The accuracy of the Heat Release Rate (HRR) model of Internal Combustion Engines (ICEs) is highly depended on the ratio of specific heats, gamma ($\gamma )$. Previous $\gamma$ models were largely expressed as functions of temperature only. The effects of the excess air ratio ($\lambda )$ and the Exhaust Gas Recirculation (EGR) rate on $\gamma$ were neglected in most of the existing $\gamma$ functions. Furthermore, previous HRR models were developed for stoichiometric or near – stoichiometric air - fuel mixtures in an engine condition. However, Compression Ignition (CI) engines operate over a wide range of $\lambda$. No work has been done to model the HRR of CI engines under non – stoichiometric conditions. Also, no work has been done to investigate the accuracy of existing $\gamma$ functions specifically with respect to the modelling of the HRR of CI engines for non – stoichiometric conditions. The aim of this work was to develop an improved HRR model for the analysis of the HRR of CI engines for non – stoichiometric conditions ($\lambda >1)$. In this work, a modified $\gamma (T,\lambda )$, 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 $\gamma (T,\lambda )$. 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.

内燃机（ICE）的放热率（HRR）模型的准确性高度取决于比热的比值（$\gamma ）$。以前$\gamma$模型主要表示为仅温度的函数。空气过量比的影响（$\lambda ）$ 和废气再循环（EGR）率 $\gamma$ 被大多数现有的人忽视 $\gamma$职能。此外，以前的HRR模型是针对发动机工况下的化学计量或接近化学计量的空气-燃料混合物开发的。但是，压缩点火（CI）发动机的运行范围很广$\lambda$。在非化学计量条件下，尚未完成对CI发动机的HRR建模的工作。另外，没有做任何工作来调查现有的准确性$\gamma$该功能特别针对非化学计量条件下CI发动机的HRR建模。这项工作的目的是开发一种改进的HRR模型，用于分析非化学计量条件下CI发动机的HRR（$\lambda >\mathrm{1个}）$。在这项工作中，$\gamma （Ť，\lambda ）$用来模拟96千瓦，多次燃油喷射，欧V，直接喷射（DI）发动机的HRR。改进的HRR模型（利兹HRR模型）预测了发动机的燃油消耗，平均误差为1.41％，这证实了CI发动机的HRR模型的准确性通过使用来提高。$\gamma （Ť，\lambda ）$。其他模型预测中的典型平均误差为16％。经过改进的HRR模型可以更准确地预测燃油消耗，从而可以开发并增强用于发动机和燃油的燃油消耗管理策略。在这项工作中还确定，在中低负荷时，EGR对CI发动机的HRR影响不大。