Effect of Engine Operating Condition on Thermodynamic Cycle

Abstract

A sophisticated software is developed for the calculation of thermodynamic cycle and entropy change in a turbocharged, direct-injection, diesel engine based upon the measured cylinder pressure and shaft encoder output. Assumptions of homogeneous mixture and equilibrium thermodynamic properties for the products of combustion are made and the temporal variation in fluid thermodynamic state is effectively progress in a pseudo quasi-steady manner through a series of adjacent equilibrium states, each separated by a relatively small but finite interval of one-degree crank angle. The thermodynamic properties are calculated by either of two equivalent formulations-equilibrium constants or minimisation of Gibbs free energy, and are expressed in algebraic equations for the partial derivative of internal energy and gas constant with respect to temperature, pressure and equivalence ratio. The effect of engine operating conditions on the thermodynamic cycle is studied. Results show that the dynamic fuel injection timing and hence the ignition delay are strongly dependent on the operating conditions, which explains the reason for incorporating a fuel injection control system in modern vehicular engines for the oprimisation of engine combustion cylcle.