Gasoline direct injection

Gasoline direct injection (GDI) (also known as petrol direct injection, direct petrol injection, spark-ignited direct injection (SIDI) and fuel-stratified injection (FSI)), is a form 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 multipoint fuel injection that injects fuel into the intake tract or cylinder port. Directly injecting fuel into the combustion chamber requires high-pressure injection, whereas low pressure is used injecting into the intake tract or cylinder port. Gasoline direct injection (GDI) (also known as petrol direct injection, direct petrol injection, spark-ignited direct injection (SIDI) and fuel-stratified injection (FSI)), is a form 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 multipoint fuel injection that injects fuel into the intake tract or cylinder port. Directly injecting fuel into the combustion chamber requires high-pressure injection, whereas low pressure is used injecting into the intake tract or cylinder port. In some applications, gasoline direct injection enables a stratified fuel charge (ultra lean burn) combustion for improved fuel efficiency, and reduced emission levels at low load. GDI has seen rapid adoption by the automotive industry over the past years, from 2.3% of production for model year 2008 vehicles to just over 45% expected production for model year 2015. 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. GDI engine operates into two modes 1) overall lean equivalence ratio composition during low load and low speed operation. 2) Homogeneous stoichiometric mode at higher loads and at all loads and higher speed. At medium load region charge is lean or stoichiometric. The combustion systems are classified into air guided, wall guided and spray guided system. 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 (mass), 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. It is also possible to inject fuel 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, However, certain octane fuels have caused exhaust valve erosion. Direct injection may also be accompanied by other engine technologies such as turbocharging or supercharging, variable valve timing (VVT) or continuous variable cam phasing, 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; modern turbocharged engines use continuous cam phasing in place of EGR. 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 intake 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 do not inject during the exhaust cycle because doing so would waste fuel. Hence, all other factors being equal, an FSI engine needs higher-capacity injectors to achieve the same power as a conventional engine. Some engines overcome this limitation as well as contamination issues by using both direct injection and multiport fuel injection, including Toyota 2GR-FSE V6 and Volkswagen Group TSI Engines. The first Otto cycle engine direct injection system was designed by German engineer Otto Mader. It was used for a Junkers airplane engine in 1916. Initially, Junkers planned developing an aviation Diesel engine, because Diesel engines were deemed more efficient and less prone to catching fire than Otto cycle engines. Due to the German ministry of war demanding aircraft engines running on either benzene or petrol, Junkers modified their design to use the Otto cycle rather than the Diesel cycle. Being a two-stroke engine, the design had crankcase scavenging, which would result in engine misfire destroying the engine. Therefore, Mader developed a direct injection system to overcome this problem.