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Several methods have been proposed to use pressure signal for air/fuel ratio estimation, knock detection and optimal spark timing selection. In this paper some of these methods were compared, and their accuracy and effectiveness was checked. In order to avoid the misleading effects of measurement errors, the comparison was performed using a database of test conditions obtained by means of the WAVE code (Ricardo). New correlations physically based were introduced to evaluate the trapped air mass and the Exhaust Gas Recycling (EGR), cylinder per cylinder. These correlations can give a very important contribution to balance the air-fuel ratio in each cylinder and to improve EGR control strategies.

A simple model of combustion and pollutant formation has been set up. It is part of an engine simulator to be used for the study of engine control strategies. The calculation of inlet and exhaust phases is performed by an emptying and filling method, based on the knowledge of mean inlet and exhaust conditions. A single zone thermodynamic model has been utilized for the calculation of the combustion phase. The values of the shape factors of heat release patterns have been modeled to take into account air/fuel ratio, EGR, load and turbulence at ignition starting. Crevice storage of unburned mixture has been considered as the dominant mechanism for unburned HC production. A model for mixing and burning of HC inside the cylinder has been proposed. NO is calculated using the three steps Zeldovich approach. The model produces realistic calculations of combustion pressure and pollutants emission at various speed, load, ignition timing and EGR.