纵向直进气道电喷天然气发动机进气过程的数值模拟

提出了渐缩形直进气道发动机的进气过程的多维数值解析方法，探明了气缸内纵向滚流的存在，通过与实验结果对比，验证了该计算方法的可行性。在此基础上，考察了渐缩形直进气道应用于多点电喷(MPI)天然气发动时，天然气喷射后进气岐管内的天然气浓度场和压力场，以及随后天然气—空气混合气在气缸内的质量分布和速度分布。结果表明，若仅把MPI汽油机的喷油器用天然气喷射阀更换，大量的天然气喷到进气阀后反射，造成天然气发动机进气岐管内的燃料浓度场、压力场与MPI汽油机明显不同；并且进气阀被打开后，先期吸入气缸的天然气在纵向滚流的作用下被挤向进气阀底部下方，与后期吸入气缸的空气形成明显的分层充气构造。

Numerical Simulation of Intake Process for Longitudinal Straight Inlet Port Multi-Point Injection (MPI) Natural Gas Engine

A multi-dimensional numerical simulation method was proposed for analyzing the intake process of a gradual contracting straight inlet port engine. Based on it, the formation of a longitudinal vortex in the cylinder was numerically predicted. And compared with the experimental results, the feasibility of this numerical calculation method was verified. With a gradual contraction longitudinal straight inlet port applied on the Multi-Point Injection natural gas engine, the concentration of natural gas and the pressure field in the intake manifold after the injection of natural gas were investigated, then in the following intake process the velocity vector map and mass distribution of natural gas inside the cylinder were also numerically examined. As a result, by merely replacing the gasoline injector with natural gas injector, a large volume of natural gas is injected on the intake valve and then reflected, which makes the fuel concentration and pressure field in the intake manifold after the natural gas injection for the natural gas engine differ greatly from those for gasoline engine. Furthermore, after the intake valve is opened, due to the influence of the longitudinal vortex, the primal inbreathed natural gas is forced to centralized under the bottom of intake valve, this primal inbreathed natural gas and the following inbreathed air show appearance of a dis- tinct layered gas mixture structure inside the cylinder.