Computational model of the fuel consumption and exhaust temperature of a heavy duty diesel engine using MATLAB/SIMULINK

Abstract

A model of a diesel engine and its electronic control system was developed to investigate the engine behaviour in a vehicle simulation environment. The modelled quantities were brake torque, fuel consumption and exhaust gas temperature and were based on engine speed and pedal position. In order to describe these outputs the inlet air flow and boost pressure were also modelled and used as inner variables. The model was intended to be implemented on board a vehicle in a control unit which had limited computational performance. To keep the model as computationally efficient as possible the model basically consists of look-up tables and polynomials. First order systems were used to describe the dynamics of air flow and exhaust temperature. The outputs enable gear shift optimization over three variables, torque for vehicle acceleration, fuel consumption for efficiency and exhaust temperature to maintain high efficiency in the exhaust after treatment system. The engine model captures the low frequent dynamics of the modelled quantities in the closed loop of the engine and its electronic control system. The model only consists of three states, one for the pressure build up in the intake manifold and two states for modelling the exhaust temperature. The model was compared to measured data from an engine test cell (as got in INNOSON NIG. LTD.) and the mean absolute relative error were lower than 6.8%, 7.8% and 5.8% for brake torque, fuel consumption and exhaust gas temperature respectively. These results were considered good given the simplicity of the model.