cool info guys!

ive heard of (dont know if its true) that they(no idea who) are trying to achieve higher fuel pressure levels coming from an injector.

imagine having hundreds if not thousands of PSI coming out of an injector, wouldnt this go a long way in helping fuel atomization. of course i imagine the injectors would have to be designed to operate at such high pressure and fuel lines etc to handle high pressure also.

i know we cant simply just jack the FP up on our cars as it causes the FP to be so high the injector can have a hard time opening.

anyone got any more info on this?

 

Not to throw a wrench in anything, but the typical stock style EFI setups fire the injector on a closed intake valve. This is done to vaporize the fuel on the hot valve before it enters the combustion chamber.....better atomization.

Also, as to power vs power on EFI vs Carb..... Anytime you bend the air flow, you lose energy. Carb setups typically have a much straighter airflow shot at the valve....& therefore lose less energy & make more power. (Stock style Ford EFI intake that turns the air 180 degrees in the plenum which KILLS airflow velocity....boosted or not).

 

^ I was under the impression that as the fuel hits the valve it tends to pool up, not vaporize.

 

Check out Direct Injection system on some of the newer OEM vehicles. One example if the turbo engine in the MazdaSpeed 6. Direct Injection fires the fuel directly into the combustion chamber at very high pressure.

 

Or fuel pressure on diesels.

 

Sure, when the motor is cold fuel will puddle. & Obviously if the valve was open when the injector sprayed fuel, it'd go directly into the chamber.

When the motor is up to operating temp the intake valve is HOT.....hotter than the head & coolant running through the motor. Combustion chamber temps get very high. The fuel will flash vaporize when hitting a surface at that temp. It'll also cool off the valve & air charge when it obsorbs all that heat/energy.

 

Have you actually looked at these setup's tho? You paint a picture of an injector pointed directly at an intake valve that's only 1" away. In the SBF the injector is located in the intake manifold at least 5" away from the valve and at a right angle to the valve. It's far from spraying the fuel right onto the valve.

Also, the injection event is timed so that the fuel is injecter while the valve is open, not closed. Although at high injector duty cycle, there is a lot of overlap.

 

Yes, I have looked at these setups. The injectors are mounted at the exit of the intake manifod, near the head and points very close in line to the valve head. The injectors start spraying fuel before the intake valve opens.....on a stock HO 5.0. (as RPM increases, the injectors fire earlier) On a motor with a large camshaft, with lots of overlap the injectors are still timed the same & thus the injectors may or may not be firing on a closed intake valve (depends on the size of the cam).

 

OK. But as you reach 90% duty cycle, most of the time that the injector is spraying the valve is closed. Without any airflow the fuel is hitting the other side of the manifold and the intake port floor... not the valve. This is why you run into puddeling problems. You cannot draw a straight line from the injector tip to the intake valve... so how could the injector spray onto the back of the valve?

 

How hot is the intake manifold? 180+ degrees?
Most of the fuel will vaporize on contact with the hot intake/valve.

All this points to more efficiency from direct injection into the chamber....like the good'ol Diesels with 25000+psi injection pressures.

 

Sure it'll vaporize. I doubt on contact tho... not when there's a nearly constant flow of cold fuel hitting that part of the manifold. It WILL puddle, especially when you talk about 120lb injectors. Back to the topic at hand tho... I still believe that you will see better vaporization the further the injector is away from the valve. Non-vaporized fuel will fall to the intake manifold's floor and will vaporize then... with more time to do so. More surface area will mean better vaporization.

Direct injection is a whole other animal. I suspect that there's a reason why this isn't done tho. If there was a worthwhile increase in economy, power, or fuel efficiency you can bet that the major engine manufactures would be doing it. It's far from a new idea after all.

 

Change is a hard thing to accomplish when something ends up in the hands of consumers(due to complexity and expense). Direct injection is now making its way into new non-diesel cars. Audi, Cadillac, Chevy, Pontiac, and VW all have direct injection vehicles.

 

Not sure I follow you here... what do you mean?

Interesting to hear that it's finally being used in newer vehicles. But I'm still skeptical towards it's value... In the period of 2 years, pretty much every major engine manufacturer converted to EFI. That was certainly a big change which involved brand new technology and it was implemented very quickly because the manufacturers recognized the value. Direct injection technology has been around for decades... yet is only beginning to be used now.

Maybe direct injection is more difficult to do with gasoline? Perhaps there isn't a lot of benifit?

 

Carb vs. Fuel injection...... READ THIS...

http://www.dragracingonline.com/technical/vii_6-sonny-1.html

 

I remember reading an SAE paper quite a while ago talking about DI gasoline fuel pump design. In the introduction they discussed how it was more difficult to design a high pressure pump for gasoline because gasoline does not lubricate as well as diesel fuel. Obviously they have it figured out now.

One benefit to DI is the potential for running in Stratified Charge mode. Basically, you can throttle the engine by the amount of fuel you inject, like a diesel, with manifold pressure at atmospheric. Throttling conventionally via manifold pressure with an air valve creates a pumping loss (negative work) during the intake stroke, so you can gain efficiency here. DI can allow higher compression ratios due to fuel cooling from latent heat of vaporization. Higher compression ratios are more efficient thermodynamically because the chamber volume is a volume that does no work. It's the volume swept by the piston that does the work. The problem with 'fuel throttling' is that, IIRC, gasoline does not spark ignite well in lean mixtures. Stratified Charge will concentrate the fuel that is injected near the spark plug so that the localized AFR is rich enough to ignite. I don't think that is something that is easy to tune. Also, I think lean mixtures create High NOx? so there may have been emissions difficulties as well. IIRC, potential efficiency improvements of 30% overall, give or take?

This is all from memory ~5 years ago, so you may want to research it yourself to be sure. Feel free to correct any errors you find.

 

I believe Porche is claiming a 10% increase in performance along with better fuel economy from their direct injection motors compared to the traditional EFI setups.

Fuel pressure has been a major hurtle with direct injection.

 

I believe Otto versus Diesel cycle is something like 15% according to the book I have.

 

Interesting. So their experience has been that carb looks better on the dyno, but EFI is faster at the track.

Too bad they don't disclose why they think their EFI setups have dyno'd slightly less. If it's from the cooling effect, I wonder what would happen if they went with throttle body injection? The best of both worlds?

 

That would make sense. Thanks for sharing.

 

Bottlefed.. did you read the hotrod article posted earlier. It explains why the injectors are placed at varying distances from the valve.