| 1. |
- Huang, Chen, 1981, et al.
(författare)
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A Study of Two Basic Issues Relevant to RANS Simulations of Stratified Turbulent Combustion in a Spray-Guided Direct-Injection Spark-Ignition Engine
- 2014
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2014-October
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Tidskriftsartikel (refereegranskat)abstract
- A Spray-Guided (SG) Direct-Injection (DI) Spark-Ignition (SI) engine is widely recognized to be a promising technology capable for substantially reducing fuel consumption and carbon dioxide emissions. Accordingly, there is a strong need for developing models of some effects specific to stratified turbulent burning under conditions of elevated and rapidly varying pressure. Two such effects were addressed in the present work by performing unsteady three-dimensional URANS simulations of stratified turbulent combustion in a SG DISI engine. First, a simple method of evaluation equilibrium combustion temperature, implemented into the CFD code OpenFOAM ® , was improved in order to take into account the dissociation of the combustion products. Second, stratified turbulent combustion is affected by fluctuations in mixture composition. A widely used approach to modeling this effect consists of invoking a presumed Probability Density Function (PDF) for mixture fraction f . Because parameters of this PDF are determined using the first and second Favre moments of the mixture fraction field, the PDF is density-weighted. However, the canonical PDF P f is required to average certain important combustion characteristics that are straightforwardly relevant to local burning rate e.g. the laminar flame speed or the product density. In the present work, the relation between the Favre and canonical PDFs was investigated under conditions associated with burning in a SG DISI engine. Finally, the stratified turbulent combustion model which invo
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| 2. |
- Huang, Chen, 1981, et al.
(författare)
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Application of Flame Speed Closure Model to RANS Simulations of Stratified Turbulent Combustion in a Gasoline Direct-Injection Spark-Ignition Engine
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 188:1, s. 98-131
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Taylor & Francis. The present work aims at development and validation of a tool for numerically modeling stratified turbulent combustion in a gasoline direct injection (GDI) engine. For this purpose, an open source code called OpenFOAM ® , which has been attracting growing interests from both industries and academies due to an opportunity to access the source code and to test new models without paying license fees, is further developed by implementing advanced models relevant to stratified turbulent burning. In particular, first, the Flame Speed Closure model of premixed turbulent combustion is implemented in order to simulate flame propagation through inhomogeneously premixed reactants. Second, a newly calculated approximation of the laminar flame speed of gasoline-air mixtures as a function of the equivalence ratio, pressure, and temperature is implemented in order to simulate dependence of burning rate on the local mixture composition. Third, a newly calculated approximation of the combustion temperature of gasoline-air mixtures as a function of the equivalence ratio, pressure, and product enthalpy is implemented in order to allow for dissociation of combustion products and heat losses. Fourth, a presumed mixture-fraction probability density function (PDF) approach is implemented in order to simulate the influence of turbulent fluctuations in the mixture fraction on the local burning rate. In addition to commonly used mass-weighted mixture-fraction PDF, a more consistent model that deals also with the canonical mixture-fraction PDF is developed and the two approaches are compared. Numerical results that show the influence of the aforementioned implementations on computed global characteristics of stratified combustion in a research GDI engine are discussed. The developed numerical tool is quantitatively validated by comparing computed pressure traces in the GDI engine with experimental data obtained in three different cases associated with two different loads, late injection timings, and short time intervals between the injection and spark ignition.
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| 3. |
- Huang, Chen, 1981, et al.
