- Gasoline direct injection
In internal combustion engines, gasoline direct injection (GDI), also known as petrol direct injection or direct petrol injection, is a variant of fuel injection employed in modern two-stroke and four-stroke gasoline engines. The gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder, as opposed to conventional multi-point fuel injection that happens in the intake tract, or cylinder port.
Theory of operation
The major advantages of a GDI engine are increased fuel efficiency and high power output. Emissions levels can also be more accurately controlled with the GDI system. The cited gains are achieved by the precise control over the amount of fuel and injection timings that are varied according to the load conditions. In addition, there are no throttling losses in some GDI engines, when compared to a conventional fuel injected or carbureted engine, which greatly improves efficiency, and reduces 'pumping losses' in engines without a throttle plate. Engine speed is controlled by the engine control unit/engine management system (EMS), which regulates fuel injection function and ignition timing, instead of having a throttle plate that restricts the incoming air supply. Adding this function to the EMS requires considerable enhancement of its processing and memory, as direct injection plus the engine speed management must have very precise algorithms for good performance and drivability.
The engine management system continually chooses among three combustion modes: ultra lean burn, stoichiometric, and full power output. Each mode is characterized by the air-fuel ratio. The stoichiometric air-fuel ratio for gasoline is 14.7:1 by weight, but ultra lean mode can involve ratios as high as 65:1 (or even higher in some engines, for very limited periods). These mixtures are much leaner than in a conventional engine and reduce fuel consumption considerably.
- Ultra lean burn mode is used for light-load running conditions, at constant or reducing road speeds, where no 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 near the spark plug. This stratified charge is surrounded mostly by air, which keeps the fuel and the flame away from the cylinder walls for lowest emissions and heat losses. The combustion takes place in a toroidal (donut-shaped) cavity on the piston's surface. The cavity is displaced to one side of the piston, the side that has the fuel injector. This technique enables the use of ultra-lean mixtures that would be impossible with carburetors or conventional fuel injection.
- Stoichiometric mode is used for moderate load conditions. Fuel is injected during the intake stroke, creating a homogenous fuel-air mixture in the cylinder. From the stoichiometric ratio, an optimum burn results in a clean exhaust emission, further cleaned by the catalytic converter.
- Full power mode is used for rapid acceleration and heavy loads (as when climbing a hill). The air-fuel mixture is homogenous and the ratio is slightly richer than stoichiometric, which helps prevent knock (pinging). The fuel is injected during the intake stroke.
Direct injection may also be accompanied by other engine technologies such as variable valve timing (VVT) and tuned/multi path or variable length intake manifolding (VLIM, or VIM). Water injection or (more commonly) exhaust gas recirculation (EGR) may help reduce the high nitrogen oxides (NOx) emissions that can result from burning ultra lean mixtures.
It is also possible to inject more than once during a single cycle. After the first fuel charge has been ignited, it is possible to add fuel as the piston descends. The benefits are more power and economy, but certain octane fuels have been seen to cause exhaust valve erosion. For this reason, most companies have ceased to use the Fuel Stratified Injection (FSI) operation during normal running.
Tuning up an early generation FSI power plant to generate higher power is difficult, since the only time it is possible to inject fuel is during the induction phase. Conventional injection engines can inject throughout the 4-stroke sequence, as the injector squirts onto the back of a closed valve. A direct injection engine, where the injector injects directly into the cylinder, is limited to the suction stroke of the piston. As the RPM increases, the time available to inject fuel decreases. Newer FSI systems that have sufficient fuel pressure to inject even late in compression phase do not suffer to the same extent; however, they still do not inject during the exhaust cycle (they could but it would just waste fuel). Hence, all other factors being equal, an FSI engine needs higher-capacity injectors to achieve the same power as a conventional engine.
