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The direct-injection systems differed from a pressure carburetor in that the fuel is introduced just up stream from the intake valve in the inlet port in each individual cylinder head in the direct fuel injection system, as opposed to the pressure carburetor where the fuel is introduced at the carburetor. Using the same principles as the pressure carburetor to measure air flow into the engine, the distributed fuel injection system used individual fuel lines to each cylinder, injecting the fuel at the intake port. In the last years of World War II, aircraft engines that exceeded a specific horsepower of greater than 1.0, were equipped first with distributed fuel injection and later with direct injection, which became the fuel system of choice.

These floatless pressure carburetors are the topic of this article. It could be looked upon as the mechanical counterpart of today's electronic fuel control system. The floatless pressure carburetor was the progenitor of today's single-port fuel injection, and was a big step forward in fuel delivery technology. After 1938, high performance aircraft engines were equipped with floatless pressure carburetors, especially those used in combat aircraft. These were typically conventional float-type carburetor that were not much different than those found on automobiles or farm tractors of that time, except for size. The first type was manufactured for low performance aircraft engines and virtually all aircraft engines produced before 1938. The Bendix Corporation marketed three types of aircraft fuel systems under the Bendix-Stromberg name:

2.2 The solution: move the fuel nozzle and remove the float.

2.1 The problems: ice, gravity and inertia.

In 1936, the first Bendix-Stromberg pressure carburetor (a model PD12-B) was installed and flown on an Allison V-1710-7. Unlike the float-type carburetor fuel system that relies on venturi suction to draw fuel into the engine, a pressure carburetor only uses the venturi to measure the mass airflow into the engine and manages the flow of fuel that is continuously under pressure from the fuel pump to the spray nozzle. Both of these types of carburetors had a relatively large number of internal parts, and in the case of the Holley Carburetor, there were complications in its "variable venturi" design.Ī floatless pressure carburetor is a type of aircraft fuel control that provides very accurate fuel delivery, prevents ice from forming in the carburetor and prevents fuel starvation during negative "G" and inverted flight by eliminating the customary float-controlled fuel inlet valve. The other two carburetor types were manufactured by Chandler Groves (later Holley Carburetor Company) and Chandler Evans Control Systems (CECO). Of the three types of carburetors used on large, high-performance aircraft engines manufactured in the United States during World War II, the Bendix-Stromberg pressure carburetor was the one most commonly found.

Cut-away Bendix-Stromberg PD12-F13 from a Pratt & Whitney R-2000 radial engine