(författare)
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Numerical and Experimental Study of Stratified Turbulent Combustion in a Spray-Guided Gasoline Direct Injection Engine
- 2015
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Ingår i: Lecture Notes in Mobility. - Cham : Springer International Publishing. - 2196-5544 .- 2196-5552. - 9783319179988 ; , s. 77-84
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Direct Injection (DI) of gasoline into cylinder of a Spark Ignition (SI) engine is widely recognized to be a promising technology capable for significantly reducing fuel consumption and carbon dioxide emissions as compared to a port-fuel injection SI engine. In particular, spray-guided (SG) GDI combustion systems allow for further improvement in fuel efficiency. Moreover, efficient CFD tools fornumerical simulations of spray and combustion processes have been becoming increasingly important in engine development. In previous papers, a so-called FlameSpeed Closure (FSC) model was implemented into an open source code OpenFOAM® with the capability of addressing important phenomena in SG GDI engines, e.g. fluctuations in mixture composition and the proper evaluation of combustion temperature for the products. In this paper, the aforementioned FSC model is applied to investigate the stratified turbulent combustion in a SG GDI enginein the frame work of unsteady 3D Reynolds-Averaged Navier–Stokes (RANS) simulations. The computed results are compared with the measured pressure traces obtained in the same research group for both low and medium load conditions.Further on, the calculated Reynolds-averaged progress variable is compared to the experimentally observed images.
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| 4. |
- Johansen, Lars Christian Riis, 1987, et al.
(författare)
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Analysis of Transient Compressible Gas Jets Using High Speed Schlieren Imaging
- 2013
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Transient compressible gas jets, as encountered in direct injection gas fuel engines, have been examined using schlieren visualization. Helium has been injected into air in a pressure chamber to create the jets examined. The structure of the jets is studied from the mean and coefficient of variation of the penetration length, jet width and jet angle. The quantities are calculated by digital image processing of schlieren images captured with a high-speed camera. Injection pressure and chamber pressure have been varied to determine whether they have an effect on the response variables. Design of experiments methods have been used to develop the scheme employed in performing the experiments. The mean normalized penetration length of the jets is found to scale with injection to chamber pressure ratio and is in agreement with a momentum conserving relation given in the literature. The dispersion of the penetration length has been found to be in agreement with a normal distribution. The Turner model for a jet has been found to be in agreement with the observed jets. The jet has been observed to transition to self-similarity within 20 nozzle diameters. The calculated penetration constant Γ has been observed to vary with the pressure ratio and is smaller than previously reported values. The jet angle approaches a constant value for all cases and has also been found to be in approximate agreement with a normal distribution.
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| 5. |
- Johansen, Lars Christian Riis, 1987, et al.
(författare)
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Comparison of E10 and E85 spark ignited stratified combustion and soot formation
- 2017
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 205, s. 11-23
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Tidskriftsartikel (refereegranskat)abstract
- The combustion process, soot formation and oxidation in spark ignited, spray guided, globally lean, stratified combustion of E10 and E85 was investigated and compared in a single cylinder optical engine with an outward opening piezo actuated injector. Two engine loads and several injection sequences were studied. Cylinder pressure measurements, high speed video recordings, OH* chemiluminescence and soot incandescence imaging were used. Stable ignition and combustion of both fuels was achieved with a spark at the end of the last the fuel spray for all injection strategy cases except for the single injection of large fuel quantities. The average rate of heat release and work output increased and the work variability decreased for both fuels with multiple injections of fuel for both engine loads. The changes for each case and variable were approximately equal for the two fuels. Single injections of E85 led to pool fires on the piston surface which were the only source of soot formation. Pool fires persisted after the end of conditions favourable to soot oxidation. For E10 the source of soot formation was a combination of pool fires and gas phase soot formation at 3.6 bar while at 5 bar pool fires were the only source. Two injections led to a significant reduction of the soot formation for both fuels and both engine loads. Pool fires remained the sole source of soot formation for E85 while the gas phase was the primary source for E10 and largely ceased during the combustion process while soot oxidizing conditions were present. The spatial distribution of combustion was remarkably similar for both fuels when multiple injections were used.
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| 6. |
- Johansen, Lars Christian Riis, 1987, et al.
