| 1. |
- Vressner, Andreas, et al.
(författare)
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Pressure oscillations during rapid HCCI combustion
- 2003
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Ingår i: SAE Technical Paper. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- This work has focused on studying the in-cylinder pressure fluctuations caused by rapid HCCI combustion and determine what they consist of. Inhomogeneous autoignition sets up pressure waves traversing the combustion chamber. These pressure waves induce high gas velocities which causes increased heat transfer to the walls or in worst case engine damage. In order to study the pressure fluctuations a number of pressure transducers were mounted in the combustion chamber. The multi transducer arrangement was such that six transducers were placed circumferentially, one placed near the centre and one at a slight offset in the combustion chamber. The fitting of six transducers circumferentially was enabled by a spacer design and the two top mounted transducers were fitted in a modified cylinder head. During testing a disc shaped combustion chamber was used. The results of the tests conducted were that the in-cylinder pressure experienced during rapid HCCI-combustion is inhomogeneous. Pressure oscillations were experienced which showed good accordance to vibration mode shapes and frequencies suggested by acoustic vibration theory. The pressure waves manifested largest intensities for the first vibration mode, a mode suggesting radial propagation of the pressure waves in the combustion chamber. Experiments showed that the direction of the pressure wave was random which hinted absence of hot spot ignition. Hot spots mean that some part of the combustion chamber is physically hotter than the rest which ignites adjacent mixture. There is no evidence available yet to demonstrate engine damage during rapid HCCI combustion. An explanation to this could be that the violent combustion reactions related to SI knock damage is not present in HCCI combustion due to the diluted mixtures. The local heat released will therefore be lower. Finally, engine tests using two other combustion chamber geometries were conducted. The results showed that altering the geometry of the combustion chamber affects the resulting frequency spectrum. The two geometries were hill- and a bowl shaped respectively. Analytical calculations on the bowl shape vibration frequencies indicate reasonably good accordance to experimental results.
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| 2. |
- Joelsson, Tobias, et al.
(författare)
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Large Eddy Simulation and Experiments of the Auto-Ignition Process of Lean Ethanol / Air Mixture in HCCI Engines
- 2008
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Ingår i: SAE International Journal of Fuels and Lubricants. - : SAE International. - 1946-3952 .- 1946-3960. ; 1:1, s. 1110-1119
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Tidskriftsartikel (refereegranskat)abstract
- Recent experiments and numerical studies have showed that piston geometry has a significant effect on the homogeneous charge compression ignition (HCCI) process. There are two effects generated by the combustor geometry: the geometry affects the flow/turbulence in the cylinder; the geometry also affects the temperature stratification. The temperature stratification is more directly responsible for the observed alteration of the auto-ignition process. To clarify this issue further we present in this paper a study of two engines with the same geometry but difference ways of cooling. Measurement of the two engines~a metal engine and quartz piston engine, both with the same piston bowl geometry~is carried out. Large eddy simulation (LES) is used to simulate the flow, the temperature field and the auto-ignition process in the two engines. The fuel is ethanol with a relative air/fuel ratio of 3.3. It is found that lower temperature stratification is established in the metal engine under similar conditions as the optical quartz engine due to the more effective cooling of the piston in the metal engine configuration. The combustion phasing in the two engines is the same by controlling the intake temperature. Both measurements and LES show a more rapid auto-ignition in the metal engine than in the optical engine with the same piston geometry. This confirms the conclusion that large temperature stratification can decrease the pressure-rise-rate and thereby increase the load of HCCI engines. The dependence of temperature stratification on the wall temperature and intake temperature is systematically studied using LES.
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| 3. |
- Lemel, Mikael, et al.
