点燃式液压自由活塞发动机高增压燃烧过程的试验与仿真研究

在快速压缩-膨胀机上进行试验,模拟液压自由活塞发动机(hydraulic free piston engine,HFPE)在不同缸内初始压力下的单次燃烧做功过程,并利用OpenFOAM和CONVERGE三维计算流体力学(computational fluid dynamics,CFD)仿真平台进行增压仿真研究。结果表明:液压自由活塞发动机随着缸内初始压力的增大,相同压缩比下发动机循环周期缩短,活塞在上止点附近停留时间缩短,爆震极限压缩比增大,抗爆能力增强。适当提高缸内初始压力有利于提高指示效率,当缸内初始压力提高至0.15MPa时,发动机指示效率由0.30提高至0.31,但当初始压力达到0.20MPa后,指示效率又降至0.30。针对缸内初始压力进一步增大后出现的效率降低问题,在仿真研究中发现采用多火花塞点火方案,即使在初始压力0.80MPa的条件下也能得到较高的指示效率而不发生爆震。

Experimental and Simulation Study on Super-Charged Combustion Process of a Spark Ignition Hydraulic Free Piston Engine

The simulation experiment of the single combustion process of a hydraulic free piston engine(HFPE) under different initial pressures in the cylinder was conducted on a rapid compression-expansion test machine, and the super-charging simulation study was carried out by using OpenFoam and CONVERGE three-dimensional computational fluid dynamics(CFD) simulation platform. Results show that under the same compression ratio, as the initial pressure in the cylinder increases, the cycle time of the engine and the residence time of the piston near top dead center are shortened, thereby increasing the compression ratio of knock limit and antiknock ability. Appropriately increasing the initial pressure is beneficial to improve the indicated efficiency. When the initial pressure in the cylinder is increased to 0.15 MPa, the engine indicated efficiency is increased from 0.30 to 0.31, but when the initial pressure reaches 0.20 MPa, the indicated efficiency drops to 0.30. In the simulation study of the problem, it is found that the multi-spark ignition scheme can achieve a higher indicated efficiency without knocking even at an initial pressure of 0.80 MPa.