The Simulation Of The Effects Of Multi-Spark Ignition On Combustion Progress And Knocking Of Free Piston Engine

Spark ignition engines have many advantages,such as direct combustion phase control,no soot emission during combustion process,convenient disposal of harmful emissions and low vibration noise.However,due to the limit of knocking phenomenon,the compression ratio and applicable bore of engines are difficult to improve.And the thermal efficiency of the SI engine is very difficult to further improve in the internal combustion engine field.In this thesis,a three-dimensional simulation model suited for combustion and knocking process of ignition free piston engine is established to study the effect of multi-spark plug on the combustion process and knocking.The effect of spark plug number on the engine combustion and detonation process is studied.The results show that multi-spark plug ignition can accelerate the combustion process,shorten the combustion duration.At the same ignition phase,starting point and center of burning are both forward.The thermal efficiency of the engine can be improved,if the knocking do not happen.Simulation of the effects of multi-plug spark ignition on knocking limit is studied.The results show that if the knocking limit is measured by the limit ignition advance phase,as the number of spark plug increases,the limit ignition phase becomes smaller,which shows that the multi-plug ignition can enhance knocking.However,when using limit CA50 as the knocking index,the results show that multi-plug spark ignition can inhibit knocking.Furthermore,the knocking index CA50 is more scientific and reasonable.The conclusion can be also set up on the crank connecting rod engine when other conditions remain unchangeable.The effects of spark plug interval on engine combustion process under multi-spark plug ignition mode is studied.The results show that both too big interval and too small interval go against the combustion process,when the interval is close to the two-thirds of the cylinder radius,the combustion efficiency is the optimal.The effects of the interval between spark ignition times on the combustion process under multi-spark plug ignition mode is studied.The results show that the indicated thermal efficiency is the optimal while the combustion is under a slight knocking condition.Asynchronous ignition goes against the engine efficiency unless the combustion is under a slight knocking condition,and with the time interval between two spark ignition becomes larger,the combustion becomes deteriorate.