Effect of the fuel injection pressure on the combustion process in a PFI boosted spark-ignition engine

In this paper, low-cast solutions were proposed to reduce the fuel consumption in a boosted port fuel injection spark ignition (FF1 SV engine, taking into account the engine performances and the pollutants emission. To this purpose, the optical characterization of the fuel injection and of the combustion process was carried out in a FF1 SI engine. The experiments were performed on a partially transparent single-cylinder SI engine, equipped with a four valve head and an external boost device. The intake manifold was optically accessible through three holes that allowed the introduction of an endoscope and of optical fibres. The standard injection condition planned by the engine manufacturer was investigated, it consisted in the fuel injection at 3.5 bar when the intake valves were closed. Moreover, the fuel injection with open intake valves was tested; 3.5 and 6.5 bar fuel pressures were studied for open and closed valves conditions. Optical techniques based on 2D-digital imaging were used to follow the fuel injection spray in the intake manifold and the flame propagation in the combustion chamber. The results of in-cylinder optical investigations were correlated with the engine performances and with the exhaust emissions.