Combustion Characteristics and Emissions of Direct Injection Neat n-Butanol in a Compression Ignition Engine
Internal combustion engines have been the major power source in the transportation sector for decades. Despite the recent developments in electric vehicles, internal combustion engines will continue to be one of the main propulsion methods for transportation sector, especially in heavy-duty applications. In order to maintain the competitiveness of internal combustion engines, renewable biofuels have been proposed to replace fossil fuels for internal combustion. The application of biofuels can greatly reduce the crisis of fossil fuel shortage and it is beneficial for reducing the life cycle carbon dioxide emissions. In this research, direct injection of neat n-butanol fuel is investigated in a compression ignition research engine. The combustion characteristics of n-butanol differ from that of diesel fuel by the longer ignition delay, shorter combustion duration, higher pressure rise rate, and narrower injection timing window. The NOx and smoke emissions from n-butanol combustion are significantly lower than those of diesel combustion. Different engine loads ranging from 2 bar to 7.5 bar are achieved with n-butanol combustion without the application of EGR. The combustion becomes more intensive with increased load, and the operation timing window is narrower due to the limits imposed by the high-pressure rise rate. To slow down the pressure rise rate, 30% EGR is applied under a load level of 6.5 bar IMEP. It is shown that EGR is not only effective in reducing the pressure rise rate but also beneficial for further reducing the NOx emissions. An EGR sweep experiment is carried out at a higher engine load of 10 bar IMEP with a CA50 of 365 °CA. Though the pressure rise rate decreases with the increase in EGR ratio, a significant increase in smoke emissions is observed when the EGR ratio increases above 35%. The trade-off between smoke emissions and the pressure rise rate can be alleviated by retarding the combustion phasing, but with a penalty of reduced indicated thermal efficiency.
This research is supported by NSERC CRD, APC, Discovery, CRC, CREATE programs; the CFI-ORF New Initiative Program; the NCE BioFuelNet programs; the Ford Motor Company, and the University of Windsor.
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