations, more and more research work has been focused on homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) or partially premixed compression ignition (PCCI) as they have the potential to produce low NOx and soot emissions without adverse effects on engine efficiency. The mixture formation and charge stratification influence the combustion behavior and emissions for PPC/PCCI, significantly. An ultra-high speed burst-mode laser is used to capture the mixture formation process from the start of injection until several CADs after the start of combustion in a single cycle. To the authors' best knowledge, this is the first time that such a high temporal resolution, i.e. 0.2 CAD, PLIF could be accomplished for imaging of the in-cylinder mixing process. The capability of resolving single cycles allows for the influence of cycle-to-cycle variations to be eliminated. This ability to study individual cycles aids the understanding of the mixture formation process as well as the cycle-to-cycle variations. Strong air entrainment at the boundary layer can be clearly observed and followed as the mixing process progresses. The formation of eddies created by the shear force and their rotational motion can be continuously observed during the mixing process. The interaction between two adjacent spray plumes in the recirculation zone is well captured and studied. In addition, the mixing process resulting in the stratified fuel charge being located in the recirculation zone before the SOC while the areas along the original spray axis are leaned out after the end of injection, can be followed in one time sequence. Moreover, the auto-ignition position and early flame development can be studied, from the high-speed chemiluminescence imaging, together with the fuel distribution in the combustion chamber.
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| 6. |
- Abou Nada, Fahd Jouda, et al.
(författare)
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A first application of thermographic phosphors in a marine two-stroke diesel engine for surface temperature measurement
- 2014
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Ingår i: Proceedings of the ASME 2014 Internal Combustion Engine Division Fall Technical Conference (ICEF2014). ; , s. 001-001
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Konferensbidrag (refereegranskat)abstract
- Phosphor thermometry is applied for the first time in a large-bore two-stroke diesel engine. The work proves the practicality of phosphor thermometry in large-bore engines. The experiments were conducted on the MAN 4T50ME-X marine research engine equipped with an optical cylinder head. By employing a thin surface coating of CdWO4 phosphor, cycle resolved temperature measurements of the cylinder wall were obtained. Motored and fired engine operations were tested at engine loads covering the low and medium engine load range. Phosphor thermometry proved to be successful in retrieving the temperature with standard deviations ranging around 1-8 K. Experimental considerations like detector linearity, coating thickness and an automated phosphor calibration routine will be addressed.
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| 7. |
- Abou Nada, Fahd Jouda, et al.
(författare)
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Development of an automatic routine for calibration of thermographic phosphors
- 2014
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Ingår i: Measurement Science & Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- An automated routine for the continuous calibration of thermographic phosphors was developed as a replacement for the conventional calibration scheme that relied on fixed temperature points. The automated calibration routine was validated using Mg 3 F 2 GeO 4 :Mn as a calibration phosphor. Hardware and software aspects of the calibration process were addressed in this development. The hardware aspect included a new substrate design using a high performance alloy, the Hastelloy-C alloy, whereas the software aspect included an automated acquisition system which was capable of acquiring simultaneous thermocouple temperatures and phosphor decay waveform in real time. The design of the calibration process eliminates the need for a system in thermal equilibrium during a phosphor calibration measurement. Temperature ramping rates of up to 4 K min −1 were employed in the oven without a delay in the temperature response being measured between the phosphor and the thermocouples involved. In addition, the automated calibration setup allowed for detailed investigations on the effect of heat being delivered to the phosphor coating by the laser. These findings were confirmed by a simple heat transfer model, based on lumped system analysis. In comparison to the data acquisition performed at several fixed points with the conventional calibration scheme, the experiment duration was shortened by a factor of 4 with the overall accuracy improved by 1–2 K.
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| 8. |
- Abou Nada, Fahd Jouda, et al.
(författare)
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Improved measurement precision in decay time‑based phosphor thermometry
- 2016
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 1432-0649 .- 0946-2171. ; 122
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Tidskriftsartikel (refereegranskat)abstract
- This study comprises a continuation of the previous efforts of the authors to characterize different sources of errors in phosphor thermometry based on the determination of luminescence decays from thermographic phosphors. Whereas earlier investigations focused on point detectors utilizing different sensor technology, this work presents a comparison of four PMTs that are identical in terms of their product type. These detectors are supposedly identical, but the investigations revealed that their response is strictly individual. This study also shows a linear excitation energy dependence for the decay time of cadmium tungstate (CdWO4), the phosphor being used in this work. In addition, the potential influence of the intense and short fluorescence peak preceding the weaker and longer exponential decay in some phosphor materials, was investigated using the electrical signal gating capability of the PMT. Finally, the evaluated decay time also appeared to be affected by the oscilloscope settings used when recording the phosphorescence signals. The presented results indicate that all operating parameters from the calibration measurement need to be rigorously reproduced in order to avoid systematic temperature errors in phosphor thermometry experiments that are based on reproducible measurements of the decay time. These results should be of more general interest also outside the phosphor community as the findings, presented herein, in principal concern all kinds of measurements that are dependent on reproducible measurements of signal shapes or time-transients.
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| 9. |
- Abou Nada, Fahd Jouda, et al.
(författare)
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Investigation of the effect of engine lubricant oil on remote temperature sensing using thermographic phosphors
- 2016
-
Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 179, s. 568-573
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Tidskriftsartikel (refereegranskat)abstract
- Phosphor thermometry, a remote temperature sensing technique, is widely implemented to measure the temperature of different combustion engines components. The presence of engine lubricant can influence the behavior of the applied sensor materials, known as thermographic phosphors, and thus leading to erroneous temperature measurements. The effect of two engine lubricants on decay times originating from six different thermographic phosphors was investigated. The decay time of each thermographic phosphor was investigated as a function of lubricant/phosphor mass ratio. Tests were conducted at temperatures around 293 K and 376 K for both lubricants. The investigations revealed that ZnO:Zn and ZnS:Ag are the only ones that exhibit a change of the decay time as function of the lubricant/phosphor mass ratio. While the remaining thermographic phosphors, namely BaMg2Al16O27:Eu (BAM), Al2O3-coated BaMg2Al16O27:Eu, La2O2S:Eu, Mg3F2GeO4:Mn, displayed no sensitivity of their characteristic decay time on to the presence of lubricant on the porous coating. Biases in the calculated temperature are to be expected if the utilized thermographic phosphor displays decay time sensitivity to the existence of the engine lubricant within the sensor. Such distortions are concealed and can occur undetected leading to false temperature readings for the probed engine component.
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| 10. |
- Abou Nada, Fahd Jouda, et al.
(författare)
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On the automation of thermographic phosphor calibration
- 2014
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Ingår i: Proceedings of the 60th International Instrumentation Symposium.
