Abstract
Reactivity controlled compression ignition (RCCI) engines have a high thermal efficiency as well as low emissions of soot and nitrogen oxides (NOx). However, there is a conflict between combustion stability and harmful emissions at high engine load. Therefore, this work presented a novel approach for regulating n-butanol/methyl oleate dual fuel RCCI at high engine load in attaining lower pollutant emissions while maintaining stable combustion and avoiding excessive in-cylinder pressure. The tests were conducted on a single cylinder engine under rated speed and 90% full load. In this study, n-butanol was selected as a low-reactivity fuel for port injection, and n-butanol/methyl oleate blended fuel was used for in-cylinder direct injection. Combustion and emission characteristics of the engine were first investigated with varied ratios of n-butanol port injection (PFI) and direct injection (DI). Results showed that as the ratio of n-butanol PFI and DI rose, the peak cylinder pressure and heat release rate increased, while NOx and soot emissions reduced, and carbon monoxide (CO) and hydrocarbon (HC) emissions increased under most test conditions. When RNBPI = 40% and RNBDI = 20%, the soot and NOx emissions of the engine were near the lowest values of all test conditions, yet the peak in-cylinder pressure and fuel consumption could not increase significantly. Therefore, the possibility of optimizing the combustion process and lowering emissions by adjusting the pilot injection strategy was investigated utilizing these fuel injection ratios. The results revealed that with an appropriate pilot injection ratio and interval, the peak in-cylinder pressure and NOx emission were definitely reduced, while soot, CO, and HC emissions did not significantly increase.
Highlights
Reactivity controlled compression ignition (RCCI) engines have a high thermal efficiency as well as low emissions of soot and nitrogen oxides (NOx)
Abbreviations ATDC After top dead center brake specific fuel consumptions (BSFCs) Brake specific fuel consumption CA Crankshaft angle CA50 Crankshaft angle corresponding to 50% accumulative heat release rate carbon monoxide (CO) Carbon monoxide CO2 Carbon dioxide direct injection (DI) Direct injection EGR Exhaust gas recirculation fatty acid methyl esters (FAMEs) Fatty acid methyl esters HC Hydrocarbon homogeneous charge compression ignition (HCCI) Homogeneous charge compression ignition indicated mean effective pressures (IMEP) Indicated mean effective pressure mMO The mass of methyl oleate DI mNBDI The mass of n-butanol DI mNBPI The mass of n-butanol PFI NOx Nitrogen oxides
In order to guarantee that the RCCI combustion process does not produce excessive in-cylinder pressure at high load while generating low pollutant emissions, this study proposed a novel RCCI combustion approach using port injection of n-butanol and in-cylinder injection of n-butanol/methyl oleate blend
Summary
Reactivity controlled compression ignition (RCCI) engines have a high thermal efficiency as well as low emissions of soot and nitrogen oxides (NOx). Results showed that as the ratio of n-butanol PFI and DI rose, the peak cylinder pressure and heat release rate increased, while NOx and soot emissions reduced, and carbon monoxide (CO) and hydrocarbon (HC) emissions increased under most test conditions. The compression ignition combustion mode of the conventional diesel engine results in higher NOx and soot emissions These two pollutants could be reduced by lowering the combustion temperature and raising the premixed combustion ratio as much as possible[1]. According to the research findings, as compared to traditional compression ignition, the RCCI combustion mode significantly reduced soot emissions while increasing CO and HC emissions, and the NOx emissions change trend was related to engine load and port injection ratio. CO and HC emissions of the RCCI combustion mode rose as the ratio of n-butanol PFI increased, whereas the CO and HC emissions of the blended mode were less sensitive
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