Semi-Empirical Correlations of Physical and Chemical Delay Period of Diesel-Gasoline Combustion

Abstract

This study focuses on developing a semi-empirical ignition delay (ID) correlation which is able to predict the ID of various diesel-gasoline fuel blends under steady-state conditions. Prediction from chemical kinetic modelling is compared to experimental data to determine the influential parameters which control the change of ID with operating conditions. Physical and chemical processes are discriminated and the governing factors for both are identified. These governing factors or parameters are fitted into the Assanis’ correlation, and parametric adjustment to the activation energy constant is performed to form the new chemical delay correlation. A physical delay correlation is developed from experimental findings. Finally, an empirical physical delay correlation and a theoretical chemical delay correlation are combined to form the new ID correlation. This correlation produces an average error of 4.9 % and a maximum error of 14 %. It is shown to perform better at high engine speed-load condition (at 2,000 rev/min and 8.5 bar BMEP), with an average error of only 2.6 % and a maximum error of 8.7 %. Physical and chemical processes are shown to be separate events under engine conditions such as steady-state, pre-ignition, fully warmed-up, and undiluted intake air.