The Study On LPG Combustion Process Of Dual-spark Plug Ignition By CFD

Liquefied Petroleum Gas (LPG) with abound resoures,lower price,cleanercombustion,is widely used of all automobile alternative energy at present throughout theworld，but there are still some defects,such as, slower flame propagation and easy to knockon the large bore LPG engine cylinder.In this paper,the dual-spark combustion model oflarge bore LPG engine is established, thorough research of dual-spark ignition structure isconducted on the combustion process of the large bore LPG turbocharged engine for theearly exploration of the efficient use of large bore LPG engine.First,the combustion model and the knock model are corrected by experimental data.Secondly, it is discussed that the effects of single plug ignition mode and synchronousdual-spark ignition and asynchronous ignition model on the performance of the large boreLPG engine byωcombustion chamber.The results obtained: Compared with single plugignition system, dual-spark ignition can shorten flame propagation distance,improve flamepropagation rate, enabling fast lean burn, improve engine thermal efficiency. Compared withsingle-spark ignition and synchronous dual-spark ignition models，the rapid combustionperiod of asynchronous ignition model is shorten,which is helpful to fast burning. In2800r/min full load condition,when the initial ignition angles are same,the best ignitionangle step is about5oCA.when the intial ignition angles and ignition steps are all same,leftand right ignition has no effect on the combustion performance of the LPG engine with theright and left. Dual spark-plug ignition system can increase compression ratio.Whencompression ratio comes to10,the knock is dectected in the single spark-ignition engine,butsynchronization ignition do not.When the Asynchronous ignition initial angle is the same,thesmaller,the step is,the worse the antiknock.Finally,the influence of dual-park plug locationsand ignition energy on combustion performance of the large bore engine is discussed foroptimizing the dual-spark igniton locations and energy.The results obtained: Spark locationsare arranged symmetrically about combustion chamber, when the distance A is0.5, averageturbulent kinetic energy in the cylinder is larger at the top dead center,the burning speed isfaster and the combustion duration period is shorter.When the distance between dual-sparkplug is too short,the flame meets with each other earlier and interferes with eachother,decreasing the flame speed of the overlapping zone of the flame surface and increasingthe thermal loss.when the distance between dual-spark plugs near the combustion chamberwall is long,the space of combustion is narrow,hindering the flame developing.In aword,whether the distance of dual-spark plugs is too short or long all decrease the burningvelocity and increase the duration of the combustion periond,which result in bad fueleconomy and high emission.When ignition energy increases to45mJ,the initial flame radiusbecomes larger and the flame development period is reduced than that of35mJ.The suitalble ignition energy can promote the formation and stable development of flame kernel andbroaden the combustion limit of weak mixture,however,the concentration and regionalvolume of NOxincreases greatly.In this simulation conditions,using the ignition energy45mJcan make sure the engine stable working.Engine performance has little improvement bycontinuing to increase ignition energy. Meanwhile,it can be seen that increasing the energycan only increase the initial flame kernel size,shorten the flame development duration of theflame development,in other periods,ignition energy has no effect on the flame propagationand flame development.