| 1. |
- Clasén, Kristoffer, 1992, et al.
(författare)
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High Load Lean SI-Combustion Analysis of DI Methane and Gasoline Using Optical Diagnostics with Endoscope
- 2021
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Konferensbidrag (refereegranskat)abstract
- Homogeneous lean spark-ignited combustion is known for its thermodynamic advantages over conventional stoichiometric combustion but remains a challenge due to combustion instability, engine knock and NOx emissions especially at higher engine loads above the naturally aspirated limit. Investigations have shown that lean combustion can partly suppress knock, which is why the concept may be particularly advantageous in high load, boosted operation in downsized engines with high compression ratios. However, the authors have previously shown that this is not true for all cases due to the appearance of a lean load limit, which is defined by the convergence of the knock limit and combustion stability limit. Therefore, further research has been conducted with the alternative and potentially renewable fuel methane which has higher resistance to autoignition compared to gasoline. Operation with a gaseous fuel on high load was achieved by high pressure direct injection and boosting in a single cylinder research engine. To analyse the combustion further, an endoscope allowing optical access to the combustion chamber was utilized to acquire combustion chamber flame images. High load lean operation with methane could confirm the hypothesis that without a knock limit, optimal ignition timing could be maintained resulting in high combustion stability, and the lean load limit mitigated. Instead, limitation was reached due to peak cylinder pressure. Direct injected methane resulted in overall higher combustion stability compared to gasoline. However, methane also provided an overall lower fuel conversion efficiency by 1-2 %-units compared to gasoline. Despite higher combustion stability using methane, the maximum air-dilution could only be marginally extended. Flame images using the endoscope revealed that the flame growth post ignition was prohibited, possibly due to flame quenching, at high turbulence conditions.
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| 2. |
- Melaika, Mindaugas, 1986, et al.
(författare)
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48V Mild-Hybrid Architecture Types, Fuels and Power Levels Needed to Achieve 75g CO2/km
- 2019
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2019-April:April
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Tidskriftsartikel (refereegranskat)abstract
- 48V mild hybrid powertrains are promising technologies for cost-effective compliance with future CO2 emissions standards. Current 48V powertrains with integrated belt starter generators (P0) with downsized engines achieve CO2 emissions of 95 g/km in the NEDC. However, to reach 75 g/km, it may be necessary to combine new 48V powertrain architectures with alternative fuels. Therefore, this paper compares CO2 emissions from different 48V powertrain architectures (P0, P1, P2, P3) with different electric power levels under various driving cycles (NEDC, WLTC, and RTS95). A numerical model of a compact class passenger car with a 48V powertrain was created and experimental fuel consumption maps for engines running on different fuels (gasoline, Diesel, E85, CNG) were used to simulate its CO2 emissions. The simulation results were analysed to determine why specific powertrain combinations were more efficient under certain driving conditions. As expected, the greatest influence on emissions was from powertrain architectures. Increased electric power levels (from 8 kW to 20 kW) allowed more brake energy to be recovered, reducing CO2 emissions by 2 - 16% depending on the driving cycle. The P2 and P3 architectures with even low electric motor power level offered substantially better fuel efficiency (by 19% on average) than a conventional powertrain with a start-stop system, whereas the P0/P1 architectures offered average improvements of only 4% for different power levels and driving cycles. In the P0 and P1 architectures, engine friction severely limited energy recovery during braking and made electric propulsion infeasible due to significantly increased power demands. The P2 and P3 architectures allow the engine to be decoupled from the powertrain and so avoid this problem. Overall, the 48V P2/P3 powertrains allowed for significant improvements in CO2 emissions when used with CNG, E85 or diesel fuel. 75 g/km target value was predicted to be achievable with CNG-fuelled systems under the NEDC and WLTC cycles, and possibly even under RTS95 on a well-to wheel basis when using a renewable fuel such as E85.
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| 3. |
- Melaika, Mindaugas, 1986, et al.