The first use of direct gasoline injection was on the Hesselman engine invented by Swedish engineer Jonas Hesselman in 1925. Hesselman engines used the ultra lean burn principle and injected the fuel in the end of the compression stroke and then ignited it with a spark plug, it was often started on gasoline and then switched over to run on diesel or kerosene. The Hesselman engine was a low compression design constructed to run on heavy fuel oils. Direct gasoline injection was used on production aircraft during WWII, with German (Junkers Jumo 210, Daimler-Benz DB 601, both 1937), Soviet (Shvetsov ASh-82FN, 1943, Chemical Automatics Design Bureau - KB Khimavtomatika) and US (Wright R-3350, 1944) designs. The first automotive direct injection system used to run on gasoline was developed by Bosch, and was introduced by Goliath and Gutbrod in 1952. The 1955 Mercedes-Benz 300SL, the first production sports car 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 favored the less-expensive indirect injection methods.
In the early-1970s, research was conducted with the backing of American Motors Corporation (AMC) to develop a Straticharge Continuous Fuel-Injection (SCFI) system. The conventional spark ignited internal combustion AMC straight-6 engine was modified with a redesigned cylinder head. The system incorporated a mechanical device that automatically responded to the engine’s airflow and loading conditions with two separate fuel-control pressures supplied to two sets of continuous-flow injectors. Flexibility was designed into the SCFI system for trimming it to a particular engine. Prototype "straticharge" engine road testing was performed using a 1973 AMC Hornet, but the mechanical fuel controls had teething problems.
During the late-1970s, the Ford Motor Company developed a stratified-charge engine they called "ProCo" (programmed combustion), utilizing a unique high-pressure pump and direct injectors. At least one hundred and fifteen (115) Crown Victoria cars were built at Ford's Atlanta Assembly in Hapeville, Georgia using a ProCo V8 engine. The project was canceled for several reasons: electronic controls, a key element, were in their infancy; pump and injector costs were extremely high; and lean combustion produced nitrogen oxides in excess of near future United States Environmental Protection Agency (EPA) limits. The three-way catalytic converter proved to be a less expensive solution.
In 1996 gasoline direct injection reappeared in the automotive market. Mitsubishi was the first with a GDI engine in the Japanese market with its Galant/Legnum's 4G93 1.8 L inline-four. It was subsequently brought to Europe in 1997 in the Carisma, although Europe's then high-sulfur unleaded fuel led to emissions problems, and fuel efficiency was less than expected. It also developed the first six-cylinder GDI powerplant, the 6G74 3.5 L V6, in 1997. Mitsubishi applied this technology widely, producing over one million GDI engines in four families by 2001.
In 1998, Toyota's D4 direct injection system first appeared on various Japanese market vehicles equipped with the SZ and NZ engines. Toyota later introduced its D4 system to European markets with the 1AZ-FSE engine found in the 2001 Avensis. and US markets in 2005 with the 3GR-FSE engine found in the Lexus GS 300. Toyota's 2GR-FSE V6 uses a more advanced direct injection system, which combines both direct and indirect injection using two fuel injectors per cylinder, a traditional port fuel injector (low pressure) and a direct fuel injector (high-pressure) in a system known as D4-S.
In 1999, Renault introduced the 2.0 IDE (Injection Direct Essence), first on the Megane. Rather than following the lean burn approach, Renault's design uses high ratios of exhaust gas recirculation to improve economy at low engine loads, with direct injection allowing the fuel to be concentrated around the spark. Later gasoline direct injection engines have been tuned and marketed for their high performance as well as increased fuel efficiency. PSA Peugeot Citroën, Hyundai and Volvo licensed Mitsubishi's GDI technology in 1999. Although other companies have since developed gasoline direct injection engines, the acronym 'GDI' (with an uppercase final "I") remains a registered trademark of Mitsubishi Motors.
In 2000, the Volkswagen Group introduced its gasoline direct injection engine in the Volkswagen Lupo, a 1.4 L inline-four unit, under the product name "Fuel Stratified Injection" (FSI). The technology was adapted from Audi's Le Mans prototype race car R8. Volkswagen Group marques use direct injection in its 2.0 L FSI turbocharged and naturally aspirated four-cylinder engines. Later, a 2.0 L inline-four unit was introduced in the model year 2003 Audi A4. PSA Peugeot Citroën introduced its first GDi (HPi) engine in 2000 in the Citroën C5 and Peugeot 406. It was a 2.0-liter 16-valve EW10 D unit with 140 hp (104 kW), the system was licensed from Mitsubishi.
