Lean-Burn Characteristics of a Heavy-Duty Diesel Engine Retrofitted to Natural-Gas Spark Ignition

Liu, Jinlong; Dumitrescu, Cosmin E.

doi:10.1115/1.4042501

Cited by 23 publications

(13 citation statements)

References 30 publications

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“…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: 97%

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: Introductionmentioning

confidence: 97%

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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“…For predicting knocking [45,46], the in-cylinder needs to be divided into at least two zones (the burnt zone and the unburnt zone or end-gas zone), in order to characterize the flame propagation and end-gas auto-ignition. Thus, the 0-D combustion models for knocking prediction are commonly associated with the cylinder volume division similarly to the two-zone models [47,48] and multi-zone models [49][50][51]. Xiang et al [47] proposed a two-zone model based on the Douaud-Eyzat correlation [37] to predict the knocking performance of the SI natural gas engines by assuming that the burnt and unburnt zones have a cylindrical shape.…”

Section: Introductionmentioning

confidence: 99%

“…As concluded from the discussed literature [44][45][46][47][48], a two-zone 0-D model could be an effective tool for the knocking behaviour analysis in NG engines as it is capable of characterising the end-gas zone temperature with the simplest combustion zone division. In addition, a 1-D model [56,57] could be employed for simulating the gas exchange process in order to improve the simulation accuracy of the entire engine cycle.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, a two-zone 0-D combustion model coupled with a 1-D gas exchange model could effectively be employed for predicting both the engine performance as well as knocking compromising between the model complexity and the required computational time. Another conclusion drawn from the previous studies on knocking [47][48][49][50][51][52][53][54][55][56][57] is that few studies focused on comparing and comparatively analysing the SI natural gas engines and the diesel/NG DF engines, which may exhibit different knocking behaviour due to their distinct ignition methods. In particular, the flame propagation in SI natural gas engines initiates from a single ignition source [10], whilst that in CI dual fuel engines starts from multiple ignition points by employing a pilot fuel injection [18,19].…”

Section: Introductionmentioning

confidence: 99%

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Parametric Knocking Performance Investigation of Spark Ignition Natural Gas Engines and Dual Fuel Engines

Xiang

Theotokatos

Cui

et al. 2020

JMSE

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Both spark ignition (SI) natural gas engines and compression ignition (CI) dual fuel (DF) engines suffer from knocking when the unburnt mixture ignites spontaneously prior to the flame front arrival. In this study, a parametric investigation is performed on the knocking performance of these two engine types by using the GT-Power software. An SI natural gas engine and a DF engine are modelled by employing a two-zone zero-dimensional combustion model, which uses Wiebe function to determine the combustion rate and provides adequate prediction of the unburnt zone temperature, which is crucial for the knocking prediction. The developed models are validated against experimentally measured parameters and are subsequently used for performing parametric investigations. The derived results are analysed to quantify the effect of the compression ratio, air-fuel equivalence ratio and ignition timing on both engines as well as the effect of pilot fuel energy proportion on the DF engine. The results demonstrate that the compression ratio of the investigated SI and DF engines must be limited to 11 and 16.5, respectively, for avoiding knocking occurrence. The ignition timing for the SI and the DF engines must be controlled after −38°CA and 3°CA, respectively. A higher pilot fuel energy proportion between 5% and 15% results in increasing the knocking tendency and intensity for the DF Engine at high loads. This study results in better insights on the impacts of the investigated engine design and operating settings for natural gas (NG)-fuelled engines, thus it can provide useful support for obtaining the optimal settings targeting a desired combustion behaviour and engine performance while attenuating the knocking tendency.

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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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Lean-Burn Characteristics of a Heavy-Duty Diesel Engine Retrofitted to Natural-Gas Spark Ignition

Cited by 23 publications

References 30 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

Parametric Knocking Performance Investigation of Spark Ignition Natural Gas Engines and Dual Fuel Engines

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

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