Effects Of EGR On Diesel/Natural Gas Dual-fuel Engine Combustion And Emission

Compared with the traditional diesel engine,found that the efficient and clean combustion diesel/natural gas dual-fuel engine has a great application prospect.The current diesel/natural gas dual-fuel engine coupling with EGR technology can effectively inhibit NOx production.However,EGR major component（CO₂ and H₂O）of diesel/natural gas dual-fuel engine chemical kinetics researches are still lack.So as to analyze EGR major components’contribution to the pollutantion.So it is necessary for EGR major component in the application of diesel/natural gas dual-fuel engine.In this paper,coupling with the natural gas simplified mechanism and diesel chemical kinetics mechanism,and the pre-exponential factors are adjusted.The DN mechanism is verificated by chemical kinetics and three-dimensional CFD methods,the diesel/natural gas dual-fuel chemical kinetics mechanism is constructed.Based on the DN dual-fuel mechanism,the EGR major component thermal,chemical and combined effects on the combustion and emission characteristics of diesel/natural gas dual-fuel engines are studied,and the contribution of EGR major componen’thermal,chemical and combined effects on the dual-fuel combustion and emission is analyzed qualitatively and quantitatively.Finally,the EGR major components on diesel/natural gas dual-fuel combustion on NO₂ production characteristics are studied.Coupling with the simplified Aramcomech 3.0 natural gas mechanism and the diesel skeleton mechanism,the soot phenomenological production mechanism,soot oxidation mechanism and NOx production mechanisms are added.Containing 117species and 559 elementary reactions of the diesel/natural gas dual-fuel mechanism is constructed.The diesel/natural gas dual-fuel mechanism is verifited by the chemical kinetics and CFD methods respectively.The results show that the DN dual fuel mechanism can accurately predict the combustion delay period of single fuel and the formation and development of important components.This mechanism can accurately predict the combustion and emission of diesel and diesel/natural gas under two working conditions.The simulation results of natural gas substitution rate show that mixing natural gas is helpful to reduce NOx emission.According to the influence of EGR thermal,chemical and combined effects on diesel/natural gas dual-fuel combustion and emission,the EGR combined effect is the sum of the EGR thermal and chemical effects,and the EGR thermal effect is greater than the EGR chemical effect.For the EGR major component,the CO₂ thermal effect is greater than that of H₂O,while the CO₂ chemical effect is smaller than that of H₂O.At the 50%EGR rate,the together CO₂and H₂O thermal effect accounts for 65.3%of the combined effect,and the chemical effects accounts for 36.7%of the combined effect,respectively in diesel mode.At the 50%EGR rate,the together CO₂ and H₂O thermal effect accounts for 62.2%of the combined effect and the chemical effect accounts for 39.2%of the combined effect in dual-fuel mode.The diesel and dual-fuel engine combustion on NO₂ production characteristics is studied by the chemical kinetics method in diesel and dual-fuel modes.The results showed that the NO₂ mole fraction first increases and then decreases with the increase of natural gas replacement rate,under the condition of constant calorific value of the fuel.The NO₂ mole fraction is the maximum value at 30%natural gas replacement rate.The NO₂/NOx ratios firstly increase and then decrease with the increase of EGR rate in diesel and dual-fuel modes.At the EGR rate is 20%,the NO₂/NOx ratio is the maximum in the diesel and dual-fuel modes.In addition,H₂O can increase the NO₂mole fraction by 66.7%and 63.6%compared with CO₂ in diesel and dual-fuel modes,respectively.And the NO₂ mole fraction in dual-fuel mode is twice that of the diesel mode.