Study Of Fuel Spatial Distribution And Combustion Characteristics Under Different Tumble Ratio Based On An Optical GDI Engine

It has been well proved that intake tumble flow is effective in promoting in-cylinder air-fuel mixing and combustion,and hence enhancing engine performance.In this research,the effect of tumble ratio on combustion characteristics and cylinder pressure was assessed on a SIDI optical engine.Variable tumble ratios were achieved by adjusting the cross-section area of the intake manifold.Tumble ratios are estimated by CONVERGE simulation.A high speed color camera was applied to record crank angle resolved flame images through the quartz window in piston bowl.In the meantime,the instantaneous cylinder pressure was monitored by a pressure transducer.The blue and yellow flames can be captured separately with the help of color camera.The blue flame is considered to be the chemiluminescence generated by intermediate species such as CH~*(430.5nm),Whereas the yellow part is considered to be the incandescence emitted by soot associated to liquid combustion,hence the position and intensity of yellow flame represent the distribution and quantity of soot.Besides,in order to evaluate fuel mixture formation under different tumble ratio and find out the fuel spatial distribution around spark plug.Laser induced fluorescence(LIF)experiments is conducted focusing on fuel distribution in combustion chamber.A 266 nm laser sheet from frequency-quadrupled Nd:Yag laser was applied from pent roof window into cylinder through the gap of spark plug.A signal intensified CCD camera is used to record fluorescence equipped with a 320-420 nm band-pass filter.Results show that higher tumble ratio results in more blue flame and less yellow flame,as well as a higher IMEP and burning rate.It shows a strong correlation between blue flame area and burning rate in engine.Meanwhile,with a higher tumble ratio,yellow flame is getting later and lesser,which indicates that the soot formation is reduced.Besides,higher tumble ratio can suppress cycle to cycle variation with stable IMEP.Results also show that spray is distorted by tumble flow to another direction with shorter penetration and wider spray angle.Fuel spatial distribution is more uniform in high tumble while concentrated area are randomly distributed in chamber in low tumble ratio.Also,a high tumble is more helpful for the formation of repeatable mixture compared to low tumble ratio.