Study On The Effects Of Two Stage Injection On Combustion And Emission Of N-butanol Engine

Against the background of the current energy crisis and increasingly serious environmental pollution problems,energy conservation and emission reduction have become the development needs of the internal combustion engine industry,and the alternative fuels for internal combustion engines and their efficient utilization have become research hotspots.The n-butanol fuel contains oxygen and can be regenerated.It has the advantages of fast flame propagation and high energy density.When it is applied to a direct-injection ignition engine,the optimization strategy of two stage injection is proposed based on the characteristics of it.This experiment is based on a spark ignition engine to build a test bench and establish a d SPACE engine control platform to achieve precise control of test parameters.Under a fixed operating condition with the 10% throttle opening and the engine speed of 1500 r/min,different second injection timings,second injection ratios,excess air coefficients and ignition timings were changed in this experiment.A single injection test group with 0%second injection ratio was set as a control group at the same time.At last,analyze the effects of two stage injection strategies on the combustion and emissions of n-butanol engines through the data recorded by measuring instruments.By analyzing the effects of the two stage injection strategy on the combustion characteristics of the engine,the following conclusions are obtained:1)Different second injection ratios correspond to different MBT(Maximum Brake Torque Timing).In the case of small proportions of 20% and 40% second injection ratios,the MBT is near 5°CA BTDC.When the second injection ratio increases to 60% and 80%,the MBT appears earlier which is near 10°CA BTDC.2)The timing of the second injection has an important influence on the combustion in the cylinder.At the MBT,two stage injection with the second injection timing of 100°CA BTDC and 125°CA BTDC makes mixture better,compared with single injection,the peak of cylinder pressure,cylinder temperature,and heat release rate are all increased.The stagnation period and the rapid combustion period are relatively shortened,and the IMEP and torque of the engine are significantly improved.3)The second injection ratio also significantly affects the combustion situation.Other conditions are certain and at the MBT,when the second injection ratio is 20%and 40%,less fuel hits the cylinder wall and the mixture formation is better.Compared with single injection,The peak of cylinder pressure,cylinder temperature,and heat release rate are relatively increased,the stagnation period and rapid combustion period are significantly shortened,the combustion is more rapid and full,and the IMEP and torque are significantly increased.4)When λ=1.0 and 1.1,the second injection ratio of 20% is the best.Whenλ=1.3,the secondary injection ratio of 40% is the best.In the case of λ=1.3 lean mixture,reasonable second injection timing and second injection ratio can improve the engine’s in-cylinder combustion more significantly.By analyzing the effects of the two stage injection strategy on the emission characteristics of the engine,the following conclusions are obtained:1)When other conditions are certain,the emission of HC at the MBT under different second injection ratios are always the lowest.When at the MBT,the HC emission at the second injection timing of 125°CA BTDC and the second ratio of20% and 40% are significantly reduced.At different λ,compared with λ=1.0,whenλ=1.1,the HC emission under different secondary injection ratios decrease overall.When λ=1.3,the HC emission rises,but under the optimal second injection time and ratio,the HC emission level can still be well controlled.2)When other conditions are certain,the CO emission with different secondary injection ratios do not change significantly with the ignition timing.When λ=1.0,the influence trend of the second injection ratio and the second injection timing on CO emission is basically the same as that of the HC emission.When at the MBT,at125°CA BTDC which is optimal second injection timing and the best second injection ratio of 20% and 40%,CO emission is the lowest.When λ=1.1 and 1.3,the CO emission level is lower overall,and the change trend with the ratio of second injection and the timing of second injection is not obvious.3)When other conditions are certain.Under different second injection ratios,NOx emissions gradually increase with the advance of the ignition timing.When at the MBT,at 125°CA BTDC second injection timing and 20% and 40% second injection ratios,NOx emission is the highest respectively.At different λ,compared with λ=1.0,when λ=1.1,the NOx emission corresponding to different second injection ratios increase overall,and when λ=1.3,the NOx emission at different second injection ratios overall decrease.