I just found an old photograph I shot in a museum. It shows a fuel injector protruding into the combustion chamber of a cutaway engine. Things I've seen and learned since that day have made this old picture tell a new story that explains how an old technology has come full circle.
Fuel injection was first tried in the 1890s, but it wasn't developed for gasoline engines until 40 years later. The Daimler Benz DB601 — a 4-valve, V-12 aircraft engine first built in Germany in 1934 — was fitted with direct fuel injection. The nozzle protruded through the cylinder wall between the intake valves and was angled so the spray promoted combustion chamber swirl. Fuel was supplied by a modified version of the Bosch Type A diesel injection pump: an inline "block" with a camshaft operating 12 plunger-type pumping elements. The pump and governor plus the injectors had more parts than the engine itself, but fuel injection provided important advantages over carburetors of the day, especially in aircraft.
In addition to improving fuel economy and high-altitude performance, fuel injection gave combat pilots a tactical advantage. Carburetors use a float-operated valve to control fuel level in the bowl. To initiate a dive, the pilot must first half-roll the airplane to maintain positive gravity on the float. Depending on the design, failure to do this will cause fuel starvation or flooding, and the engine will temporarily lose power. With fuel injection, the pilot can "push over" directly into a dive to escape pursuit.
By 1943, Bendix-Stromberg had developed the "injection-type carburetor" for aircraft engines. Essentially throttle body injection, it was mounted at the inlet of the centrifugal-flow supercharger with the single injector nozzle pointed directly at the eye of the impellor. The rotating impellor helped atomize fuel, and the fuel absorbed heat generated by compressing the air charge. It provided most of the same advantages as direct injection, but it was simpler and cost much less. Later systems had multiple injectors, and fuel pressure was controlled as a function of engine speed and manifold pressure, reducing the pilot's work load.
A decade later, the Mercedes-Benz 300SL became the first fuel injected production car, using another version of that same Bosch direct injection system. In 1958, Bendix produced the first electronically controlled port fuel injection system for Chrysler, and Rochester built a mechanical fuel injection system for Chevrolet. Electronics of the day were unreliable, and the Bendix system was quickly withdrawn from production (and sold to Bosch). Other mechanical port-injection systems were better, but given the engine technology of the day and the fact that carburetors were also getting better, fuel injection didn't offer enough advantage in automotive engines to justify the cost. Bosch finally introduced a reliable, inexpensive electronic port fuel injection system in 1967 to solve a vapor lock problem.
The focus on reducing emissions in the 1970s made fuel injection a necessity, and while several different systems have been developed, today's engines all use sequential multi-port injection. It's relatively inexpensive, reliable and effective at reducing emissions. But now the emphasis has shifted to reducing fuel consumption, and so the technology has finally come full-circle.
Mitsubishi introduced gasoline direct injection (GDI) in the late 1990s. Today almost every major automaker in the world is either using GDI or planning to, because engines designed to use reduce specific fuel consumption by roughly 20 percent. A 2-liter, 200 hp engine returning 31 mpg in a 3,700-pound car is a common sight today. That's a whole new picture.
