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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.

Multidimensional calculations axe presented of the behaviour of sprays injected into the combustion chambers of motored reciprocating engines, in circumstances giving rise to three-dimensional spatial variations in the droplet and gas flow fields. The calculations were performed using the implicit EPISO algorithm, extended to include a Lagrangian description of the spray. The gas-phase turbulence is represented by the κ-ε model and its effect on the droplets is modelled stochastically. Two applications of the method are reported: one involves the simulation of, and comparison with data from, published experiments on a laboratory engine fitted with a single-hole injector in the cylinder wall. The second case is a demonstration calculation for a direct-injection Diesel with a cylindrical piston bowl and a four-hole injector.

This paper describes a spray impingement model which is formulated on the basis of literature findings and mass, momentum and energy conservation constraints. The model involves the analysis of the relevant impingement regimes and the associated post-impingement characteristics. In order to reflect, to some extent, the stochastic nature of the impingement process, a random procedure is introduced to determine some of the quantities representing the post-impingement status. This allows secondary droplets resulting from splash to have a distribution of sizes and velocities. Numerical simulations for several test cases are presented, showing satisfactory agreement with experimental data.

Multidimensional model predictions and laser Doppler anemometer measurements are presented of the flow in a motored model engine equipped with a central shrouded valve. Although the accuracy of prediction, as assessed against the data, is at best moderate, the simulation is sufficiently close to provide valuable insight into the flow behaviour. an important finding in this regard is that the shrouded valve generates a long-lived tumbling vortex which is sustained and amplified by the compression process and in turn causes amplification of the turbulence, the TDC levels of which are more than twice those observed in similar studies with non-shrouded valves. It is concluded that inlet arrangements which produce such tumbling motions are likely to lead to enhanced flame propagation rates.

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.

This paper presents a mathematical model for the prediction of the dynamic characteristics of wall films formed by impinging sprays. The model takes into account the impingement pressure due to bombardment of impinging droplets, tangential momentum transfer resulting from oblique droplet impingement on the film surface, and the gas shear force at the film surface. The general transport equations of mass, momentum and energy for wall film flows are established in the boundary-layer framework. It is shown that this set of equations can be substantially simplified if local equilibrium occurs and a dimensional analysis is performed to identify the conditions for the applicability of the local equilibrium model. Solution of the full film equations is obtained by an efficient hybrid integral/numerical method, which allows numerical calculations to be performed in a two-dimensional framework. An implicit finite volume scheme is employed for this purpose.

A mathematical model of formation and transport of liquid films, incorporating a droplet-wall impaction model and exchange mechanisms with the gas-phase, has been developed and incorporated into the STAR-CD computational fluid dynamics code. It has been applied to a test case representation of the multi-point fuel injection in four stroke SI engines. The results indicate that the major features of droplet impaction and film development are reproduced by the model. The qualitative agreement with data in the region of spray impaction is good.

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.