The Effect Of Substitution Rate And Diesel Injection Time On The Low Load Performance Of Dual Fuel Engine

The use of clean fuels in internal combustion engines is an effective way to solve the problem of energy crisis and environmental problems.Natural gas is favored due to its abundant reserves,high energy density,high octane value and low emission.The influence of percentage energy substitution rate and injection time on engine performance,fuel economy,the combustion process and emission performance are investigated in a diesel/natural gas dual fuel engine,in low load condition.First,the research carried out three kinds of rotational speed and the effect of percentage energy substitution rate on engine performance,fuel economy,the combustion process and emission performance.The study found that,at different speeds,the substitution rate of natural gas was consistent with the effect of engine power and economy.With the increase of substitution rate,reduced the volume of diesel spray,extended diesel ignition delay,and gas injection increase,results in the decrease of temperature and pressure in cylinder compression,reduce power namely dynamic performance and effective specific fuel consumption increase;In addition,at the same substitution rate,compared the high speed with the middle and low speed,the dynamic performance and economy are significantly lower.Under the low load condition,middle and low speed,with the increase of the substitution rate,the pressure of the cylinder decreased,the maximum pressure peak gradually decreased,and the corresponding crankshaft angle was advanced.Under high speed and low load conditions,as the substitution rate increases,the pressure in the cylinder decreases,while the pressure peak in the cylinder decreases gradually,but the crankshaft angle of the pressure peak corresponds to the back.Under low,middle and high speed,with the increase of substitution rate,heat release rate were decreased,and the twin peaks turn to single peak,the combustion start point backwards,burning center of gravity move backwards after previous trends,combustion ignition delay period shorten after first extend,volatile combustion duration.Under the three different speeds,with the increase of substitution rate,CO emissions overall presented an increasing trend,NO_X emission decreased and HC emissions increased.In addition,under high natural gas substitution rate,the effect of different diesel injection time on the power,economy,combustion process and emission.In the three different natural gas substitution rate,the diesel injection time has the same effect on engine power and economy.With the increase of the injection time,the engine power and economy are in the trend of getting better and worse.Under the same diesel injection time,with the increase of the substitution rate,both the dynamic and the economic performance are worse.With the advance of the diesel injection time,the pressure of the cylinder increases and then decreases,and the cylinder pressure peak also shows the same trend.The change in the diesel injection time can cause a change in ignition mode.Under the traditional injection time,spark ignition of diesel model for traditional compressive ignition,dual fuel engine to traditional dual fuel combustion mode,as the injection time in advance,the heat release rate reduced after the first increases,the peak heat release rate corresponding crank angle after the previous move backwards.When the natural gas substitution rate is 85%,the peak heat release rate appears near CA15.When the fuel injection time greatly in advance,diesel ignition mode is QHCCI combustion mode,at this point,the dual fuel engine combustion reaction at low temperature and the heat release rate single peak caused by gas multipoint combustion,as the injection time in advance,the heat release rate increases,the peak heat release rate corresponding crank corner backwards,heat release rate peak near the CA50,and heat release rate of the peak heat release rate and CA50 values are the same.In the three different natural gas substitution rates,with the advance of the injection time,the combustion start point and the burning center of gravity shift after the previous shift;In addition,with the increase of natural gas substitution rate,both the starting point and the center of the combustion center move backward.This is mainly due to the change in ignition mode of ignition diesel.When the natural gas substitution rate is 85%,the CO emission decreases with the advance of the diesel injection time,and then rises sharply.When the substitution rate of natural gas is 90%,the CO emissions decreases and then rises with the advance of the diesel injection time.When the substitution rate of natural gas is 95%,the change of CO emissions is basically unchanged.When the substitution rate is 85%,the NO_X emission decreases with the advance of the diesel injection time.When the substitution rate of natural gas is 90%and 95%,NO_X emission decreases with the advance of the diesel injection time.When the substitution rate was 85%,the HC emission showed a change trend that decrease,remain unchanged and increase with the advance of the diesel injection time.When the substitution rate is 90%and 95%,the HC emission decreases first and then increases with the advance of the injection time.