[hotrod]

I finally found the reference I mentioned in the post above regarding valve head cooling from fuel injectors.

It is in this post:
http://www.supras.com/~riemer/sonict...rs/RCtech.html


Here's the excerpt:

At 8000 RPM the intake valve is opening and closing at 66 times a sec. and is only open for an average of 9 Mil/Sec. At this cyclic rate the transient time to complete the delivery of fuel, from injector to valve, is critical. This is why; Indy car injectors are very precisely targeted and timed to provide a solid stream of fuel with non-existent atomization, LBDS, "Laser Beam Delivery System". In these engines the injectors can discharge fuel, at a "just prior to valve -open position", and get it all down the hole. As the fuel impinges the hot intake valve it virtually vaporizes and mixes quite well with the incoming air forming a very homogenous charge. This is one of the most extreme situations but it's a real interesting one. As an added benefit, the latent heat of fuel vaporized in the chamber also provides charge cooling that makes the mixture denser. A denser, heavier mixture (cold and thick) will produce more power then a thin (hot and light) charge.

...

It's a known fact that you can't burn fuel until it's atomized. It's also known that you can't burn fuel without air. The most important, of all known facts is that you can't burn anything, if it's not in the combustion chamber. The secret is to provide adequately atomized fuel with as much air as possible. Adequately atomized is the Secret Word of the day. Fuel does not have to be completely atomized at the injector tip (SMD of 10um - 20um) but it does have to get past the valve to do us any good. The more condensed the fuel delivery is the faster it will travel, (regulated by discharge area and pressure) and the more accurately it can be targeted. Resent (S.A.E.) "Injector Atomizing and Targeting" studies have provided us with one of the most prominent advances in High Performance Engine Management. These test programs have concluded that "accurate impingement onto the center of the valve head is vital for good vaporization" and "The targeting orientation of the injected fuel spray is a critical parameter in fuel evaporation" also that " Fuel injected directly onto the intake valve yields a significantly better engine response" (SAE950506) What all this means is, different engine designs require a different type of injector to operate efficiently and that 100% atomization is not always required or desired. In racing situations we usually have to do the best we can with what we have, or what's available. The goal, is of course, is to do the best in all cases, and in all situations. The best injector for your engine is the one that will yield an optimal fuel-air mixture and provide the required power output consistent with smooth and reliable operation. This is our goal, and all things considered, we feel that we provide an excellent service in this very specialized field.

The whole article is a very interesting read in its own right as well.

Larry