(författare)
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Quantification of the Formaldehyde Emissions from Different HCCI Engines Running on a Range of Fuels
- 2005
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Ingår i: SAE Transactions, Journal of Fuels and Lubricants. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0096-736X. ; 114:4, s. 1347-1357
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, the formaldehyde emissions from three different types of homogenous charge compression ignition (HCCI) engines are quantified for a range of fuels by means of Fourier Transform Infra Red (FTIR) spectroscopic analysis. The engines types are differentiated in the way the charge is prepared. The characterized engines are; the conventional port fuel injected one, a type that traps residuals by means of a Negative Valve Overlap (NVO) and finally a Direct Injected (DI) one. Fuels ranging from pure n-heptane to iso-octane via diesel, gasoline, PRF80, methanol and ethanol were characterized. Generally, the amount of formaldehyde found in the exhaust was decreasing with decreasing air/fuel ratio, advanced timing and increasing cycle temperature. It was found that increasing the source of formaldehyde i.e. the ratio of heat released in the cool-flame, brought on higher exhaust contents of formaldehyde. The application of a standard three-way catalyst completely removed formaldehyde from the exhaust stream.
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| 4. |
- Olofsson, Jimmy, et al.
(författare)
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High-Speed Lif Imaging for Cycle-Resolved Formaldehyde Visualization in Hcci Combustion
- 2005
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Ingår i: SAE, Session: Combustion and Flow Diagnostics. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. ; 114:3, s. 645-652
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Konferensbidrag (refereegranskat)abstract
- High-speed laser diagnostics was utilized for single-cycle resolved studies of the formaldehyde distribution in the combustion chamber of an HCCI engine. A multi-YAG laser system consisting of four individual Q-switched, flash lamp-pumped Nd:YAG lasers has previously been developed in order to obtain laser pulses at 355 nm suitable for performing LIF measurements of the formaldehyde molecule. Bursts of up to eight pulses with very short time separation can be produced, allowing capturing of LIF image series with high temporal resolution. The system was used together with a high-speed framing camera employing eight intensified CCD modules, with a frame-rate matching the laser pulse repetition rate. The diagnostic system was used to study the combustion in a truck-size HCCI engine, running at 1200 rpm using n-heptane as fuel. By using laser pulses with time separations as short as 70 μs, cycle-resolved image sequences of the formaldehyde distribution were obtained. Thus, with this technique it is possible to follow the formaldehyde formation and consumption processes within a single cycle. The combustion evolution was studied in terms of the rate and spatial structure of formaldehyde formation and consumption for different engine operating conditions, e.g. different stoichiometries. Also, the impact on the rate of heat-release was investigated.
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| 5. |
- Seyfried, Hans, et al.
(författare)
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High-Speed PLIF Imaging for Investigation of Turbulence Effects on Heat Release Rates in HCCI Combustion
- 2007
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Ingår i: Session: Homogeneous Charge Compression Ignition (HCCI) (Part 4 of 8) Combustion Modeling / Optical Diagnostics. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Konferensbidrag (refereegranskat)abstract
- High-speed laser diagnostics was utilized for single-cycle resolved studies of the fuel distribution in the combustion chamber of a truck-size HCCI engine. A multi-YAG laser system consisting of four individual Nd:YAG lasers was used for planar laser-induced fluorescence (PLIF) imaging of the fuel distribution. The fundamental beam from the lasers at 1064 nm was frequency quadrupled in order to obtain laser pulses at 266 nm suitable for excitation of acetone that was used as fuel tracer. Bursts of up to eight pulses with very short time separation were produced, allowing PLIF images with high temporal resolution to be captured within one single cycle event. The system was used together with a high-speed framing camera employing eight ICCD modules, with a frame-rate matching the laser pulse repetition rate. The combustion evolution was studied in terms of spatial distribution and rate of fuel consumption for different engine hardware configurations as well as operating conditions e.g. different stoichiometries and combustion phasing. Two different piston crown geometry were used for altering the degree of turbulence in the combustion chamber. In addition to the optical investigations, the impact of turbulence effects was also studied by calculating the rate of heat-release and combustion phasing from the pressure trace.
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| 6. |
- Strandh, Petter, et al.
