摘要
为探究气道及燃烧室形状对汽油机缸内流场的影响,以某1.4L多点进气道喷射(MPI)汽油机为研究对象,利用AVL-FIRE软件对原机进气道形状进行稳态数值模拟计算,并对原汽油机在2 800r/min最低比油耗工况点进气及燃烧过程进行瞬态数值模拟计算。基于计算结果对进气道及燃烧室形状进行优化设计,提出4种计算方案,对优化前后各计算方案的缸内速度场、湍动能场、火焰前锋面密度和瞬时放热率进行对比分析。结果显示:改进气道的滚流比明显高于原机气道;结合改进气道,进气侧凸起活塞能够更好地维持滚流;在点火时刻,改进气道结合进气侧凸起活塞这一计算方案的缸内湍流分布及湍动能优于改进气道结合大曲率凹坑活塞、原机气道结合原机活塞(压缩比12)与原机计算方案,点火后火焰传播速度最大,燃烧速度最快。优化进气道及燃烧室形状能够加强缸内气流运动,提高点火时刻缸内湍流强度,加速火焰传播,改善燃烧过程。
To investigate the effects of intake port and combustion chamber on in-cylinder flow field of gasoline engine,a simulation analysis was carried out based on a 1.4L MPI gasoline engine.First,a model covering intake port,intake valve,intake valve seat,combustion chamber and piston was built and verified by the engine bench test.Then the steady numerical simulation of the intake port and combustion chamber of the engine and transient numerical simulation of the intake and combustion processes at 2 800r/min,the condition of the lowest brake specific fuel consumption(BSFC),were conducted using the AVL-FIRE software.The take port and combustion chamber were optimized based on the simulation results.Four simulation schemes were put forward:the optimized port+the optimized piston with a protrusion on intake side(scheme 1),the optimized port+the optimized piston with a large radii recess(scheme 2),the original port+the original piston +increased compression ratio(scheme 3),and the original port+ the original piston(scheme 4).The comparison analysis was performed of in-cylinder velocity fields,turbulent kinetic energy fields,flame surface densities and transient heat releases of the four schemes.The results show that the optimized intake port has a much greater tumble ratio than the original intake port;the scheme 1can best maintain tumble,has the best turbulence distribution and the highest turbulent kinetic at ignition,and has the quickest flame spread and combustion compared with the other three schemes.The optimization of intake port and combustion chamber can enhance in-cylinder air motion,increase turbulent intensity at ignition,speed up the propagation of flame,and improve combustion process.
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