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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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Analysis on flow motion and combustion process in pre-chamber and main chamber for low-speed two-stroke dual-fuel engine

China Ship Power Institute Co. Ltd.-Teng Liu
Harbin Engineering University-Long Liu, Yue Wu, Qian Xiong
  • Technical Paper
  • 2019-01-2175
Published 2019-12-19 by SAE International in United States
Low-speed two-stroke dual-fuel engines has been paid more attention due to the energy efficiency design index and Tier III emissions limitations issued by International Marine Organization. Although the dual-fuel engines have strong merits on emissions reduction, which can reach the IMO Tier III without aftertreatment, the power output is much lower than that of diesel engines. Therefore, the dual-fuel engine is also needed to improve continuously. However, the mixing and combustion processes in the engine have not been fully understood. In this study, a 3D-CFD model of the dual-fuel engine was established using CONVERGE to explore the mixing and combustion processes. Locally embedding fine grids are considered at scavenging ports, natural gas injection ports, pre-chamber. The model was validated by experimental in-cylinder pressure. Then, the flow motion, mixing of natural gas and air, flow in pre-chamber, torch and combustion in main-chamber were analyzed based on swirl variation, flow velocity distribution, equivalence ratio distribution and torch propagation.
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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

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
  • Technical Paper
  • 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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Effects of Piston Bowl Diameter on Combustion Characteristics of a Natural gas/Diesel Dual Fuel Engine

Kyoto University-Keigo Takizawa, Hidetake Tanaka, Naoto Horibe, Takuji Ishiyama
Osaka Gas Co., Ltd.-Takahiro Sako
  • Technical Paper
  • 2019-01-2173
Published 2019-12-19 by SAE International in United States
Natural gas/diesel dual fuel engines have potential for a high thermal efficiency and low NOx emissions. However, they have the disadvantages of high unburned species emissions and lower thermal efficiencies at low loads (at low equivalence ratio). A way to solve this problem is to properly distribute the pilot fuel vapor in a natural-gas premixture. The combustion chamber geometry affects the combustion process since it influences the distribution of the pilot fuel vapor. This study investigates the influence of injection conditions and the piston bowl geometry on the performance and emissions of a dual fuel engine. Experiments were carried out using two pistons with different bowl diameters, 52 mm and 58 mm, at single-and two-stage diesel-fuel injection. The results show that the larger bowl provides lower hydrocarbon emissions at a lower equivalence ratio in the case of single-stage injection. For two-stage injection, the influence of the bowl diameter depends on the timing of the first injection. To elucidate the effects of pilot fuel distribution, computational fluid dynamics (CFD) calculations were conducted for non-reacting pilot fuel…
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Investigation of the High-Pressure-Dual-Fuel (HPDF) combustion process of natural gas on a fully optically accessible research engine

Technical University of Munich-Stephan Gleis, Stephanie Frankl, Dominik Waligorski, Dr.-Ing. Maximilian Prager, Prof. Dr.-Ing. Georg Wachtmeister
  • Technical Paper
  • 2019-01-2172
Published 2019-12-19 by SAE International in United States
In the “high-pressure-dual-fuel” (HPDF) combustion process, natural gas is directly injected into the combustion chamber with high pressure at the end of the compression stroke, and burned in a diffusion flame similar to conventional diesel combustion. As natural gas does not self-ignite when injected into hot air, a small amount of diesel fuel is injected directly before the gas injection to provide an ignition source for the gas jets. The HPDF combustion process has the potential to substantially reduce methane slip compared to today’s state of the art premixed lean burn gas engines, and furthermore, phenomena like knocking or misfire can be avoided completely. In this paper, the influences of in-cylinder air density and swirl motion on HPDF combustion is studied via high-speed recordings in a fully optically accessible 4.8 Liter single-cylinder research engine.
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A Study on PCCI Combustion Control in Medium Speed Dual-Fuel Engine

