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Energy Release Characteristics inside a Spark-Ignition Engine with a Bowl-in-Piston Geometry

West Virginia University-Jinlong Liu, Cosmin Emil Dumitrescu
  • Technical Paper
  • 2020-01-5003
Published 2020-01-16 by SAE International in United States
The conversion of compression ignition (CI) internal combustion engines to spark-ignition (SI) operation by adding a spark plug to ignite the mixture and fumigating the fuel inside the intake manifold can increase the use of alternative gaseous fuels (e.g., natural gas) in heavy-duty applications. This study proposed a novel, less-complex methodology based on the inflection points in the apparent rate of heat release (ROHR) that can identify and separate the fast-burning stage inside the piston bowl from the slower combustion stage inside the squish region (a characteristic of premixed combustion inside a diesel geometry). A single-cylinder 2L CI research engine converted to natural gas SI operation provided the experimental data needed to evaluate the methodology, at several spark timings, equivalence ratios, and engine speeds. The results indicated that the end of the bulk combustion traditionally defined as the location of 90% energy release was not greatly affected by the change in operating conditions. Moreover, the actual duration of the rapid-burning stage was 60-80% shorter than the crank angle interval between 10% and 90% energy release.…
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Methodology to Determine the Fast Burn Period Inside a Heavy-Duty Diesel Engine Converted to Natural Gas Lean-Burn Spark Ignition Operation

SAE International Journal of Advances and Current Practices in Mobility

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
  • Journal Article
  • 2019-01-2220
Published 2019-12-19 by SAE International in United States
The conversion of existing diesel engines to natural-gas operation can reduce the dependence on petroleum imports and curtail engine-out emissions. A convenient way to perform such conversion is by adding a gas injector in the intake manifold and replacing the diesel fuel injector with a spark plug to initiate and control the combustion process. However, challenges may appear with respect to engine’s efficiency and emissions as natural-gas spark-ignition combustion inside a diesel combustion chamber is different to that in conventional spark ignition engines. For example, major difference is the phasing and duration of the fast burn, defined as the period in which the rate of heat release increases linearly with crank angle. This study presents a methodology to investigate the fast burn inside a diesel geometry using heat release data. The algorithm was applied to experimental data from a single-cylinder research engine that operated at several lean-burn conditions that changed spark timing, equivalence ratio, and engine speed. More, a 3D CFD RANS engine simulation was used to validate the developed methodology. As results showed that…
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Specifics of the Combustion Phenomenon Inside a Heavy-Duty Diesel Engine Converted to Natural Gas Lean-Burn Spark Ignition Operation

Center for Alternative Fuels Engines and Emissions (CAFEE),-Jinlong Liu, Cosmin E. Dumitrescu, Hemanth Bommisetty
  • Technical Paper
  • 2019-01-2221
Published 2019-12-19 by SAE International in United States
The conversion of existing diesel engines to natural gas with the least amount of modifications can reduce the dependence on conventional oil and enhance national energy security. This study investigated such engine conversion using an experimental platform that consisted of a single-cylinder diesel engine modified for lean-burn natural-gas spark-ignition operation through the addition of a gas injector and a spark plug. Following steady-state experiments at several operating conditions that changed spark timing, mixture equivalence ratio, and engine speed, the experimental results suggested that the combustion phenomena in diesel engines retrofitted to lean-burn natural gas spark ignition presents significant differences compared to that in a conventional stoichiometric spark ignition engine. For example, the apparent heat release rate inferred from recorded pressure data is the addition of two separate, sequential combustion events: a fast burn inside the piston bowl and a slow event inside the squish region. To model the heat release in such converted engine, each combustion event was approximated to a Gaussian curve, with the total heat release during the engine cycle being the superimposition…
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CFD Investigation of the Effects of Gas’ Methane Number on the Performance of a Heavy-Duty Natural-Gas Spark-Ignition Engine

