| As the energy crisis and environmental pollution problems intensify,governments have introduced various strict regulations restricting motor vehicle emissions and fuel consumption.Therefore,this is an important topic of looking for clean alternative energy sources to meet increasingly stringent energy conservation and emission reduction laws and regulations.The coalbed methane as an alternative fuel has significant advantages in terms of economy and emissions.Studying the combustion and emission processes in diesel/coalbed methane engine cylinders is of great significance for the application of diesel/coalbed methane engines.The detailed research contents are as follows:The chemical kinetic analysis software CHEMIKIN-PRO is used to simplify the mechanism of LLNL N-Heptane 3.1,GRI 3.0 and USC.The detailed reaction mechanism of LLNL N-Heptane 3.1 is used as a substitute for diesel reaction.The NOx mechanism of GRI3.0 mechanism is used to simulate the formation of NOx.The methane,ethane,propane and butane fractions in the USC mechanism are used as substitutes in the mixed coalbed methane.The three components constitute the chemical reaction mechanism of diesel/coal methane combustion.Based on this reaction mechanism,the combustion process and emission characteristics of the diesel/coalbed methane dual-fuel engine are analyzed.The results are as follows:(1)In order to study the combustion characteristics of coalbed methane,the diesel/coal gas reaction mechanism is used to analyze the combustion process and emission characteristics caused by the change of coalbed methane composition.The study found that the higher the methane content,the higher the combustion pressure in the cylinder,the more intense fuel combustion,the more heat released,the higher the temperature,and the promotion of NOx formation,while the low methane content will incompletely burn the fuel,resulting in a large amount of UHC and CO.The increase in the content of ethane and butane can suppress the formation of NOx,but the UHC emissions will increase,the fuel combustion will be insufficient,and the increase in propane content will lead to an increase in NOx,a decrease in UHC emissions,and an improvement in the combustion performance of the engine.(2)In order to realize the control of the combustion process of the dual fuel engine,the fuel injection amount and the injection advance angle in the single injection are studied by changing the diesel injection strategy.The pre-injection advance angle,the main spray advance angle and the pre-spray ratio in the secondary injection process are studied about the influence on engine combustion and emission performance.It is found that the delay of the fuel injection advance angle and the decrease of the fuel injection amount reduce the pressure in the cylinder,reduce the heat release from combustion,and cause the temperature to decrease,thereby reducing the NOx emissions and increasing the UHC emissions,but causing the torque to decrease and the economy to deteriorate;A premature injection advance angle or an excessive amount of pilot diesel may result in a maximum pressure rise rate greater than 1MPa/°CA.Appropriate main spray advance angle,pre-spray advance angle and pre-spray ratio can keep the overall exhaust of the engine at a low level,while reducing the maximum pressure rise rate and improving the reliability of the engine.(3)Since the NOx emissions of some operating conditions are high,the control of the combustion emissions of the dual fuel engine is achieved by changing the EGR rate and the fuel-air equivalent ratio.The results show that high EGR rate and high equivalence ratio can effectively inhibit the formation of NOx,but increase the emission of CO and UHC.At the same time,it is found that the optimal equivalence ratio and EGR rate can make the overall emission at a low level. |
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