基于变海拔柴油撞壁喷雾着火特性可视化研究

Visualization on Ignition Characteristic of Wall-Impinging Diesel Spray at Different Altitudes

使用定容燃烧弹模拟一款重型柴油机在海拔为0、3.0和4.5 km条件下运行时缸内的热力学状态,研究了不同海拔下柴油撞壁喷雾的着火特性.分别使用背光散射成像技术和广域低通化学发光成像技术,实现了喷雾和着火过程的可视化.研究结果表明:高海拔对撞壁着火过程有明显的抑制效果,撞壁距离为57 mm时,海拔从0 km升高到4.5 km,着火延迟从0.57 ms延长到0.89 ms,着火距离从14.83 mm增大到18.68 mm,而且高温着火区域面积增加,出现多区域同时着火的概率增大;相同海拔下不同撞壁距离对着火延迟的影响很小,但是由于平板的存在限制了喷雾向下游的发展,不同撞壁距离会显著影响着火位置,而且海拔越高,不同撞壁距离对着火位置的影响效果越明显.

Ignition characteristics of wall-impinging diesel fuel spray were investigated in a high-temperature highpressure constant volume combustion chamber,which was adopted to reproduce diesel-like thermodynamic conditions of a heavy-duty diesel engine operated at altitudes of 0(sea level),3.0 and 4.5 km above sea level.Techniques of diffused back-illumination imaging and broadband chemiluminescence imaging were used to visualize the liquid phase of the spray and the ignition process respectively.Results reveal that,increasing altitude has a distinct inhibitory effect on ignition process.As the altitude increases from 0 km to 4.5 km at impingement distance of 57 mm,the ignition delay increases from 0.57 ms to 0.89 ms and the ignition distance from 14.83 mm to 18.68 mm,accompanying with lager area and higher probability of multiple kernels of high temperature chemiluminescence.At the same altitude,impingement distance has a little influence on ignition delay.However,the impingement distance has a significant influence on ignition position as the flat wall restricts spray propagation towards to the downstream,and higher altitude shows stronger influence.