Study On The Performance Of Two-stage Successive Supercharging Of Marine Medium-speed Diesel Engine In Full Working Condition

At present,the power density of domestic marine diesel engines is still far from the advanced level of foreign countries.The Brake Mean Effective Pressure(BMEP)of modern foreign advanced high-power density and high-power diesel engines is 2.4-3.0MPa.In order to meet the increasing power density requirements and the higher BMEP requirements of a new generation of marine diesel engines,and the requirements of meeting and exceeding the BMEP of foreign diesel engines,research on high pressure ratio and wide flow supercharging systems is needed.Based on the original machine of a 270 diesel engine and ensuring that the rated speed is the same as that of the original machine,the diesel engine BMEP is regarded as the reinforcement target.The two-stage sequential boosting system is modified to meet the need of rated power density of the diesel engine and the need of the performance of partial working conditions.The main research contents include:(1)Carry out the simulation model of marine medium speed machine,establish a one-dimensional simulation calculation model of a 270 diesel engine,carry out the loading performance experiment on the original machine,and use the data of each working condition of the experiment to check the diesel engine model,The results shows that the error between the test value and the calculated value of each working condition point is within 3%;(2)For the target of diesel engine strengthening,a two-stage sequential supercharging scheme is proposed and its matching method is studied.Because the two-stage sequential supercharging system has multiple operating modes in the multi-supercharger cooperative work,the matching parameters are numerous and the matching is difficult.A matching method of this special turbocharging system is proposed in this paper based on parameter analysis.Based on the equal turbine area ratio scheme and the variable turbine area ratio scheme,matching the diesel engine with the appropriate supercharger.The matching results show that the two matching schemes can both make the operating point of the enhanced diesel engine in the high efficiency region of the supercharger;(3)Establish a simulation calculation model for the two-stage sequential supercharging system after the transformation,and obtain the steady-state calculation results under the full working conditions of the two matching schemes.The switching boundary of the two schemes under the full working condition of the supercharged system is obtained by the principle of economical optimality.Comparing the two schemes,the results show that the fuel consumption rate of variable turbine area ratio scheme is reduced by 1.21% compared with the equal turbine area ratio scheme below 60% load.By adopting the equal turbine area ratio scheme,the boosting system is simplified,the number of control valves,control difficulty and costs are reduced,the system reliability is improved.(4)The transient switching process is studied for the equal turbine area ratio scheme.The transient simulation calculation model is established.Based on the switching control strategy under the whole working condition,the opening and closing of valves in the switching process is studied.Determined the order of opening and closing and the optimal opening and closing delay of each valve during the switching process.