-
Konferensbidrag (refereegranskat)abstract
- Thermographic phosphors can be robust temperature remote sensors. The accuracy of the temperature measured by the phosphor is highly dependent on the quality of the phosphor calibration used. Conventionally, thermographic phosphors are calibrated by measuring a series of decay curves at known stable oven temperatures. The process is then repeated covering the thermal sensitivity range of the phosphor chosen. Heating and cooling rates of high temperature ovens are usually low. Also, thermal equilibrium of the system is required at each calibration temperature before acquiring luminescence decay curves. Thus, the process is usually time consuming and the number of calibration points achieved is limited to a couple of dozen points. This study presents and validates the development of an automatic routine for the calibration of thermographic phosphors. It was designed to continuously and simultaneously acquire phosphor decay curves along with their corresponding thermocouple temperatures. The developed routine required software and hardware improvements. An updated design of the calibration substrate was implemented to improve the thermal conditions during calibration. Thermal gradients were further studied using a heat transfer model. The routine implemented a specially designed sparsing algorithm that reduced the sampling rate of the decaying luminescence curve without influencing the calculated decay time. The upper heating rate is set at 4 K.min-1 due to limitation imposed by the ceramic calibration oven. The phosphors CdWO4 and Mg3F2GeO4:Mn were chosen to validate the finalized routine. After the completion of the calibration process, a library-based calibration is created as the final product. The automated calibration routine delivered an overall accuracy improvement of 1-2 K, reduced calibration duration by factor of four and provided the possibility of deriving signal recognition algorithms. The condensed calibration dataset produced by the proposed calibration routine was further employed to develop a novel signal shape recognition algorithm for temperature evaluation.
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| 11. |
- Abou Nada, Fahd Jouda, et al.
(författare)
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Remote temperature sensing on and beneath atmospheric plasma sprayed thermal barrier coatings using thermographic phosphors
- 2016
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 302, s. 359-367
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Tidskriftsartikel (refereegranskat)abstract
- Investigations on remote temperature sensing of yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) at the surface and at the bond-coat/top-coat interface were carried out. Using Y2O3:Eu thermographic phosphor as an embedded temperature sensing layer, sub-surface temperature probing through 300 μm of atmospheric plasma sprayed YSZ is demonstrated. The Y2O3:Eu thermographic phosphor displays a temperature sensitivity ranging between 400 °C up to a maximum of 900 °C when utilizing the luminescence originating from the 611 nm emission band. Dysprosium stabilized zirconia (10 wt.% DySZ), a TBC material, is also investigated and established as a temperature sensor from 400 °C up to a temperature of 1000 °C using both the intensity decay time and emission intensity ratio methods. In addition, the luminescence of presumed optically inactive YSZ materials was spectroscopically investigated in terms of optical interferences caused by impurities. A validation temperature probing measurement through 300 μm of YSZ top-coat was successfully performed in a SGT-800 Siemens burner running at six different operating conditions in an atmospheric combustion rig.
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| 12. |
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| 13. |
- Aldén, Marcus, et al.
(författare)
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Development and application of high-speed laser visualization techniques in combustion research
- 2017
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Ingår i: The Micro-World Observed by Ultra High-Speed Cameras : We See What You Don't See - We See What You Don't See. - Cham : Springer International Publishing. - 9783319614908 - 9783319614915 ; , s. 241-259
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Bokkapitel (refereegranskat)abstract
- In order to fulfil the requirements of available energy resources, there is a great need to obtain a sustainable and environmentally friendly energy utilization using combustion processes. In order to do this, it is of utmost importance to utilize non-intrusive diagnostic techniques with high spatial and temporal resolution which can characterize the combustion process and also validate combustion models. During the last decades different laser techniques have proven to fulfil these requirements. A special requirement in practical applications when highly turbulent flames are to be investigated, is to be able to follow the phenomena in time, i.e. it is important to develop and apply high speed laser diagnostics. In the present chapter we are describing the use of high speed lasers together with high speed detectors which make it possible to probe in two dimensions even the fastest combustion phenomena in real time. The chapter is describing the use of a so called Multi YAG laser which together with a framing camera is able to record up to eight images. Also the use of a high repetition rate laser and a high power burst laser together with CMOS cameras and their application for studies of turbulent combustion phenomena are described. The examples are mainly taken from the author's laboratory and include more academic studies of turbulent flames but also practical applications in engines.
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| 14. |
- Aldén, Marcus, et al.
(författare)
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Laser-induced phosphorescence spectroscopy: development and application of thermographic phosphors (TP) for thermometry in combustion environments
- 2014
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Ingår i: Laser Spectroscopy for Sensing Fundamentals, Techniques and Applications. - : Elsevier. - 2050-1501. - 9780857092731 - 9780857098733 ; , s. 258-291
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Bokkapitel (refereegranskat)abstract
- In this chapter a temperature probing technique based on the spectroscopy of inorganic luminescent materials is described and exemplified in experiments related to combustion. The basic features of thermographic phosphors which enable remote temperature diagnostics to be performed with a high degree of sensitivity and accuracy, are outlined. This technique is superior to those based on thermocouples and pyrometry, particularly in the vicinity of flames and when the measured surface is subjected to random movements. Many thermographic phosphors have the property of being insensitive to variations in pressure up to 1 GPa. This property extends the use and development of thermographic thermometry to such domains as internal combustion engines and gas turbines, for which examples are also provided.
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| 15. |
- Aldén, Marcus, et al.
(författare)
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Thermographic phosphors for thermometry: A survey of combustion applications
- 2011
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Ingår i: Progress in Energy and Combustion Science. - : Elsevier BV. - 0360-1285. ; 37:4, s. 422-461
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Forskningsöversikt (refereegranskat)abstract
- Temperature is a fundamental thermodynamic parameter used to describe physical, chemical and biological processes. In combustion as in many other applications, knowledge about temperature plays a substantial role in helping to maintain an efficient and clean environment Being able to measure temperature accurately in combustion and in fire-related applications is important for giving a better understanding of heat transfer phenomena and improving existing models. In the present review paper a method based on the spectroscopy of inorganic luminescent materials is described and exemplified in experiments related to combustion. The method involves the use of thermographic phosphors which enable remote temperature diagnostics to be performed with a high degree of sensitivity and accuracy. The technique is superior to those based on thermocouples and pyrometry, particularly in the vicinity of flames and when the measured surface is subjected to random movements. Several phosphor materials suitable for temperature probing are described. The application of thermographic phosphors to temperature measurements in one-point and in two-dimensions in flame spread scenarios, and in pyrolysis experiments involving different construction materials and polymers are described. Many thermographic phosphors have the property of being insensitive to variations in pressure up to 1 GPa. This property extends the use and development of thermographic thermometry to other domains, such as internal combustion engines. The temperature has been measured in a point and in two-dimensions inside the combustion chamber. The complex procedures required to implement the use of thermocouples on moving objects inside an engine make thermocouples an expensive choice. It also limits the possibilities of altering the measurement locations and thereby also complicating the investigation of different engine geometries and components. Thermographic phosphors have also been employed in gas turbine applications. Temperature probing in the afterburner of a full-size aircraft engine is described with the aim to study the effects of various engine loads on the wall temperature. Furthermore, the application of thermographic phosphors to study the temperature of droplets in relation to sprays is described. In spray dynamics, temperature is a crucial parameter for gaining an understanding of atomisation, evaporation and heat convection from the surrounding gases. Finally the application of thermographic phosphors for gas temperature measurement by seeding the particles into a gas flow is described together with the challenges associated with seeding the particles for in-situ flame measurements. (C) 2010 Published by Elsevier Ltd.
