Direct Injection vs. Port Injection

[jcp123]

I understand that direct injection is supposed to make new strides in terms of efficiency and power. But what is it that makes direct injection so much "better" than port injection?

[KnifeEdge_2K1]

direct injection would mean you can calculate the exact amount of fuel to inject into each cylinder but i was under the impression that port injection would allow a more even air/fuel mixture since the turbulence from the intake manafold would help mix the air/fuel like a carburator would (crappy analogy i know)

[jcp123]

that's what i always thought, too...

[PerfAdv]

I admit not being an expert on the technology but my understanding is that by squirting fuel directly into cylinder has tremendous power/economy benefits. Squirting at the precise moment before combustion assures a throughly atomized mixture.

I think similar technology for Diesels is common-rail injection. It's been a breakthrough helping them produce amzing output. Here too fuel is injected directly into the cylinders. Also doing away with the need for a pre-chamber.

[Matra et Alpine]

With direct injection, you can delay putting fuel in till you've compressed most of the air and then create a burning wave front in the droplets as injected. This gives a more even burn.

Also with direct injection you can control the spray more accurately than relyign on swirl in the inlet ports. I saw some research on direct injection years ago and they used innovate chamber design to pre-mix the diret injection and create the near perfect burn. I'm not aware that any of this is done in todays DI's

[cossie]

as fuel is heavier than air the air arrives at the cylinder first and the fuel after thus it doesn't mix properly,when the fuel is sprayed closer to the valve head it ensures both mix and arrive together thus giving a more atomised and correct fuel/air ratio.This is more pronounced in carby cars which gives more fuel to try and counteract this and give the correct fuel/air ratio to cylinders :)