Heat release rate of FPEG based on the piston motion

The piston motion of FPEG is quite different from the traditional engine. To study the influence of motion on the combustion heat release rate, this paper puts forward the concept of equivalent speed transformation. Using equivalent crank angle as the unit of measurement to express heat release rate calculated from the experimental data, analyzing the difference between FPEG and traditional engine heat release rate, and comparing experimental result and CFD result. Results show that FPEG piston velocity and acceleration are larger than that of traditional engine during compression stroke. This is favorable to evaporation and oil-gas mixture, leading to pre-mixed combustion ratio up to 80%,. The fast cylinder volume change leads to quick drop in cylinder temperature. The duration of normal combustion period and post burning period is decreased. When double-wiebe function is used to calculate combustion heat release rate, pre-mixing combustion quality coefficient is 3.451 and diffusion combustion quality coefficient is 10.24. They are all larger than those of traditional engine. Under the influence of piston motion, the combustion pressure of FPEG is smaller than traditional engine with same cylinder diameter. For FPEG, maximum combustion pressure is retarded and ignition delay time is decreased.