In recent decades, “physics-based” gas-dynamics simulation tools have been employed to reduce development timescales of IC engines by enabling engineers to carry out parametric examinations and optimisation of alternative engine geometry and operating strategy configurations using desktop PCs. However to date, these models have proved inadequate for optimisation of in-cylinder combustion and emissions characteristics thus extending development timescales through additional experimental development efforts.This research paper describes how a Stochastic Reactor Model (SRM) with reduced chemistry can be employed to successfully determine in-cylinder pressure, heat release and emissions trends from a diesel fuelled engine operated in compression ignition direct injection mode using computations which are completed in 147 seconds per cycle. The model was successfully validated against 46 steady state operating points in terms of in-cylinder pressure and exhaust gas emissions over a three-dimensional matrix comprising ranges of EGR, boost pressure and injection timing. The resulting model was then employed to examine the local in-cylinder temperatures and equivalence ratios and to highlight the main sources of excessive exhaust gas emissions.With a view of identifying the optimal operating strategy, a parametric sweep comprised of 968 computations were then completed, the results of which were narrowed based on satisfying stable operating limits (i.e. peak pressure, knocking combustion). Excessive exhaust gas emissions were identified to highlight the most suitable regime for minimal emissions. Finally, the potential of this technology is examined by discussing aspects of engine development process which can be accelerated using the tool.