Spectral analysis of combustion process of common rail Diesel engine

Polychromatic extinction and chemiluminescence techniques, from ultraviolet to visible, were applied in an optical diesel engine, in order to analyze the temporal and spatial evolution of a high pressure fuel jet interacting with a swirling air motion. A fully flexible Common Rail fuel injection system equipped with a single hole nozzle was used. The experiments were performed at fixed engine speed and air/fuel ratio for three injection strategies. The first one consisted of a main injection to compare with those operating at low pressure injection. The other ones were based on a pilot and main injections, typical of current direct injection diesel engines, with different dwell time. A detailed investigation of the mixture formation process inside the combustion chamber during the ignition delay time was performed. The liquid and vapor fuel distribution in the combustion chamber was obtained analyzing the polychromatic extinction spectra. It was observed that the high pressure had a considerable influence on the mixture formation and on the spray vaporization through the improvement of the jet atomization. Moreover, both liquid and vapor fuel were influenced by the high swirling flow moving the air-fuel mixture in the chamber region far from the tip of the jet. The autoignition occurred in the region at higher vapor concentration characterized by the chemiluminescence emission arisen from radical species like OH, CH and HCO.