Visualization Researches On Combustion Process Of Natural Gas Ignited By Pilot Diesel

In order to deal with the incresingly dire energy situation,the new-energy vehicles are booming,but the traditional energy engine still occupys a dominant position in many fields,with the exhaustion of diesel and the high pollution of the fuel engines,more and more attention has been paid to explore nature gas engine at home and abroad.Most of the researches of nature gas pilot ignited by fuels are engine performance and CFD numerical simulation.In order to perfect the basic combustion mechanisim and provide the theoretical basic for developing engines which pilot ignited by fuels,the comubstion process of the nature gas pilot ignited by fuels has been studied in this paper by the visual method.Based on the visualization experimental platform of constant volume vessel,shadowgraph meyhod was used to study the tempurture、ambient pressure、equivalence ratio、inject pluse、inject pressure and premixed time(from the end of methane injection to the beginning of desiel injection)which have great influence to the comubustion progress.By analyzing pictures and achieving datas,the changes of fuel atomization、fuel ignition time and fuel flame projection area were studied.The main ideal of this paper was to study the combustion progress of nature gas ignited by n-hexadecane and diesel under different environment and injection conditions.The experinment results show that: When the temperature,back pressure and equivalent ratio are changed,the projected area of fuel flame changes faster with the increase of temperature;When the equivalence ratio is 0.15,with the increase of ambient pressure,the projected area of fuel flame changes slower,While the equivalence ratio is 0.2,with the increase of ambient pressure,the projected area of fuel flame changes faster,so the influence of the ambient is related to the equivalence ratio;other things equal,the equivalence ratio is 0.15,although n-hexadecane has higher cetane value and shorter ignition delay period,it has bigger projected area at the beginning of the combustion,However,as the combustion progresses,due to the bigger kinematic viscosity and poor atomization of n-hexadecane,the projected area of diesel flame will be changed faster than that of n-hexadecane;With the increase of equivalent ratio,fuel flame projection area change rate is accelerated.However,the combustion of fuel is incomplete,which produced a large number of smoke.The nature gas ignited by n-hexadecane will lead to the local combustion which greatly speed up the change of the projection area of flame.diesel has low cetane number,partial combustion cannot happen in the same situation,so n-hexadecane flame projection area change rate will be greater than that of diesel.When it comes to the injection conditions,which are consist by premixed time,injection pressure and premixed time.with the increase of premixed time and injection pressure,the kinetic energy,turbulence intensity,spark energy of fuel was increased,the flame projection area is more widely distributedand which speed up the change rate of the flame projection area.When the premixed time is small(less than 500 ms),with the increase of the premixed time,the flame projection area of nature gas ignited by n-hexadecane changes faster and generated lots of smoke.The smaller the premixed time is,the more insufficient the mixture will be.The local concentration of natural gas will lead to insufficient combustion of the premixed gas,while it accelerates the combustion rate.When the premixed time is big(more than 3000 ms),the premixed gas is mixed evenly,so that it can combusted completely less soot will be generated,the change rate of the projected area of the flame is roughly similar.