Direct Fuel Injection

[Gerard]

I don't know if this has ever been discussed before, but I have a simple and probably stupid question.
Lately someone told me formula one cars use port injection on their engines.
First of all, I don't even know what port injection is, and I wondered why they don't use direct fuel injection.
Teach me!

Gerard.

[Sparky]

Hi Gerard! I wouldn't say it was a stupid question. I believe the terms are a little cofusing, that's all.

A fuel injection system is a highly efficient way of metering the exact amount of fuel required to produce maximum power with maximum economy of fuel.

Some economy systems use single-point injection. A single injector, placed at the 'mouth' of the intake manifold, pulsing fuel as required by each cylinder. However, this does not produce optimum fuel atomization.
Multi-point injection is the answer. Some systems, such as the Rover Mini Cooper, use just two injectors, as the intake runners are siamesed for each pair of cylinders.
The ideal arrangement is one injector per cylinder. This allows accurate metering of the fuel, for each induction stroke of each cylinder.

Now, to answer your question. These injectors are placed in the intake port, just before the manifold to cylinder head joint. This allows the most direct injection into the cylinder, not obstructed by bends in the intake runner etc.
The manifold location also insulates the delicate injector from dissipated heat from the cylinder head. this is necessary to keep the fuel cool, and the injector functioning correctly. As far as I'm aware, the injector is never actually placed directly in the combustion chamber, as this would destroy the delicate nozzle and hence the atomization of the fuel, which is how the fuel is introduced into the intake charge. If the fuel was allowed to puddle or flow as a liquid, the combustion process would be slow, and hence power production would be restricted.

I'm sorry if my description is confusing. I hope you can make some sense of my rambling!

Basically, direct injection and port injection - the same thing.

[Leo]

Well you're wrong here Sparky. Port injection is the system you describe. But direct fuel injection (as on Mitsubishi's GDI engines, or the Mercedes 300SL 'Gull wing') has its injector directly inside the cylinder. It is indeed far more complicated to get the right nozzle for layered inginition. Mitsubishi uses a specially designed piston for this. The up side of the piston is designed so, that it creates the nescesary turbulence in the cylinder.
Why is the system not used in F1? I'm not sure, but I think it's due to the extremely high engine rpm. The system still cannot be controlled sufficiently at 17.000 rpm.

[Marco94]

Here's my contribution to this question:

In very simple terms, indirect injection uses fuel nozzles in the intake manifold, placed somewhere between the throttle and the intake valve. This way you already have a mixture of fuel and air entering the combustion chamber through the inlet valve.

When an engine uses direct injection, the fule nozzle is lacated somewhere in the combustion chamber itself. There is only air entering through the inlet valve. The mixture will have to be formed inside the combustion chamber.

This also results in the complications Leo mentioned. Whereas with indirect injection the fuel and air have sufficient time to mix while they are entering the combustion chamber, direct injection does not have this luxury.

Second complication is the injection system itself. With direct injection it is subjected to high temperatures and because of the characteristics of petrol it is hard to lubricate.

All in all, it is only now becoming iterresting to use direct fuel injection. According to Autosport magazine, Renault will use it for their new F1 engine. Rumours for now though.

I have done some diging, and found research projects on direct injection for petrol engines from Subaru, Toyota, Volkswagen and Ford (2-stroke, Orbital). I have also heard seen what is probably a prototype cilinder head, with DI, from Opel when I visited a engine overhaul company some years ago.

[This message has been edited by Marco94 (edited 07 December 1999).]

[Sparky]

Jeez Guys!! I never knew that! Sorry Gerard! Talk about the blind leading the blind!!

The technical difficulties with this set-up must be immense! What are the benefits? Surely more con's than pro's? No?

Anybody fancy a job as tech moderator?

[Leo]

Mitsubishi claims: more power and a lower fuel consumption.
The main advantage of direct injection is that you can use very lean air/fuel mixtures. I think Mitsubishi uses up to 60:1 (air:fuel), where 14:1 is the regular value. This has a positive effect on the fuel consumption.
I can't explain the 'more power' part, sorry...

[This message has been edited by Leo (edited 06 December 1999).]

[THR]

More power because they can run the mixture richer because its more efficent?

Having such low rates of feul comsumption in F1 car would be silly i think, so they would run it richer?

[Marco94]

THR, using such lean mixtures as Leo mentioned in not silly at all. If you can get the same power while using a lot less fuel, your car will be lighter and thus quicker. Alternatively, you will have more power with the same fuel consumption. Also quicker. That's what its all about.

[THR]

Yes, but...

wouldnt it be better to run a richer mixture and have even more power?

of course there is a trade off to weight/power.

but in f1 when the cars are under the 600kg anyway it wont matter that much

[Marco94]

At the present time engine designers are well able to use stratified injection to run very lean mixtures. I have no data as to how efficient it is (relative to max performance of course), but it does save fuel.

Running your mixture richer wouldn't bring you anything. If you use a lean mixture, you end up not using all the air. That is not "part of the car." When you run richer mixture you don't use all the fuel. And that is contained inside the car! You would then basically just throwaway fuel, so why take it with you.

However all these theories assume partial load on the engine. When asking for maximum performance it may well be that there are no benefits. Of course things are very subtle, unfortunatly for us engineers.

[yelwoci]

A company called Adrenaline Research have developed (1999) an new ignition system.
Uses a standard CDi to drive the initial spark but then puts a 100A (YUP!) over the same path using a radio technology microwave channel.
The Plasma ignition can fire 22:1 air:fuel ratios and at normal stoichimetric ratios burns all the fuel even from cold. In F1 they recon its worth between 3-5% in hp!

Showed the stuff to a radio ham friend who builds his own kit.
He said it would work but the tricky part would be making small and packaged for a car.

The SmartFire unit is the sixe of two coffee mugs.

Looked at their web site $50,000 for a setup is a little outside my range!

See http://www.atlasf1.com/99/oct06/burckmyer.html http://www.adrenalineresearch.com/
(Its slow!)

IanC