Investigations And Analysis Of Torch Flame Behavior And Effects In Pre-chamber Type Gas Engine

In recent years,the influence of thermal engines on the environment has become a problem.Therefore,natural gas(NG),which has excellent environmental and economic features,is attracting attentions as alternative fuel of conventional petroleum oils.Gas engines burning NG based gaseous fuel are usually classified under two major variations according to their main combustion mode.One variation is pre-mixture combustion of fuel gas and air initiated by some ignition sources.The other is diffusive combustion of high-pressure fuel gas jets into in-cylinder air.It can be expected for the pre-mixture combustion mode to pass the rigorous IMO tier III NO_x emission regulations without any after-treatment devices as long as the fuel density of the premixture is so lean that the combustion temperature is kept from a NO_x generation range over 2,200 K.The fuel density should be counted as 2 or larger values in an air-excessive factor.However,such lean combustion conditions may result in more unstable combustion or higher emission level of unburned methane that is very harmful with its global warming potential(GWP)as high as 25.To stabilize and to complete the combustion of the lean premixture,various kinds of enhanced ignition systems have been applied especially in medium-or low-speed engines of large dimensions.Torch flames from nozzle holes of a pre-combustion chamber are a popular choice in the case of mediumspeed gas engines.The objective of this study is to investigate combustion behavior and progress of torch flame generation in a pre-chamber type gas engine.It is difficult to realize these inside phenomena of a main chamber and a pre-chamber by experiment,so this study revealed these by using CFD solver.In addition,since complicated factors are involved in the combustion phenomenon,the timing of ignition and the progress of flame propagation change every time.Therefore,an experiment is conducted to see the flow of fluid due to the shape of the pre-chamber nozzle by experimenting with a jet flow based on the pressure difference between the pre-chamber and the main chamber instead of the jet due to combustion.Thereby,the complicated combustion energy in each experiment can be ignored and the same jet behavior can be obtained.As a result,the combustion behavior of the torch flame ejected from a pre-chamber was clarified.The experimental data and the calculated data are consistent in the comparison verification between simulation and experiments.Also,the jet behavior without combustion in the cylinder was clarified.