Simulation Research On Combustion Process In A LNG-Diesel Duel-Fuel Marine Engine

Natural gas is rich in reserves and bargain in price. Natural gas is also regard as cleanfuel.But previous natural gas engine can not achieve the assumptive power.Therefore, weshould take advantage of natural gas engines.It not only reduces the engine emission, butalso reserves the high efficiency that using pilot diesel fuel ignites directly injected liquefiednatural gas.The dual fuel engines is an important development orientation in the word.In this paper, AVI-FIRE is used for simulating the conclusion on cylinder injection andcombustion.Get the following conclusion to analyze simulation results:1） Spraying diesel before LNG has batter combustion characteristic, powerperformance and emission performance;2）As the ahead of injection timing of liquefied natural gas, maximum of cylinderpressure and cylinder temperature increase gradually and the timing for the maximum valueis bring forward. As the delay of LNG injection timing, the range of high temperaturedecreases, which is advantage to the NOxemissions; Indicated power gradually reduced and,fuel consumption is rising;3）As the decrease of injection duration angle, the injection speed and injectionpressure increases. With the decrease of injection duration angle, the maximum averagepressures in cylinder increase, and are all appeared in the729°CA; But the maximumincreasing percentage of cylinder pressure is less than2%, so we can included thatdecreasing the injection angle has little effect on the cylinder pressure; With the decrease ofinjection duration angle, the maximum value of cylinder temperature increases continuously,and LNG injection duration angle is smaller, the time of cylinder temperature at maximumvalues is earlier; Meanwhile, the mixture mixing process in cylinder is strengthened, and thearea of the high temperature in cylinder is expanded; Indicated power gradually reducedand, fuel consumption is rising;4）This paper studies the effect on natural gas’s combustion of different amount of pilotdiesel, which energy is0.5%,1%,4%,7%, and10%of the total energy.When I=0.5%the pilot diesel can not ignite the natural gas, so we can concluded that the pilot diesel needto be greater than a certain amount. With the increase of the pilot diesel, the maximum ofthe cylinder pressure and the cylinder temperature ascend.When I=1%, I=4%, I=7%andI=10%, the maximum cylinder pressure increase by4.80%,7.90%,10.45%. The amount ofthe pilot diesel has little influences on NOxemissions. In this paper,the NOxemissions all reach the TierⅢ; indicated power is rising, but the specific fuel consumption get minimumvalue at7%;5) Thought the comparison of LNG liquid fuel supply and gas fuel supply, it is littledifferent between liquid fuel supply and diesel engine in cylinder pressures andtemperatures.So we can summary that LNG liquid fuel supply has more advantages thanLNG gas jet fuel supply.