(författare)
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Ion Current Sensing for HCCI Combustion Feedback
- 2003
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Ingår i: SAE Technical Papers. - 0148-7191. ; :2003-01-3216
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Konferensbidrag (refereegranskat)abstract
- Measurement of ion current signal from HCCI combustionwas performed. The aim of the work was to investigateif a measurable ion current signal exists and if it is possible to obtain useful information about the combustion process. Furthermore, influence of mixture quality in termsof air/fuel ratio and EGR on the ion current signal wasstudied. A conventional spark plug was used as ionizationsensor. A DC voltage (85 Volt) was applied acrossthe electrode gap. By measuring the current through thegap the state of the gas can be probed. A comparisonbetween measured pressure and ion current signal wasperformed, and dynamic models were estimated by usingsystem identification methods.The study shows that an ion current signal can be obtainedfrom HCCI combustion and that the signal levelis very sensitive to the fuel/air equivalence ratio. Themost important result from this study is that the ion current signal proved to be an excellent indicator of the actual combustion timing which is crucial piece of information for HCCI control.
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| 7. |
- Särner, Gustaf, et al.
(författare)
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Cycle Resolved Wall Temperature Measurements Using Laser-Induced Phosphorescence in an HCCI Engine
- 2005
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Ingår i: SAE technical paper series.
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Tidskriftsartikel (refereegranskat)abstract
- Cycle-resolved wall temperature measurements have been performed in a one-cylinder, port-injected optical Scania D12 truck engine run in HCCI mode. Point measurements at various locations were made using Laser-Induced Phosphorescence (LIP). Single point measurements with thermographic phosphors utilize the temperature dependency of the phosphorescence decay time. The phosphorescence peak at 538 nm from the thermographic phosphor La2O2S:Eu was used to determine temperature. A frequency tripled 10 Hz pulsed Nd:YAG laser delivering ultraviolet (UV) radiation at 355 nm was used for excitation of the phosphor. Detection in the spectral region 535 - 545 nm was performed every cycle with a photo multiplier tube connected to a 3 GHz oscilloscope. Measurements were made at four points on the cylinder head surface and two points on the outlet and inlet valves respectively. For each location measurements were made at different loads and at different crank angle degrees (CAD). The aim of the presented work was to study the feasibility of using LIP for single-shot, cycle-resolved wall temperature measurements.
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| 8. |
- Vressner, Andreas, et al.
(författare)
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Fuel Effects on Ion Current in an HCCI Engine
- 2005
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Ingår i: SAE Transactions, Journal of Engines. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0096-736X. ; 114:3, s. 1382-1395
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Tidskriftsartikel (refereegranskat)abstract
- An interest in measuring ion current in Homogeneous Charge Compression Ignition (HCCI) engines arises when one wants to use a cheaper probe for feedback of the combustion timing than expensive piezo electric pressure transducers. However the location of the ion current probe, in this case a spark plug, is of importance for both signal strength and the crank angle position where the signal is obtained. Different fuels will probably affect the ion current in both signal strength and timing and this is the main interest of this investigation. The measurements were performed on a Scania D12 engine in single cylinder operation and ion current was measured at 7 locations simultaneously. By arranging this setup there was a possibility to investigate if the ion current signals from the different spark plug locations would correlate with the fact that, for this particular engine, the combustion starts at the walls and propagates towards the center of the combustion chamber. The fuels investigated were isooctane, n-heptane, PRF80, gasoline, diesel, ethanol and methanol. A special interest was how the ion current timing was affected by low temperature reactions, which were present with the n-heptane and diesel fuels as well as mixtures of isooctane and n-heptane, i.e., PRF80. The most interesting results were that ion current is both affected by the ion current probe location in the combustion chamber and the fuel used. Fuels with higher octane numbers seem to provoke ion current more easily, thus with LTR fuels as n-heptane and diesel ion current was only achieved at richer mixtures. The cycle-to-cycle variations of ion current increased with leaner mixtures. Ion current was also affected by combustion phasing and engine speed.
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| 9. |
- Vressner, Andreas, et al.
