gemellocattivo.com :: View topic - How is a "Pseudo-Direct Injection" system tuned with a WBO2?

It's a trade off.

The fuel with a PFI engine will always take some heat from the valve and port. You are right and valve timing can improve this. However at high speed/load you would have to keep injector duty cycle below ~25% which might not be possible.

If you are very knock limited, an extra degree of advance can result in a % or more indicated torque improvement and DI can allow a few degrees.

We have tested upstream (top of the runner) and downstream (directly at the port) injector locations and made slightly more power with upstream injectors than any calibration of the downstream injector (on E85). We have not tested DI yet, but I'm looking at it.

The important piece of this thread is optimizing the air cooling prior to the intake valve closing.....to stuff more air into the cylinder. With DI you know you are cooling the air but the intake is closed so while you may be able to run slightly higher CR you don't make a lot more power. With standard port injection more of the cooling is done on the valve and port walls which also doesn't help make HP. But with a short, well timed fuel pulse most of the latent heat to vaporize the fuel comes from the air and you gain .....5%ish on air density and therfore hp & torque.

Didn't one of the Japanese OEM's (Toyota probably) have an engine out for a few years that used both GDI and PFI? Under some conditions only the port injectors were firing and under others, the direct injectors were, and probably under still others, both were.

Seems like it was their last generation of V8's, perhaps the UR family?

mk e wrote:

I was under the impression that DI systems like to inject while the intake valve is still open.

Author:	apalrd [ Mon Nov 02, 2015 9:47 pm ]
Post subject:	Re: How is a "Pseudo-Direct Injection" system tuned with a W
It's a trade off. The fuel with a PFI engine will always take some heat from the valve and port. You are right and valve timing can improve this. However at high speed/load you would have to keep injector duty cycle below ~25% which might not be possible. If you are very knock limited, an extra degree of advance can result in a % or more indicated torque improvement and DI can allow a few degrees. We have tested upstream (top of the runner) and downstream (directly at the port) injector locations and made slightly more power with upstream injectors than any calibration of the downstream injector (on E85). We have not tested DI yet, but I'm looking at it.

Author:	mk e [ Tue Nov 03, 2015 5:50 am ]
Post subject:	Re: How is a "Pseudo-Direct Injection" system tuned with a W
apalrd wrote: It's a trade off. The fuel with a PFI engine will always take some heat from the valve and port. You are right and valve timing can improve this. However at high speed/load you would have to keep injector duty cycle below ~25% which might not be possible. If you are very knock limited, an extra degree of advance can result in a % or more indicated torque improvement and DI can allow a few degrees. We have tested upstream (top of the runner) and downstream (directly at the port) injector locations and made slightly more power with upstream injectors than any calibration of the downstream injector (on E85). We have not tested DI yet, but I'm looking at it. Air is flowing on my engine for 240 degrees so I can be spraying fuel into the moving air with a 33% duty cycle.....which depending where the HP comes out is just about exactly where I'll be. I've never tried this before so no data I've personally collected, but my motec dealer told me he does all his engines this way and they all make more power from a V8 at 6k to sportbikes that came with high/low injection, always a 3-5% increase...or so he says. As for knock limited I guess the key is don't go there. It just works out better to go low enough compression to allow spark to be optimized for power, not optimized for knock avoidance. Going from 9:1 to 13:1 only adds about 8% more hp IIRC which is roughly what you lose with a 2-3 deg timing retard so unless it's a combination you know well I've always found its just best to be conservative on CR. I've never even installed a knock sensor on anything....playing with fire in my mind.

Author:	cribbj [ Tue Nov 03, 2015 7:38 am ]
Post subject:	Re: How is a "Pseudo-Direct Injection" system tuned with a W
Didn't one of the Japanese OEM's (Toyota probably) have an engine out for a few years that used both GDI and PFI? Under some conditions only the port injectors were firing and under others, the direct injectors were, and probably under still others, both were. Seems like it was their last generation of V8's, perhaps the UR family?

Author:	TheDarkSideOfWill [ Tue Nov 03, 2015 7:40 am ]
Post subject:	Re: How is a "Pseudo-Direct Injection" system tuned with a W
mk e wrote: The important piece of this thread is optimizing the air cooling prior to the intake valve closing.....to stuff more air into the cylinder. With DI you know you are cooling the air but the intake is closed so while you may be able to run slightly higher CR you don't make a lot more power. With standard port injection more of the cooling is done on the valve and port walls which also doesn't help make HP. But with a short, well timed fuel pulse most of the latent heat to vaporize the fuel comes from the air and you gain .....5%ish on air density and therfore hp & torque. I was under the impression that DI systems like to inject while the intake valve is still open.

Author:	mk e [ Tue Nov 03, 2015 9:38 am ]
Post subject:	Re: How is a "Pseudo-Direct Injection" system tuned with a W
cribbj wrote: Didn't one of the Japanese OEM's (Toyota probably) have an engine out for a few years that used both GDI and PFI? Under some conditions only the port injectors were firing and under others, the direct injectors were, and probably under still others, both were. Seems like it was their last generation of V8's, perhaps the UR family? I read that the the little subaru/scion 4cyl has it...subaru engine but toyota controls I think they said

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Author:	mk e [ Tue Nov 03, 2015 9:40 am ]
Post subject:	Re: How is a "Pseudo-Direct Injection" system tuned with a W
TheDarkSideOfWill wrote: mk e wrote: The important piece of this thread is optimizing the air cooling prior to the intake valve closing.....to stuff more air into the cylinder. With DI you know you are cooling the air but the intake is closed so while you may be able to run slightly higher CR you don't make a lot more power. With standard port injection more of the cooling is done on the valve and port walls which also doesn't help make HP. But with a short, well timed fuel pulse most of the latent heat to vaporize the fuel comes from the air and you gain .....5%ish on air density and therfore hp & torque. I was under the impression that DI systems like to inject while the intake valve is still open. You might be right. I guess for them the key is to start injecting after the exhaust closes so they certainly could be.....not sure

Author:	apalrd [ Tue Nov 03, 2015 10:38 am ]
Post subject:	Re: How is a "Pseudo-Direct Injection" system tuned with a W
Technically they could inject at any time after the exhaust valve closes (or even slightly before, if they know the fuel can't make it through the cylinder in the remaining time). If they are running homogenous (I believe all current GDI production engines do homogenous, I haven't heard of one which actually stratifies yet) it would be beneficial to inject as early as possible to get the best charge mixing. DI engines suffer from this a lot, which is why DI engines are now known for having issues passing the new very strict Diesel soot limits. If the charge isn't well mixed, there will be locally rich and locally lean pockets, and the locally rich pockets will produce soot. Split injection is also an option, two or three separate injections could hit different parts of the cloud as it moves through the cylinder for even better mixing. For stratified, the injections will be much later since the cloud velocity is important (usually the cloud needs to disperse just enough so there is roughly lambda 1 at the spark plug). Where the piston is during this is crucial since the piston drives all of the in cylinder flow.

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