Simulation And Control Of Diesel Brayton Combined Cycle Engine

Improving the thermal efficiency and power density are the two most important aims in the development of special use vehicle power system. The diesel engine has high thermal efficiency but low power density, while the gas turbine has high power density but low thermal efficiency. In this paper, the Diesel Brayton combined cycle engine, a new concept engine which has the potential to meet the future needs of high power density and low fuel consumption, was researched.The Diesel Brayton combined cycle engine is consisted of a turbo-charging intercooling diesel engine and a gas turbine. By opening or closing the four electric valves, the air inlet and outlet systems of the diesel engine and the gas turbine can be changed according to the power needs of the vehicle, thus the single diesel mode, the single gas turbine mode and the combined mode can be implemented.In this paper, the configuration of the Diesel Brayton combined cycle engine was presented. The theory cycles of the three modes of the engine was studied. The formula of thermal efficiency and work weight ratio were deduced. According to the set parameters of the cycle, the thermal efficiency and work weight ratio of the three modes were calculated. On the basis of the set parameters, the influences of compression ratio, pressure rising ratio, pre expansion ratio, the distribution coefficient of diesel mass flow rate, pressure ratio of the compressor of the gas turbine and temperature increasing ratio of the gas turbine on the theory cycle were studied.One diesel engine and one gas turbine were chosen to make the Diesel Brayton combined cycle engine. The simulation models based on GT-Power of the combined engine was built. The influences of back pressure, inlet pipe diameter, inlet electric valve diameter on the diesel engine were analyzed. The two methods to restrict the diesel engine inlet mass flow rate, reducing the speed of the diesel engine or reducing the opening angle of the inlet electric valve, were studied, and the power density and the fuel efficiency were evaluated.The dynamic simulation model of the combined engine was built in Matlab/Simulink, based on the method of volume inertia and the experiment MAPs. The static working points and the process of mode changing were simulated.The control system of the combined engine was designed. And the control software was designed in Labview to meet the demands of the experiments of the combined engine. The principles of mode selecting and the control strategy in the process of mode changing were presented. The work in this paper lays a basic foundation for the combined engine experiments.