Research On The Influence Of Exhaust Gas Recirculation On Natural Gas Engine Performance And Emissions

Problems such as the energy crisis and environmental pollution have caused rapid development of vehicles using natural gas as an alternative fuel.However,natural gas has the disadvantages of low calorific value and slow combustion speed.In order to meet the requirements for becoming a high-quality fuel for automotive engines,increasing the compression ratio,incorporating hydrogen,and changing the ignition advance angle have become common methods for improving the combustion of natural gas engines,but increasing the compression ratio,incorporation of hydrogen and changing the ignition advance angle will lead to increased NOx emissions.In order to meet the increasingly stringent emission regulations,EGR(Exhaust gas recirculation)has been widely introduced into natural gas engines.Therefore,it is very important to study the impact of EGR on natural gas engines.There are practical issues.In this study,a heavy natural gas engine with high compression ratio,exhaust gas turbocharging,spark plug ignition,and premixed combustion was first refined for fuel,installed with an EGR device,and improved to increase the compression ratio.Then,through high-precision test equipment,reasonable sensor distribution and rigorous test research have obtained accurate and reliable test data.Finally,the test data are sorted,analyzed and summarized to obtain the effect of EGR rate on natural gas engines,and the relevant theoretical knowledge is used to produce the effect factor analysis.The main conclusions obtained in this paper: at a speed of 1000r/min,1400r/min,1800r/min,and a BMEP of 6bar,with the increase of EGR rate,the specific gas consumption increases slightly(the increase is less than 2%),and the effective thermal efficiency is small decline(less than 2% decrease),50% combustion position,heat release peak position and maximum temperature in the cylinder will be delayed,10-90% combustion duration will be extended,and the cumulative heat release rate will be slowed down.Effective expansion ratio,in-cylinder pressure,peak heat release rate,and in-cylinder temperature will decrease,NOx emissions will decrease significantly,and the decrease rate will reach more than 60%.Indicated power ratio,effective power ratio,friction loss ratio,the proportion of pumping loss,the proportion of exhaust energy,and the proportion of cooling water energy have all decreased,while the proportion of combustion loss and the proportion of unaccountedlosses have increased.The efficiency of natural gas engines and the proportion of exhaust gas have decreased slightly.The proportion of exergy loss has increased,while the proportion of cooling water exergy has hardly changed.At the same time,the cooling water accounted for only 14% of the cooling water energy,while the exhaust gas accounted for 39% of the exhaust energy,indicating that the available energy of the exhaust energy is much higher than the cooling water energy.The research results reveal the influence of EGR on the combustion performance,economic performance and NOx emission performance of natural gas engines with high compression ratio and natural gas with high methane content as well as the heat and power conversion laws.The law is of great significance to improve the thermal power conversion efficiency of natural gas engines and tap the energy saving potential.