Universita degli Studi di Perugia-Luca Ambrogi, Michele Battistoni, Lorenzo Gasbarro
West Virginia Univ.-Jinlong Liu, Cosmin Dumitrescu
Published 2019-09-09 by SAE International in United States
Natural gas (NG) is an alternative fuel for spark-ignition engines. In addition to its cleaner combustion, recent breakthroughs in drilling technologies increased its availability and lowered its cost. NG consists of mostly methane, but it also contains heavier hydrocarbons and inert diluents, the levels of which vary substantially with geographical source, time of the year and treatments applied during production or transportation. To investigate the effects of NG composition on engine performance and emissions, a 3D CFD model of a heavy-duty diesel engine retrofitted to NG spark ignition simulated lean-combustion engine operation at low speed and medium load conditions. The work investigated three NG blends with similar lower heating value (i.e., similar energy density) but different Methane Number (MN). The results indicated that a lower MN increased flame propagation speed and thus increased in-cylinder pressure and indicated mean effective pressure. In addition, a low MN increased the thermal efficiency despite the higher heat transfer to the surroundings. Also, a higher MN reduced the nitrogen-oxides emissions but increased unburned hydrocarbons (UHC) emissions. Moreover, while UHC emissions…
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Experimental Investigation of Combustion Characteristics in a Heavy-Duty Compression-Ignition Engine Retrofitted to Natural-Gas Spark-Ignition Operation

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-09-09 by SAE International in United States
Recent development in hydraulic fracking made natural gas (NG) to be a promising alternative gaseous fuel for heavy-duty diesel engines. The existing compression ignition (CI) engine can be retrofitted to NG spark ignition (SI) operation by replacing the diesel injector with a spark plug and fumigating NG into the intake manifold. However, the original diesel piston geometry (flat head and bowl-in-piston chamber) was usually retained to reduce modification cost. The goal of this study was to increase the understanding of the NG lean-burn characteristics in a diesel-like, fast-burn SI combustion chamber. The experimental platform can operate in conventional (i.e., all engine parts are metal) or in optical configuration (i.e., the stock piston and cylinder block are replaced with a see-through piston and an extended cylinder block). The optical data indicated a fast-propagated flame inside the piston bowl. However, this rapid-burning process did not shorten the combustion duration, which can be explained by an important fuel mass trapped in the squish that burned slowly during the expansion stroke. Steady-state experiments that operated at the metal engine…
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Heavy-Duty Compression-Ignition Engines Retrofitted to Spark-Ignition Operation Fueled with Natural Gas

Universita degli Studi di Perugia-Lorenzo Gasbarro, Michele Battistoni, Luca Ambrogi
West Virginia Univ-Jinlong Liu, Cosmin Dumitrescu, Christopher Ulishney
  • Technical Paper
  • 2019-24-0030
Published 2019-09-09 by SAE International in United States
Natural gas is a promising alternative gaseous fuel due to its availability, economic, and environmental benefits. A solution to increase its use in the heavy-duty transportation sector is to convert existing heavy-duty compression ignition engines to spark-ignition operation by replacing the fuel injector with a spark plug and injecting the natural gas inside the intake manifold. The use of numerical simulations to design and optimize the natural gas combustion in such retrofitted engines can benefit both engine efficiency and emission. However, experimental data of natural gas combustion inside a bowl-in-piston chamber is limited. Consequently, the goal of this study was to provide high-quality experimental data from such a converted engine fueled with methane and operated at steady-state conditions, exploring variations in spark timing, engine speed and equivalence ratio. The results showed that a higher engine speed reduced the motoring pressure, advanced maximum brake torque timing, and reduced the power output per cycle. Moreover, advanced spark timing increased and advanced the cylinder pressure, and increased both hydrocarbon and nitrogen oxides emissions. Leaner operation retarded the flame…
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Experimental Investigation of a Natural Gas Lean-Burn Spark Ignition Engine with Bowl-in-Piston Combustion Chamber

