Study On The Mechanism And Performance Of Natural Gas—Biodiesel Dual Fuel Combustion Based On Marine Diesel Engine

In the context of increasingly stringent emission regulations and energy shortages,internal combustion engines using conventional fuels are faced with many challenges.Developing clean alternative fuels and combustion technologies is an important solution.It is of theoretical and engineering value to study the combustion of biofuels and natural gas.Based on L.Brakora’s biodiesel mechanism,a mechanism model of biodiesel that can predict Soot generation was constructed by adding PAHs,Soot generation and oxidation mechanism.After combining with the simplified natural gas mechanism,a natural gas-biodiesel double Fuel Chemical Kinetic Model was built.By coupling with the mathematical model constructed in AVL FIRE,the influence of injection parameters and injection strategy on the combustion characteristics of biodiesel was explored,and the effect of different natural gas replacement rates on the combustion and emission of natural gas-biodiesel dual fuel was explored.Selected 1100 r / min,fuel injection 20.383 mg,1500r / min,fuel injection 25.858 mg two conditions in the study of combustion and emission of biodiesel,the influence laws of injection timing,injection pressure and injection strategy on combustion and emissions were explored.Under the condition of both combustion and emission,the optimal injection was determined At 20 ° CA BTDC,the injection pressure was 100 MPa.Eight kinds of fuel injection strategies were designed.The results show that when the main injection position is constant,the increase of the pre-injection quantity is favorable for the rapid combustion of the main fuel and the decrease of Soot emissions but the increase of NO emissions.The interval angle will make the cylinder form a two-stage heat release and lead to an increase of NO emission and a decrease of Soot emission.The fixed pre-injection amount and pre-injection angle increase the pre-injection and main injection-spray angle,and then the cylinder temperature and pressure drop,The main fuel injection rate of combustion gradually reduced,NO and Soot also exist in the shift of the contradictions.For natural gas-biodiesel dual fuel combustion,the effect of natural gas replacement ratios on combustion and emissions was studied.The results showed that in the medium-speed,30% replacement ratio was selected to obtain moderate in-cylinder combustion rate and exothermic concentration,which was beneficial to improve combustion efficiency and power output,while NO and Soot emissions were lower.In the high-speed,2000r/min,When 50% alternative ratio is selected,cylinder temperature,cylinder pressure and heat release rate are significantly higher than other alternative ratios and Soot emissions are lower.According to the comprehensive analysis,30% natural gas replacement rate is adopted for medium-speed and 50% natural gas replacement rate for high-speed,so that higher combustion efficiency and lower emission can be obtained.