The objective of the present work was to develop the existing ODES code, using an essentially zero-dimensional approach to provide detailed insights into the internal processes of the modern high speed direct injection (HSDI) Diesel engine with high pressure common rail (HPCR) fuel injection. Therefore, this work has concentrated on the development of new submodels for incorporation in an extended form, of ODES, as follows: The Marzouk-Watson semi-empirical heat release formulation has been replaced by a new fully analytical model for diffusion burning under medium to high load conditions and represents a development of the work of Chmela and Orthaber. The Wolfer ignition delay period formulation which does not account explicitly for injection conditions and was developed for engines with relatively low injection pressures has been replaced by a comprehensive semi-analytical model based in part on the work of Siebers and Higgins on the concept of lift-off length. A phenomenological fuel spray propagation and entrainment model for nonevaporating, evaporating and ultimately combusting sprays, both in undeflected and deflected form. A generalized analytical model for swirl generation in combustion bowl of various geometries, starting with a known swirl ratio at inlet valve closing (IVC). The swirl model, in turn, interacts and is part of, a combined spray-swirl model. o Finally, all new submodels have been fully integrated into a new comprehensive simulation package designated ODES 4-4. The code has been extensively validated with respect to performance and heat release against experimental limiting torque curve (LTC) results obtained on a 1.8 litre HSDI Diesel engine with HPCR fuel injection. In the absence of optical access to the combustion space the predictions concerning swirl and spray/swirl interactions cannot be correlated with experimental results but could be checked independently against predictions from appropriate CFD codes