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High power output, four stroke, motorcycle engines are characterised by a complex combustion evolution strongly influenced by the properties of the averaged and turbulent flow field. In the present paper, state-of-the-art detailed computational methods are used to investigate the combustion evolution in a four cylinder, four valve per cylinder engine with a four-in-one exhaust where volumetric efficiencies and mixture compositions have been previously computed. Three dimensional unsteady computations of intake, compression, combustion and expansion strokes are performed. The method proves to be effective in qualitatively predicting heat release rate variations with engine speed and volumetric efficiency, while the simple modelling of the turbulent combustion does not allow to precisely define the magnitude of these variations.

This paper presents a numerical study of the combustion chamber design influence on the performance of racing engines. The analysis has been applied to the Ferrari 10 cylinder 3.0 liter S.I. engine adopted in Formula One racing. The numerical investigation aimed to asses the influence of stroke-to-bore ratio changes on engine performance within real life design constraints. The effects of the stroke-to-bore ratio on both the volumetric efficiency and the thermal conversion efficiency have been investigated. Flame front area maps, wall areas wetted by burned gases, mean flow field patterns and main turbulent parameters have been compared for two different S/B ratios. Since higher intake and exhaust valve areas per unit displaced volume result in a higher volume of piston bowls, a lower S/B ratio leads to a lower compression ratio, which strongly limits the indicated mean effective pressure.

The Common-rail injection system has allowed achieving a more flexible fuel injection control in DI-diesel engines by permitting a free mapping of the start of injection, injection pressure, rate of injection. All these benefits have been gained by installing this device in combustion chambers born to work with the conventional distributor and in-line-pump injection systems. Their design was aimed to improve air-fuel mixing and therefore they were characterized by the adoption of high-swirl ports and re-entrant bowls. Experiments have shown that the high injection velocities induced by common rail systems determine an enhancement of the air fuel mixing. By contrast, they cause a strong wall impingement too. The present paper aims to exploit a new configuration of the combustion chamber more suited to CR injection systems and characterized by low-swirl ports and larger bowl diameter in order to reduce the wall impingement.