四气门天然气发动机缸内瞬态流场数值模拟

Numerical Simulation of Instantaneous Flow Filed in Cylinder of Four-Valve Natural Gas Engine

采用K-ε双方程模型对四气门天然气发动机进气道及缸内的瞬态流场进行数值模拟,模拟了发动机进气、压缩及燃烧过程。结果表明:四气门发动机缸内涡流由外向内形成;缸内平均湍动能强度在进气冲程中总体呈先增大后减小的趋势,压缩冲程中耗散作用使湍动能降低,但挤流作用使气缸中部的湍动能升高;进气过程中存在流动分层,为改善小负荷时发动机性能,天然气应尽可能在进气冲程中、后期进入气缸;缸内涡流中心的位置和气流速度梯度对火焰径向传播的均匀性有很大影响。

The instantaneous flow field in the cylinder and intake port of four-valve natural gas engine was studied by numerical simulation using K-ε double equation in this paper. The intake and compression stroke of the engine was simulated. The results of the simulation show that the swirl in-cylinder of a fourvalve engine is formed from the outside to the inside, on the whole the mean turbulence kinetic energy in cylinder first increases then decreases during the intake stroke. During the compression stroke the turbulence kinetic energy decreases due to the dissipation effect, while the turbulence kinetic energy in the center of the cylinder increases as a result of the squish effect. There is flow lamination phenomenon during the intake stroke, so the natural gas should be injected to the cylinder in the end of intake stroke in order to improve the performance of the engine when the load is small. Both the position of the in-cylinder swirl center and the flow velocity gradient has a great effect on the evenness of the flame spreading along the radius.