燃料理化特性与进气压力耦合对碳氢化合物排放的影响

Study on the Coupling Effect of Fuel Physicochemical Characteristic and Intake Pressure on HC Emission

通过一台改进的单缸轻型柴油机,研究3种进气压力(120、150和180 kPa)下燃料的滞燃期、十六烷值与进气压力的耦合对柴油机碳氢化合物(HC)排放的影响。使用纯柴油(B00)、B20燃料(按质量分数混合20%正丁醇和80%纯柴油的燃料)和B20+EHN(B20中添加0.7%质量分数的2-乙基己基硝酸盐)作为燃料进行实验研究。对B00和B20+EHN的碳氢排放进行比较,可知在进气氧浓度高于13%时,HC排放差值几乎不随进气氧浓度发生变化,不同压力的HC排放差异基本维持在0~1 g/(kw·h)范围内。对B20和B20+EHN的碳氢排放进行比较,可知在120、150和180 kPa的入口压力下,临界氧浓度分别为16%、15%和13%,缸内燃烧温度和燃烧持续期是影响两种燃料HC排放差异的主要因素,当进气氧浓度值低于各进气压力下的临界点时,不同的十六烷值引起的缸内燃烧温度差异加大了HC排放的差异,随着氧浓度的降低,缸内燃烧温度的影响程度增大。

In this study,the effect of coupling three intake pressures(120,150,and 180 kPa)and the Cetane number,ignition delay period of fuel on hydrocarbon(HC)emissions was investigated by using a modified single-cylinder light-duty diesel engine.Pure combustion diesel(B00),B20 fuel(mixed with a mass fraction of 20%n-butanol and 80%pure diesel),and B20+2-ethylhexyl nitrate(EHN)(0.7%mass fraction of EHN added to B20)were used as fuels for experimental research.Experiment results show that,comparing the hydrocarbon emissions of B00 and B20+EHN,HC emissions almost does not change with the intake oxygen concentration when the intake oxygen concentration is higher than 13%,and the HC emissions under different pressures is basically maintained in the range of 0~1 g/(kw·h).The comparison of hydrocarbon emissions of B20 and B20+EHN shows that the critical oxygen concentration is 16%,15%and 13%respectively under intake pressures of 120,150 and 180 kPa.The in-cylinder combustion temperature and combustion duration are the main factors affecting the difference of HC emissions between the two fuels.When the intake oxygen concentration is lower than the critical point of each intake pressure,the difference of combustion temperature in cylinder caused by different cetane number increases the difference of HC emission.With the decrease of oxygen concentration,the influence degree of combustion temperature in cylinder increases.