(författare)
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Drive Cycle Particulate and Gaseous Emissions from a Parallel Hybrid Combustion Engine and Electric Powertrain
- 2015
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2015-September
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Tidskriftsartikel (refereegranskat)abstract
- The emissions from a parallel hybrid combustion engine and electric powertrain operated on a modified New European Drive Cycle (NEDC) was investigated in order to determine the relation between emissions and the road and engine load profile. The effect of simulated electric motor assistance during accelerations on emissions was investigated as a means to reduce particulate and gaseous emissions. The time resolved particulate number and size distribution was measured in addition to gaseous emissions. The combustion engine was a downsized, three cylinder spark ignited direct injection (SIDI) turbocharged engine fuelled with gasoline. Electric motor assistance during accelerations was simulated by reduction of the vehicle mass. This reduced engine load during accelerations. Fuel rich engine transients occurred during accelerations. NOx emissions were reduced with electric assistance due to a reduction in engine load. CO emissions were the result of air to fuel ratio transients and increased slightly with electric assist. HC emissions occurred during deceleration with downshifts. Particulate emissions were attributed to soot formation from fuel rich engine transients during accelerations and fuel rich engine operation at large load and both particulate number and mass emissions peaked during accelerations. Particulate number emissions increased with electric assistance. The reduction of in cylinder temperatures with electric assist due to reduction in engine load is hypothesized to have resulted in reduced in-cylinder soot oxidation and the observed increase in particulate number emissions with electric assist. Both with and without electric assist the particle size distributions were centered at 100 nm. Simulated electric motor assistance during load accelerations reduced fuel consumption as expected.
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| 7. |
- Johansen, Lars Christian Riis, 1987, et al.
(författare)
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In cylinder visualization of stratified combustion of E85 and main sources of soot formation
- 2015
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 159, s. 392-411
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Tidskriftsartikel (refereegranskat)abstract
- The combustion process and soot formation in spark ignited spray guided stratified combustion of E85 was investigated in a single cylinder optical engine with direct injection of fuel using an outward opening piezo actuated injector. The effect of engine rotation frequency, fuel quantity, injection sequence and ignition timing was studied. Combustion, soot formation and soot oxidation was analyzed using cylinder pressure measurements, images recorded using high speed video cameras, the flame emission spectrum and OH∗ chemiluminescence and soot incandescence imaging. A maximum injection duration was found to exist for direct ignition of the fuel spray. Engine rotation frequency had little effect on the initial and maximum rate of combustion. The maximum rate of combustion decreased with increasing cycle fuel mass when a single injection was used. The rate of combustion and indicated mean effective pressure increased and the combustion variability decreased when the single injection was split into multiple injections in close succession to deliver the same total fuel mass and the last fuel spray was ignited. Ignition of the first fuel spray resulted in a more pronounced change. The absence of soot incandescence during the initial flame propagation suggested flame propagation in a partially mixed fuel and air mixture with stoichiometric to fuel lean regions. A single fuel injection resulted in piston pool fires due to fuel spray impingement on the piston and was the primary source of soot formation. The pool fires persisted until after conditions favorable to oxidation of the soot had ended. Soot formation in the gas phase occurred while favorable soot oxidation conditions existed and was efficiently oxidized. The magnitude of the piston pool fires was reduced using multiple injections. The reduction is attributed to a reduction of the fuel spray penetration length and a smaller effective injection orifice area, resulting in a shorter total duration of fuel spray impingement on the piston crown. Soot formation occurred primarily in the gas phase when the first of two fuel sprays was ignited and persisted due to the second fuel spray entering an existing flame leading to fuel rich combustion.