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| 16. |
- Aldén, Marcus, et al.
(författare)
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Visualization and understanding of combustion processes using spatially and temporally resolved laser diagnostic techniques
- 2011
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 33, s. 69-97
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Forskningsöversikt (refereegranskat)abstract
- Laser diagnostic techniques have for more than 30 years added very valuable input for a deepened understanding of combustion processes. The present paper will focus on techniques developed for visualization of important parameters with the ability to get detailed information in space and time. The paper is not meant to be a complete review of the entire research field but rather a survey with a majority of the contributions from the authors' laboratory. After a short introduction and background, essentially three techniques will be highlighted. Planar Laser-Induced Fluorescence, PLIF, will be described in terms of further development directed towards the use of a high-power Alexandrite laser, in some cases yielding a substantially increased sensitivity as compared to the more conventional Nd:YAG and Excimer lasers. There will also be a description of possibilities for high-speed visualization, 3D imaging and the potential to visualize species requiring a two-photon excitation process. Regarding thermometry, the paper will describe and exemplify the use of Thermographic Phosphors, mainly for surface measurements but also in droplets and gas flows. The third area to be described is the use of Polarization Spectroscopy, PS, for spatially and temporally resolved measurements in the IR spectral region, e. g. CO2 and H2O, various hydrocarbons, HCl and HCN. The last chapter focuses on present challenges and future applications. A major challenge is diagnostics in environments with limited optical access. Two methods that are applicable under such conditions are discussed, namely endoscopic approaches and picosecond LIDAR. Another challenging area addressed is application of diagnostics in optically dense environments, e. g. sprays, where a new technique, Structured Laser Illumination Planar Imaging, SLIPI, has been developed for suppressing the influence of multiple scattering. Finally, approaches for measurements of "new" species, challenges associated with LIF quantification, as well as measurements in environments possessing strong background radiation are discussed. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 17. |
- Algotsson, Martin, et al.
(författare)
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In-cylinder Surface Thermometry using Laser Induced Phosphorescence
- 2012
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Ingår i: [Host publication title missing]. ; , s. 482-487
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Konferensbidrag (refereegranskat)abstract
- Surface temperature in internal combustion engines is of high interest when studying heat losses. Two approaches for retrieving the surface temperatures are thermocouples and Laser Induced Phosphorescence, LIP. This study aims to analyze LIP as a technique for measuring surface temperature in internal combustion engines. The motivation for this study is the need for accurate surface temperatures which can be used by predictive models and increase knowledge about heat transfer. In this work LIP measurements have been carried out in two optical engines. In the first engine a thermographic phosphor was applied on top of a metal piston. The second engine was fitted with a quartz liner which was coated with phosphor material. Several coating thicknesses have been tested and the LIP temperature was extracted from both opposing sides of the phosphor. Both engines were run in HCCI mode with reference fuels and electrically heated air. In a previous publication, the authors showed that a layer of phosphor can show different temperatures i.e. a higher temperature on the side facing the cylinder gas than on the side facing the wall. In this study it is shown which thickness is needed to accurately present the temperature for typical engine combustion. With an increasing thickness of the phosphor material, the surface gets gradually insulated and the phosphor temperature reading becomes inaccurate. LIP measurements from a quartz ring and a metal piston have been compared and the temperature increase during combustion is similar although the heat conductivity of quartz is 40-200 times smaller than the metal piston. Measurements with thermocouples often show a lower temperature increase than what is seen in the LIP results. The difference in heat conductivity between the phosphor coating and the underlying surface is of importance for understanding what temperature is actually measured.
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| 18. |
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| 19. |
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| 20. |
- Askmyr, Maria, et al.
(författare)
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Modeling chronic myeloid leukemia in immunodeficient mice reveals expansion of aberrant mast cells and accumulation of pre-B cells.
- 2014
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Ingår i: Blood Cancer Journal. - : Springer Science and Business Media LLC. - 2044-5385. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm that, if not treated, will progress into blast crisis (BC) of either myeloid or B lymphoid phenotype. The BCR-ABL1 fusion gene, encoding a constitutively active tyrosine kinase, is thought to be sufficient to cause chronic phase (CP) CML, whereas additional genetic lesions are needed for progression into CML BC. To generate a humanized CML model, we retrovirally expressed BCR-ABL1 in the cord blood CD34(+) cells and transplanted these into NOD-SCID (non-obese diabetic/severe-combined immunodeficient) interleukin-2-receptor γ-deficient mice. In primary mice, BCR-ABL1 expression induced an inflammatory-like state in the bone marrow and spleen, and mast cells were the only myeloid lineage specifically expanded by BCR-ABL1. Upon secondary transplantation, the pronounced inflammatory phenotype was lost and mainly human mast cells and macrophages were found in the bone marrow. Moreover, a striking block at the pre-B-cell stage was observed in primary mice, resulting in an accumulation of pre-B cells. A similar block in B-cell differentiation could be confirmed in primary cells from CML patients. Hence, this humanized mouse model of CML reveals previously unexplored features of CP CML and should be useful for further studies to understand the disease pathogenesis of CML.
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| 21. |
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| 22. |
- Berrocal, Edouard, et al.
(författare)
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Application of structured illumination for multiple scattering suppression in planar laser imaging of dense sprays.
