Numerical prediction of research octane numbers via a quasi-dimensional two-zone cylinder model

Abstract

Sustainably produced synthetic fuels offer great potential for a fast reduction of the greenhouse gas emissions of the transport sector. For an immediate application within the existing infrastructure and vehicle fleet, synthetic fuels need to comply with existing standards such as the EN 228 for gasoline. Beyond these standards and with optimized fuel design, certain properties can be improved compared to conventional fuels. For this purpose, methods for evaluating the properties are needed.This work discusses the development of a simplified numerical quasi-dimensional two-zone cylinder model, combined with chemical kinetic models, for the estimation of octane numbers. The model emulates fuel specific operating conditions of the standardized procedure for the determination of octane numbers in the cooperative fuel research engine with variable compression ratios. The two zones represent the burned and unburned in-cylinder volume and are modeled with homogeneous reactors. The octane numbers are determined by the identification of the critical compression ratio, for which premature ignition occurs in the unburned reactor.A two-zone cylinder model is validated against experimental data for various primary reference fuels, blended with toluene, ethanol, isobutanol and ethyl tert-butyl ether. The successful application of different kinetic models is demonstrated and enables the application on a wide range of fuels. It is shown that the simulated research octane numbers are in good agreement with the experimental data.