Numerical Investigation On The High Efficiency And Clean Combustion Technology For A Low-speed Two-stroke Marine Diesel Engine

With the advantages of high power and high reliability,low speed two-stroke diesel engines have been the main propulsion power of ships.Restricted by environmental and energy issues,the Tier?emission regulation proposed by IMO will come into force in 2016,which requires 75%reduction of NO_x emission than Tier?emission standard.In order to address the challenge,we must investigate the optimum way to realize Tier?emission regulation.Using numerical simulation,this project studies the influence of different strategies on the NO_x emission of two-stroke diesel engines,which will provide reference and practical value for research and development of two stroke diesel engines.One-dimensional simulation is used to simulate the two-stroke diesel engine.In addition,multi-objective integrated optimization is used to validate the model.Based on the established GT-POWER model,several potential in-cylinder control approaches(Exhaust Gas Recirculation?Miller-cycle?Humid Air Motor)on a low-speed two-stroke marine diesel engine to meet the IMO Tier?NO_x emission standard are considered.The influences of EGR coupled withed Miller-cycle,HAM and optimization of injection timing on both NO_x emission and BSFC are also studied to find the best way to reach Tier?emission regulation.Results show that EGR is the most efficient way to reduce NO_x emission among the approaches considered.With 26%EGR,the NO_x emission can be decreased to 3.0 g/kW·h.Using mere Miller-cycle or Humid Air Motor is not capable of meeting Tier III emission standards;when combing Miller-cycle with Humid Air Motor,although NO_x emission could be largely decreased,the Brake Specific Fuel Consumption would also increase significantly.Therefore,combing Miller-cycle with Humid Air Motor is not the best way to meet Tier III emission standards.Combining EGR with Miller-cycle and Humid Air Motor,could improve the trade-off between NO_x and BSFC,and reduce the demand of EGR rate.Therefore,EGR combing Miller-cycle and HAM is the feasible route to meet Tier?emission regulation.