The accuracy of the Heat Release Rate (HRR) model of Internal Combustion Engines (ICEs) is highly depended on the ratio of specific heats, gamma ( ). Previous models were largely expressed as functions of temperature only. The effects of the excess air ratio ( ) and the Exhaust Gas Recirculation (EGR) rate on were neglected in most of the existing functions. Furthermore, previous HRR models were developed for stoichiometric or nearstoichiometric air -fuel mixtures in an engine condition. However, Compression Ignition (CI) engines operate over a wide range of . No work has been done to model the HRR of CI engines under nonstoichiometric conditions. Also, no work has been done to investigate the accuracy of existing functions specifically with respect to the modelling of the HRR of CI engines for nonstoichiometric conditions. The aim of this work was to develop an improved HRR model for the analysis of the HRR of CI engines for nonstoichiometric conditions ( > 1). In this work, a modified ( , ), was used to model the HRR of a 96 kW, multiple fuel injection, Euro V, Direct Injection (DI) engine. The modified HRR model (Leeds HRR model) predicted the fuel consumption of the engine with an average error of 1.41% confirming that the accuracy of the HRR model of CI engines is improved by using ( , ). The typical average error in the prediction of the other models was 16%. The much improved HRR model leads to more accurate prediction of fuel consumption, which enables the development of and enhances better fuel consumption management strategies for engines and fuels. It was also ascertained in this work that EGR has insignificant effect on the HRR of CI engines at low and medium loads.
Heat Release Rate (HRR) analysis is indispensable in engine research. The HRR of Internal Combustion Engines (ICEs) is most sensitive to gamma ( ). The proposed HRR models in literature were largely based on expressed as functions of temperature. However, is depended on temperature as well as the excess air ratio ( ). In this work, an improved HRR model based on ( , ) was used to investigate the combustion behaviour of standard diesel, Gas-to-Liquid (GTL) diesel and Hydrotreated Vegetable Oil (HVO) diesel in a 96 kW, multiple fuel injection, Euro V, Direct Injection (DI) engine. The improved HRR model (Leeds HRR model) was validated for the alternative fuels by comparing the fuel masses predicted by the model to the measured fuel masses. The fuel masses predicted by the Leeds HRR model were also compared to the predictions from four HRR models that were based on ( ). No work has been done in the past to investigate the combustion behaviour of GTL and HVO diesel in a multiple fuel injection, Compression Ignition (CI) engine. This work also featured two novel approximation techniques that were used to estimate the rate of evaporation of the injected fuel from the HRR profiles and the actual SoC from the HRR and fuel burn profiles (for the case of significant heat release bTDC). The overall average error in the predictions of the Leeds HRR model was 4.86% with a standard deviation of 2.39 while the typical error in the other models ranged from 14.66% to 19.99%. The accuracy of the HRR model of CI engines for the HRR analysis of GTL and HVO diesel is therefore, improved by using ( , ). The combustion of HVO diesel was found to be the smoothest of the three fuels due to the narrow distillation range of HVO diesel.
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