不同海拔条件下柴油机撞壁喷雾燃烧特性的可视化研究

使用定容燃烧弹模拟一款重型柴油机在海拔0m、3 000m和4 500m条件下运行时缸内的热力学状态,利用多种成像技术实现了撞壁燃烧过程的可视化,研究了不同海拔对撞壁喷雾燃烧的高温着火、火焰传播和碳烟生成特性的影响。结果表明,海拔从0m升高到4 500m,撞壁着火延迟从0.55ms延长到0.88ms,撞壁着火距离从20.38mm增大到26.87mm,高海拔对撞壁着火过程有明显的抑制效果;撞壁火焰呈现圆盘状火焰形态,火焰发展进入稳定阶段后,由于前锋区域的涡流强度增大,撞壁火焰铺展高度、撞壁火焰铺展宽度和撞壁火焰面积都随海拔升高而增大,但在火焰发展初期,由于撞壁平板的冷却作用,撞壁火焰尺寸在海拔升高到4 500m时减小;空间积分火焰亮度和时间积分火焰亮度均随海拔升高而增大,海拔升高到4 500m时碳烟生成速率和氧化速率均增大。

Visualization of Combustion Characteristics of Diesel Spray Wall Impingements at Different Altitudes

Combustion characteristics of wall-impinging diesel spray were investigated in a high-temperature high-pressure constant volume combustion chamber, reproducing diesel-like thermodynamic conditions of a heavy-duty diesel engine operating at altitudes of 0 m, 3000m and 4500 m. The effects of different altitudes on high-temperature ignition, flame propagation and soot formation characteristics were optically studied via different imaging techniques. Results reveal that, as altitude increases from 0 m to 4500 m, the impinging ignition delay increases from 0.55 ms to 0.88 ms and the impinging ignition distance from 20.38 mm to 26.86 mm, showing a distinct inhibitory effect on impinging ignition process at higher altitude; the impinging flame presents a disc-shaped flame, neither a lift-off flame upstream of the impinging flame; the impinging flame height, width and area all increase with arising altitude at quasi-steady stage as higher vortex intensity inside the impinging head region, while at early stage of impinging flame, its size is the smallest at altitude of 4500m compare with 0 m and 3000 m due to the cooling effect of impinging wall; spatially integrated natural luminosity and time integrated natural luminosity both increase with arising altitude, and both soot generation rate and oxidation rate are accelerated at altitude of 4500 m.