Self-Ignition Delay Prediction in PCCI Direct Injection Diesel Engines Using Multi-Zone Spray Combustion Model and Detailed Chemistry

Abstract

A multi-zone direct-injection (DI) diesel combustion model has been implemented for full cycle simulation of a turbocharged diesel engine. The above combustion model takes into account the following features of the spray dynamics: • the detailed evolution process of fuel sprays; • interaction of sprays with the in-cylinder swirl and the walls of the combustion chamber; • the evolution of a Near-Wall Flow (NWF) formed as a result of a spray-wall impingement as a function of the impingement angle and the local swirl velocity; • interaction of Near-Wall Flows formed by adjacent sprays; • the effect of gas and wall temperatures on the evaporation rate in the spray and NWF zones. In the model each fuel spray is split into a number of specific zones with different evaporation conditions including in zones formed on the cylinder liner surface and on the cylinder head. The piston bowl in the modelling process is assumed to have an arbitrary axi-symmetric shape. The combustion model considers all known types of injectors including non-central and side injection systems. A NOx calculation sub-model uses detailed chemistry analysis which considers 199 reactions of 33 species. A soot formation calculation sub-model used is the phenomenological one and takes into account the distribution of the Sauter Mean Diameter in injection process. The ignition delay sub-model implements two concepts. The first concept is based on calculations using the conventional empirical equations. In the second approach the ignition delay period is estimated using relevant data in the calculated comprehensive 4-D map of ignition delays. This 4-D map is developed using CHEMKIN detailed chemistry simulations which take into account effects of the temperature, the pressure, the Air/Fuel ratio and the EGR. The above approach is also planned to be used in future for calculations of ignition delays in diesel engines fuelled by bio-fuels. The model has been validated using published experimental data obtained on high-and medium-speed engines. Comparison of results demonstrates a good agreement between theoretical and experimental sets of data. The above sub-models were integrated into DIESEL-RK software, which is a full-cycle engine simulation tool, allowing more advanced analysis of PCCI and HCCI diesels.