SI engine simulations have in the past been used as an R & D tool to predict performance and emissions. The advent of turbocharged SI engines has broadened the requirements for simulations of this kind and, in particular, predictions of transient performance are required due to turbocharger lag. Such a model is described in this paper.
The simulation models cylinders as thermodynamic control volumes. Manifolds may also be modelled as control volumes or combinations of control volumes (for plena) and pipes for which gas-dynamic calculations are performed. The combustion model is based on zero-dimensional two -zone principles. The novelty of the model is the extension to cover transients by incorporating engine and turbocharger dynamics, a combustion correlation covering wide ranging conditions, and a thermal response model, so that successive cycles can be calculated.
Measured and predicted performances are compared in some detail, under steady-state conditions and for second and fourth-gear accelerations. Having established the accuracy of the model, it is then used to predict the benefit of a range of design changes on transient response.