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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.

The objective of this paper is to present a numerical simulation method for the calculation of an unsteady, one-dimensional flow and heat transfer in the branched intake manifolds of multi-cylinder engines. The method operates on the one-dimensional differential conservation equations for a variable-area duct network with friction and heat transfer at the walls. The latter processes are represented by appropriate drag and heat transfer coefficient correlations, as also are the losses which occur at junctions and other geometrical irregularities. The equations are solved by a time-marching finite-volume method, on a computational mesh in which the velocities are located between the pressures which drive them.

A method is described of calculating the flow, temperature and turbulence fields in cylinder configurations typical of a direct-injection diesel engine. The method operates by solving numerically the Navier Stokes equations that govern the flow, together with additional equations representing the effects of turbulence. A general curvilinear-orthogonal grid that translates with the piston motion is used for the calculations in the complex-shaped piston bowl, whilst an expanding/contracting grid is used elsewhere. Predictions are presented showing the evolution of the velocity and turbulence fields during the compression and expansion phases of a motored engine cycle, for various shapes of axisymmetric piston bowl and various initial swirl levels. These results illustrate the strong influence of these factors on the TDC flow structure.

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.