燃油温度对正庚烷喷雾和着火特性的影响

Impact of Fuel Temperature on n-Heptane Spray and Ignition Characteristics

在计算流体力学软件Converge上搭建定容燃烧弹模型,在环境温度为775 K和850 K下,以正庚烷为表征燃料,研究燃油温度从353 K降至233 K时对喷雾和着火特性的影响.结果表明:随着燃油温度的降低,喷雾的气相贯穿距基本不变,液相贯穿距显著增加,最大增幅达16%;当喷雾处于准稳态时,高油温的蒸发比例增大,剩余油包数减少,但油滴尺寸更大,其粒径最多增大24%;沿喷孔轴线方向混合气峰值浓度最多增大16%;滞燃期随燃油温度的增加而近似线性下降.正庚烷低温反应的开始时刻几乎不受油温影响,但随油温升高,低温反应速率加快、高温反应中间产物OH会更早生成,同时燃烧效率也更高.环境温度不同时油温对滞燃期有两种影响机制,在环境温度为850 K时,油温降低影响着火特性的原因是局部混合气浓度和温度下降,滞燃期可增加0.14 ms;在环境温度为775 K时,油温降低影响着火特性的原因是减缓着火前的低温反应进程,滞燃期可增加0.49 ms.

A constant volume combustion chamber model was built on the computational fluid dynamics software Converge,and n-heptane was used as the surrogate fuel.At two ambient temperatures of 775 K and 850K,the impact of fuel temperature dropping from 353 K to 233K on spray and ignition characteristics was studied.The results show that,with the dropping of fuel temperature,the vapor penetration length of the spray keeps nearly the same,and the liquid penetration length increases by up to 16%.When the spray is quasi-steady,the evaporation ratio of higher fuel temperature increases,and the number of remaining parcels decreases but their sizes increase by up to 24%.The peak value of the mixture concentration along the nozzle axis rises by up to 16%.The ignition delay decreases nearly linearly with the increase of fuel temperature.The start time of low temperature reaction of nheptane changes little as the fuel temperature rises,but its speed increases,and the formation of high temperature reaction production OH is earlier,as well as the higher combustion efficiency.Fuel temperature has two methods to affect ignition delay at different ambient temperatures.At the ambient temperature of 850 K,the dropping of fuel temperature increases the ignition delay mainly by decreasing the local concentration and temperature of the mixture,and the ignition delay can rise by 0.14 ms.At the ambient temperature of 775 K,the dropping of fuel temperature increases the ignition delay mainly by slowing down the process of chemical reaction before ignition,and the ignition delay can rise by 0.49 ms.