(författare)
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DI-CNG injector nozzle design influence on SI engine standard emissions and particulates at different injection timings
- 2022
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 317
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Tidskriftsartikel (refereegranskat)abstract
- Compressed natural gas direct injection (DI-CNG) systems in spark ignition (SI) internal combustion engines have shown that it can give several benefits compared to CNG port fuel injection systems. However, the DI-CNG injector nozzle head design and gas jet formation may greatly influence engine exhaust gas emissions and performance. Present experimental study investigated the influence of 7 different nozzle head designs of sprayguided DI-CNG injectors on the combustion process, engine performance, standard emissions, and particulate number (PN) when methane fuel was injected at different injection timings (SOI) and injection pressures (18 bar and 50 bar). The nozzle heads had two main design patterns – heads with small multi holes/orifices and heads with larger crevices (swirl or umbrella spray pattern). Naturally aspirated SI engine tests were conducted at part load (6 bar IMEP) and wide-open throttle (WOT) at 2000 rpm engine speed. The results revealed that the difference between the nozzle heads was small when the fuel was injected at an early stage of the intake stroke (310–350 CAD bTDC) either at part load or high load. However, for late injection timing (130–190 CAD bTDC), the design of the DI-CNG injector nozzle head had a large impact on the combustion stability, standard emissions formation and particulates. Multi-hole nozzle heads showed improved CO2, CO, THC, total PN, and slightly higher NOx emissions compared to nozzle heads with larger crevices. For some of the nozzles, the SOI could be retarded more than for other injector head designs at higher injection pressure whilst still ensuring an acceptable engine performance in terms of combustion stability, power output and emissions formation. Overall, 50-bar injection pressure and a late injection timing under WOT conditions achieved higher engine load levels with all injector nozzle types. Images acquired using an optical endoscope technique with a high-speed video camera showed that a yellow flame was present for all nozzle types at a low injection pressure and late SOI. Increasing the injection pressure reduced the injection duration, improved air/fuel mixing which resulted in the reduced byellow flame formation and lower PN for most of the nozzle heads.
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| 4. |
- Melaika, Mindaugas, 1986, et al.
(författare)
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Experimental Investigation of Methane Direct Injection with Stratified Charge Combustion in Optical SI Single Cylinder Engine
- 2016
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- This paper assesses methane low pressure direct injection with stratified charge in a SI engine to highlight its potential and downsides. Experiments were carried out in a spark ignited single cylinder optical engine with stratified, homogeneous lean and stoichiometric operational mode, with focus on stratified mode. A dual coil ignition system was used in stratified mode in order to achieve sufficient combustion stability. The fuel injection pressure for the methane was 18 bar. Results show that stratified combustion with methane spark ignited direct injection is possible at 18 bar fuel pressure and that the indicated specific fuel consumption in stratified mode was 28% lower compared to the stoichiometric mode. Combustion and emission spectrums during the combustion process were captured with two high-speed video cameras. Combustion images, cylinder pressure data and heat release analysis showed that there are fairly high cycle-to-cycle variations in the combustion. Both blue pre-mixed flame and soot luminescence occurred in the combustion. The occurrence of soot luminescence was also supported by the emission spectrum. Soot formation sources were found to be localized randomly in the bulk flame but not on the piston nor in the vicinity of the spark plug. These findings illustrate the difficulty of achieving proper mixing between air and methane resulting in fairly high cycle-to-cycle variations in the combustion and fuel rich areas which create a source of soot.
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| 5. |
- Melaika, Mindaugas, 1986, et al.
(författare)
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Methane Direct Injection in an Optical SI Engine - Comparison between Different Combustion Modes
- 2019
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2019-January:January
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 SAE International. All Rights Reserved. Natural gas, biogas, and biomethane are attractive fuels for compressed natural gas (CNG) engines because of their beneficial physical and chemical characteristics. This paper examines three combustion modes - homogeneous stoichiometric, homogeneous lean burn, and stratified combustion - in an optical single cylinder engine with a gas direct injection system operating with an injection pressure of 18 bar. The combustion process in each mode was characterized by indicated parameters, recording combustion images, and analysing combustion chemiluminescence emission spectra. Pure methane, which is the main component of CNG (up to 98%) or biomethane (> 98 %), was used as the fuel. Chemiluminescence emission spectrum analysis showed that OH∗ and CN∗ peaks appeared at their characteristic wavelengths in all three combustion modes. The peak of OH∗ and broadband CO 2 ∗ intensities were strongly dependent on the air/fuel ratio conditions in the cylinder. Lower OH∗ and CO 2 ∗ intensities were observed with lean air/fuel mixtures because under these conditions, more air was present, the combustion reactions were slower, and the cylinder pressure was higher. CN∗ was formed by the spark plasma and was detected over a particularly long period when using a dual coil ignition system. The intensities of the OH∗ and CN∗ signals correlated when using this ignition system. Combustion image analysis showed that the flame had a wrinkled boundary in stoichiometric and lean burn modes and was especially distorted in stratified mode. No yellow soot luminescence was observed during homogeneous combustion. However, the emission spectra and combustion images acquired during stratified combustion showed that soot formation occurred due to the presence of fuel-rich areas with inadequate mixing in the cylinder. The difficulty of maintaining stable fuel injection, achieving proper air/fuel mixing, and ensuring stable flame propagation in lean air/fuel mixtures increased cycle-to-cycle variations. However, the homogeneous lean burn and stratified combustion modes achieved significantly lower indicated specific fuel consumption values than stoichiometric combustion.
