Gasoline direct injection

Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a fuel injection system for internal combustion engines that run on gasoline. It injects fuel directly into the combustion chamber, unlike manifold injection systems, which inject fuel into the intake manifold so that it mixes with the incoming airstream before reaching the combustion chamber.

Use of GDI can improve engine efficiency and specific power output, and can also reduce exhaust emissions from vehicles.

The first production engine to use GDI was the Swedish Hesselman engine, a low-compression multi-fuel spark-ignition design that was more efficient than traditional carbureted engines. It could also run on diesel, kerosene, ethanol and tar oil. Because gasoline was more expensive than less-refined fuels, it was usually only used for starting; once running, the engine was switched to a cheaper fuel.

Introduced in 1925, the Hesselman engine was used by truck and heavy equipment manufacturers in Sweden and by stationary engine and heavy vehicle manufacturers in the United States throughout the 1940s. The first mass-produced GDI engine to use Bosch's mechanical fuel injection system (the same type used in pre-chambers in diesel engines) was the DB601 V12 for the Messerschmitt Bf 109 in 1936.

Use of the Bosch mechanical fuel injection system in a direct-injection configuration allowed the Germans to employ extremely high compression ratios and very high-pressure forced induction to produce high power reliably from low-quality gasoline with an octane rating of only 87. In addition, the fighter's engine did not stall in negative‑G turns, unlike carbureted engines such as the Rolls-Royce Merlin.