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THE HOT-SPOT METHOD OF HEAVY-FUEL PREPARATION
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Abstract
The development of intake-manifolds in the past has been confined mainly to modifications of constructional details. Believing that the increased use of automotive equipment will lead to a demand for fuel that will result in the higher cost and lower quality of the fuel, and being convinced that the sole requirement of satisfactory operation with kerosene and mixtures of the heavier oils with alcohol and benzol is the proper preparation of the fuel in the manifold, the authors have investigated the various methods of heat application in the endeavor to produce the minimum temperature necessary for a dry mixture.
Finding that this minimum temperature varied with the method of application of the heat, an analysis was made of the available methods on a functional rather than a structural basis. Three of these are discussed: (a) When the heat from the walls of the manifold is applied through the medium of the air; (b) when it is applied to the fuel alone, or partly to the fuel and partly to the air; and (c) when a spray of atomized fuel and air is directed against a heated surface. A device was constructed by which the three main variables, the exhaust temperature, the exhaust flow and the area of the heating surface, might be regulated and the three remaining variables, the quantity of air, the quantity of fuel supplied and the quantity of fuel vaporized, might be controlled.
Taking into account the wide range of temperatures that the air charge and fuel supply undergo before entering the intake-manifold system, a quantitative computation of heat transfer was made and the conclusions were drawn that only by a combination of centrifugal force, surface tension and the force of gravity could the unvaporized drops be separated from the fuel charge and that the conditions of combustion are governed by the rate of fuel feed from the manifold to the cylinder and not from the carbureter to the manifold.
Recent years have witnessed increasing attention to the design of intake-manifolds and to the varied methods of handling automotive fuels in preparing them for introduction into the combustion-chamber. The resulting development, however, has been limited in direction, being confined usually to slight modifications of the construction that has been followed ever since automotive engines began to have more than one cylinder. The improvement in economic conditions that all authorities agree is approaching will certainly result in considerably increased use of automotive equipment, and it is not impossible that the demand for motor fuel may bring about a condition of higher cost and lower quality. As it might require three or four years to develop a change of design to meet such a change of fuel, it would seem that now is a fitting time to make a survey of the problems involved in the preparation of our present fuels and of heavier ones and to make a fresh analysis of the situation, entirely apart from and unhampered by the conditions of previous practice.
It is true that many 1922-model cars have operated satisfactorily with the motor fuels at present in use, both in summer and in winter, but many have not. We are convinced that it is possible to operate on mixtures of gasoline, kerosene and some heavier oils, combined with alcohol, benzol or other anti-knock component, as well or better than a number of cars today operate on gasoline, by the use of improved methods of fuel preparation in the intake-manifold.