Parametric Study on the Effect of Increasing the Amount of Diesel Fuel in Dual Fuel Engines at Part Load Conditions

One of the best strategies for using natural gas in diesel engines is dual fuel technology. In dual fuel engines, UHC and CO emissions increase and engine thermal efficiency decreasesat part loadsdue to the lack of suitable flame propagation in the combustion chamber. In this paper, the effect of increasingthe amount of diesel fuel on combustion, performance and emission characteristics of dual fuel engine was studied while keeping the total amount of energy input per cycle constant at part load condition. KIVA-3V codewas used to simulate the in-cylinder eventat closed part of engine cycle. Results show that the in-cylinder pressure historiesand emissions values ​​predicted by the models are in good agreement with thecorresponding experimental data. Also it can be resulted that at part loads,the unburned methane is remained in the most remote areas from diesel fuel injectors such as the bottom of the piston bowl and in four directions wherediesel fuel is not injected. By injection of diesel fuel into the combustion chamber, a fuel-rich zone is formed in the upper areas of combustion chamber and in four directions of injection in which the bulk of CO is formed in these regions due to the lack of oxygen for complete combustion. Hence by increasing the amount of diesel fuel at part loads, diffusion flame penetration of diesel fuel is increased into the combustion chamber and then natural gas combustion is improved.Also, the percentage of natural gas in the mixture that charged in intake stroke is reducedand consequently more oxygen enterscombustion chamber. This excess oxygen in the fuel-rich regions leads to complete combustion. Hence, on the top of the combustion chamber, formation of CO decreaseswhileformation of NO is slightly increased.