Simulation Study On Premixed Natural Gas Ignited By Blending Fuel

With the increasing number of vehicle,the shortage of petroleum resources and environmental pollution are more and more serious.Finding clean alternative fuels for internal combustion engines has become an important research direction to achieve the goal of energy saving and emission reduction.Natural gas has been extensively studied.because of its abundant reserves,low price and good emission performance.N-butanol has advantages of good miscibility with diesel,good volatility and oxygen content.Diesel and n-butanol blends ignite natural gas can improve the combustion and emission performance of the dual-fuel engine.In order to study the effects of n-butanol blending ratio,combustion phase and EGR rate on the performance of natural gas dual-fuel engine at low,medium and high loads,the numerical simulation coupled with combustion mechanism was adopted.The combustion phase was fixed by adjusting injection timing.The results are as follows:(1)With the increase of n-butanol blending ratio,the ignition delay is prolonged and the burning duration is shortened.The peak of pressure is increased and the peak of heat release rate is increased first and then decreased at low and medium loads.The peak of pressure and heat release rate are increased gradually and the indicated thermal efficiency is increased first and then decreased at high load.In addition,the combustion efficiency are increased at three loads.CO,THC and soot emissions are decreased,while NO_x emissions are slightly increased.NO_x emission is insensitive to n-butanol blending ratio at low load.(2)With the retarded combustion phase,the ignition delay is first shortened and then prolonged.The burning duration is prolonged and the indicated thermal efficiency is decreased at low and medium loads.While the burning duration is first shortened and then prolonged,the indicated thermal efficiency of B0 and B10 is increased first and then decreased,and the indicated thermal efficiency of B20 and B30 is increased gradually at high loads.Besides,NO_x emission is decreased,while CO and soot emissions are increased.High n-butanol blending ratio can improve the indicated thermal efficiency and reduce soot,THC and CO emissions at the same time at fixed combustion phases.(3)With the increase of EGR rate,the ignition delay and combustion duration are gradually prolonged.EGR can reduce NO_x emission,but increase CO,soot and THC emissions.With the increase of n-butanol blending ratio,soot,CO and THC emissions are less sensitive to EGR rate.Diesel and n-butanol blends can alleviate the incomplete combustion and the reduction of indicated thermal efficiency caused by EGR effectively.High indicated thermal efficiency and low CO,soot and THC emissions can be achieved by choosing appropriate EGR rate,combustion phase and n-butanol blending ratio,with a slight increase of NO_x emission.