- 2008
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Ingår i: Optics Express. - 1094-4087. ; 16:22, s. 17870-17881
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Tidskriftsartikel (refereegranskat)abstract
- A novel approach to reduce the multiple light scattering contribution in planar laser images of atomizing sprays is reported. This new technique, named Structured Laser Illumination Planar Imaging (SLIPI), has been demonstrated in the dense region of a hollow-cone water spray generated in ambient air at 50 bars injection pressure. The idea is based on using an incident laser sheet which is spatially modulated along the vertical direction. By properly shifting the spatial phase of the modulation and using post-processing of the successive recorded images, the blurring effects from multiple light scattering can be mitigated. Since hollow-cone sprays have a known inner structure in the central region, the efficiency of the method could be evaluated. We demonstrate, for the case of averaged images, that an unwanted contribution of 44% of the detected light intensity can be removed. The suppression of this diffuse light enables an increase from 55% to 80% in image contrast. Such an improvement allows a more accurate description of the near-field region and of the spray interior. The possibility of extracting instantaneous flow motion is also shown, here, for a dilute flow of water droplets. These results indicate promising applications of the technique to denser two-phase flows such as air-blast atomizer and diesel sprays.
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| 23. |
- Berrocal, Edouard, et al.
(författare)
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Multiple Scattering Suppression In Planar Laser Imaging Of Dense Sprays By Means Of Structured Illumination
- 2010
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Ingår i: Atomization and Sprays. - 1044-5110 .- 1936-2684. ; 20:2, s. 133-139
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Tidskriftsartikel (refereegranskat)abstract
- A novel method to reduce the multiply scattered light contribution to images recorded with planar laser imaging is demonstrated. The technique, structured laser illumination planar imaging (SLIPI), is based on spatially modulated excitation light and is tested here within the dense region of a hollow-cone spray. The main idea is to use a laser sheet that is spatially modulated along the vertical direction. By both shifting the spatial phase of the modulation and using adequate image post processing of the successive recorded images, it is possible to remove a significant amount of the multiply scattered light detected. In this paper, SLIPI is applied for imaging within a typical hollow-cone water spray generated in ambient air at 50 bars injection pressure from a pressure-swirl nozzle. Because this type of spray has a known inner structure, the method can be evaluated, demonstrating that 47% of the detected light arising from multiple scattering can be suppressed, resulting in an increase from 61% to 89 % in image contrast. Such an improvement allows more accurate interpretation and analysis of the near-field region of atomizing sprays. The possibility of extracting instantaneous flow motion is also demonstrated for the case of a dilute nebulizer. All these results indicate promising applications of the technique in denser turbid media, such as air-blast atomizer or diesel sprays.
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| 24. |
- Brackmann, Christian, et al.
(författare)
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Picosecond excitation for reduction of photolytic effects in two-photon laser-induced fluorescence of CO
- 2013
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 34, s. 3541-3548
-
Tidskriftsartikel (refereegranskat)abstract
- Two-photon laser-induced fluorescence for detection of carbon monoxide (CO) frequently shows interferences by emission from photolytically produced C-2 radicals encountered under fuel-rich combustion conditions. Reduced C-2 interference for excitation with laser pulses in the picosecond regime is here demonstrated by comparison with excitation using nanosecond pulses for measurements in laminar premixed ethene-air flames. Compared with nanosecond pulses of 8 ns duration and 4 mJ pulse energy, picosecond pulses of 80 ps duration and around 0.5 mJ pulse energy gave similar to 10 times higher peak power, which allowed for efficient CO excitation and resulted in stronger signal with lower C-2 interference. CO fluorescence with picosecond excitation showed a linear to quadratic power dependence, indicating photoionization, whereas a more quadratic dependence was found for the C-2 interference. A sub-nanosecond effective lifetime of CO resulted in a rapid fluorescence decay compared with C-2 and allowed for efficient reduction in C-2 interference by minimizing the detection gate. In addition, interference compensation using time-resolved detection could be demonstrated. Altogether, picosecond pulses provide efficient two-photon excitation of CO in terms of signal strength as well as reduced C-2 interference. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 25. |
- Chartier, Clement, et al.
(författare)
-
Air-Entrainment in Wall-Jets Using SLIPI in a Heavy-Duty Diesel Engine
- 2012
-
Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3936 .- 1946-3944. ; 5:4, s. 1684-1692
-
Tidskriftsartikel (refereegranskat)abstract
- Mixing in wall-jets was investigated in an optical heavy-duty diesel engine with several injector configurations and injection pressures. Laser-induced fluorescence (LIF) was employed in non-reacting conditions in order to quantitatively measure local equivalence ratios in colliding wall-jets. A novel laser diagnostic technique, Structured Laser Illumination Planar Imaging (SLIPI), was successfully implemented in an optical engine and permits to differentiate LIF signal from multiply scattered light. It was used to quantitatively measure local equivalence ratio in colliding wall-jets under non-reacting conditions. Mixing phenomena in wall-jets were analyzed by comparing the equivalence ratio in the free part of the jet with that in the recirculation zone where two wall-jets collide. These results were then compared to φ predictions for free-jets. It was found that under the conditions tested, increased injection pressure did not increase mixing in the wall-jets. Comparisons with free-jet predictions further indicated that mixing in wall-jets is less effective than in free-jets for identical conditions and downstream distances. The confined nature of the wall-jet in the optical engine is suspected to be the reason for these observations. A rapid leaning-out of the jet after end of injection was observed for all cases, but this enhanced mixing was not transmitted to the wall-jet.
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| 26. |
- Chartier, Clement, et al.
(författare)
-
Analysis of Smokeless Spray Combustion in a Heavy-Duty Diesel Engine by Combined Simultaneous Optical Diagnostics
- 2009
-
Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; 2009-01-1353
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A heavy-duty diesel engine operating case producing no engine-out smoke was studied using combined simultaneous optical diagnostics. The case was close to a typical low-load modern diesel operating point without EGR. Parallels were drawn to the conceptual model by Dec and results from high-pressure combustion vessels. Optical results revealed that no soot was present in the upstream part of the jet cross-section. Soot was only observed in the recirculation zones close to the bowl perimeter. This indicated very slow soot formation and was explained by a significantly higher air entrainment rate than in Dec's study. The local fuel-air equivalence ratio, Φ, at the lift-off length was estimated to be 40% of the value in Dec's study. The lower Φ in the jet produced a different Φ-T history, explaining the soot results. The increased air entrainment rate was mainly due to smaller nozzle holes and increased TDC density. Furthermore, increased injection pressure was believed to reduce the residence time in the jet, thus reducing the soot formation. OH was detected at the periphery of the jet, upstream of the location where fuel started to react on the jet centerline. The OH region extended relatively far into the jet, further supporting the conclusion of a less fuel-rich jet in the current case. Partially oxidized fuel (POF) was found at the center of the jet, downstream of the lift-off position. This indicated that the temperature needed to start chemical reactions inside the jet had not been obtained at the lift-off position. The high-temperature reaction zone at the periphery thus added heat over a distance before POF was observed on the centerline.
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| 27. |
- Choong, FX, et al.