In 2003, A new 1.8 L Duratec SCi naturally aspirated engine made its production debut in the Ford Mondeo in 2003. Ford introduced its first European Ford engine to use direct injection technology in 2001, badged SCi (Smart Charge injection) for Direct-Injection-Spark-Ignition (DISI). The range will include some turbocharged derivatives, including the 1.1 L, three-cylinder turbocharged unit showcased at the 2002 Geneva Show.
In 2003, BMW introduced a low-pressure gasoline direct injection N73 V12. This initial BMW setup could not enter lean-burn mode, but the company introduced its second-generation High Precision Injection (HPI) system on the updated N52 straight-6 in 2006, which used high-pressure injectors. 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 that made its first appearance in the 2007 MINI Cooper S. Honda released their own direct injection system on the Stream sold in Japan. Honda's fuel injector is placed directly atop the cylinder at a 90-degree angle rather than a slanted angle.
Since 2004, General Motors has released three such direct injected engines: in 2004, a 155 hp (116 kW) version of the 2.2 L Ecotec used in the Opel/Vauxhall Vectra and Signum in 2005, a 2.0 L turbocharged Ecotec for the new Opel GT, Pontiac Solstice GXP, and the Saturn Sky Red Line, in 2007 the same engine was used in the Super Sport versions of the Chevrolet Cobalt and the HHR. Also in 2007, the 3.6 L LLT became available in the redesigned Cadillac CTS and STS. The 3.6 L was added to the 2009 model GMC Acadia, Chevrolet Traverse, Saturn Outlook, Buick Enclave, and the 2010 Chevy Camaro. In 2004 Isuzu 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 (10.3:1 versus 9.1:1) that boosts output by 20 hp (15 kW), and that 0-to-60 mph times drop from 8.9 to just 7.5 seconds, with the quarter-mile being cut from 16.5 to 15.8 seconds.
In 2005, Mazda began to use their own version of direct-injection in the Mazdaspeed6 and later on the CX-7 sport-utility, and the new Mazdaspeed3 in the US and European market. It is referred to as Direct Injection Spark Ignition (DISI).
In 2006, BMW released the new N54 twin-turbo-charged direct injection inline-six engine for its 335i Coupe and later for the 335i Sedan, 535i series and the 135i models. Mercedes-Benz released its direct injection system (Charged Gasoline Injection, or "CGI") on the CLS 350 CGI featuring common rail, piezo-electric direct fuel injectors. The CLS 350 CGI offers 292 BHP versus 272 BHP for the CLS 350, with reduced carbon dioxide emissions and improved fuel economy.
In 2007, Ford introduced its new Ford EcoBoost engine technology designed for a range of global vehicles (from small cars to large trucks). The engine first appeared in the 2007 Lincoln MKR Concept under the name TwinForce. The new global EcoBoost family of 4-cylinder and 6-cylinder engines features turbocharging and direct injection technology (GTDI - Gasoline Turbocharged Direct Injection). A 2.0 L version was unveiled in the 2008 Ford Explorer America Concept.
In 2009, Ferrari began selling the front-engine California with a direct injection system, and announced that its new 458 Italia car will also feature a direct injection system, a first for Ferrari mid-rear engine setups. Porsche also began selling the 997 and Cayman equipped with direct injection. Ford produced the new generation Taurus SHO and Flex with a 3.5 L twin-turbo EcoBoost V-6 with direct injection. Holden has also added two direct injection engines as standard on the V6 variant Commodores under the name of SIDI or Spark Ignition Direct Injection. The Infiniti Essence concept car is powered by a direct injected twin turbo V6. The Jaguar Land Rover AJ-V8 Gen III 5.0 L engine (introduced in August 2009 for the 2010 model year) features spray-guided direct injection.