Yanmar Co., Ltd.-Kazuteru Toshinaga, Masaki Kuribayashi
  • Technical Paper
  • 2019-01-2176
Published 2019-12-19 by SAE International in United States
To achieve simultaneous reduction of CO2 and NOx emission from the Dual-Fuel (DF) engine using natural gas and diesel fuel, Premixed Charge Compression Ignition (PCCI) type combustion is a promising technology. However, to apply this technology to the practical operation of the DF engine, combustion control is key challenge because the ignition of PCCI type combustion is governed by chemical reaction of natural gas/air and diesel fuel premixture and not controlled by direct control parameter such as spark timing of spark-ignition natural gas engine or diesel fuel injection timing of micro-pilot type DF engine. The focus of this study is to understand the effect of engine control parameters on DF-PCCI combustion characteristics to establish the combustion control strategy in medium speed DF engine. Engine experiments using a 4-stroke medium speed single cylinder engine were carried out. Firstly, early two stage diesel pilot injection was applied to realize DF-PCCI combustion. As a result, brake thermal efficiency was successfully improved by 2%pt compared with conventional micro-pilot combustion while achieving low NOx emission to meet the stringent emission…
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Effects of Engine Operating Condition and Fuel Property on Pre-Ignition Phenomenon in a Highly Boosted Premixed Natural Gas Engine

Chiba University-Run Chen, Tatsuya Kuboyama, Yasuo Moriyoshi
GDEC Inc.-Shinji Yasueda
  • Technical Paper
  • 2019-01-2154
Published 2019-12-19 by SAE International in United States
The stochastic pre-ignition phenomenon plays a vital role to limit the further increasing BMEP for natural gas engines. In this study, the pre-ignition propensities were examined in a highly boosted premixed natural gas engine by various engine loads and air/fuel ratios, as well as different methane number (MN) altered by hydrogen addition. A proper pre-ignition evaluation method was proposed referring to intake temperature. Moreover, the limits of in-cylinder temperature and pressure for the onset of pre-ignition were estimated. The results show that both higher IMEP and richer mixture conditions readily lead to pre-ignition. The significant increases of pre-ignition frequency and heavy-knocking pre-ignition cycle present with lowering MN.
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Improving the Low Load Operation of a Dual-Fuel Diesel/Natural Gas Engine by Premixing the Diesel Fuel

University of Zagreb, Faculty of Mechanical Engineering and-Darko Kozarac, Mario Sremec, Ante Vučetić, Mladen Božić
  • Technical Paper
  • 2019-01-2174
Published 2019-12-19 by SAE International in United States
The paper evaluates different strategies of dual fuel (DF) operation in search of a solution that enables DF at low load. The strategies that were explored are conventional DF with increased intake temperature, split injection, and reactivity controlled compression ignition (RCCI) combustion. The RCCI operation enabled DF operation at higher natural gas mass fractions, with higher efficiency, and lower THC, CO and NOX emissions than in DF operation, while the efficiency of normal diesel operation (NDO) remained highest. If CO2 emission or cost effectiveness is used as a measure of performance then RCCI provided better performance than NDO as well.
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Considerations for Hydrogen Fuel Cells in Airborne Applications

SAE EUROCAE Fuel Cell Task Group
  • Aerospace Standard
  • AIR7765
  • Current
Published 2019-11-18 by SAE International in United States
The scope of this joint EUROCAE/SAE report is to compile the considerations relating to airborne application of hydrogen fuel cells. This document provides a comprehensive analysis of the use of hydrogen as a fuel by describing its existing applications and the experience gained by exploiting fuel cells in sectors other than aviation. The use of hydrogen fuel cells in aircraft can help in meeting aviation environmental targets (including noise pollution) and can be vital to achieving efficient electrically propelled air vehicles. The experience gained with mature fuel cells in terrestrial applications and the handling of other gases in aviation, as presented herein, will help in alleviating safety concerns and in demystifying the usage of hydrogen in aviation.
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