Numerical Simulation Of Flame Jet Quenching And Igniting The Premixed Gas

The use of alternative fuels is an important way to alleviate the energy crisis and environmental pollution problems caused by the massive use of fossil fuels.It is also an important part of our country's energy economy development in the future.Jet ignition system can accelerate the burning rate by providing ultra high ignition energy and shorten the flame propagation path,and it is considered to be an effective method to solve the problems that the burning rate of fuel gas and the propagation velocity of lean burn flame are relatively slow.In order to study the general characteristics of the process of flame jet quenching and igniting the premixed gas,and the general design method of ignition chamber,method of visualization experiment combined with numerical simulation was adopted.Schlieren method and natural flame luminescence were adopted to measure the development of flame jet and the luminous intensity of flame,respectively.Some simulation analysis of the jet ignition and combustion in the constant volume vessel was also been done for further understanding the mechanism of jet ignition.At the end,by simulating the operation of a jet ignition engine with different ignition chamber designs,to exploratively obtain the general design method of small volume ignition chamber.The visualization experiment studied on the effect of methane injection quantity,intake pressure and intake temperature on the flame jet structure and the combustion process of premixed gas.The simulation work included the gas mixing process in the constant volume vessel and the jet ignition and combustion process.The results showed that the ignition chamber reached a higher equivalent ratio while the main chamber reached a lower equivalent ratio at the ignition timing because of the intake control.The jet igniting the premixed gas is the outcome of ignition energy accumulation in main chamber when the high temperature zone extends to the low temperature zone because of heat transfer and the turbulent kinetic energy dissipation.The mixture equivalent ratio in the ignition chamber has a great influence on the operating of jet ignition system.Accurate control of mixture equivalence ratio in the ignition chamber is beneficial to the ignition phase control of premixed combustion and to improve the ignition stability,as well as to broaden the lean limit of premixed combustion.With the increase of the intake pressure,the ignition energy of the jet increased,the starting point of combustion in the main combustion chamber was advanced,and the combustion duration becomes shorter.Under the same pressure condition,the jet ignition process was affected by both gas temperature and gas density.Increasing the gas temperature can increase the initial flame propagation velocity.Study of ignition chamber design method was based on CFD simulations of a modified natural gas engine.Through simulating engine operations under different ignition timings,ignition chamber volumes,nozzle hole structures of ignition chamber and main chamber shapes,to get the conclusion as follows.The jet ignition system maintained good ignition performance in a wide range of ignition timing,and it showed better ignition performance with advanced ignition timing in a certain range.It is detrimental for jet ignition system with a too large or too small ignition chamber volume ratio.The ignition performance can be improved effectively by controlling the ignition chamber volume ratio near 3%.There was no obvious connection between ignition performances with nozzle area to volume ratio of ignition chamber.However,the diameter and length of the nozzle had a great influence on the jet ignition energy,and medium size diameter and length of the nozzle was better for improving the ignition performance.For small bore engine,the deep ? combustion chamber shape was better for flame jet transmission,to obtain smaller combustion duration.Increasing the nozzle angel of ignition chamber would shorten the flame jet transmission distance,which could increase the heat release rate of the shallow ? combustion chamber shape.The nozzle number of ignition chamber could affect the combustion heat release rate via changing the distribution characteristics of jet ignition energy.Ignition chamber with six nozzles showed better ignition performance in the small bore engine.