Search Results

A multidimensional computational method is extended to include the methodology for modelling of partially-mixed inhomogeneous charge combustion and is applied to investigation of combustion and simultaneous mixing process of an inhomogeneous mixture in a lean-burn spark-ignition engine. The in-cylinder flow and charge mixture distribution pertain to a helical intake port with manifold fuel injection, and were obtained through complete simulation of the induction and compression processes. The engine compression ratio is 12:1 and the study pertains to the operating condition of 2500 rpm. The results show that the flow and charge distribution at the time of ignition is predominantly characterised by the evolution of the induction flow. The effect of heat release on enhancement of charge mixing is marginal and the pre-ignition charge distribution is preserved throughout the combustion.

A program of development and experimental validation of a multidimensional spray prediction method, based on the discrete droplet model, has been broadened to include computational investigations of the effects of random perturbations of the injection velocity on the spray characteristics, and further detailed examination of the spray structure and development. The results demonstrate strong dependence of the predicted spray penetration length on the precise start-of-injection time and injection velocity data, and relative insensitivity to subsequent variations of the injection velocity. Specifically, it is found that under imposition of random variations of the injection velocity, the variation of the spray-tip penetration and velocity remain smooth, bearing no correspondence to the instantaneous spray injection velocity.

A mathematical model of formation and transport of liquid films, incorporating a droplet-wall impaction model and exchange mechanisms with the gas-phase, has been developed and incorporated into the STAR-CD computational fluid dynamics code. It has been applied to a test case representation of the multi-point fuel injection in four stroke SI engines. The results indicate that the major features of droplet impaction and film development are reproduced by the model. The qualitative agreement with data in the region of spray impaction is good.

This paper is concerned with the calculation of combustion in an idealised homogenous-charge spark-ignited engine having a disc-shaped combustion chamber equipped with a central spark plug and inlet/exhaust valve. The purpose of the study is to assess the ability of a class of turbulence combustion models, first developed for steady flows, to simulate the major features and trends of reciprocating engine combustion. The models are based on the supposition that the time scales of the turbulence energy dissipation will be the controlling rates at which reactions can take place. Experimental evidence lends support to this supposition. Hitherto, in multi-dimensional engine prediction methods, combustion predictions have almost invariably been based on chemical-kinetics reaction models.

A multidimensional computational method is employed to investigate the details of the in-cylinder flow and gas exchange process in a loop-scavenged two-stroke cycle spark-ignition engine. The engine geometric compression ratio is 15:1 and the study pertains to the operating condition of 5000 rpm. The inlet and outlet boundary conditions (c.f. the instantaneous thermodynamic properties and the intake and exhaust mass flow rates) were obtained from a gas dynamic calculation procedure. This enabled incorporation of the effect of the pressure waves causing strong flow oscillations in the scavenge and exhaust ports. The results reveal that the in-cylinder flow structure established early during the scavenge phase comprises of a three-dimensional loop and a pair of toroidal vortices. This vortex structure is responsible for impairment of the scavenging efficiency. The flow structure was found to be sensitive to the details of the scavenge system layout.