Study On The Comprehensive Performance Of Methanol/Diesel Dual-Fuel RCCI Engine

Methanol/diesel reactivity controlled compression ignition（RCCI）technology through the inlet injection the low activity,volatile methanol fuel,and in cylinder direct injection diesel ignite methanol-air homogeneous mixture.RCCI use of diesel fuel features of good ignitability and methanol features of fast burning rate and good ant-detonating quality,the strategy controls the ratio of the two fuels to achieve a clean and efficient combustion control.The results show that the methanol/diesel RCCI combustion strategy can reduce the emissions of nitrogen oxides（NO_x）and particulate matters（PM）while maintaining a high thermal efficiency,but it has the problem of high emissions of total hydrocarbon（THC）and carbon monoxide（CO）.The formation of THC and CO is related to excess air coefficient,combustion temperature and mixture composition.In order to investigate the influence of methanol substitution rate and excess air coefficient on the economy and pollutant emission characteristics of RCCI engine,the electronic throttle assembly is installed in the inlet manifold of a four-cylinder high pressure common rail diesel engine,and the methanol injector is installed in the intake manifold to realize methanol/diesel RCCI combustion.By controlling the injection ratio of two kinds of fuels and controlling the throttle opening to adjust the intake air flow,study the effects of different methanol substitution rates and excess air coefficient on the performance of methanol/diesel RCCI engine.The main conclusions are as follows:（1）At the maximum torque speed（1600 r/min）of the diesel engine,the loading rate from 25%to 50%,the maximum methanol substitution rate was limited by THC emissions and fuel consumption rate,and the optimal methanol substitution rate from 5%to 10%.The loading rate from 50%to75%,the maximum methanol substitution rate was limited by detonation and incomplete combustion,the optimal substitution rate from 30%to 40%.The loading rate from 75%to 100%,the maximum methanol substitution rate was limited by the pressure in the cylinder and the exhaust temperature,and the optimal substitution rate was 30%.Under 100%load,the maximum methanol substitution rate can be increased from 30%to 36%by adjusting the excess air coefficient,and the effective fuel consumption rate was 6.2%lower than the pure diesel strategy.（2）Under 2000 r/min,75%load and 100%load,the effective fuel consumption rate was decreased,and the effective thermal efficiency was increased with the increase of methanol substitution rate.At 75%load,the40%replacement rate compared to the pure diesel strategy,the effective fuel consumption was reduced by 6.1%,effective thermal efficiency was increased by 2.9%.At 100%load,the 30%replacement rate compared to the pure diesel strategy,the effective fuel consumption was reduced by 4.8%,effective thermal efficiency was increased by 3.4%.（3）At 2000 r/min and different load conditions,with the increase of methanol substitution rate,NO_x,PM,CO₂ and non-methane total hydrocarbon emissions are reduced,CO,THC,methanol and formaldehyde emissions are increased.When the load rate was 100%and the methanol replacement rate was 30%,compared with the pure diesel strategy,NO_xemissions was reduced by 18.1%,PM emissions was reduced by 36%,CO₂emission was reduced by 6.8%,non-methane total hydrocarbon emissions was reduced by 6.8%,CO emission is 20 times as much as the pure diesel strategy,THC emissions is 8 times as much as the pure diesel strategy,the dual-fuel strategy of alcohol and aldehyde emission account for approximate99%of total hydrocarbon emissions.（4）At the different load condition and optimal methanol replacement rate,the effective fuel consumption rate and the exhaust temperature was reduced and the effective thermal efficiency was increased with the increase of excess air coefficient.At 25%load,the replacement rate was 10%,the excess air coefficient from 3.04 to 3.38,the effective fuel consumption rate was reduced by 2.7%,and the effective thermal efficiency was increased by3.7%,and the exhaust temperature was decreased by 27℃.At 100%load,the replacement rate was 27%,the excess air coefficient from 1.35 to 1.65,the effective fuel consumption rate was reduced by 6.7%,the effective thermal efficiency was increased by 4.7%,and the exhaust temperature was decreased by 6.2%.（5）When the 25%load and the replacement rate was 10%,the excess air coefficient from 3.04 to 3.38,PM emissions was reduced by 44%,NO_xemissions were reduced by 8.3%,CO₂emission was reduced by 9.1%.When the 100%load and the replacement rate was 27%,the excess air coefficient from 1.35 to 1.60,PM emissions was reduced by 25%,CO₂ emission was reduced by 9.4%,SO₂ emission was reduced by 10.1%,aromatic hydrocarbon emissions was reduced by 83.1%;NO_x emissions was increased by 8.3%,methanol emission was increased by 78.3%,formaldehyde emission was increased by 52.3%,CO and non-methane total hydrocarbon emissions has a small change with the excess air coefficient.