Gasoline Direct Injection - Companion Technologies

Companion Technologies

Direct injection may also be accompanied by other engine technologies such as variable valve timing (VVT) or continuous variable cam phasing, tuned/multi path or variable length intake manifolding (VLIM, or VIM), and turbocharging. 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 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. Some engines overcome this limitation by using both direct injection and multiport fuel injection (Toyota 2GR-FSE V6).