Gasoline Direct Injection
Encyclopedia : G : GA : GAS : Gasoline Direct Injection
Gasoline direct injection or GDI is a variant of fuel injection employed in modern four stroke petrol engines. The gasoline or biobutanol is injected right into the combustion chamber of each cylinder, as opposed to conventional multi point fuel injection that happens in the intake manifold.
Theory of operation
The major advantages of a GDI engine are increased fuel efficiency and high power output. This is achieved by the precise control over amount of fuel and injection timings which are varied according to the load conditions. In addition, there are no throttling losses when compared to a conventional fuel injected or carburated engine, which greatly improves efficiency. Basically, the engine management system continuously chooses between three different modes of combustion: ultra lean burn combustion, stoichiometric combustion and high power output mode.Each mode is characterized by air-fuel ratio, the amount of fuel in the air-fuel mixture; the stoichiometric ratio for petrol is 14.7 to 1 by weight, but in ultra lean mode, it could be as high as 65 to 1. These leaner mixtures than those ever achieved in the conventional engines are desired because of reduced fuel consumption.
- Ultra lean combustion mode is effective under normal running conditions, when little acceleration is required. The fuel is not injected at the intake stroke but rather at the latter stages of the compression stroke, so that the small amount of air-fuel mixture is optimally placed just near the spark plug. This stratified charge is surrounded by mostly air which keeps the fuel away from the cylinder walls for lowest emissions. The combustion takes place in a toroidal cavity on the piston's surface. This technique enables the usage of ultra lean mixtures with very high air-fuel ratio, impossible with traditional carburetors or even intake port injection.
- Stoichiometric combustion mode is activated for moderate load conditions. In this mode, fuel is injected during the intake stroke. The air-fuel mixture is homogeneous with the stoichiometric rates necessary for the catalytic converter to remove a maximum of the major pollutants CO and NOx from the exhaust gas.
- In full power mode, the air-fuel mixture is homogeneous as well and contains the maximum amount of fuel that is possible to ignite without knocking out, as defined by the compression ratio of the engine. The fuel is injected during the intake stroke. This mode activates at high load conditions and provides maximum output and torque.
History
The 1955 Mercedes-Benz 300SL, the first gasoline-powered automobile to use fuel injection, used direct injection. The Bosch fuel injectors were placed into the bores on the cylinder wall used by the spark plugs in other Mercedes-Benz six-cylinder engines (the spark plugs were relocated to the cylinder head). Later, more mainstream applications of fuel injection favoured less expensive indirect injection methods.It was not until 1996 that gasoline direct injection reappeared on the market. Mitsubishi Motors was the first with a GDI engine in Japan, the Galant/Legnum's 4G93, which it brought to Europe in 1998. Mitsubishi applied this technology widely, producing over 400,000 GDI engines in four families before 1999, but high-sulphur fuel led to emissions problems, and fuel efficiency was less than expected. PSA Peugeot Citroën also launched a GDI engine (with licensed Mitsubishi technology) in 1999, but both were withdrawn from the market in 2001. DaimlerChrysler produced a special engine for 2000, offered only in markets with low sulphur fuel.
Later GDI engines have been tuned and marketed for their high performance. Volkswagen/Audi led the trend with their 2001 GDI engine, under the product name Fuel Stratified Injection (FSI). The technology, adapted from Audi's Le Mans racecars, induces an electric charge in the fuel-air mixture.
BMW followed with a GDI V12. This initial BMW system used low-pressure injectors and could not enter lean-burn mode, but the company introduced its second-generation High Precision Injection system on the R6 straight-6 in 2006. This system surpasses many others with a wider envelope of lean-burn time, increasing overall efficiency. PSA is cooperating with BMW on a new line of engines for future introduction.
General Motors had planned to produce a full range of GDI engines by 2002, but so far only two such engines have been introduced - in 2004, a version of the 2.2 L Ecotec used by the Opel Vectra and in 2005, a 2.0 L Ecotec with VVT technology for the Pontiac Solstice GXP.
In 2004 Isuzu Motors produced the first GDI engine sold in a mainstream American vehicle. Standard on the 2004 Axiom and optional on the 2004 Rodeo. Isuzu claimed the benefit of GDI is that the vaporizing fuel has a cooling effect, allowing a higher compression ratio (10.3 to 1 versus 9.1 to 1) that boosts output by 20 horsepower and that 0-to-60 times drop from 8.9 to just 7.5 seconds, with the quarter-mile being cut from 16.5 seconds to 15.8 ticks. [Edmunds Article] [Popular Science Article]
Toyota's 2GR-FSE V6 will use a combination of direct and indirect injection in 2006. It uses two injectors per cylinder, a traditional port injector and a new direct injector.
Mazda uses their own version of direct injection in the new Mazdaspeed 6 / Mazda 6 MPS. It is referred to as Direct Injection Spark Ignition. Isuzu offered a direct injection 6 cylinder engine in the 2004 Axiom and Rodeo, and both were the least expensive direct-injection models offered in the United States from then until present (April 2006). Ű
External links
- [Mitsubishi's Page on Gasoline Direct Injection]
- [AutoWeek article]
- [Channel 4 article on Fuel Stratified Injection]
References
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.