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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.

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.

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.

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.

In this paper a multidimensional method is described and evaluated for the prediction of Diesel sprays. The method, which shares many features with similar approaches developed elsewhere, embodies an Eulerian description of the gas flow and a stochastic Lagrangian treatment of the spray droplets. Gas phase turbulence effects are represented by the k-ε model and their influence on the droplets is modelled stochastically, as are the processes of collision and coalescence. Comparisons are made with the spray penetration measurements in a quiescent bomb of Yule et al [1] covering a range of pressures and temperatures. Satisfactory agreement is obtained at combinations of low pressure and temperature and high pressure and temperature, but not for high-pressure, low-temperature cases. The sensitivity of the predicted penetration rates to the assumed initial droplet size distribution is relatively weak, but the calculated vaporization rates are strongly sensitive.

The results are reported of a combined experimental and computational study of steady flow through an axisymmetric valve/port assembly, the main objective of which was to assess the accuracy of the multidimensional model predictions of this flow. Measurements of the discharge coefficient, mean velocity and the turbulent Reynolds stress fields were obtained by hot-wire anemometry at various valve lifts. These were supplemented by flow visualisation studies. Predictions were made using a finite-volume method employing a body-fitted computational mesh and the k-ε turbulence model. Good agreement was found at low lifts, but at higher values this deteriorated due to the inability of the turbulence model to provoke the flow separations which occurred in the experiments. The conclusion is that for both idealised and practical ports multidimensional predictions will be of limited accuracy until better turbulence models become available.