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A voltage was applied between the nozzle unit and fine needles, rods, and screens inserted at various axial and radial positions into atomizing full-cone water sprays and the corresponding electrical resistance was measured in an attempt to determine the shape and length of the intact liquid core. The parameters of the experiment were: room temperature; air compressed at 0.1, 1.0, and 2.9 MPa; injection Δp = 13.7 MPa; and five straight-hole nozzles with diameters of 127, 178, 305, 343, and 508 µm, and the same length-to-diameter ratio of 4. The results show that current is carried not only by intact liquid cores but also by atomized unconnected sprays and even across such sprays. Thus the shape of the intact core could be deduced only in the vicinity of the nozzle exit. In the atomization regime, the length of the intact core is found to be proportional to the nozzle diameter and to increase as the square root of the liquid-to-gas density ratio, i.e. xl = Cd(ρℓ /ρg)1/2 where C≈7.

Propagation of turbulent flames in spark-ignition engines is considered from the viewpoint of the different possible regimes of premixed turbulent combustion. Nondimensional parameters defining known combustion regimes are reviewed, and numerical values of these parameters are estimated for both research and production engines. The reaction-sheet regime is inferred to apply at least for some operating conditions, and therefore literature on turbulent flame propagation in the reaction-sheet regime is reviewed. Implications of these results on interpretations of existing experimental observations of combustion in engine cylinders and on modeling of turbulent flame propagation in engines are discussed.

The problem of modeling combustion within internal combustion engines is considered. A method is explained to evaluate the comprehensiveness, detail and predicting capability of a model. It consists of considering the equations for the most comprehensive and detailed model and in making successively more restrictive assumptions, thus getting progressively less detailed models. Particular attention is paid to the reasons for the assumptions, how they influence the accuracy of a model, and what basic information is missing. In so doing, the most detailed of the available models, and their predictive capabilities and limitations, are introduced. They include models for reciprocating and rotary engines, with uniform and stratified charges from dual carburetion and direct fuel injection. Examples of their results are given. One of them has been available since 1971, and another one is currently and fruitfully employed to aid the development of a production engine.