Development of a Fuel-Injection Spark-Ignition Oil Engine
Authors: Fodor Nicholas 
Published: February 2023

The author describes a fuel-injection spark-ignition oil engine which was designed to operate on the same fuel as a Diesel engine and with approximately the same fuel economy, but with pressures throughout the entire cycle which would not exceed those of a gasoline engine of equal size and speed designed for the same service.

In the oil engine only air is admitted to the cylinder during the suction stroke. This air is then compressed to 160 lb per sq in., corresponding to about 6.35 to 1 compression ratio. At the end of the compression stroke, at about 60 deg before top dead center, the fuel is injected into the cylinder in finely atomized state by the fuel pump and injector. The fuel pump and injector are of the same design as those used for Diesel engines. Injection continues until the piston reaches top dead center. The spark occurs 15 deg before top dead center. Due to the time necessary for the vaporization of the injected fuel and its mixing with the air inside the cylinder, not all the fuel injected during the time from the beginning of injection until the spark occurs, will ignite at once, but a rather orderly combustion will take place and the maximum pressure is reached after 10 to 12 deg top dead center, when the engine is running at its rated speed and carries full load. At part-load operation, the beginning of injection is correspondingly later, but the spark timing is fixed. The rate of combustion is controlled by the rate of discharge of the fuel.

The expansion and the exhaust strokes have the same functions in this engine as in gasoline and Diesel engines.

As in the case of the gasoline engine, the spark can ignite a mixture in the fuel-injection spark-ignition oil engine only when it is constituted of the proper amount of fuel and air necessary to sustain combustion, i.e., a mixture must have the proper air-fuel ratio. In order to maintain this proper air-fuel ratio at all loads, it is necessary that the quantities of fuel and air he controlled in accordance with the momentary load.

At full load the total quantity of air available in the engine is utilized and an air-fuel ratio of approximately 16 to 1 is maintained. At part loads the air admitted to the cylinders is reduced in accordance with the momentary load. For metering the fuel, the vacuum of the manifold is used, which acting upon the fuel pump will set the corresponding quantity of fuel.

Electric current for the spark plug is supplied from either a magneto or a battery by the customary coil and distributor.

The fuel consumption at full load of the production engine amounts to 0.44 lb per bhp-hr, and the part-load fuel economy approaches very closely that of the Diesel engine. The engine can run on gasoline, on fuel oils used in house-heating furnaces, or on regular fuel oils used for Diesel engines. The engine seems to be very insensitive toward its fuel.

The engine has a very flat torque characteristic and is highly flexible, therefore, ideal for automotive use.

Inasmuch as the maximum pressures are the same as those in gasoline engines, the fuel-injection spark-ignition oil engine is built with the same weight per horsepower as that of the gasoline engine.