FUEL injection offers two main advantages over the carburetor: Low volatile fuels (safety fuel), which reduce the fire hazard, can be used; and the combustion chamber can be scavenged without the loss of fuel by the use of large valve overlap. Other advantages are improved starting, acceleration, maneuverability, and distribution of fuel, as well as freedom from icing.
The National Advisory Committee for Aeronautics has investigated the factors influencing the injection of fuel into the engine cylinder. This investigation included the time of start of injection, the length of the injection period, the location of the fuel-injection valve in the cylinder, the rate of fuel injection, the type of fuel spray, and the maximum injection pressure. Tests were conducted on cylinders with two and four valves having pent-roof, disc, and spherical combustion-chamber forms. The performances of a modern air-cooled cylinder fitted with a carburetor, a fuel system injecting into the manifold, and a system injecting into the cylinder were investigated. Tests with different pumps and injection valves, with gasoline and with four safety fuels of different volatility, and with and without valve overlap, also were made.