Search Results

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.