The Effect Of EGR On The Performance Of Diesel/natural Gas Dual-fuel Engines At Different Altitudes

The dual-fuel engine has a good application prospect because of its flexible use of fuel,less carbon smoke emission,small engine modification and low modification cost,and has become an effective technical solution for improving engine fuel economy,emissions and noise.The application technology development of natural gas/diesel dual-fuel diesel engine is in line with the characteristics of Yunnan’s economic and industrial development,and the use of alternative energy has important strategic significance.Diesel/natural gas dual-fuel engine can effectively improve the environmental pollution caused by soot emissions.After adding EGR system,it can simultaneously improve NOx emissions.Therefore,the effect of EGR on the performance of diesel/natural gas dual-fuel engine at different altitudes is studied.It is of practical significance to achieve high efficiency and low pollution combustion in the region.When the diesel engine is running at high altitudes,the intake air volume is reduced,resulting in a decrease in the excess air ratio and effective power of the diesel engine,an increase in the fuel consumption rate,and further discharge of more harmful substances in the exhaust gas of the diesel engine.Based on the YN33 diesel engine,a diesel/natural gas dual-fuel engine modification scheme was designed.The test of the dynamics,economy,combustion characteristics and emission characteristics of the diesel/natural gas dual-fuel engine in the plateau environment was carried out on the engine rig.The one-dimensional and three-dimensional simulation models of dual-fuel engines were established by GT-POWER and AVL FIRE simulation software.Combined with the test bench,the effects of EGR on the performance of diesel/natural gas dual-fuel engines at different altitudes were studied.Research indicates:(1)At 80kPa,the external characteristic torque of the diesel/natural gas dual-fuel engine is comparable to that of the pure diesel mode,and the partial speed is slightly higher than the pure diesel mode.As the load increases,the specific fuel consumption of the dual fuel engine gradually decreases,which is lower than the specific fuel consumption in the pure diesel mode.(2)The NOx and CO2 emissions in the dual fuel mode are higher than the pure diesel mode,in which the NOx emission is reduced by 7.3%on average at 1200r/min,and the maximum reduction in CO2 emissions is 13%.The dual fuel mode has a lower cylinder pressure peak than the pure diesel mode.The power and economy of a diesel/natural gas dual fuel engine deteriorates as the EGR rate increases(3)At 80kPa,when the EGR ratio is 0.2,the engine torque is reduced by 5.45%on average compared with the EGR rate of 0.At 90kPa and 100kPa,the average reduction ratio is 1.48%and 1.37%,respectively.The increase in atmospheric pressure can reduce the magnitude of deterioration of torque and specific fuel consumption with increasing EGR rate(4)With the increase of EGR rate,the cylinder pressure,cylinder temperature and heat release rate of the diesel/natural gas dual fuel engine decrease under the same working conditions.Under the condition of 2000r/min-200 N·m at 80kPa,the EGR ratio is 0.5,the cylinder pressure peak is decreased by 33.74%when the EGR rate is 0;the peak temperature of the cylinder is decreased by 22.26%;and the peak of the heat release rate is decreased by 81.65%.Under the three atmospheric pressures,the drop is the largest at 80kPa,and the temperature drop at 90kPa is the smallest(5)The NOx emission of the diesel/natural gas dual-fuel engine decreases with the increase of the EGR rate,and the maximum drop is 80kPa under the same working conditions.As the EGR rate increases,the NOx emission peak corresponds to a phase shifting trend.Overall,SOOT emissions increase with increasing EGR rate.At 1200r/min,210N·m and 2000r/min,320N·m,and 3200r/min,242N·m,CO emissions increase with increasing EGR rate.