Fuel injection

Fuel injection is a technology used in internal combustion engines to mix the fuel with air prior to combustion.

As in a traditional carburetor, fuel is converted to a fine spray and mixed with air. However, where a traditional carburetor forces the incoming air through a venturi to pull the fuel into the air stream, a fuel injection system forces the fuel through nozzles under pressure to inject the fuel into the air stream without requiring a venturi.

The use of a venturi reduces volumetric efficiency by approximately 15%, which results in a reduction in engine power. Thus, a fuel injection system increases the power that an engine with the same engine displacement will produce. Additionally, fuel injection allows for more precise control over the mixture of fuel and air, both in proportion and in uniformity.

The fuel injection may be purely mechanical, purely electronic or a mix of the two. Early systems were mechanical but from about 1980 onward more and more systems were completely electronic. By the middle of the decade, nearly all new passenger vehicles were equipped with electronic fuel injection. The 1990 Subaru Justy was the last passenger car sold in the United States with a carburetor.

The modern electronic systems that cars are equipped with today utilise a number of sensors to monitor engine conditions, and an electronic control unit (ECU) to accurately calculate the needed amount of fuel. Thus fuel injection can increase fuel efficiency and reduce pollution.

Indirect injection

Typical gasoline engines are usually equipped with indirect injection systems. They may be single point where the fuel is injected using one nozzle, usually in the throttle housing, or multi point where each cylinder has its own injector in the inlet manifold. The nozzles may be opened using the pressure in the fuel system or there may be a solenoid on the injector that will pulse it open and closed in a duty cycle according to the desired fuel requirement.

Throttle-body injection

Electronic throttle-body injection (normally called TBI, though Ford used the abbreviation, CFI) was introduced in the early 1980s as a transition technology to fully-electronic port injection. The system injects fuel into the throttle-body (a wet system), so fuel can condense and cling to the walls of the intake system, harming emissions. Computer-controlled TBI was inexpensive and simple, however, and lasted well into the 1990s.

Central port injection

General Motors developed a new "in-between" technique called central port injection or CPI. It uses tubes from a central injector to spray fuel at the intake port rather than the throttle-body (it is a dry system). However, fuel is continuously injected to all ports simultaneously, which is less than optimal.

Sequential central point injection

GM refined the CPI system into a sequential central port injection (SCPI) system in the mid-1990s. It used valves to meter the fuel to just the cylinders that were in the intake phase. This worked well on paper, but the valves had a tendency to stick. Fuel injector cleaner sometimes worked, but the system remained problematic.

Multi-port fuel injection

The goal of all fuel injection systems is to carefully meter the amount and timing of fuel to each cylinder. This is achieved with the more sophisticated fuel injection systems, often called multi-port fuel injection (MFI) or sequential port fuel injection (SFI). It uses a single injector per cylinder and sprays the fuel right above the intake valves.

Direct injection

See also: Gasoline Direct Injection

Since mid-2000s, many diesel engines feature direct injection (DI). The injection nozzle is placed inside the combustion chamber itself and the piston incorporates a depression (often toroidal) which is where initial combustion takes place. Direct injection diesel engines are generally more efficient than indirect injection engines, but tend to be noisier; that is being adressed in newest common rail designs.

Some hi-tech petrol engines utilise this system as well, since it gives a better volumetric efficiency as only air is drawn in through the induction system, increasing amount of air induced and minimising fuel losses. The injector also features several spray modes so that the fuel is better distributed and a powerful air-fuel mixture is created.

History

Frederick William Lanchester joined the Forward Gas Engine Company Birmingham, England in 1889. He carried out what was possibly the earliest experiments with fuel injection.

Indirect fuel injection has been used in diesel engines since the mid 1920s, almost from their introduction (due to the higher energy required for diesel to evaporate). The concept was adapted for use in petrol-powered aircraft during World War II, and direct injection was employed in some notable designs like the Daimler-Benz DB 603 and later versions of the Wright R-3350 used in the B-29 Superfortress.

An injection system developed by Bosch was first used in a car in 1955 with the introduction of the Mercedes-Benz 300SL. An electronic fuel injection system was also developed by the Bendix Corporation.

In 1957, Chevrolet introduced a mechanical fuel injection option for its 283 V8 engine, made by General Motors' Rochester division. This system used a single central plunger to feed fuel to all eight cylinders, in contrast to Mercedes' individual plunger for each of the six cylinders, but it nevertheless produced 283 hp (211 kW) from 283 in³ (4.6 L), making it the first production engine in history to exceed 1 hp/in³ (45.5 kW/L).

Fuel injection became widespread with the introduction of electronically controlled fuel injection systems in the 1980s and the gradual tightening of emissions and fuel economy laws. Meeting modern emissions standards whilst retaining acceptable performance would be impossible without it. In addition, the development of microprocessor technology made it possible to control the amount of fuel injected precisely.