Ignition delay time correlations for a diesel fuel with application to engine combustion modelling

Abstract

New diesel engine combustion concepts, such as the homogeneous charge compression ignition (HCCI), have encouraged the development of ignition delay correlations allowing the reliable prediction of the chemical auto-ignition time of the fuel, which depends on its oxidation kinetics. These correlations permit one to design and optimize the most adequate control strategies leading to both low emission levels of pollutants and proper engine performance. Although some diesel ignition correlations can be found in the literature, most of them consider the physical delay time and have been obtained only for high temperature values, which are usual at the end of the compression stroke in traditional diesel engines. However, there is still a significant lack of information regarding the complex three-stage oxidation (low-, intermediate-, and high-temperature range) of a diesel fuel under HCCI conditions. Thus the proposal of delay time correlations for the three temperature ranges is the objective of the present work. The correlations have been assumed as Arrhenius-type equations and consider the effect of the main parameters affecting the auto-ignition time, i.e. pressure, temperature, and equivalence fuel/air ratio. The adjustment coefficients have been calculated by using multiple linear regression and least-squares techniques, and a very good fit between modelling-predicted and correlation-predicted delay values has been obtained ( R2 higher than 0.95 in all cases).