Experimental Investigation of a Heavy-Duty CI Engine Retrofitted to Natural Gas SI Operation

Liu, Jinlong; Bommisetty, Hemanth; Dumitrescu, Cosmin E.

doi:10.1115/icef2018-9611

Cited by 14 publications

(11 citation statements)

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“…As a result, the amount of fuel burned per crank angle inside the squish decreased, which then delayed the EOC for “fast-burn” cycles. This matches the findings in Liu et al, 18 in which, in a similar retrofitted engine, a similar EOC was reported despite a 20 CAD change in spark timing.…”

Section: Resultssupporting

confidence: 92%

“…a more evident second peak in the heat release rate) would appear if the operating conditions increased the separation between the fast- and slow-burning stages. 18,19 These results suggest that an approach to increase the thermal efficiency in such an engine is to optimize the flame propagation inside the bowl, which would decrease the duration of the first combustion stage and probably lower the unburned mass fraction inside the slow-burning region. Consequently, it is of interest to first improve the fundamental understanding of the lean-burn SI NG operation inside the piston bowl.…”

Section: Introductionmentioning

confidence: 96%

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Optical analysis of flame inception and propagation in a lean-burn natural-gas spark-ignition engine with a bowl-in-piston geometry

Liu

Dumitrescu

2019

International Journal of Engine Research

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Heavy-duty diesel engines can convert to lean-burn natural-gas spark-ignition operation through the addition of a gas injector in the intake manifold and of a spark plug in place of the diesel injector to initiate and control combustion. However, the combustion phenomena in such converted engines usually consist of two distinct stages: a fast-burning stage inside the piston bowl followed by a slow-burning stage inside the squish area. This study used flame luminosity data and in-cylinder pressure measurements to analyze flame propagation inside a bowl-in-piston geometry. The experimental results showed a low coefficient of variation and standard deviation of peak cylinder pressure, moderate rate of pressure rise, and no knocking for the lean-burn (equivalence ratio 0.66), low-speed (900 r/min), and medium-load (6.6 bar IMEP) operating condition. Flame inception had a strong effect on the flame expansion velocity, which increased fast once the flame kernel established, but it reduced near the bowl edge and the entrance of the narrow squish region. However, the burn inside the bowl was very fast. In addition, the long duration of burn inside the squish indicated a much lower flame propagation speed for the outside-the-bowl combustion, which contributed to a long decreasing tail in the apparent heat release rate. Furthermore, cycles with fast flame inception and fast burn inside the bowl had a similar end of combustion with cycles with delayed flame inception and then a retarded burn inside the bowl, which indicated that the combustion inside the squish region determined the combustion duration. Overall, the results suggested that the spark event, the flame development inside the piston bowl, and the start of the second combustion stage affected the phasing and duration of the two combustion stages, which (subsequently) can affect engine efficiency and emissions of diesel engines converted to a lean-burn natural-gas spark-ignition operation.

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Section: Resultssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 96%

Optical analysis of flame inception and propagation in a lean-burn natural-gas spark-ignition engine with a bowl-in-piston geometry

Liu

Dumitrescu

2019

International Journal of Engine Research

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“…The results obtained showed that the maximum cylinder pressure increased, two peak formations can be seen in the heat release depending on the spark time, the maximum brake torque and thermal efficiency decrease, the Turbulence Kinetic Energy (TKE) and turbulence dissipation rate in the cylinder increase and the combustion time increased by taking the SIT advanced. 7,[9][10][11][12][13][14][15] When the literature studies are examined in general, it is seen that studies are carried out in engines using natural gas at low compression ratios such as 11:1-16:1. [7][8][9][10][11][12][13][14][15][16][17][18][19] In this study, unlike other studies in the literature, three-dimensional numerical studies were carried out at high speed (2300 rpm) and under full load in an engine with a high compression ratio of 17.5:1 and a special combustion chamber design (stepped lip bowl).…”

Section: Introductionmentioning

confidence: 99%

“…7,[9][10][11][12][13][14][15] When the literature studies are examined in general, it is seen that studies are carried out in engines using natural gas at low compression ratios such as 11:1-16:1. [7][8][9][10][11][12][13][14][15][16][17][18][19] In this study, unlike other studies in the literature, three-dimensional numerical studies were carried out at high speed (2300 rpm) and under full load in an engine with a high compression ratio of 17.5:1 and a special combustion chamber design (stepped lip bowl). In the study, besides the performance and emission values, incylinder cold flow and combustion phenomena were investigated and the effects of bowl-in piston geometry on in-cylinder combustion characteristics were examined in detail.…”

Section: Introductionmentioning

confidence: 99%

Spark ignition timing effects on a converted diesel engine using natural gas: A numerical study

Aktas

2022

Proceedings of the Institution of Mechanical Engineers, Part D:

