Development Of A Chemical Mechanism And Study On The Combustion Characteristics Of A Hydrogen/diesel Dual Fuel Engine

Under the background of greenhouse effect,energy conservation,emission reduction,the"double carbon"policy and upgrading of the energy industry,the internal combustion engine is facing the challenge of technological upgrading.At present,the internal combustion engine industry is moving towards low-carbon and zero-carbon fuel.Hydrogen-diesel engine has become a new development direction of internal combustion engine due to its low carbon,high operability,good adjustable performance and low cost.A hydrogen-diesel dual-fuel engine was obtained by modifying a pure diesel engine and tested.In order to fill the gap in the mechanism of hydrogen-diesel dual-fuel engine,a mechanism that can predict combustion characteristics and emissions of hydrogen-diesel dual-fuel engine was developed.According to the mechanism and test results,the effects of hydrogen substitution rate,diesel pre-injection starting angle and pre-injection quantity on the combustion characteristics of dual-fuel engine were studied,as follows:70%mole fraction of n-decane and 30%volume fractionα-methylnaphthalene（IDEA fuel）were chosen as diesel surrogate,the mechanism is constructed according to the general framework of the mechanism.α-Methylnaphthalene,NO_x,PAH,soot and H₂/C₁-C₃ sub-mechanisms are analyzed,and the reaction path of each sub-mechanism is combined into the hydrogen-diesel dual-fuel mechanism.Through the sensitivity analysis of the fire delay period,the pre-index factors of some elementary reactions are adjusted to optimize the original mechanism,and the final hydrogen-diesel dual-fuel mechanism is obtained.The sensitivity analysis of the final hydrogen-diesel dual-fuel mechanism to ignition delay is performed,and the reactions that are most sensitive to IDEA fuel ignition at 800,900 and 1100 K are analyzed.The ignition delay time,JSR oxidation and laminar flame velocity profiles of different components in the mechanism were verified,and the average errors between the simulation and the experimental values were within a reasonable range;The hydrogen-diesel dual fuel mechanism is verified by CFD,and the combustion and emission of hydrogen-diesel dual-fuel engine can be predicted by the mechanism.Using this mechanism coupled with CFD model,the influence of hydrogen replacement rate on combustion characteristics was studied.The results show that with the increase of hydrogen replacement rate,the cylinder pressure is separated from the quick-burning period,the range of cylinder pressure rise rate,the peak value of diffusion combustion and premixed combustion in the heat release rate curve,and the proportion of premixed combustion also increases,and the late combustion is advanced;The hydrogen substitution rate increased from 0%to 5%,15%,30%and 45%respectively,and the maximum cylinder pressure increased by 0.7%,4.2%,11.8%and28.8%respectively,with the increase amplitude increasing in turn.With the increase of hydrogen replacement rate,the average in-cylinder temperature will rise faster,and the highest average temperature in the cylinder will rise in turn.The hydrogen substitution rate increased from 0%to 5%,15%,30%and 45%respectively,and the maximum cylinder pressure increased by 0.7%,4.2%,11.8%and 28.8%respectively.0.2%,1.6%,6.9%and 17.3%,and their increasing range increased in turn.The combustion duration is shortened with the increase of hydrogen substitution rate,and the combustion center is also advanced.The hydrogen substitution rate increased from 0%to 5%,15%,30%and 45%respectively,and the combustion duration shortened by 0.3%,5.5%,15.7%and 25.9%respectively,and the reduction of combustion duration increased in turn.The research on the influence of diesel pilot injection starting angle and pre-injection quantity on combustion characteristics shows that when the pilot injection quantity is the same,with the advance of the pilot injection starting angle,the cylinder pressure,heat release rate and temperature separate from the compression section curve and show a point lag of rising trend,and the maximum cylinder pressure decreases with the advance of the pilot injection,and the crankshaft angle corresponding to the maximum cylinder pressure also gradually delays;With the advance of the pilot injection starting angle,the combustion center of gravity gradually lags behind,while the combustion duration is not significantly affected by the advance of the pilot injection starting angle;When the initial angle of pilot injection is advanced from-35°CA ATDC to-25°CA ATDC,the maximum average temperature rise in the cylinder is greater than when the initial angle of pre-injection is advanced from-35°CA ATDC to-15°CA ATDC.When the initial angle of pilot injection is the same,the separation point of cylinder pressure,heat release rate and average in-cylinder average temperature will advance with the increase of pilot injection quantity,and the maximum cylinder pressure and in-cylinder average temperature will also increase;However,the change law of the combustion center of gravity and the combustion duration affected by the pilot injection quantity is not obvious.Under three initial angles of pilot injection,the pilot injection volume increased from 6.69 mg to 9.28 mg,from 6.69 mg to 11.6 mg,the maximum cylinder pressure increased by 7.1%and 11.9%respectively,and the maximum average in-cylinder temperature increased by 3.6%and 5.2%respectively.When the pilot injection mass accounts for a large proportion of the total fuel volume,compared with the working condition where the pilot injection volume accounts for a small proportion of the total fuel volume,the temperature and internal energy in the cylinder under the hydrogen-diesel dual-fuel combustion mode distribute much better,and the proportion of premixed combustion increases,which can be reflected in the single-peak heat release rate curve.