高海拔条件下PODE/柴油着火与燃烧特性研究

Study on Ignition and Combustion Characteristics of PODE/Diesel Blended Fuel at High Altitude

基于柴油与PODE化学反应机理,构建了TRF-PODE化学反应动力学模型(包含219种组分、903个基元反应)并验证,开展了高海拔条件下PODE/柴油着火与燃烧特性数值模拟研究。结果表明:在高海拔低压力下,PODE增加了着火瞬时放热率,降低了着火最高温度对应时间;PODE对燃料着火起到促进作用,着火促进率最大值出现在负温度特性(NTC)区域范围内,且随着PODE掺混比例的增加而增大;高海拔条件下低温氧化中PODE增加了反应中OH·生成,促进nC7H16前期氧化,反应中羟基的最高摩尔分数随压力下降明显增加,使基元反应速率降低;高温条件下,PODE本身含氧增加了反应中的OH·的生成,降低了O_(2)参与生成OH·反应的比例,使更多的O_(2)能够氧化反应中的小分子,促进自由离子生成,提升反应活性,改善柴油机高海拔燃烧特性。

Based on the chemical reaction mechanism of diesel fuel with PODE,the TRF-PODE chemical kinetics model was constructed and verified,the ignition and combustion characteristics of PODE/diesel fuel were studied by numerical simulation at high altitude.The results show that the addition of PODE increases the instantaneous heat release rate and decreases the corresponding time of the highest point of ignition temperature under the condition of low pressure at high altitude.The maximum ignition promotion rate occurs in the region of negative temperature coefficient(NTC),which is increased with higher PODE blending ratio.PODE increases the formation of OH·and promotes the pre-oxidation of nC7H16 in the low temperature oxidation at high altitude.As a result,the highest mole fraction of hydroxyl group in the reaction increases obviously with the decrease of pressure,which leads to the decrease of reaction rate.Under high temperature,the oxygen of PODE itself increases the formation of OH·in the reaction,leading to a reduction of the proportion of O_(2)participating in the formation of OH·.Therefore,more O_(2)could oxidize the small molecules in the reaction,promote the formation of free ions,and enhance the reaction activity,which is beneficial to improve the combustion characteristics of diesel engines at high altitude.