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Since it is not expected to switch to fully electric and/or fuel cell vehicles in the near future, the search for alternative fuels for systems using internal combustion engines has accelerated. At the forefront of these studies is the use of natural gas instead of diesel fuel in on-road, off-road vehicles, or stationary power generation plants. Diesel engines with their special combustion chamber (i.e. bowl in-piston) can be converted to run entirely on natural gas by installing a natural gas fuel injector on the intake manifold and a spark plug instead of a diesel fuel injector. In this study, in-cylinder combustion characteristics, performance, and emission values for different Spark Ignition Time (SIT) of natural gas usage at 2300 rpm and full load in a tractor engine with a compression ratio of 17.5:1 were investigated numerically using ANSYS Forte three-dimensional analysis program. G-equation combustion model, RANS k-ε turbulence model, and methane chemical kinetic mechanism representing natural gas consisting of 29 species and 171 equations (a reduced mechanism) were used. First SIT was accepted as a 719.5 Crank Angle Degree (CAD) which is diesel injection start time. As a result, due to the special shape of the combustion chamber of diesel engines (re-entrant bowl in-piston), it was seen that the flame was faster and thicker in the bowl, while it was slower and thinner in the squish zone. With the advanced of SIT, the in-cylinder pressure ratio increased. By taking SIT too advanced (i.e. 690, 695, and 700 CAD SIT), more than one peak formation was observed in the heat release graph depending on the combustion characteristic. With the effect of both natural gas use and SIT, it was observed that HC and CO formations were almost not seen, while NOX formation remains above a certain level.

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“…Weaver et al [11] reported that the roof-type head geometry in conventional SI engines is not optimal for lean combustion due to combustion instabilities and increased cycle-to-cycle variations. Consequently, gasoline engines with a roof-type head are more likely to be modified to NG stoichiometric operation [46,47]. In other words, the slow-burn geometry of conventional gasoline engines and NG's low laminar flame speed at lower equivalence ratio are not ideal to converting SI engines to NG lean burn operation.…”

Section: Natural Gas In Gasoline Enginesmentioning

confidence: 99%

Investigation of Combustion Characteristics of a Heavy-Duty Diesel Engine Retrofitted to Natural Gas Spark Ignition Operation

Liu¹

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The conversion of existing diesel engines to natural-gas spark ignition operation by adding a gas injector in the intake manifold for fuel delivery and replacing the diesel fuel injector with a spark plug to initiate and control the combustion process can reduce U.S. dependence on petroleum imports and curtail engine-out emissions. As the conventional diesel combustion chamber (i.e., flat head and bowl-in-piston) creates high turbulence, the engine can operate leaner, which would increase its efficiency and reduce emissions. However, natural gas combustion in such retrofitted engines presents differences compared to that in conventional spark ignited engines. Subsequently, the main goal of this study was to investigate the characteristics of natural gas combustion inside a diesel-like, fast-burn combustion chamber using a unique array of experimental and numerical tools. The experimental platform consisted of a heavy-duty single-cylinder diesel engine converted to natural-gas spark ignition and operated at a low-speed, lean equivalence ratio, and medium-load condition. The engine can also operate in an optical configuration (i.e., the stock piston and cylinder block can be replaced with a see-through piston and an extended cylinder block), which was used to visualize flame behavior. The optical data indicated a thick and fast-propagated flame in the piston bowl but slower flame propagation inside the squish region. In addition, a 3D numerical model of the optical engine was built to better explain the geometry effects. The simulation results suggested that while the region around the spark plug location experienced a moderate turbulence that helped with the ignition process, the interaction of squish, piston motion, and intake swirl created a highly-turbulent environment that favored the fast burn inside the bowl and stabilized the combustion process. However, the squish region experienced a much lower turbulence, which, combined with the reduced temperature and pressure during the expansion stroke and its higher surface-to-volume ratio, reduced the burning velocity and the flame propagation, but also avoided knocking. Consequently, the bowl-in-piston geometry separated the leanburn natural gas combustion into two distinct events. To extend the optical findings, the metal engine configuration was used to investigate the effects of gas composition, spark timing, equivalence ratio, and engine speed on the two-stage combustion. The results suggested that operating conditions controlled the magnitude and phasing of the two combustion events. Moreover, 3D CFD simulations of the metal engine configuration showed that the squish region contained an important mixture fraction that would burn much slower and can increase the phasing separation between the two combustion events to a point that a second peak would appear in the heat release rate. Moreover, the rapidburn event in such an engine was much shorter compared to its traditional definition (i.e., the time in crank angle degrees between the 10% and 90% energy-releas...

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Experimental Investigation of a Heavy-Duty CI Engine Retrofitted to Natural Gas SI Operation

Cited by 14 publications

References 0 publications

Optical analysis of flame inception and propagation in a lean-burn natural-gas spark-ignition engine with a bowl-in-piston geometry

Optical analysis of flame inception and propagation in a lean-burn natural-gas spark-ignition engine with a bowl-in-piston geometry

Spark ignition timing effects on a converted diesel engine using natural gas: A numerical study

Investigation of Combustion Characteristics of a Heavy-Duty Diesel Engine Retrofitted to Natural Gas Spark Ignition Operation

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