(författare)
-
Real-time optotracing of curli and cellulose in live Salmonella biofilms using luminescent oligothiophenes
- 2016
-
Ingår i: NPJ biofilms and microbiomes. - : Springer Science and Business Media LLC. - 2055-5008. ; 2, s. 16024-
-
Tidskriftsartikel (refereegranskat)abstract
- Extracellular matrix (ECM) is the protein- and polysaccharide-rich backbone of bacterial biofilms that provides a defensive barrier in clinical, environmental and industrial settings. Understanding the dynamics of biofilm formation in native environments has been hindered by a lack of research tools. Here we report a method for simultaneous, real-time, in situ detection and differentiation of the Salmonella ECM components curli and cellulose, using non-toxic, luminescent conjugated oligothiophenes (LCOs). These flexible conjugated polymers emit a conformation-dependent fluorescence spectrum, which we use to kinetically define extracellular appearance of curli fibres and cellulose polysaccharides during bacterial growth. The scope of this technique is demonstrated by defining biofilm morphotypes of Salmonella enterica serovars Enteritidis and Typhimurium, and their isogenic mutants in liquid culture and on solid media, and by visualising the ECM components in native biofilms. Our reported use of LCOs across a number of platforms, including intracellular cellulose production in eukaryotic cells and in infected tissues, demonstrates the versatility of this optotracing technology, and its ability to redefine biofilm research.
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| 28. |
- Choong, Ferdinand X., et al.
(författare)
-
Nondestructive, real-time determination and visualization of cellulose, hemicellulose and lignin by luminescent oligothiophenes
- 2016
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- Enabling technologies for efficient use of the bio-based feedstock are crucial to the replacement of oil-based products. We investigated the feasibility of luminescent conjugated oligothiophenes (LCOs) for non-destructive, rapid detection and quality assessment of lignocellulosic components in complex biomass matrices. A cationic pentameric oligothiophene denoted p-HTEA (pentamer hydrogen thiophene ethyl amine) showed unique binding affinities to cellulose, lignin, hemicelluloses, and cellulose nanofibrils in crystal, liquid and paper form. We exploited this finding using spectrofluorometric methods and fluorescence confocal laser scanning microscopy, for sensitive, simultaneous determination of the structural and compositional complexities of native lignocellulosic biomass. With exceptional photostability, p-HTEA is also demonstrated as a dynamic sensor for real-time monitoring of enzymatic cellulose degradation in cellulolysis. These results demonstrate the use of p-HTEA as a non-destructive tool for the determination of cellulose, hemicellulose and lignin in complex biomass matrices, thereby aiding in the optimization of biomass-converting technologies.
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| 29. |
- Choong, Ferdinand X., et al.
(författare)
-
Stereochemical identification of glucans by oligothiophenes enables cellulose anatomical mapping in plant tissues
- 2018
-
Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Efficient use of plant-derived materials requires enabling technologies for non-disruptive composition analysis. The ability to identify and spatially locate polysaccharides in native plant tissues is difficult but essential. Here, we develop an optical method for cellulose identification using the structure-responsive, heptameric oligothiophene h-FTAA as molecular fluorophore. Spectrophotometric analysis of h-FTAA interacting with closely related glucans revealed an exceptional specificity for beta-linked glucans. This optical, non-disruptive method for stereochemical differentiation of glycosidic linkages was next used for in situ composition analysis in plants. Multi-laser/multi-detector analysis developed herein revealed spatial localization of cellulose and structural cell wall features such as plasmodesmata and perforated sieve plates of the phloem. Simultaneous imaging of intrinsically fluorescent components revealed the spatial relationship between cell walls and other organelles, such as chloroplasts and lignified annular thickenings of the trachea, with precision at the sub-cellular scale. Our non-destructive method for cellulose identification lays the foundation for the emergence of anatomical maps of the chemical constituents in plant tissues. This rapid and versatile method will likely benefit the plant science research fields and may serve the biorefinery industry as reporter for feedstock optimization as well as in-line monitoring of cellulose reactions during standard operations.
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| 30. |
- Collin, Robert, et al.
(författare)
-
Simultaneous OH- and Formaldehyde-LIF Measurements in an HCCI Engine
- 2003
-
Ingår i: SAE Transactions, Journal of Fuels and Lubricants. - 0096-736X. ; 112:4, s. 2479-2486
-
Tidskriftsartikel (refereegranskat)abstract
- Simultaneous OH- and formaldehyde LIF measurements have been performed in an HCCI engine using two laser sources working on 283 and 355 nm, respectively. Two ICCD camera systems, equipped with long-pass filters, were used to collect the LIF signals. The simultaneous images of OH and formaldehyde were compared with heat-release calculated from the pressure-trace matching the cycle for the LIF measurements. The measurements were performed on a 0.5-l, single-cylinder optical engine equipped with port-fuel injection system. A blend of iso-octane and n-heptane was used as fuel and the compression ratio was set to 12:1. The width of the laser sheet was 40 mm and hence covered approximately half of the cylinder bore. At some 20 CAD BTDC low temperature reactions are present and formaldehyde is formed. The formaldehyde signal is then rather constant until the main heat-release starts just before TDC, where the signal decreases rapidly to low values. From some 15 CAD to 5 CAD BTDC the formaldehyde is uniformly distributed in the imaged area. As formaldehyde decreases, OH increases and follows the main rate of heat release curve, though with a slight lag in phase. Thereafter OH is formed in the areas from which the formaldehyde has disappeared and the OH signal is present to some 20 CAD ATDC.
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| 31. |
- Collin, Robert, et al.
(författare)
-
The Effect of Fuel Volatility on Hcci Using Simultaneous Formaldehyde and Oh Plif
- 2004
-
Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :2004-01-2948
-
Tidskriftsartikel (refereegranskat)abstract
- Simultaneous formaldehyde and OH PLIF have been applied in a direct-injected HCCI engine. The engine is a 0.5 l single-cylinder optical engine equipped with EGR system. PLIF measurements were performed with the engine run with two different fuels of low and high volatility, respectively. Different ratios of EGR were also examined. The aim of the study was to investigate how fuels with different volatility and EGR affect the HCCI combustion and measurements were performed for early and late injection timings. Measurements are presented for different injection timings showing formaldehyde and OH from start of injection until late in the expansion stroke. Also, formaldehyde distributions obtained from after the low temperature regime and before the high temperature regime are studied for different tuning of the start of injection from 300 CAD to 20 CAD before top dead center. In this investigation the spatial homogeneity of the formaldehyde distributions and the surface fraction of LIF signal covering the image are compared for the different fuels and EGR ratios.
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| 32. |
- Duong, Jeudi, et al.
