Energy Efficiency Comparison between Butanol and Ethanol Combustion with Diesel Ignition

摘要

The use of low temperature combustion (LTC) in diesel engines tends to suppress the NO_x and dry soot emissions from diesel engines. However, due to the limitations of conventional diesel fuel properties, such as the high reactivity and low volatility, implementation of LTC is highly dependent on the application of exhaust gas recirculation (EGR). While the replacement of some of the fresh air intake with the burnt exhaust gas using EGR prevents premature combustion, it also results in a reduction in thermal efficiency. In this work, the use of two different alcohol fuels, ethanol and butanol, in a high compression ratio diesel engine has been investigated to examine their potential as substitutes for conventional diesel fuel when operating under low temperature combustion mode. The effect of diesel injection timing, alcohol fuel ratios, and EGR on engine emissions and efficiency were studied at indicated mean effective pressures in the range 0.8 to 1.2 MPa. From the data obtained it indicates that combustion with ultra-low smoke and nitrogen oxides emissions can be achieved with port injection of butanol at low to medium engine loads, and with port injection of ethanol at high engine loads. The major challenges encountered in these alternative fuel investigations were the control of the onset of combustion of butanol and the peak cylinder pressure of ethanol combustion. The peak pressure rise rate was also higher than diesel baseline for both butanol and ethanol combustion. To some extent these issues were overcome by a combination of the use of exhaust gas recirculation and changes to the diesel injection timing. However, while the use of these alcohol fuels has been shown to be promising, more work on their practical implementation with LTC mode operation is still required.