EXPERIMENTS made and methods employed to obtain satisfactory engine operation without the addition of heat to the fuel-air mixture are described, as it is known that the power output of an engine is greater as the temperature of the mixture is lower and that higher compression can be used with lower mixture-temperature.
The work was initiated with a single-cylinder engine in which kerosene was used as a fuel to ascertain the results that could be obtained without vaporizing the fuel in the manifold, the liquid being added to the air in the valve-chamber as the air entered the combustion-chamber.
As satisfactory results followed, the next step was to devise and apply a mechanism based on the same principle to a multi-cylinder engine. The first and succeeding carbureter-manifold combinations used are illustrated and described. The basic idea in these is the provision of small-diameter fuel manifolds or tubes in which a small volume of air is admitted to carry the fuel from the carbureter orifices to the valve ports, and large-diameter manifold tubes for the main air-supply to the cylinders. Very little vaporization occurs in the manifold. Throttles are placed in both the air and the fuel manifolds.
Experiments were made using a glass main-manifold and a neon-tube stroboscope for observation of the action of the fuel-flow and mixture distribution. Sufficiently good distribution was obtained with one fuel-orifice for each pair of cylinders of a six-cylinder engine, but a jet for each cylinder and individual valve-ports are suggested as likely to give most perfect distribution.
Details of the carbureter and the throttles are given, together with their action when idling and when accelerating. The obtaining of precisely equal fuel-flow from the three orifices presented an intricate problem, owing to air eddies and unequal pressures in the carbureter. Another important problem was presented by the difficulty of obtaining prompt acceleration.
Application of the cold-carburetion system to an engine is comparatively simple, as no connection is made with the exhaust manifold. It is desirable to considerably separate the intake system from the exhaust manifold to keep the air temperature low. Better results were obtained from the system applied to an overhead-valve engine than to an engine of the L-head type.
Cold-carburetion still involves some difficult problems and the final results of this development cannot safely be predicted, but the advantages are so great that the author believes that cold carburetion should soon become commercial practice.