The Fuel Injector Story – Part 1

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In the internal combustion engine, a tank full of liquid fuel is directly unusable. The exact nature of how these three stages are executed has been under constant development for over 140 years, becoming a key element to the advancement of the internal combustion engine.

Early on, in the internal combustion engine’s history, carburation was developed to both meter and vaporize fuel.

In 1872, American mechanical engineer and inventor, George Bailey Brayton had patented a unique internal combustion engine design known as the constant pressure internal combustion engine. An engine-driven camshaft would then open a valve that allowed the pressurized air/fuel mixture to flow from the reservoir into the large combustion cylinder. Brayton’s engine suffered from a fatal flaw. To counter this hazard, Baryton would go on to develop a system that used compressed air created by the engine to blast liquid fuel oil into the induction pipe of the combustion chamber, onto a porous material.

Baryton’s air-blast fuel injection concept would resurface almost two decades later when German inventor Rudolf Diesel, struggled to figure out how to fuel his new, highly efficient engine design. Ultimately, he would successfully adopt a high-pressure air-blast injection system similar to that of Brayton. When injection occurred, the injector valve was opened by a cam-actuated mechanism and high-pressure air then flowed into the engine cylinder carrying with it a metered, finely atomized spray of fuel.

Around the turn of the 20th century, a new type of airless injection system began to appear among various engine manufacturers that used a plunger mechanism to deliver fuel at high pressure. The plunger-style injection mechanism would evolve in the jerk pump, incorporating metering into its function.

That same year Vickers Ltd of England would develop its own multiple cylinder fueling systems called common rail injection. The fundamentals of common rail injection can still be found in most modern diesel engines.

The fuel delivery nozzles of diesel injection systems had also simultaneously evolved. Even today, pintle-based injectors are common across most forms of fuel injection due to these characteristics.

Early on, there were many experiments to simplify the complexity of diesel injection. In 1905, Carl Weidman made one of the first known successful attempts by combining the injection pump and the injector into a single mechanism known as a unit injector.

The first gasoline fuel injection systems were crude and operated indirectly, pre-mixing with air just before entering a cylinder. These injection systems first began to appear around 1900.

Within two decades direct gasoline fuel injection that operated in a manner similar to diesel jerk pump systems would start appearing on aircraft engines. These injection systems operated at far lower pressures, typically 30-40 bar, and offered far greater mixture consistency over carburetors as well as eliminating backfire. In Germany, most aircraft engines ran on direct injection systems, most of which were supplied by Bosch.

During the 1950s, manufacturers began to pursue a more practical form of gasoline fuel injection suitable for mass production. From these developments, came the introduction of mass-produced manifold fuel injection systems. Manifold fuel injection introduces fuel upstream of the cylinder, mixing it with air within the intake tack, often just before the intake valve. While not as efficient as direct injection, this approach allowed for significantly lower system pressures, inherently reducing component costs.

Bosch introduced its own indirect mechanical injection system for the new Mercedes-Benz 220 SE. This was accomplished by using a unique camshaft within the pump that was designed with a variable lobe that adjusted fuel flow based on the engine operating’s conditions, effectively making it one of the first forms of fuel mapping.

Timed fuel injection systems in particular proved to be superior to both constant flow injection and carburetion in meeting these new standards.


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