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-04-02 by SAE International in United States
On- and off-road heavy-duty diesel engines modified to spark-ignition natural gas operation can reduce U.S. dependence on imported oil and enhance national energy security. Engine conversion can be achieved through the addition of a gas injector in the intake manifold and of a spark plug in place of the diesel injector. This paper investigated combustion characteristics and engine performance at several lean-burn operating conditions that changed spark timing, mixture equivalence ratio, and engine speed, using methane as NG surrogate. The results show that the bowl-in-piston geometry separated the combustion process into two distinct events: an inside-the-bowl burning (due to the squish effect) that had a short duration and consumed a high fraction of fuel, and a slower inside-the-squish burning process, most probably due to the large surface/volume ratio (that increased the heat transfer to the boundaries) and to the lower in-cylinder pressure and temperature during the expansion stroke. While the operating conditions affected the overlapping of these two combustion stages, conditions that increased their phasing separation produced a second peak in the rate of heat…
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CFD Simulation of Metal and Optical Configuration of a Heavy-Duty CI Engine Converted to SI Natural Gas. Part 2: In-Cylinder Flow and Emissions

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-01-15 by SAE International in United States
Internal combustion diesel engines with optical access (a.k.a. optical engines) increase the fundamental understanding of combustion phenomena. However, optical access requirements result in most optical engines having a different in-cylinder geometry compared with the conventional diesel engine, such as a flat bowl-in-piston combustion chamber. This study investigated the effect of the bowl geometry on the flow motion and emissions inside a conventional heavy-duty direct-injection diesel engine that can operate in both metal and optical-access configurations. This engine was converted to natural-gas spark-ignition operation by replacing the fuel injector with a spark plug and adding a low-pressure gas injector in the intake manifold for fuel delivery, then operated at steady-state lean-burn conditions. A 3D CFD model based on the experimental data predicted that the different bowl geometry did not significantly affect in-cylinder emissions distribution. In addition, while in-cylinder flow motion was similar for both engine configurations, the different combustion chamber geometry affected the combustion-induced flow motion. Similar turbulence-generating mechanisms for engines with or without optical access show promise for optical investigations of cold-flow turbulence measurements representative…
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CFD Simulation of Metal and Optical Configuration of a Heavy-Duty CI Engine Converted to SI Natural Gas. Part 1: Combustion Behavior

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-01-15 by SAE International in United States
Internal combustion engines with optical access (a.k.a. optical engines) provide additional information in the quest for understanding the fundamental in-cylinder combustion phenomena. However, most optical engines have flat bowl-in-piston combustion chamber to optimize the visualization process, which is different, for example, from the traditional re-entrant bowl in compression ignition engines. A conventional heavy-duty direct-injection compression ignition engine was converted to spark ignition operation by replacing the fuel injector with a spark plug in both optical and metal setups to investigate the effect of the bowl geometry on flame propagation. Experimental data from steady-state lean-burn conditions was used to develop and validate a 3D CFD model of the engine. Numerical simulation results show that flame propagation in the radial direction was similar for both combustion chambers despite their different geometries. However, there were differences in the late combustion behavior. As a result, the similar flame propagation inside the optical engine suggests that such engines are best used to investigate flame inception and early flame propagation inside heavy-duty CI engines converted to natural gas spark ignition operation.
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Choice of Tuning Parameters on 3D IC Engine Simulations Using G-Equation

Oak Ridge National Laboratory-James Szybist
West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2018-04-03 by SAE International in United States
3D CFD spark-ignition IC engine simulations are extremely complex for the regular user. Truly-predictive CFD simulations for the turbulent flame combustion that solve fully coupled transport/chemistry equations may require large computational capabilities unavailable to regular CFD users. A solution is to use a simpler phenomenological model such as the G-equation that decouples transport/chemistry result. Such simulation can still provide acceptable and faster results at the expense of predictive capabilities. While the G-equation is well understood within the experienced modeling community, the goal of this paper is to document some of them for a novice or less experienced CFD user who may not be aware that phenomenological models of turbulent flame combustion usually require heavy tuning and calibration from the user to mimic experimental observations. This study used ANSYS® Forte, Version 17.2, and the built-in G-equation model, to investigate two tuning constants that influence flame propagation in 3D CFD SI engine simulations: the stretch factor coefficient, Cms and the flame development coefficient, Cm2. After identifying several Cm2-Cms pairs that matched experimental data at one operating conditions,…
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