Combustion Characteristics Of Turbulent Jet Based On Rapid Compression Machine

At present,countries all over the world are faced with the severe challenges of energy crisis and environmental pollution,which urge researchers to propose advanced combustion strategies to improve the efficiency of internal combustion engines and reduce pollutant emissions.As a low-temperature combustion method,rarefied combustion can reduce pollutant emission,improve efficiency and reduce carbon dioxide emission.However,the development of lean-burn engines is limited by the combustion instability caused by highly diluted mixtures.Therefore,the turbulence jet ignition technology in pre-chamber is proposed to enhance the ignition.This method,which uses turbulent jet as distributed ignition source,can improve combustion speed,shorten flame propagation distance and improve combustion characteristics.Therefore,turbulent jet ignition is the most promising next generation ignition method for internal combustion engine.In this paper,the porous pre-chamber turbulent jet ignition combustion with auxiliary fuel was realized on the rapid compression machine.The independent fuel injection and ignition system realized accurate combustion control,and the combustion of the mixture concentration of the main combustion chamber lambda= 2.6 was realized.The combustion characteristics of turbulent jet ignition were investigated by the cooperative measurement of pressure sensor and high-speed camera.The results show that the turbulent jet presents a bright blue flame and diffused outward continuously,and the flame morphology is closely related to the flow of the mixture in the main combustion chamber.After a period of time,the spontaneous combustion of the thin mixture in the main combustion chamber is observed.The increase of fuel injection in the precombustion chamber on the one hand will advance the combustion phase,on the other hand,it will also enhance the intensity of turbulent jet.However,too much auxiliary fuel will also have a more serious post-combustion phenomenon at the orifice.By means of simulation,the combustion characteristics of turbulent jet ignition are further understood.The spray shape and penetration distance of the injector,the cold field compression curve and the hot field combustion curve of the fast compressor were calibrated respectively,which were in accordance with the test results.Simulation results show that turbulent jet ignition combustion system through three processes,respectively:(Ⅰ)jet penetration stage,(Ⅱ)jet ignition(Ⅲ)the main combustion chamber and combustion phase.The spray droplets form a strong hedging effect with the air flow into the precombustion chamber,and the ideal mixing effect can be formed in the precombustion chamber under the reasonable control of the spray direction and the fuel injection time.In addition,the mixture concentration of the initial precombustion chamber has a great influence on the jet velocity at the outlet of the orifice,while the mixture concentration of the initial main combustion chamber has a great influence on the jet propagation distance.The effect of the nozzle structure on the flame structure of turbulent jet is simulated under three thermodynamic conditions.The results show that the turbulence intensity in the precombustion chamber increases with the decrease of the orifice diameter,and the turbulence promotes the combustion rate under the same thermodynamic condition.During the jet invasion stage,pressure difference is formed between the precombustion chamber and the main combustion chamber.The increase of the absolute combustion mass and the acceleration of combustion speed in the precombustion chamber will lead to the increase of the pressure difference,and the jet velocity at the outlet of the orifice presents a positive correlation with the pressure difference.In general,the initial velocity of the jet flame is high,the propagation velocity of the hot jet is fast,and the invasion period of the jet is short.On the other hand,in the case of a large aperture,the velocity gradient between the hot jet and the environment is small,so the jet combustion stability is good.In addition,at low ambient pressure,high ambient temperature and with the cold jet effect,a stable jet flame structure can be formed.