Realization And Research Of Hot-Surface Assisted Compression Ignition Combustion On Hydraulic Free Piston Engine

Homogeneous Charge Compression Ignition(HCCI)is a kind of high efficiency and low emission combustion mode,but its controllability of combustion phase and heat release rate is poor,which limits the HCCI application.In this paper,a hot-surface assisted combustion HCCI combustion process is realized by utilizing the variable piston movement law of hydraulic free piston engine(HFPE)and the glow plug hot-surface combustion technology.This combustion mode inherits the advantages of HCCI combustion mode of lean,fast and efficient combustion.Besides it can solve the combustion phase control and combustion rate control problems,and then achieve the purpose of expanding the working load.Hot-Surface Assisted Compression Ignition(HACI)can be achieved by using a glow-plug in a hydraulic free piston engine.It is found that the HACI combustion mode had two stages during heat release,one was the slow stage,and another was rapid stage.compared with the HCCI combustion mode,the heat release rate of HACI was lower,so the operating conditions to heavy load could be expanded,and the IMEP could up to 0.74 MPa.Compared with the SI combustion mode,the HACI could achieve lean high compression combustion,with high thermal efficiency;compared with spark-assisted HCCI(SICI)combustion,ignition energy of HACI hot-surface is higher,and HCCI combustion process can be realized at low compression ratio without intake heating,thus reducing the knocking area and expanding the working range.The experimental results show that the increase of heating power,the engine compression ratio and the mixed gas equivalent ratio can increase the HACI combustion phase,shorten the combustion duration and increase the heat release rate.However,Excessive increase of the above parameter can cause the indication thermal efficiency decreased,or even lead to knock.There is a best match among mixed gas concentration,glow plug heating power and compression ratio.When the equivalence ratio is equal to 0.6,the optimum compression ratio is 14-16,the optimal glow plug heating power is 30-34 W,then the HACI combustion is running at high efficiency.The one-dimensional simulation and prototype experiment were studied in this paper.The results show that there is a unique adaptive relationship between the HFPE piston motion and the combustion process.When the combustion phase is advanced or the accumulated heat release increases,the compression ratio can be reduced automatically,to avoid knocking phenomenon.When the burning phase delay,or the accumulated heat release decreases,the compression ratio can automatically increase,to avoid the occurrence of post-combustion and misfire phenomenon.This adaptive feature can effectively avoid the occurrence of knocking and misfire,to ensure the HACI mode in the hydraulic free piston engine in high efficiency and stable operation.