| 1. |
- Bergman, Miriam, 1978, et al.
(author)
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CFD-Based Optimization of a Diesel-fueled Free Piston Engine Prototype for Conventional and HCCI Combustion
- 2008
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In: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 1:1, s. 1118-1143
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Journal article (peer-reviewed)abstract
- This paper presents results of a parametric CFD modeling study of a prototype Free Piston Engine (FPE), designed for application in a series hybrid electric vehicle. Since the piston motion is governed by Newton’s second law, accounting for the forces acting on the piston/translator, i.e. friction forces, electrical forces, and in-cylinder gas forces, having a high-level control system is vital. The control system changes the electrical force applied during the stroke, thus obtaining the desired compression ratio. Identical control algorithms were implemented in a MATLAB/SIMULINK model to those applied in the prototype engine. The ignition delay and heat release data used in the MATLAB/SIMULINK model are predicted by the KIVA-3V CFD code which incorporates detailed chemical kinetics (305 reactions among 70 species). Since the piston motion and frequency, the rate of heat release and the initial in-cylinder conditions all affect each other, while predicted using different modelling tools with no direct coupling between them, an iterative procedure was used among models describing:1. Piston dynamics governed by Newton’s second law including a high-level control system (using MATLAB/SIMULINK)2. Combustion processes (using KIVA-3V)3. Intake and exhaust system dynamics (using the GT-POWER module of the GT-SUITETM)Effects of varying parameters such as compression ratios, power supplied to the compressor, fuel injection timings and injection pressures have been studied in both conventional diesel and HCCI modes, the target being to identify optimal conditions for the combustion process in which the engine can be operated highly efficiently with very low-emissions.
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| 2. |
- Ehleskog, Malin, 1980, et al.
(author)
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Effects of High Injection Pressure, EGR and Charge Air Pressure on Combustion and Emissions in an HD Single Cylinder Diesel Engine
- 2009
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In: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 2:2, s. 341-354
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Journal article (peer-reviewed)abstract
- When increasing EGR from low levels to a level that corresponds to low-temperature combustion, soot emissions initially increase due to lower soot oxidation before decreasing to almost zero due to very low soot formation. At the EGR level where soot emissions start to increase, the NOx emissions are low, but not sufficiently low to comply with future emission standards and at the EGR level where low-temperature combustion occurs CO and HC emissions are too high.The purpose of this study was to investigate the possibilities for shifting the so-called soot bump (where soot levels are increased) to higher EGR levels, or to reduce the magnitude of the soot bump using very high injection pressures (up to 240 MPa) while reducing the NOx emissions using EGR. The possibility of reducing the CO and HC emissions at high EGR levels due to the increased mixing caused by higher injection pressure was also investigated and the flame was visualized using an endoscope at chosen EGR values. In addition, flame temperatures and soot volume fractions were determined using two-color pyrometry.A single-cylinder heavy-duty direct injection diesel engine equipped with an electronically controlled unit injector with variable needle opening pressure was used in the investigations, with geometry based on the Volvo D12C production engine but with the compression ratio reduced from 18.5 to 14.The results from the studied cases showed that increasing EGR from 0 to 30% reduces both soot formation and oxidation resulting in higher engine-out soot emissions. Also, an increase in NOP for a case without EGR was found to give both high soot formation and high soot oxidation, resulting in reduced engine-out soot emissions. When EGR was added, increased NOP resulted in increased soot oxidation and thus in lower engine-out soot emissions. An increase in NOP was also found to reduce HC and CO emissions at high EGR levels.
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| 3. |
- Johansson, Thomas, et al.
(author)
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The Effect of Intake Temperature in a Turbocharged Multi Cylinder Engine operating in HCCI mode
- 2009
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In: ICE 2009. - : SAE International. ; 2:2, s. 452-466
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Conference paper (peer-reviewed)abstract
- The operating range in HCCI mode is limited by the excessive pressure rise rate and therefore high combustion induced noise. The HCCI range can be extended with turbocharging which enables increased dilution of the charge and thus a reduction of combustion noise. When the engine is turbocharged the intake charge will have a high temperature at increased boost pressure and can then be regulated in a cooling circuit. Limitations and benefits are examed at 2250 rpm and 400 kPa indicated mean effective pressure. It is shown that combustion stability, combustion noise and engine efficiency have to be balanced since they have optimums at different intake temperatures and combustion timings. The span for combustion timings with high combustion stability is narrower at some intake temperatures and the usage of external EGR can improve the combustion stability. It is found that the standard deviation of combustion timing is a useful tool for evaluating cycle to cycle variations. One of the benefits with HCCI is the low pumping losses, but when load and boost pressure is increased there is an increase in pumping losses when using negative valve overlap. The pumping losses can then be circumvented to some extent with a low intake temperature or EGR, leading to more beneficial valve timings at high load.
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| 4. |
- Manente, Vittorio, et al.
(author)
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Effects of Different Type of Gasoline Fuels on Heavy Duty Partially Premixed Combustion
- 2009
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In: SAE International Journal of Engines. - : SAE International. - 1946-3944. ; 2:2, s. 71-88
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Journal article (peer-reviewed)abstract
- The effects of fuel properties on the performance and emissions of an engine running in partially premixed combustion mode were investigated using nine test fuels developed in the gasoline boiling point range. The fuels covered a broad range of ignition quality and fuel chemistry.The fuels were characterized by performing a load sweep between 1 and 12 bar gross IMEP at 1000 and 1300 rpm. A heavy duty single cylinder engine from Scania was used for the experiments; the piston was not modified thus resulting in the standard compression ratio of 18:1.In order to properly run gasoline type of fuels in partially premixed combustion mode, an advanced combustion concept was developed. The concept involved using a lot of EGR, very high boost and an advanced injection strategy previously developed by the authors.By applying this concept all the fuels showed gross indicated efficiencies higher than 50% with a peak of 57% at 8 bar IMEP. NOx were mostly below 0.40 g/kWh only in few operative points 0.50 g/kWh was reached. At high load the soot levels were mostly a function of the octane number; with RON higher than 95 it was possible to be below 0.5 FSN while for the more reactive fuels a peak value of 3 FSN was reached at 13 bar IMEP.The pressure rise rate reached a peak of 19 bar/CAD with fuels which had a RON above 95, when the octane number decreased below 90 the pressure rise rate was always below 14 bar/CAD.
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