In 2010 Infiniti will produce the M56 which includes DI. Motus Motorcycles is developing, with Katech Engines, a direct-injected V4 engine named the KMV4 as the powertrain for their MST motorcycles.  The Hyundai Sonata 2011 model will come with GDI engines. Hyundai's Theta I-4 engine family is a proprietary design, engineered in Namyang, Korea and currently in production for applications all over the world.
In two-stroke engines
The benefits of direct injection are even more pronounced in two-stroke engines, because it eliminates much of the pollution they cause. In conventional two-strokes, the exhaust and intake ports are both open at the same time, at the bottom of the piston stroke. A large portion of the fuel/air mixture entering the cylinder from the crankcase through the intake ports goes directly out, unburned, through the exhaust port. With direct injection, only air comes from the crankcase, and fuel is not injected until the piston rises and all ports are closed.
Some Goliath two stroke cars built in the early 1950s had direct injection, but their engines were soon superseded by four strokes.
Two types of GDi are used in two-strokes: low-pressure air-assisted, and high-pressure. The former, developed by Orbital Engine Corporation of Australia (now Orbital Corporation) injects a mixture of fuel and compressed air into the combustion chamber. When the air expands it atomizes the fuel. The Orbital system is used in motor scooters manufactured by Aprilia, Piaggio, Peugeot and Kymco, in outboard motors manufactured by Mercury and Tohatsu, and in personal watercraft manufactured by Bombardier Recreational Products (BRP).
In the early 1990s, Ficht GmbH of Kirchseeon, Germany developed a high-pressure direct injector for use with two stroke engines. Outboard Marine Corporation (OMC) licensed the technology in 1995 and introduced it on a production outboard engine in 1996. OMC purchased a controlling interest in Ficht in 1998. Beset by extensive warranty claims for its Ficht outboards and prior and concurrent management-financial problems, OMC declared bankruptcy in December 2000 and the engine manufacturing portion and brands (Evinrude Outboard Motors and Johnson Outboards), including the Ficht technology, were purchased by BRP in 2001.
Evinrude introduced the E-Tec system, an improvement to the Ficht fuel injection, in 2003, based on U.S. patent 6,398,511. In 2004, Evinrude received the EPA Clean Air Excellence Award for their outboards utilizing the E-Tec system. The E-Tec system has recently also been adapted for use in performance two-stroke snowmobiles.
Yamaha also has a high-pressure direct injection (HPDI) system for two-stroke outboards. It differs from the Ficht/E-Tec and Orbital direct injection systems because it uses a separate, belt driven, high-pressure, mechanical fuel pump to generate the pressure necessary for injection in a closed chamber. This is similar to most current 4-stroke automotive designs.
EnviroFit, a non-profit corporation sponsored by Colorado State University, has developed direct injection retrofit kits for two-stroke motorcycles in a project to reduce air pollution in Southeast Asia, using technology developed by Orbital Corporation of Australia. The World Health Organization says air pollution in Southeast Asia and the Pacific causes 537,000 premature deaths each year. The 100-million two-stroke taxis and motorcycles in that part of the world are a major cause.
Code named Bobcat, the new twin-fuel engine from Ford is based on a 5.0L V8 engine block but uses E85 cylinder injection and gasoline port injection. The engine was co-developed with Ethanol Boosting Systems, LLC of Cambridge, Massachusetts, which calls its trademarked process DI Octane Boost. The direct injection of ethanol increases the octane of regular gasoline from 88-91 octane to more than 150 octane. The Bobcat project was unveiled to the United States Department of Energy and the SAE International in April 2009.
As part of the rule changes under discussion for the 2013 season, GDI has been mentioned as a potential technology of interest by Ferrari.
- Alfa Romeo JTS engine
- BMW N53
- BMW N63
- Ford EcoBoost engine
- Mitsubishi 4G93
- Nissan VQ engine
- Nissan VK engine
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