Numerical Study Of Diesel/Natural Gas Dual-fuel Conversion For Marine Engine

In order to meet the more stringent emission requirement of the engine,converting a marine diesel engine to a diesel-natural gas dual-fuel engine becomes a trend.The paper carry outs the preliminary study for transformation of dual-fuel engine for 4190 Z_LC marine diesel engine.The numerical simulation is adopted in the research.By steady flow simulation for the intake system,the number of nozzle hole of natural gas injector,the injection direction and the installation depth of the injector are studied for the effects on the natural gas-air mixture’s homogeneity.By transient simulation for high pressure process inside the cylinder,the influences on combustion and emission are studied of the nature gas substitution rate,pilot diesel injection timing and the injection pulse width.The results of steady state calculation for the intake system shows: 1)The more the number of the nozzle hole in the natural gas injector,the better the air and the natural gas mixed;2)When the inject direction of the natural gas is directly face to the air inlet direction,the better mixture will be obtained,but the natural gas will collected inside the intake manifold and the amount of the nature gas injected into the cylinder cannot be controlled accurately;though the mixture will not be so good near the injector,the leeward injection will cause a better mixture and a higher concentration of the natural gas inside the cylinder;the natural gas will not collected inside the intake manifold also.3)Increasing the installation depth of the injector into intake port will decrease the quantity of the natural gas collected in the upper part of the intake port,and facilitate the natural gas flow into the cylinder.The simulation on the high pressure process in cylinder shows that: 1)Along with the increase of the substitution rate of the nature gas,the explosion pressure and the temperature inside the cylinder will increase,but when the substitution rate reaches 90% the explosion pressure and the temperature reduce,the CO and NO emissions will reduce greatly;2)The increasing of the advanced angle for pilot diesel injection will lead to higher pressure and temperature;when the advanced angle is smaller the temperature in cylinder will reduce,so NO produced will drop but CO produced will increase;the incomplete combustion will occur;3)In condition that the pilot diesel quantity and advanced injection angle are the same,with the increase of the injection pulse width,the ignition delay would extend and the increasing rate of the temperature and pressure will reduce;the explosion pressure drops;meanwhile NO produced reduce,but CO produced increased which means the incomplete combustion become more serious.The research provides the theoretical guidance for converting 4190 ZLC diesel engine to a diesel-natural gas dual-fuel engine.