Numerical Simulation On Combustion Of Premixed Gas Ignited By Flame Jet

With the increasingly stringent emission regulations,efficient and clean alternative fuels attracted more and more attention.Natural gas has many advantages such as low pollution,good antiknock performance and abundant reserves.The jet igniting method can provide more active radicals and ignition energy through the jet flame to accelerate the burning rate of the gaseous fuel,thereby improving the combustion effect and the lean limit of the gaseous fuel.In this paper,the constant volume chamber with pre-chamber is taken as the research object.The combustion model is established by using 3D CFD software.By calibrating the simulation with experimental data,it is found that the two are in good agreement,and the accuracy of the models are verified.Numerical Simulation on combustion of premixed gas ignited by Flame Jet are carried out with multiple parameters.The parameters of the orifice diameter,volume,length-to-diameter ratio and orifice number of the pre-chamber,the premixed gas equivalent ratio,the initial temperature and the initial pressure are studied in this paper.The results show that increasing the diameter of the nozzle will advance the timing of the jet flame entering the main chamber,but the velocity of the jet flame in the main chamber is slow because the pressure difference between the prechamber and the main chamber is small.If the diameter of the nozzle is too small,quenching will occur at the orifice due to the throttling effect,resulting in the jet flame can't enter the main chamber to ignite the premixed gas.Increasing the volume of the pre-chamber while maintaining the length-to-diameter ratio of it can increase the pressure difference between the pre-chamber and the main chamber,and accelerate the propagation speed of the jet flame in the main chamber.However,since the jet flame travels a long distance in the pre-chamber,the jet flame is injected into the main chamber at a later time,and a certain ignition delay is formed.When the length-to-diameter ratio of the pre-chamber is relatively small,the jet flame travels a short distance in the pre-chamber,so that the premixed gas in the main chamber can be ignited earlier,but due to the insufficient combustion in the pre-chamber,the ignition energy in the jet flame is less,therefore the jet flame ignites the premixed gas in the main combustion chamber at a slower rate.When the length-to-diameter ratio of the pre-chamber is too large,the partial ignition energy of the jet flame is lost and the moment when the jet flame enters the main chamber is delayed due to the long travel distance of the jet flame in the pre-chamber,which are unfavorable for igniting the premixed gas in the main chamber.When the cross-sectional area of the nozzle hole keeps constant,appropriately increasing the number of nozzle holes can speed up the speed of igniting the premixed gas in the main chamber.However,if the number of nozzles is too large,the diameter of the nozzles will be too small to cause quenching.Properly increasing the equivalence ratio of the premixed gas in the pre-chamber is beneficial to extend the lean burn limit of the lean mixture in the main chamber.Increasing the initial temperature and initial pressure can shorten the combustion duration and accelerate the ignition of the premixed gas in the main chamber.