The Research Of Exhaust Gas Recirculation Effects On Low Speed Marine Diesel Engine Performance And Emission Characteristics

In 2016, the International Maritime Organization (IMO) will enforce stricter nitrogen oxide (NOx) emissions standards, and exhaust gas recirculation (EGR) technology is an effective way to achieve IMO Tier III standards. However, marine two-stroke diesel engine EGR technology is currently in the country has made little article analysis. This paper selects 6S50ME-C8.2 vessels two-stroke diesel engines for the study, making use of GT-POWER simulation modeling software, the high-pressure and low-pressure EGR system EGR systems were compared, in-depth analysis of the EGR rate and EGR cooling temperature on engine performance and the impact of emissions, analyzed the influence of Miller timing on high pressure loop EGR system combined EGR diesel engines; the author made evaluations for high and low pressure EGR system by using the fuzzy comprehensive assessment model, in order to provide theoretical reference for the design of the ship two-stroke diesel engine EGR system. In addition, the author optimized the high-pressure EGR system to add an cylinder bypass, which can optimize the compressor and account to the IMO Tier Ⅲ. This article did the following works and reached the following conclusions:1) In the article, the author built the simulation model of the 6S50ME-C8.2 diesel engine,and built the high pressure EGR system and the low pressure EGR system, and then analyzed the effects on the engine performance when changed the EGR rate and the EGR cooling temperature. Here are the conclusions : With the EGR rate rising,the engine worked on a worse conditions, but the meanwhile, with the lower NOx emissions; with the EGR cooling temperature rising, the NOx emissions are down, but the engine power dropped, the maximum explosion pressure and the maximum combustion temperature decreased, the fuel consumption increased;2) On comparison of high and low pressure EGR system, here are the conclusions: the adjustable range of the low-pressure EGR rate is greater than the high-pressure EGR rate;EGR cooling temperature had little effect on the performance of the engine in the low-pressure EGR system;3) By changing the Miller timing, high pressure EGR system economy and NOX emissions performance are analyzed. After adjusting the exhaust valve closing time, fuel consumption rate has risen obviously, at the same time, NOx emission is controlled effectively; When the Miller cycle is combined with EGR, the author adjusted the closing time to 302℃A,and it is obvious to see that NOx emission has been controlled effectively,while fuel consumption rate has risen again;4) The author built a fuzzy comprehensive evaluation model which based on the maximum degree of membership criteria for power,high and low pressure EGR system solutions were evaluated, the final outcome of the overall show that the high-pressure EGR diesel engines is better;5) The author adopted the technology of cylinder bypass for high pressure EGR diesel engine, which optimized the operating point of the compressor, keeping it away from the surge line and in high efficiency area; At the same time, after adopting the cylinder bypass,the power and fuel consumption of diesel engine have been improved, while NOx emissions were reduced less than the high-pressure EGR system. Based on these, the author get the conclusion: when the marine diesel engine operate in low EGR ratio(<20%), it is no need to open the cylinder bypass; while when the engine operate in high EGR ratio (20%～40%), it is a must to open the cylinder bypass to reduce the NOx emissions to 3.4g/(kW·h) or lower and optimize the compressor.Based on the above conclusions, the research results obtained in this paper can offer reference for the turbocharged diesel engine with EGR technology to reduce NOx emissions and improve fuel economy.