THERMODYNAMICS IN A TURBOCHARGED DIRECT-INJECTION DIESEL-ENGINE

Software has been developed for the calculation of the thermodynamic c ycle and the entropy changes in a turbocharged, direct injection, dies el engine based upon the measured cylinder pressure and a shaft encode r output. Assumptions of homogeneous mixture and equilibrium thermodyn amic properties are made for the products of combustion and the tempor al variation in the fluid thermodynamic state is followed in a quasi-s teady manner through a series of adjacent equilibrium states, each sep arated by finite intervals of one degree crank angle (1 degrees CA). T he thermodynamic properties are calculated by either of two equivalent formulations - equilibrium constants or minimization of Gibbs free en ergy, and are expressed in algebraic equations for the partial derivat ive of internal energy and gas constant with respect to temperature, p ressure and equivalence ratio. The effect of the engine operating cond itions on the thermodynamic cycle is studied. Results show that the dy namic fuel injection timing and hence the ignition delay are strongly influenced by the operating conditions, and this explains the reasons for incorporating a fuel injection control system in modern vehicular engines for the optimization of the engine combustion cycle.