Modeling the power-economic characteristic of diesel-steam combined cycle in the whole spectrum of operating conditions

A mathematical model of energy conversion processes in a combined diesel-steam power plant has been developed. The investigated power plant consists of a turbocharged diesel engine and a steam turbine. The steam turbine is arranged as a heat recovery system utilizing the exhaust gas heat from the diesel engine. The mutual work of the diesel engine as a source of heat, and the system for utilization, as a consumer of heat, has been investigated in the whole spectrum of operating conditions in terms of the engine speed and load. The mathematical model describes the processes taking place simultaneously in the diesel engine cylinders, turboharger, air filter, air inlet pipes, exhaust pipes, exhaust gas boiler, steam turbine and the related auxiliary elements. The model includes non-linear differential equations, expressing the energy and mass conservation equations for modeling the processes in the diesel engine cylinders, fuel combustion rate both for premixed and diffusion flames, the gas exchange process, power balance in the turbocharger, matching the instantaneous characteristics of the turbocharger with the piston part of the engine, energy balance in the inlet pipes and exhaust system, heat balance in the exhaust gas boiler, utilization gas turbine, etc. The fifth-order Kuta-Merson method has been applied for solving these simultaneous equations. The model gives an opportunity to investigate the behavior of this combined power plant with respect to the major integral parameters, like mean indicated pressure, specific fuel consumption, hourly fuel consumption, brake power of the main diesel engine, parameters (mass flow rate, pressure, temperature) of gases and air respectively through the gas turbine and compressor (in the frame of turbocharger), exhaust gas temperatures at boiler inlet and outlet, exhaust gases mass flow rate through the boiler, parameters of superheated steam (temperature, pressure, enthalpy), steam production in terms of mass flow rate, etc. As a result, the universal power-economic characteristics for the whole spectrum of operating conditions have been created, which can be used for solving optimization problems.