The use of GDI can help increase engine efficiency and specific power output as well as reduce exhaust emissions.
[6] Compared with manifold injection, the fuel efficiency is only very slightly increased, but the specific power output is better,[7] which is why the homogeneous mode is useful for so-called engine downsizing.
[8][9] The stratified charge mode creates a small zone of fuel/air mixture around the spark plug, which is surrounded by air in the rest of the cylinder.
A "swirl cavity" in the top of the piston is often used to direct the fuel into the zone surrounding the spark plug.
This technique enables the use of ultra-lean mixtures that would be impossible with carburetors or conventional manifold fuel injection.
[25] Common techniques for creating the desired distribution of fuel throughout the combustion chamber are either spray-guided, air-guided, or wall-guided injection.
At low engine temperatures, some parts of the fuel on the relatively cold piston cool down so much, that they cannot combust properly.
The intake air must therefore have a special swirl or tumble movement in order to direct the fuel towards the spark plug.
This swirl or tumble movement must be retained for a relatively long period of time, so that all of the fuel is getting pushed towards the spark plug.
The fuel is injected during the latter stages of the compression stroke, causing very quick (and inhomogeneous) mixture formation.
[33] Also, exhaust gas recirculation can be used to reduce the high nitrogen oxide (NOx) emissions that can result from the ultra lean combustion.
[34] Gasoline direct injection does not have the valve cleaning action that is provided when fuel is introduced to the engine upstream of the cylinder.
[35] In non-GDI engines, the gasoline traveling through the intake port acts as a cleaning agent for contamination, such as atomized oil.
Third party manufacturers sell oil catch tanks which are supposed to prevent or reduce those carbon deposits.
The ability to produce peak power at high engine speeds (RPM) is more limited for GDI, since there is a shorter period of time available to inject the required quantity of fuel.
Gasoline does not provide the same level of lubrication for the injector components as diesel, which sometimes becomes a limiting factor in the injection pressures used by GDI engines.
The injection pressure of a GDI engine is typically limited to approximately 20 MPa (2.9 ksi), to prevent excessive wear on the injectors.
A strong absorber of solar radiation, black carbon possesses significant climate-warming properties.
[37] In a study published in January 2020 in the journal Environmental Science and Technology, a team of researchers at the University of Georgia (USA) predicted that the increase in black carbon emissions from GDI-powered vehicles will increase climate warming in urban areas of the U.S. by an amount that significantly exceeds the cooling associated with a reduction in CO2.
The researchers also believe the shift from traditional port fuel injection (PFI) engines to the use of GDI technology will nearly double the premature mortality rate associated with vehicle emissions, from 855 deaths annually in the United States to 1,599.
The engine was a high compression four-stroke motorcycle engine, with the gasoline fuel separately pressurised to 1000psi and admitted into the cylinder 'at the moment of highest compression' by a small rotary valve, with simultaneous ignition by a spark plug and trembler coil allowing sparking to continue throughout the combustion phase.
Being a crankcase-compression two-stroke design, a misfire could destroy the engine, therefore Junkers developed a GDI system to prevent this issue.
A demonstration of this prototype engine to aviation officials was performed shortly before development ceased due to the end of World War I.
The German company Bosch had been developing a mechanical GDI system for cars since the 1930s[44] and in 1952 it was introduced on the two-stroke engines in the Goliath GP700 and Gutbrod Superior.
During the 1970s, the United States manufacturers American Motors Corporation and Ford developed prototype mechanical GDI systems called Straticharge and Programmed Combustion (PROCO) respectively.
"[66] There are additional benefits of GDI for two-stroke engines, relating to scavenging of the exhaust gases and lubrication of the crankcase.
A low-pressure injector then sprays fuel into the combustion chamber, where it vaporizes as it mixes with the compressed air.
[68][69] The Evinrude E-Tec is an improved version of the Ficht system, which was released in 2003[70] and won an EPA Clean Air Excellence Award in 2004.