Research On The Key Technology Of Gas Supply For Natural Gas-Diesel Dual Fuel Engine

The vigorous development of the traditional automotive industry is accompanied by two problems:oil crisis and environmental pollution.The increasingly urgent problem of oil shortage and rising of oil prices,not only causes the increase of transportation cost,but also cast an ill effect on the air quality and human health,for which the main culprits are the nitrogen oxides,soot and other pollutants produced by the traditional fossil fuel combustion.From the perspective of environmental protection and economic efficiency,it is urgent to search alternative clean and efficient fuels.Natural gas,as aclean,efficient,and economical energy,its main component is methane,of which the combustion process almost produces no smoke,and the nitrogen oxide emission much less than that of oil fuel.Otherwise,China is rich in natural gas reserves,of which the cost of exploitation is also comparatively cheaper than that of oil and coal.Therefore the natural gas is very suitable to be the substitute fuel of the internal combustion engine.Consequently,the dual fuel engine has become the research hotspot in the field of internal combustion engine.This paper uses the SL4108Z supercharged diesel engine as the prototype of the natural gas-diesel dual-fuel engine,with the original gas distribution system and oil supply system being constant,adds in a natural gas supply system and ECU that can control injection mass and the moment of the injection,and by bench test standardizes the natural gas flow of the gas injection valve,in order to ensure the normal supply of the natural gas.At the same time,using the CFD(CONVERGE)to simulate the combustion process of the dual fuel engine,and combining with the engine bench test,to analyze the effect of natural gas injection on the combustion process and emission of dual fuel engine under different load conditions of engine.The paper makes the following conclusions:(1)This paper studies the calibration scheme of the flow characteristics of natural gas injection valve,and studies the factors which influencing the flow rate of the injection valve in the pipeline of natural gas supply system by combining theoretical analysis with test.In the natural gas supply system,when the tube pressure is constant and other conditions remain unchanged,jet pulse width and injection valve flow is basically a linear relationship.Under the same experimental conditions,the linear relationship between the jet pulse width and the flow remainswell.With the increase of the number of the injection valves,the flow rate of the valve group also increases,but not in strict linear style.(2)This paper based on the internal combustion engine simulation software CONVERGE,establishes the combustion model of the engine under the dual fuel mode.The combustion process of the diesel and natural gas in cylinders is numerically simulated.To studies the effects of natural gas substitution rate and natural gas injection on the dual fuel on the combustion and emissions of the engine.Simulation results and bench test study shows that under the low load(throttle opening 25%)condition,with the natural gas replacement rate between 25%-30%,the engine cylinder combustion efficiency reaches the highest,not only ensures the power similar to the original one and the BFSC being low,but alsoreducesthe NOx emission significantly,and remains the soot emission at a lower level.Under the medium load(throttle opening 50%)condition,the best replacement rate is 50%,the engine economic performancereaches a good state,and the BFSC remains low,and the NOx and soot emission achieves relatively good indicators simultaneously.Under high load(throttle opening 75%)condition,the replacement rate that can simultaneously guarantee the ideal economic performance and emissions is 60%.(3)According to the results of CFD simulation,designing the engine bench test scheme.Based on the results of the bench test,analyzing the influence of the replacement rate of natural gas on the economy and emission of the dual fuel engine under different load and the engine at 1500 rpm.And to studies the impact of natural gas substitution rate on the performance and emissions of the engine basing on the equivalent fuel consumption(BSFC),engine exhaust temperature and NO emissions.