A satisfactory answer to the future severe normative on emissions and to the market request for spark ignition engines seems to be the use of downsized engines for passenger cars. Downsizing permits the increase in engines power and torque without the increase in cylinder capacity. The downsizing benefits are evident at part loads; on the other hand, more work should be done to optimize boosted engines at higher and full load. To this goal, a detailed knowledge of the thermo-fluid dynamic processes that occur in the combustion chamber is fundamental.
The aim of this paper is the experimental investigation of the effect of the fuel injection in the intake manifold on the combustion process and pollutant formation in a boosted spark ignition (SI) engine. The experiments were performed on a partially transparent single-cylinder port fuel injection (PFI) SI engine, equipped with a four-valve head and boost device. Different injection strategies at closed and open valve conditions were considered. Moreover the splitting of fuel injection in two and three injections at open-valve conditions were investigated. The effects on performances, gas emissions and pollutant formation were evaluated.
Optical techniques based on 2D-digital imaging were used to follow the flame propagation in the combustion chamber. In particular, the diffusion-controlled flame near the valves and the cylinder walls due to the fuel film burning at different fuel injection strategies were studied. Natural emission spectroscopy was applied to detect the chemical markers of combustion process. Two color pyrometry was employed to measure the soot temperature and concentrations. In-cylinder optical investigations were correlated with the engine parameters and to the exhaust emissions measured by conventional methods.
