Simulation On Performance Of Marine Low-speed Two-stroke Diesel Engine

With the demand of ship around the world increasing,pollution from marine engine becoming more and more serious,IMO has formulated stringent NO_x emission regulations.Due to the high test cost of large marine engines,this paper studies the impact of main engine parameters,EGR and injection strategies on emissions through one-dimensional and three-dimensional simulation software,and explores the technical route to meet Tier?emission regulations.Based on GT-Power,a one-dimensional simulation model was built to study the effects of engine scavenging parameters?including supercharging pressure,scavenging port area and exhaust valve closing timing?,fuel injection timing and intake composition on engine NO_x emissions,fuel consumption and output power.The results show that increasing the boost pressure can improve the output power and reduce the fuel consumption but increase the NO_x emission.Reducing the scavenging port area or delaying the exhaust valve closing timing can reduce the NO_x emission,but they can not meet IMO emission regulations.Early injection timing does not reduce NO_x emissions but worsen engine fuel consumption;postponing fuel injection timing reduces NO_x emissions but does not meet regulatory limits and fuel consumption and power output deteriorate.EGR is the only measure within this study that directly achieves the reduction of NO_x emission to Tier?emission regulations but there is a problem of more fuel consumption increase.The 25%EGR rate shows the least increase in fuel consumption based on meeting Tier?emission limits.To obtain more accurate results,a three-dimensional model was built by Converge.The effect of different injection strategies?pre-injection,post-injection and sequential injection?and injector parameters?injection timing,injector location?on NO_x emissions and fuel consumption of engine was studied.The results show that the pre-main injection interval of 5°CA with the pre-injection fuel ratio of 15%,the main-post injection interval of 5°CA with the post-injection fuel ratio of 10%,the combination of one pre-spray and one post-spray,sequential injection interval of2°CA and injector downwards of 5°meet Tier?and reduce fuel consumption compared to only 25%EGR rate.25%EGR rate with pre-pilot injection of 5°CA and pilot fuel ratio of 15%,make BSFC rise least,only 3.56 g·?kW·h?^-1.To sum up,25%EGR rate can make the engine NO_x emission meet the Tier?standard,but the fuel consumption rises more,about 4%⁵%.Combined with the pre-injection,25%EGR rate allows the engine to meet the Tier?and fuel consumption is optimized to reduce fuel consumption rise to 2.0%.