fuel injection

Fuel injection is used on almost all compression ignition reciprocating engines and on most spark ignition engines of more than a few cubic inches displacement manufactured since strict emissions laws were introduced.

Fuel injection has only recently eliminated carburetors from liquid fuel spark ignition engines, but it is not new. In various forms it dates back to the 1920s.

On spark ignition engines, there is a great deal of variety in fuel injection systems. They may be of the direct injection or indirect injection type, and if indirect injection may be continuous flow, semi-timed or timed. They may also be fully mechanical, hydromechanical, or electronic and may utilize a number of inputs to control fuel metering.

Compression ignition engines may be said to use direct or indirect injection as well, but these terms have a different meaning in that context. All CI engines have precisely timed (relatively) high pressure injectors which ejaculate directly into the combustion space. Indirect injection, in this case, means there is a segregated prechamber or energy cell connected to or partially cordoned off from the main combustion chamber space. The injector has to cope with combustion pressures, temperatures, and thermal cycling at least at its tip. CI engines are, however, peripheral to the main purpose of this document, which is SI (gasoline, alcohol, LPG) engine fuel injection technology.

Early SI fuel injection technologies were mechanical and of two primary types: indirect continuous flow, such as Hilborn, Bendix, and Continental, and direct high-pressure timed injection adapted from compression-ignition practice, primarily Bosch inline "jerk pump" and pressure nozzles modified to handle unlubricious fuels and connected to the air throttle on the intake manifold.

Bosch direct timed fuel injection systems were used primarily by German engines, starting with the DB 601 and similar V12 aeroengines during WWII and continuing with the Mercedes-Benz W196 Grand Prix and 300SLR straight-eight DOHC and 300SL SOHC six racing and sports car engines.

American aircraft during and after WWII and drag and circle-track racing cars in the 1950s and 1960s used simpler, less expensive, and often more reliable indirect continuous flow systems. The simplest was (and still is) the Hilborn system, which has a simple centrifugal engine driven pump,a metering block hooked to the air throttle, and a return line to the tank which is restricted by a pill or a needle valve which is changed to adjust mixture. Teledyne Continental aircraft engines use essentially this exact system. Lycoming aircraft engines (with one exception,the Simmonds injected GSO-480) and turbocharged circle track racing engines such as the Offfenheuser and DFX Cosworth, usually running on methanol, used a Bendix system relying on air flow density and speed, similar in concept to the much later Bosch L-Jetronic or CIS.

By the 1960's, no auto manufacturer was content to not have a fuel injected offering in its lineup on its more performance or luxury oriented models. In the US, Chrysler pioneered an electronic system from Bendix called the Electrojector in the late 1950's, but due to lack of experience in building sufficiently ruggedized electronics, the systems failed and Chrysler retrofitted every single car so equipped with carburetors. (Bendix found that automobiles were actually a more hostile and difficult environment than aircraft, or at least light ones, to design for.) General Motors introduced a continuous flow system by Rochester on some Chevrolet and Pontiac models. It lasted considerably longer but had some design flaws which GM never sufficiently addressed, particularly a small flexible driveshaft from the distributor that failed frequently.

European carmakers became enamored of fuel injection slightly later. Mercedes stuck with Bosch, adapting the diesel style pumps to indirect injection with the nozzle moved to the intake manifold. Alfa Romeo used a similar system using the Italian Spica, and BMW used a Kugelfischer system. But it was Volkswagen who, with Robert Bosch, re-introduced electronic FI to the world with the D-Jetronic system, a solid state version of the old Bendix system. With the somewhat later adoption of emissions control in Europe, Bosch systems-D-Jet, K-Jet, and L-Jet-became de rigeur for most European cars, while Asian manufacturers used similar systems under license.

These systems-except for Bosch CIS, a more physically awkward but more detailed variant of Bendix/RSA speed density systems-all relied on an air throttle, mass air flow(MAF) and manifold absolute pressure (MAP)sensors, a constant pressure fuel rail and electromechanical solenoid injectors located between air throttle and intake valve, and an analog or digital controller which increasingly controlled not only the 'electronic' injectors but also the ignition timing, turbo wastegate (if fitted), and other parameters and which had exhaust oxygen sensors, outside air and coolant temperature sensors, vehicle road speed and gear position sensors, and other inputs as desired for emissions and other regulation.

American automotive practice closely followed European norms, with the use by GM, Ford and Chrysler of primarily in-house built systems instead of Bosch, ND, or other outside vendors' being the only major difference. Today, there is no significant difference between US and world practice in automotive engine control systems in terms of core technology, and engine controllers are becoming ever more critical to engine operation as functions like coolant temperature regulation, camshaft degree positioning, and even electronically controlled direct actuation of intake and exhaust valves become commonplace. In 1992, one still could (emissions regulations notwithstanding) convert the most modern electronically controlled engines to contact-breaker or even magneto ignition and a float-bowl carburetor. On many of the current production engines this would be impossible without major structural modification, as no place exists to mount a distributor, and the variable camshafts would have to be locked in position. However, except for a very few individuals gearing up for a nuclear war, the trend today among modifiers is not to get rid of the modern technology, but to fit older engines with the most modern engine management systems. Because performance, driveability, and fuel mileage are all substantially improved with properly designed engine management, one can see such unlikely sights as a 1953 Hudson with its original flathead engine sporting the latest Bosch Digifant system or 1950s "shoebox' Chevy sedans with the original Rochester injection air box but modern electronic control, injectors, and a Ford MAF sensor. Somehow, one gets the feeling that Zora Arkus-Duntov would approve despite corporate management-after all, his first design was a Hemi head set for the venerable flathead Ford V8 block.