ABSTRACT An ignition delay correlation was developed for a toluene reference fuel (TRF) blend that is representative of automotive gasoline fuels exhibiting two-stage ignition. Ignition delay times for the autoignition of a TRF 91 blend with an antiknock index of 91 were predicted through extensive chemical kinetic modeling in CHEMKIN for a constant volume reactor. The development of the correlation involved determining nonlinear least squares curve fits for these ignition delay predictions corresponding to different inlet pressures and temperatures, a number of fuel-air equivalence ratios, and a range of exhaust gas recirculation (EGR) rates. In addition to NO X control, EGR is increasingly being utilized for managing combustion phasing in spark ignition (SI) engines to mitigate knock. Therefore, along with other operating parameters, the effects of EGR on autoignition have been incorporated in the correlation to address the need for predicting ignition delay in SI engines operating with EGR. Unlike the ignition delay expressions available in literature for primary reference fuel blends, the correlation developed in the present study can predict ignition delay for a TRF blend, a more realistic gasoline surrogate. 1. INTRODUCTION Two of the means to achieve the objective of improved fuel economy in spark ignition (SI) engines are (a) improving the fuel conversion (thermal) efficiency by increasing the compression ratio, and (b) increasing the specific output (brake power per unit displacement) through turbocharging and downsizing the engine. The ability to raise in-cylinder peak pressures in either mechanism is, however, limited by knock. Accurate prediction of autoignition phasing is thus critical in designing engines with improved efficiency. Clearly, such a prediction also is pertinent to the homogeneous charge compression ignition (HCCI) technology, which relies on controlled autoignition through compression of the homogeneously mixed oxidizer-fuel mixture. Detailed chemical kinetic mechanisms can be employed to predict autoignition. However, their sheer complexity presents a serious challenge in terms of directly incorporating them in engine simulation or computational fluid dynamics (CFD) tools. Therefore, there is a need for a computationally feasible autoignition model that accurately captures the complexity of fuel oxidation in SI engines under varying operating conditions and is easy to use. This need has prompted the development of empirical autoignition models. A pressure-temperature correlation of the form Ignition Delay Correlation for Predicting Autoignition of a Toluene Reference Fuel Blend in Spark Ignition Engines 2011-01-0338 Published 04/12/2011 Asim Iqbal Ohio State Univ. Ahmet Selamet Ohio State Univ Ronald Reese Chrysler Roger Vick Chrysler Powertrain Engrg Copyright © 2011 SAE International doi: 10.4271/2011-01-0338