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| 8. |
- Johansen, Lars Christian Riis, 1987
(författare)
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Injection and Combustion of Alternative Fuels in Spark Ignited Direct Injection Engines
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasingly stringent vehicle emission legislation necessitates increasingly efficient combustion engines. The use of direct injection in spark ignited engines improves engine efficiency and reduces CO2 emissions. Direct injection allows stratified combustion which can further improve engine efficiencyin part load operation with the penalty of increased emissions of soot from fuel rich combustion and pool fires with gasoline. Hydrogen, methane and ethanol are alternative fuels which can reduce emissions in direct injection engines operating with homogeneous or stratified combustion and are available from renewable sources. This thesis consists of an investigation of the transient gas jets that are created from direct injection of gas fuels and the stratified combustion of E85 and main sources of soot formation.The transient structure of gas jets created during direct injection of gas fuels in conditions relevant to homogeneous and stratified engine operation was investigated using time resolved schlieren imaging of helium jets in a pressure chamber. The jets became self-similar with respect to the width to penetration length ratio after an initial transition. The jet self-similarity variable decreased with increasing injection to ambient pressure ratio. At the same pressure ratio the self-similarity scaled non linearly with the injection pressure and ambient pressure. The self-similarity parameter was larger than reported in the literature resulting in a smaller penetration length constant. The Turner model was accurate for the transient compressible jets investigated with a constant relative error in the predicted shape.Stratified combustion of E85 was studied in an optical engine in to determine the main sources of soot formation, how soot formation could be reduced and how soot oxidation could be increased. Time and spatially resolved imaging of Mie scattering of diffuse light, combustion luminosity, OH · * chemiluminescence and soot luminescence along with cylinder pressure measurements were used to study combustion, flame propagation, soot formation and soot oxidation. Pool fires consisting of diffusion flames from combustion of liquid fuel films on the piston crown were the primary source of soot formation for a single injection of fuel. The liquid fuel films, pool fires and soot formation were reduced and soot oxidation increased by splitting a single injection into multiple injections and igniting the last fuel spray. The primary source of soot formation when the first of multiple fuel sprays was ignited was rich combustion in the gas phase.
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| 9. |
- Johansen, Lars Christian Riis, 1987
(författare)
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Spark Ignition Combustion of Direct Injected Alternative Fuels
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several technologies and modifications exist to increase the fuel efficiency of passenger vehicles in general and spark ignition engines in particular. Combining a spark ignition engine with an electric drive system in hybrid powertrain and thermodynamic cycle improvements are two such approaches with the potential to greatly reduce fuel consumption. Thermodynamic efficiency can be improved by lean engine operation. Extension of the lean limit leading to unthrottled operation is possible with lean stratified combustion. Stratified combustion leads to increased soot formation in addition to NOx with standard catalyst after treatment. Ethanol is an alternative fuel for spark ignition engines which is renewable and potentially leads to a reduction in soot formation in lean stratified combustion. In addition to liquid fuels, spark ignition engines are able to operate with gaseous fuels.The potential for reduction of spark ignition engine emissions during engine load transients using assistance from the electric powertrain was investigated. NOx emissions during engine load transients were reduced with simulated electric powertrain assistance. CO, hydrocarbon and soot emissions occurred at the beginning and end of engine load transients due to transient fuel rich conditions in the engine as a result of incorrect fuel metering. Electric assistance did not reduce soot emissions as they were unconnected to the engine load value during the transient.Combustion, sources of soot formation and soot oxidation in lean, spark ignited, stratified combustion of E10 (10 % vol. ethanol, 90 % vol. gasoline) and E85 were investigated in an engine with optical access using pressure analysis, high speed imaging, OH * chemiluminescence and soot incandescence. Diffusion combustion of liquid fuel films on the surface of the piston, referred to as a pool fire, was a major source of soot formation for both E10 and E85 with a single injection due to the fuel spray impingement on the piston. The effect was magnified when the engine load was increased. For E10 soot formation also occurred in the gas phase. Pool fires were the sole source of soot formation with E85 as the fuel. Splitting the single injection into multiple injections reduced the magnitude of soot formation from pool fires for both E10and E85. Soot formation in the gas phase with E10, appeared to increase slightly with multiple injection for both engine loads. Multiple injections led to an increase in the rate and stability of combustion in all cases.Gaseous fuels such as hydrogen and methane amongst others are another class of alternative fuels for spark ignited engines. The self similarity and the Turner model for the structure of transient jets during injection with a range of injection and ambient pressures was investigated with high speed schlieren imaging of helium jets. The Turner model was found to be an accurate approximation for the structure of the jet in all cases. The ratio of the jet width to the length was found to vary with the injection pressure to ambient pressure ratio indicating that the jet width to length ratio varied with different pressure ratio.
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