(författare)
-
High Speed Combustion Imaging in a Large Bore Gas Engine: The Relationship Between Pre- and Main Chamber Heat Release
- 2014
-
Ingår i: ASME 2013 International Mechanical Engineering Congress and Exposition Volume 8A: Heat Transfer and Thermal Engineering. - 9780791856345 ; 8A, s. 08-022
-
Konferensbidrag (refereegranskat)abstract
- An experimental study is carried out to investigate the combustion process in a Wartsila 34SG spark-ignited lean burn four-stroke large bore engine (bore 340 mm) by means of optical diagnostics when operating on natural gas. The main focus of this work is to gain knowledge about in-cylinder combustion phenomena when igniting a lean air/fuel mixture with pre-combustion chamber induced jets. Especially the origin of cyclic variability is of interest. The flame propagation process in a single cycle was captured using a high speed video camera. The analysis is based on apparent heat release rates in the pre-combustion chamber and main chamber, in order to find correlations with the imaged phenomena. The results show that the flame propagation inside the main chamber starts at the end of the pre-chamber combustion heat release and that variation in main chamber heat release does not correlate with variations in the pre-combustion chamber.
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| 33. |
- Eriksson, Mia, et al.
(författare)
-
Agonistic targeting of TLR1/TLR2 induces p38 MAPK-dependent apoptosis and NFκB-dependent differentiation of AML cells
- 2017
-
Ingår i: Blood Advances. - : American Society of Hematology. - 2473-9529 .- 2473-9537. ; 1:23, s. 2046-2057
-
Tidskriftsartikel (refereegranskat)abstract
- Acute myeloid leukemia (AML) is associated with poor survival, and there is a strong need to identify disease vulnerabilities that might reveal new treatment opportunities. Here, we found that Toll-like receptor 1 (TLR1) and TLR2 are upregulated on primary AML CD34+CD38-cells relative to corresponding normal bone marrow cells. Activating the TLR1/TLR2 complex by the agonist Pam3CSK4 inMLL-AF9-driven human AML resulted in induction of apoptosis by p38 MAPK-dependent activation of Caspase 3 and myeloid differentiation in a NFκB-dependent manner. By using murineTrp53 -/- MLL-AF9AML cells, we demonstrate that p53 is dispensable for Pam3CSK4-induced apoptosis and differentiation. Moreover, murineAML1-ETO9a-driven AML cells also were forced into apoptosis and differentiation on TLR1/TLR2 activation, demonstrating that the antileukemic effects observed were not confined toMLL-rearranged AML. We further evaluated whether Pam3CSK4 would exhibit selective antileukemic effects. Ex vivo Pam3CSK4 treatment inhibited murine and human leukemia-initiating cells, whereas murine normal hematopoietic stem and progenitor cells (HSPCs) were relatively less affected. Consistent with these findings, primary human AML cells across several genetic subtypes of AML were more vulnerable for TLR1/TLR2 activation relative to normal human HSPCs. In theMLL-AF9AML mouse model, treatment with Pam3CSK4 provided proof of concept for in vivo therapeutic efficacy. Our results demonstrate that TLR1 and TLR2 are upregulated on primitive AML cells and that agonistic targeting of TLR1/TLR2 forces AML cells into apoptosis by p38 MAPK-dependent activation of Caspase 3, and differentiation by activating NFκB, thus revealing a new putative strategy for therapeutically targeting AML cells.
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| 34. |
- Feuk, Henrik, et al.
(författare)
-
Investigating photomultiplier tube nonlinearities in high-speed phosphor thermometry using light emitting diode simulated decay curves
- 2021
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 92:12
-
Tidskriftsartikel (refereegranskat)abstract
- Photomultiplier tube (PMT) nonlinearities relevant for single shot high-speed lifetime phosphor thermometry were investigated by simulating decay curves with a light emitting diode (LED) at repetition rates between 1 Hz and 10 kHz. The PMT gain, LED decay time, and background radiant flux were also varied to investigate their impact on the measured decay time error. Errors in the measured decay time due to nonlinear PMT performance lead to temperature measurement errors; therefore, having the measured decay time sensitive to only phosphor temperature is highly valuable for more reliable temperature measurements. Photocathode bleaching had a significant impact on the signal level linearity for PMTs with excitation frequency in the kHz regime but had a smaller impact on the decay time error. Space charge effects were most noticeable at high radiant flux levels and high repetition rates. Strong background radiant flux may lead to decay time errors, and a gateable photocathode could be an effective method to reduce decay time errors. The best decay time measurement configuration to maximize precision without sacrificing accuracy is to use PMT gain in the recommended range and the highest radiant flux where the PMT response is still linear. The degree of nonlinearity in the PMT response is partly detector dependent; therefore, the results in this work may differ among detectors; however, the analysis presented in this work provides guidelines for improving the temperature accuracy of kHz lifetime phosphor thermometry measurements.
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| 35. |
- Feuk, Henrik, et al.
(författare)
-
Sources of error for single-shot PMT-based phosphor thermometry in harsh conditions
- 2021
-
Ingår i: Measurement Science and Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 32:8
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates photomultiplier tube (PMT) nonlinearities, relevant for lifetime phosphor thermometry, at various decay times to assess and minimize the impact on temperature measurement accuracy. The focus is single-shot measurements performed in harsh environments where phosphor signal attenuation often is a concern. The sensitivity of decay time measurements to changing phosphorescence intensity is therefore investigated. The experimental results show that for the studied phosphors and detectors, shorter decay times between 20 ns and 6 µs, saturation effects in the PMTs decreased the measured decay time with increasing signal attenuation. For longer phosphorescence decay times, in the millisecond regime, nonlinearity effects led to an increase in the measured decay time with increasing signal attenuation. The specific detector nonlinearity response will vary among detectors, but the introduced methodology for detector analysis is a useful resource for assessing and improving accuracy in lifetime phosphor thermometry measurements.
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| 36. |
- Gong, Miaoxin, et al.
(författare)
-
An Optical Study of the Effects of Diesel-like Fuels with Different Densities on a Heavy-duty CI Engine with a Wave-shaped Piston Bowl Geometry
- 2023
-
Ingår i: SAE Technical Paper. - 0148-7191.
-
Konferensbidrag (refereegranskat)abstract
- The novel wave-shaped bowl piston geometry design with protrusions has been proved in previous studies to enhance late-cycle mixing and therefore significantly reduce soot emissions and increase engine thermodynamic efficiency. The wave-shaped piston is characterized by the introduction of evenly spaced protrusions around the inner wall of the bowl, with a matching number with the number of injection holes, i.e., flames. The interactions between adjacent flames strongly affect the in-cylinder flow and the wave shape is designed to guide the near-wall flow. The flow re-circulation produces a radial mixing zone (RMZ) that extends towards the center of the piston bowl, where unused air is available for oxidation promotion. The waves enhance the flow re-circulation and thus increase the mixing intensity of the RMZ. This flame-wall interaction is related to the momentum of the injected fuel sprays and therefore it is reasonable to investigate the impact of fuels of different densities that contain varied momentums. Conventional diesel and n-Heptane are tested in a single-cylinder optical heavy-duty compression ignition engine, as the fuels have similar characteristics but different densities. The spray and combustion processes are visualized by natural luminescence, captured by high-speed video. The experiment results indicate that there is a correlation between fuel densities and the flame-wall interaction.
