生物柴油缸内燃烧火焰温度对NO_x生成的影响

Effect of Biodiesel Combustion Flame Temperature on NO_x Formation in Diesel Engine

采用内窥镜高速摄影的方法,拍摄了柴油机燃用不同比例生物柴油-柴油调合燃料燃烧火焰的图像。基于亮度测温法的原理,计算了火焰的温度场分布。根据NOx生成的特点,提出了针对NOx生成的火焰温度评价指标:NOx生成区域的瞬态火焰面积、火焰面积变化速率、火焰面积平均变化速率、温度区域持续期、火焰面积出现效率,分析了评价指标随发动机转速、生物柴油调合比例的变化规律。研究结果表明:随着生物柴油添加比例和转速的增大,燃用B50和B100的NOx生成区域的火焰面积出现时刻和消失时刻提前,提前程度在高转速时较大,区域的峰值不断增大,对应的位置逐渐提前,火焰面积变化速率和火焰面积平均变化速率的峰值均不断增大,出现效率不断增大,持续时间逐渐缩短,这说明随着生物柴油调合比例的增大,缸内出现了有利于NOx生成的环境。

Images of combustion process of the engine fueled with diesel and biodiesel blends in different mixing ratio were captured by End Scope high-speed photography.Based on luminance of in-cylinder combustion flame pictures,the flame temperature distribution was computed.The physical and chemical characteristic parameters of flame temperature in cylinder and their changing laws with engine speed and biodiesel fuel mixing ratio were also analyzed using five indexes,NOx formation flame area（SNO）,flame area change velocity（VNO）,mean flame area change velocity（V^MNO）,flame area duration（φNO）,flame appearance efficiency（ηNO）.The results show that with the proportion of biodiesel fuel in blends increases,the positions of SNO appearance and disappearance are advanced,peak values of SNO,VNO,VMNO,ηNO become greater,φNO becomes shorter,which indicate that with the proportion of biodiesel fuel increases,more beneficial environment to NOx formation appears.