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A detailed analysis is performed upon the results of CFD combustion simulations of several diesel fuel spray flame experiments. Simulations are validated against measurements from a constant volume combustion chamber testcase [9]. Particular emphasis is made in the analyses to identify mechanisms associated with the ‘lift-off’ phenomena characteristic of contemporary high injection pressure diesel engine combustion. A recently developed industry state of the art RANS hybrid combustion model (Extended Coherent Flame Model - 3 Zones) [41] is used which takes account of both a propagating (premixed) flame combustion mode as well as the conventionally assumed diffusion flame mode used in most diesel combustion models. The location of and development of a propagating reaction front, obtained from analysis of the progress variable within the model, is studied in relation to the lift-off behaviour.

This paper uses CFD methodology to simulate a prototype Diesel engine operating at high peak pressures (HPP). Under these conditions the accurate estimation of the level of thermomechanical stress on metal components is crucial for the design process. CFD simulations have been performed of flow, combustion and heat transfer to provide detailed insight into the in-cylinder behaviour of the engine. Particular emphasis was put on improving wall heat transfer predictions which have been compared with detailed local time-resolved surface heat transfer measurements. It is demonstrated that heat transfer strongly depends on flame spread via flow field and spray-related processes. Hence local heat transfer measurements also provide a stringent testing ground for spray and combustion model performance. Additionally it is shown that widely-used empirical heat transfer correlations are incapable of estimating the critical level and nature of thermal loading.

The extension is described of an existing multidimensional method of calculating in-cylinder air motion to the representation of the injection of a liquid fuel spray. Sample calculations are presented of the droplet and gas motion and fuel-air mixing in an axisymmetric representation of an open-chamber direct-injection engine, in the absence of combustion, and are believed to be the first in which a realistic representation of the gas-phase turbulence behaviour is employed. One of the more important findings is that the spray induces velocities and turbulence levels in the gas which are comparible to, and sometimes greater than, those produced by other mechanisms such as swirl and squish. It is concluded however that considerable further work is required to make such models truly predictive and detailed experimental data is urgently required to assist this task.

Progress is described on the development of a multi-dimensional method for the prediction of the detailed in-cylinder events in a firing D.I. Diesel engine. An existing method incorporating fluid dynamics and spray representations is extended to include a combustion model, of a kind which allows in an approximate way for both chemical-kinetic and turbulence effects on the burning rate. An example calculation is presented which demonstrates that, with appropriate adjustments to the empirical coefficients of the combustion model, the method produces qualitatively realistic predictions of the major phases of the combustion process, including ignition, premixed burning and diffusion burning. The results also serve to illustrate the usefulness of multidimensional methods in revealing the causes of inadequate performance.

Multi-dimensional modelling of the flow and combustion promises to become a useful optimisation tool for IC engine design. Currently, the total simulation time for an engine cycle is measured in weeks to months, thus preventing the routine use of CFD in the design process. Here, we shall describe three tools aimed at reducing the simulation time to less than a week. The rapid template-based mesher produces the computational mesh within 1-2 days. The parallel flow solver STAR-CD performs the flow simulation on a similar time-scale. The package is completed with COVISEMP, a parallel post-processor which allows real-time interaction with the data.