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| 37. |
- Gong, Miaoxin, et al.
(författare)
-
Optical Diagnostic Study on Improving Performance and Emission in Heavy-Duty Diesel Engines Using a Wave-Shaped Piston Bowl Geometry and Post Injection Strategies
- 2023
-
Ingår i: SAE Technical Papers. - 0148-7191.
-
Tidskriftsartikel (refereegranskat)abstract
- This study explores the potential benefits of combining a wave-shaped piston geometry with post injection strategy in diesel engines. The wave piston design features evenly spaced protrusions around the piston bowl, which improve fuel-air mixing and combustion efficiency. The ‘waves’ direct the flames towards the bowl center, recirculating them and utilizing the momentum in the flame jets for more complete combustion. Post injection strategy, which involves a short injection after the main injection, is commonly used to reduce emissions and improve fuel efficiency. By combining post injections with the wave piston design, additional fuel injection can increase the momentum utilized by the flame jets, potentially further improving combustion efficiency. To understand the effects and potential of the wave piston design with post injection strategy, a single-cylinder heavy-duty compression-ignition optical engine with a quartz piston is used. The piston bowl is modified to remove waves on one side, allowing for a direct comparison between the wave and non-wave piston designs under identical engine operating conditions. Natural Luminosity is used as an optical diagnostic technique to visualize flame-piston and flame-flame interactions. The engine is operated under mid-load conditions (~9 bar IMEP) with different post injection strategies. The study provides insights into the potential benefits of combining the wave piston design with post injection strategy for improving combustion efficiency and engine performance in heavy-duty diesel engines.
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| 38. |
- Gorczyca, TW, et al.
(författare)
-
Radiative and relativistic effects in the decay of highly excited states in helium
- 2000
-
Ingår i: PHYSICAL REVIEW LETTERS. - : AMERICAN PHYSICAL SOC. - 0031-9007. ; 85:6, s. 1202-1205
-
Tidskriftsartikel (refereegranskat)abstract
- A recent experimental study [J.-E. Rubensson et al., Phys. Rev. Lett. 83, 947 (1999)] measured a significant fluorescence yield of the He(2lnl') photoexcited resonances, showing major qualitative differences from nonrelativistic predictions. We present a
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| 39. |
- Gorczyca, Thomas, et al.
(författare)
-
Radiative and Relativistic Effects in the Decay of Highly Excited States in Helium
- 2000
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 85:6, s. 1202-1205
-
Tidskriftsartikel (refereegranskat)abstract
- A recent experimental study [J.-E. Rubensson et al., Phys. Rev. Lett. 83, 947 (1999)] measured a significant fluorescence yield of the He( 2lnl′) photoexcited resonances, showing major qualitative differences from nonrelativistic predictions. We present a further theoretical study of these states, and perform R-matrix multichannel quantum defect theory calculations to extract fluorescence and ionization cross sections. These theoretical results are in excellent agreement with newer, higher-resolution measurements. Radiative and spin-orbit effects are quantified and shown to play an important role in the overall characterization of highly excited states.
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| 40. |
- Hardalupas, Y, et al.
(författare)
-
Chemiluminescence sensor for local equivalence ratio of reacting mixtures of fuel and air (FLAMESEEK)
- 2004
-
Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 24:11-12, s. 1619-1632
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a Cassegrain optics-based chemiluminescence sensor (CS) for measurements in gas turbine combustors. The chemiluminescence sensor measures the equivalence ratio of reacting fuel and air mixtures, and can identify the flame location, in partially premixed flames. It has the potential for monitoring the degree of premixedness of reacting fuel and air in industrial gas turbine combustors, where operation with lean premixed mixtures is important for reduction of NO, emissions. The spatial resolution of the sensor is evaluated by comparing OH* chemiluminescence measurement from the CS with laser induced OH fluorescence, in the cone-shaped premixed flame of a Bunsen burner. The ability of the sensor to measure in a modified micro-gas turbine environment burning a methane/air, as well as, a methane/ water/air flame (humidified flame) is also demonstrated.
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| 41. |
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| 42. |
- Hildingsson, Leif, et al.
(författare)
-
Optical Diagnostics of Hcci and Low-Temperature Diesel Using Simultaneous 2-D Plif of Oh and Formaldehyde
- 2004
-
Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :2004-01-2949
-
Tidskriftsartikel (refereegranskat)abstract
- Simultaneous OH- and formaldehyde planar-LIF measurements have been performed in an optical engine using two laser sources working on 283 and 355 nm, respectively. The engine used for the measurements was a car diesel engine converted to single-cylinder operation and modified for optical access. The fuel, n-heptane, was injected by a direct injection common-rail system and the engine was also fitted with an EGR system. The engine was operated in both HCCI mode and diesel mode. Due to the low load, the diesel mode resulted in low-temperature diesel combustion and because of limitations in maximum pressure and maximum rate of pressure increase of the optical engine, the diesel mode was run at a higher EGR percentage than the HCCI mode to slow down the combustion. A third mode, pilot combustion, was also investigated. This pilot combustion is created by an injection at 30 CAD before TDC followed by a second injection just before TDC. The OH and formaldehyde LIF images were compared with the heat-release calculated from the pressure traces. Analyses of the emissions, of for example NOx and HC, were also performed for the different operating modes.
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| 43. |
- Hildingsson, Leif, et al.
(författare)
-
Optical Diagnostics of HCCI and UNIBUS Using 2-D PLIF of OH and Formaldehyde
- 2005
-
Ingår i: SAE technical paper series.
-
Tidskriftsartikel (refereegranskat)abstract
- Simultaneous OH- and formaldehyde planar-LIF measurements have been performed in an optical engine using two laser sources working on 283 and 355 nm, respectively. The measurements were performed in a light- duty diesel engine, using n-heptane as fuel, converted to single- cylinder operation and modified for optical access. It was also equipped with a direct-injection, common-rail system as well as an EGR system. The engine was operated in both HCCI mode, using a single fuel injection, and UNIBUS (Uniform Bulky Combustion System) mode, using two injections of fuel with one of the injections at 50 CAD before TDC and the other one just before TDC. The OH and formaldehyde LIF images were compared with the heat- release calculated from the pressure-traces. Analyses of the emissions, for example NOx and HC, were also performed for the different operating conditions.
