OK we've all heard about Audi's FSI and Turbo FSI engines that are getting accolades from across the automotive world.

But what do the letters FSI stand for?

 

In the LeMans race cars it stood for Fuel Stratified Injection, but for the road cars in North America it is said to stand for Fuel Straight Injection. Basically it indicates a direct injection engine.

 

It's Fuel Stratified Injection for both the LeMans cars and the normal production cars.

 

No, "Stratified" refers to a lean burn cycle that is not possible in North America due to emissions rules and fuel, so here it is "Straight." You can see references to a couple explanations at:

Fuel system - Mkvgtiwiki

 

That Mkvgtiwiki link is based on a couple of really old articles, which are out of date. In 2006, North American gasoline sulfur content was reduced to 30 ppm. European petrol sulfur content at that time was 50 ppm.

 

^^^battle of the Clavens

 

But the issue for the lean burn cycle is the NOx emissions, which is why its not used in the North American engines.