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| 6. |
- Melaika, Mindaugas, 1986, et al.
(författare)
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Particulates from a CNG DI SI Engine during Warm-Up
- 2021
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2021:2021
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Konferensbidrag (refereegranskat)abstract
- To assist efforts reducing harmful emissions from internal combustion engines, particulate formation was investigated in a compressed natural gas (CNG) Direct Injection single-cylinder SI engine in warm-up conditions. This involved tests at low engine speed and load, with selected engine coolant temperatures ranging from 15 to 90 °C, and use of a gasoline direct injection (GDI) system as a standard reference system. Total particulate number (PN), their size distribution, standard emissions, fuel consumption and rate of heat release were analyzed, and an endoscope with high-speed video imaging was used to observe combustion luminescence and soot formation-related phenomena. The results show that PN was strongly influenced by changes in coolant water temperature in both the CNG DI and GDI systems. However, the CNG DI engine generated 1 to 2 orders of magnitude lower PN than the GDI system at all tested temperatures. The PN decreased in both systems when the coolant temperature increased. The results also show that PN was sensitive to a broader engine coolant temperature range in the GDI system. However, PN was around two orders of magnitude higher at the lowest coolant temperature (15 °C) than at the highest temperature (90 °C) in the CNG DI system. In homogeneous CNG combustion (unlike gasoline combustion) high-speed video images revealed no diffusion or yellow flame anywhere in the cylinder, even at the lowest coolant temperature. Thus, no soot formation location could be determined from the images in CNG cases. Overall, engine measurements showed that the CNG DI engine emitted lower standard emissions (CO2, CO, HC, NOx) and PN than the GDI system across the experimental range of engine coolant temperatures.
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| 7. |
- Melaika, Mindaugas, 1986, et al.
(författare)
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Spark ignition engine performance, standard emissions and particulates using GDI, PFI-CNG and DI-CNG systems
- 2021
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 293
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Tidskriftsartikel (refereegranskat)abstract
- Gaseous fuels, e.g., natural gas, biogas, have several advantages over liquid fuels owing to their favorable physical and chemical properties, e.g., lower carbon numbers in the fuel composition and no issues regarding fuel evaporation. The present study investigated compressed natural gas (CNG) port fuel injection (PFI) and direct injection (DI) systems compared to gasoline direct injection (GDI) cases in a spark ignition (SI) naturally aspirated single cylinder engine at stoichiometric conditions. The tests included usual engine working points – from 4.5 bar IMEP to 9 bar IMEP engine load at different engine speeds – from 1500 rpm to 2500 rpm. The main aim was to investigate how gaseous fuels can improve the SI engine efficiency, reduce standard emissions and particulates, and explain the benefits of a natural gas DI system versus standard gas PFI and GDI systems. Analysis of the results showed that the rate of heat release of natural gas was lower than that of gasoline fuel. However, the stable combustion process of DI-CNG gave additional benefits, e.g., increased turbulence in the cylinder, which increased the combustion rate and affected the exhaust gas formation. The highest engine efficiency was achieved with the same natural gas DI system. The highest iSHC, iSCO, iSCO2 and iSNOx emissions reduction achieved at low and part load conditions with DI-CNG compared to GDI combustion. Particulates formation was lower with the gaseous fuel compared to gasoline. Additional benefits of lower particulate numbers among three injection systems were observed with DI-CNG combustion.
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