(författare)
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Multiple Point Ion Current Diagnostics in an HCCI Engine
- 2004
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Ingår i: SAE Transactions, Journal of Engines. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0096-736X. ; 113:3, s. 544-550
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Tidskriftsartikel (refereegranskat)abstract
- Interest in ion current sensing for HCCI combustion arises when a feedback signal from some sort of combustion sensor is needed in order to determine the state of the combustion process. A previous study has revealed that ion current sensors in the form of spark plugs can be used instead of expensive piezoelectric transducers for HCCI combustion sensing. Sufficiently high ion current levels were achieved when using relatively rich mixtures diluted with EGR. The study also shows that it is not the actual dilution per se but the actual air/fuel equivalence ratio which is important for the signal level. Conclusions were made that it is possible to obtain information on combustion timing and oscillating wave phenomena from the measurements. However, the study showed that the ion current is local compared to the pressure which is global in the combustion chamber. This observation triggered the present study where the aim is to investigate the ion current at different locations in the combustion chamber. The ion current was measured simultaneously at seven locations in the combustion chamber. In order to achieve this, 6 spark plugs were fitted circumferentially in a spacer placed between the cylinder block and the head. The seventh spark plug was placed in the cylinder head. Individual DC sources of 85 volts were applied across the spark plug gaps. The present study indicates that the combustion timing seems to be dependent on the wall temperature at the different spark plug locations. The largest difference in timing between different locations in the combustion chamber was 2 CAD. The ion current amplitude varies with different spark plug locations up to 1.5 μA. The signal strength increases with decreasing air/fuel ratio and is also affected by dilution.
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| 10. |
- Vressner, Andreas
(författare)
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Studies on the Load Range of an HCCI Engine using In-Cylinder Pressure, Ion Current and Optical Diagnostics
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Internal combustion engines are continuously developed towards decreased hazardous emissions and lower fuel consumption. The homogeneous charge compression ignition (HCCI) engine is a promising concept which combines the best features of the Diesel engine and the spark ignition (SI) engine. The efficiency is in the range of the Diesel engine and the emissions are low and comparable to the emissions from an SI engine with catalyst. No flame propagation is present in the HCCI engine; instead the whole charge is gradually consumed at several locations simultaneously. The resulting pressure rise rate is therefore high which means that the engine has to be run lean or diluted with burned gases in order not to stress the mechanical parts of the engine or produce excessive noise. Due to the lean and diluted mixtures the combustion temperature is low and fairly uniform. This results in low emissions of NOx and PM but if the temperature is too low emissions of unburned hydrocarbons and carbon monoxide (CO) increase. Furthermore, the pressure rise rate limits HCCI combustion to low or part load and is therefore to be combined with either Diesel or SI operation at higher loads. In this thesis different diagnostic methods have been used to study the HCCI combustion process at different engine loads. Combustion diagnostics have been performed using cylinder pressure and ion current measurement as well as optical techniques such as chemiluminescence imaging. By pressure measurement the overall combustion behaviour in the cylinder can be studied. By ion current measurement local conditions in small volumes can be studied. This is of interest since there are differences in temperature and relative air/fuel ratio between different locations in the combustion chamber. Locations with higher temperature or richer mixtures ignite first and this affects the ongoing combustion cycle. Pressure diagnostics is accurate but expensive as feedback method of the ongoing combustion process. Ion current diagnostics is cheap but due to the low temperature nature of HCCI combustion it is only usable at higher engine loads and thus the method is not an option for low load or idle conditions. Different fuels will provoke ion current differently for the selected compression ratio, initial charge temperature, measuring location and relative air/fuel ratio. If the initial charge temperature is too low, partial or total misfire might occur. At these running conditions spark or laser assistance can be used to increase the charge temperature prior to auto ignition. This advances the combustion phasing, thus minimizing the risk of misfire. This is also interesting for control purposes since it is possible to control the HCCI combustion phasing by changing the spark or laser ignition timing. When running laser assisted HCCI, flame propagation is present from the laser ignition location and, as the pressure and temperature increase, auto ignition occurs. This operation is a mixed mode of flame propagation and auto ignition. Lastly the effect of combustion chamber geometry on HCCI combustion rate was studied. A square bowl in piston geometry compared to Disc geometry showed the possibility to extend the maximum load limit due to decreased pressure rise rates but at the cost of decreased engine efficiency. Chemiluminescence and LIF imaging as well as LES showed stratified combustion behaviour unusual for HCCI operation which normally is a more homogeneously distributed combustion process.
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