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| 44. |
- Hildingsson, Leif, et al.
(författare)
-
Simultaneous Formaldehyde and Fuel-Tracer LIF Imaging in a High-Speed Diesel Engine With Optically Accessible Realistic Combustion Chamber
- 2005
-
Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
-
Konferensbidrag (refereegranskat)abstract
- Simultaneous laser-induced fluorescence (LIF) imaging of formaldehyde and a fuel-tracer have been performed in a high-speed diesel engine. N-heptane and isooctane were used as fuel and toluene was used as a tracer. This arrangement made it possible to make simultaneous measurements of toluene by exciting at 266 nm and detecting at 270-320 nm while exciting formaldehyde at 355 nm and detecting at 400-500 nm.The aim of this study is to investigate how traditional fuel tracer and natural-occurring formaldehyde formed in the cool chemistry are transported in the piston bowl. A range of ignition delays were created by running the engine with different amounts of EGR. During this sweep the area where the low-temperature reactions take place were studied.The measurements were performed in a 0.5-l, single-cylinder optical engine running under conditions simulating a cruise-point, i.e., about 2.2 bar imep. The ignition delay was elongated compared to the normal mapping and the engine-out emissions of soot and NOx were ultra-low.It was found that the spatial location of LTR's does not shift significantly for different EGR levels. The formaldehyde signal overlaps the fuel signal in most cases before the onset of the main heat release.
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| 45. |
- Huang, Jianqing, et al.
(författare)
-
A detailed study on the micro-explosion of burning iron particles in hot oxidizing environments
- 2022
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 238
-
Tidskriftsartikel (refereegranskat)abstract
- As a promising carbon-free fuel, iron powder can directly combust with air and has great potential to provide clean and high-grad heat for various applications. The combustion characteristics of iron particles are of great significance for developing iron combustion model, designing efficient combustor, and optimizing combustion technologies. In this work, the micro-explosion behavior of burning iron particles was experimentally investigated based on optical diagnostics. With two high-speed cameras operating at 10,000 frames per second, the three-dimensional (3D) motion and mean surface temperature of burning iron particles during the micro-explosion process were measured using the stereo imaging technique and two-color pyrometry, respectively. The probability of micro-explosions in different oxidizing environments were statistically studied. Three distinct micro-explosion modes have been observed. The results showed that the micro-explosion of burning iron particles heavily depended on oxygen concentration. The micro-explosion would slightly reduce the particle surface temperature by 30–70 K within 0.5 ms, since a lot of smaller fragments were produced. In addition, the 3D velocity of most fragments would sharply increase to 2–6 times within 0.2 ms after the micro-explosion occurred. Regarding the mechanism of the micro-explosion, three types of potential gas sources inside the particle were discussed. The sharp gradients of gas temperature and oxygen concentration may facilitate the rapid increase of the internal pressure in the particle, which eventually causes the micro-explosion.
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| 46. |
- Hult, Johan, et al.
(författare)
-
Application of a high-repetition-rate laser diagnostic system for single-cycle-resolved imaging in internal combustion engines
- 2002
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Ingår i: Applied Optics. - 2155-3165. ; 41:24, s. 5002-5014
-
Tidskriftsartikel (refereegranskat)abstract
- High-repetition-rate laser-induced fluorescence measurements of fuel and OH concentrations in internal combustion engines are demonstrated. Series of as many as eight fluorescence images, with a temporal resolution ranging from 10 mus to 1 ms, are acquired within one engine cycle. A multiple-laser system in combination with a multiple-CCD camera is used for cycle-resolved imaging in spark-ignition, direct-injection stratified-charge, and homogeneous-charge compression-ignition engines. The recorded data reveal unique information on cycle-to-cycle variations in fuel transport and combustion. Moreover, the imaging system in combination with a scanning mirror is used to perform instantaneous three-dimensional fuel-concentration measurements.
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| 47. |
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| 48. |
- Hultqvist, Anders, et al.
(författare)
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A Study of the Homogeneous Charge Compression Ignition Combustion Process by Chemiluminescence Imaging
- 1999
-
Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- An experimental study of the Homogeneous Charge Compression Ignition (HCCI) combustion process has been conducted by using chemiluminescence imaging. The major intent was to characterize the flame structure and its transient behavior. To achieve this, time resolved images of the naturally emitted light were taken. Emitted light was studied by recording its spectral content and applying different filters to isolate species like OH and CH.Imaging was enabled by a truck-sized engine modified for optical access. An intensified digital camera was used for the imaging. Some imaging was done using a streak-camera, capable of taking eight arbitrarily spaced pictures during a single cycle, thus visualizing the progress of the combustion process. All imaging was done with similar operating conditions and a mixture of n-heptane and iso-octane was used as fuel.Some 20 crank angles before Top Dead Center (TDC), cool flames were found to exist. They appear with a faint structure, evenly distributed throughout the combustion chamber. There was no luminosity recorded between the end of cool flames and the start of the main heat release. Around TDC the main heat release starts. Looking at a macro scale, we find that the charge starts to burn simultaneously at arbitrary points throughout the charge. Since the thermal boundary layer is colder than the bulk of the charge, the local heat release is delayed close to the walls. As a result, the total heat release is slowed down. Ensemble averaged 1 images show this wall boundary effect clearly when plotted against CAD. The peak intensity at the main combustion event is one order of magnitude greater than that of the cool flame and the structure is a lot more protruding.Since spontaneous emission imaging is a line-of-sight integration, the flame structure appears a bit smeared. The micro scale structure is very similar from one cycle to another, but there are large variations between cycles on the macro scale.
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- Hultqvist, Anders, et al.
(författare)
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The Hcci Combustion Process in a Single Cycle-High-Speed Fuel Tracer Lif and Chemiluminescence Imaging
- 2002
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Ingår i: SAE Technical Papers.
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Tidskriftsartikel (refereegranskat)abstract
- The Homogeneous Charge Compression Ignition (HCCI) combustion progress has been characterized by means of high- speed fuel tracer Planar Laser-Induced Fluorescence (PLIF) combined with simultaneous chemiluminescence imaging. Imaging has been conducted using a high-speed laser and detector system. The system can acquire a sequence of eight images within less than one crank angle. The engine was run at 1200 rpm on iso-octane or ethanol and a slight amount of acetone was added as a fuel tracer, providing a marker for the unburned areas. The PLIF sequences showed that, during the first stage of combustion, a well distributed decay of fuel concentration occurs. During the later parts of the combustion process the fuel concentration images present much more structure, with distinct edges between islands of unburned fuel and products. The transition between the evenly distributed fuel oxidation in the beginning and the large structures at the end, is most likely the result of a gradual amplification of small temperature inhomogeneities and an expansion of burned gas compressing the unburned.
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