9 replies to this topic

[Dynojet]

Hello people,

I`ve been reading a past issue of RET (aug 2009) about the corvette GDI engine. Also i`ve been following the fuzz about Ferrari 458 Italia v8 GDI engine

I understand a lot of the gain claims for this method of fuel delivering, but one in special I don`t buy: the gains in horwepower due to charge cooling. Let me explain my point.

I`ve a bit of experience in engine fueled by ethanol and and witnessed one important characteristic that makes it a good fuel for engine performance: its great heat of vaporization. When you deliver this fuel far upstream of the intake valve, the fuel has time to vaporize and decrease the incoming charge temperature in good 30 dec Celsius. It cools down so much I`ve seen ice in carburetor body (yes, it was an old engine). Obviously this works also with gasoline, tough in a lesser extent.

My point is: the PFI and carburetor cools the air charge before the intake valve, the restriction for airflow. So more air mass can pass through, since it is cooler (same principle of air intercooler). But for GDI, it cools the air that is already trapped in the combustion chamber. Of course its cooling cause a lowering of the internal pressure encouraging more air to enter, but the air that is comming in is hot and with lower density and will be restricted at the valve.

So in my opinion PFI has more potetial for horsepower, albeit in expense of lower precision in fuel delivering quality (uniformity, vaporization, etc) and transient response. This is the reason I believe ultil today F1 engines use PFI and with fuel injector far from the throttle butterflies.

So, sorry for long text. What`s you guys opinion?

[bigleagueslider]

Dynojet,

With a pure race engine, there is a small gain in intake air mass flow rates past the valves if the fuel mass is delivered directly into the cylinder. With regards to latent heat effects of the fuel, I believe it is more effective if the fuel is injected during the compression stroke when the charge air temps are higher. Lastly, GDI can provide a measure of intake charge stratification using variable BOI timing, which can improve SFC rates at part throttle operation.

slider

[malbear]

Dynojet,

With a pure race engine, there is a small gain in intake air mass flow rates past the valves if the fuel mass is delivered directly into the cylinder. With regards to latent heat effects of the fuel, I believe it is more effective if the fuel is injected during the compression stroke when the charge air temps are higher. Lastly, GDI can provide a measure of intake charge stratification using variable BOI timing, which can improve SFC rates at part throttle operation.

slider

If I was going to use GDI in a race engine then I would also incorporate a conventional shower injector to the top of the intake trumpets . I think GDI would have trouble keeping up and supplying enough fuel above about 7000 rpm . yess the GDI would have an advantage with part throttle power but switch on the shower at full throttle high revs.
my 5 cents
malbeare

[cheapracer]

yess the GDI would have an advantage with part throttle power but switch on the shower at full throttle high revs.
my 5 cents
malbeare

Agreed, as I said in an earlier thread I also believe they will need both in 2013 for these reasons

[Spoofski]

If I was going to use GDI in a race engine then I would also incorporate a conventional shower injector to the top of the intake trumpets . I think GDI would have trouble keeping up and supplying enough fuel above about 7000 rpm . yess the GDI would have an advantage with part throttle power but switch on the shower at full throttle high revs.
my 5 cents
malbeare

I don't think flow rate should be an issue as it's just a function of injection pressure. Mixture preparation and wall-wetting might be tricky in the decreasing time available however.

[cheapracer]

I don't think flow rate should be an issue as it's just a function of injection pressure. Mixture preparation and wall-wetting might be tricky in the decreasing time available however.

Apparently it is a problem with the short time available, twin DI injectors maybe?

[Magoo]

It's fairly bloody expensive to sort out if you hope to wring the full benefit from it.

[cheapracer]

It's fairly bloody expensive to sort out if you hope to wring the full benefit from it.

No this is a "cost saving measure for F1"

[malbear]

Apparently it is a problem with the short time available, twin DI injectors maybe?

http://www.youtube.c...feature=relatedhyundai GDI
The Injector pump looks exactly like a single cylinder diesel pump and is stroked by 4 lobes on the cam . It is suplied with fuel at about 0.3 mpa from a conventional electric pump and boosts the pressure to 5mpa or more. trouble is in the stratified charge mode the injection has to take place late in the compression stroke so that a rich portion of fuel arives at the spark plug ready for ignition . Inject too early and the mixture is too lean to ignite. so the time for injection is short .

[J. Edlund]

Dynojet,

With a pure race engine, there is a small gain in intake air mass flow rates past the valves if the fuel mass is delivered directly into the cylinder. With regards to latent heat effects of the fuel, I believe it is more effective if the fuel is injected during the compression stroke when the charge air temps are higher. Lastly, GDI can provide a measure of intake charge stratification using variable BOI timing, which can improve SFC rates at part throttle operation.

slider

Injecting the fuel directly into the cylinder generally have a positive effect on the volumetric efficiency (no fuel vapor in the inlet air). The charge cooling effect tend to be greater too, allowing the use of higher compression ratios. Since there aren't any issues with wall wetting during transients, drivability is generally improved too.

With direct injected racing engines the fuel injection is performed during the intake stroke with one injection, injection is started after the exhaust valve have closed to prevent the loss of fuel during overlap. This improve fuel consumption. The charge is homogeneous at all load points, charge stratification is of no interrest really.

Porsche currently have a direct injected racing engine that operates with speeds up to 12,000 rpm using a 200 bar fuel pressure. With 500 bar, running to 15,000 rpm shouldn't be an issue. 500 bar is also the maximum fuel pressure current Bosch GDI injectors for motorsport applications can handle.