Based on diesel fuel(B0),20％volume fraction of n-butanol/diesel(B20)blend and 20％n-butanol+20％volume fraction polyoxymethylene dimethyl ether(PODE)/diesel(B20P20)blend were prepared respectively.Effect of pilot-injection ratio on the combustion and emission characteristics of B0,B20 and B20P20 were carried out in a light-duty diesel engine.The test conditions were 1 600r/min and 35％load,and the pilot-injection ratio was 20％to 50％of the total fuel quantity.Results show that the pilot-injection can significantly improve the thermal efficiency and reduce the NOx emissions compared with single fuel injection strategy.With the increase of pilot-injection ratio,the effective thermal efficiency first increases and then decreases and the NOx emissions decrease while the HC emissions increase.After adding n-butanol to diesel fuel,the combustion efficiency and effective thermal efficiency decrease,and the NOx emissions and the quality of particles decrease.But the HC and CO emis-sions and the number of particles significantly increase,and the size distribution of particulates transfers to nuclear modal particulate segments.After adding PODE to B20 fuel,the thermal efficiency significantly increases.Fur-thermore,combining the emission index and thermal efficiency index,the optimal pilot-injection ratio of B20P20 is 40％,and the addition of PODE can reduce the sensitivity of emissions to the pilot-injection ratio.
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