Throttle wins system

[dcb]

hmm, the hyundai GDI has a sparkplug?!? Guess this needs some more homework, gasoline doesn't like to autoignite in a nice way maybe?

[Old Mechanic]

I am fairly sure all of the current GDI throttle by wire (gas not diesel) systems have a throttle plate.
I could be wrong but I can't see how they could idle without a form of restricting the intake airflow.

regards
Mech

[dcb]

yah mweb is right it seems, ecoboost does the injecting at the bottom of the stroke and has a spark plug. The injection event is not the ignition event. Still not sure exactly why the diesel approach wasn't good enough in gdi.

http://www.youtube.com/watch?v=wmHxiY2J8Ok

[Old Mechanic]

Gasoline direct injection - Wikipedia, the free encyclopedia

According to this you are correct DCB. Under certain conditions the throttle plate is at WOT even at light loads, but I think that is under certain load conditions, while at other load conditions the throttle plate is still used, even in the same engine.

I read about Toyota using that strategy a few years ago even without GDI.

Also they are starting to use multiple injections of smaller amounts of fuel, even during the combustion stroke, with mixture ratios as high as 65 to 1. Apparently lean burn still lives in these operational strategies, without the NOX issues that plagued the earlier Honda lean burn systems.

I would believe (just my opinion) that the considerable research into HCCI has resulted in these new fuel delivery tactics combined with the much higher pressures used to deliver fuel into a combustion chamber even at it highest peak pressure.

regards
Mech

[Old Mechanic]

Originally Posted by dcb

hmm, the hyundai GDI has a sparkplug?!? Guess this needs some more homework, gasoline doesn't like to autoignite in a nice way maybe?

Actually gasoline will auto ignite under very narrow parameters and is the objective of the HCCI developments. In doing so at super high mixture ratios, like a diesel, the emissions have become so low that after treatment may become unnecessary. This has always been the "holy grail" of combustion engine technology to actually make the engine run clean without having to clean the exhaust after combustion.

Interesting thread when I am still learning something.

Also the new Skyactiv Mazda engine is running compression ratios at 14 to 1. Apparently they are using the valve timing to effective vary the actual compression ratio with some type of atkinization strategy.

I'll check the wifes DGI Sorento tonight, to make sure it has plugs, but I am 99% certain it does and they are always providing spark. but the 1% is still possible.

regards
Mech

[dcb]

Originally Posted by Old Mechanic

...
Interesting thread when I am still learning something...

true dat

some good summary info on GDICI (Gasoline Direct Injection Compression Ignition):
Green Car Congress: University of Wisconsin and GM team investigating Gasoline Direct Injection Compression Ignition in light-duty diesel engines

[mwebb]

Originally Posted by dcb

I don't think the ecoboost has a throttle, I don't know why it would need one either. The original (i.e. 50 years ago) direct injection schemes had a throttle, but I don't think it is a requirement these days. What am I missing here?

3.gasoline engines with direct injection still use throttle plates or variable lift intake valve to control air flow to the intake and by so doing
MUST have suction throttling loss es / pumping losses

Air Fuel Ratio in gasoline engines is controlled to be near 14.7 to 1 much but not all of the time in direct injection gasoline engine systems and it could NOT be controlled if air flow were to be UN controlled

if air flow is not controlled then AFR must be maintained by varying the amount of fuel to keep AFR at 14.7 to 1 , the net effect of this would be that the engine would only have one load condition
100%
wide open throttle
all the time

the throttle plate (or variable lift intake valves ala BMW) is not an option
on gasoline engines with direct injection
or
on diesel engines with direct injection

[dcb]

Yah, when I saw the spark plug, I kinda figured they had to control the air fuel mixture somewhat. I'll wait for GDICI maybe

[redpoint5]

Originally Posted by mwebb

3.gasoline engines with direct injection still use throttle plates or variable lift intake valve to control air flow to the intake and by so doing
MUST have suction throttling loss es / pumping losses

Air Fuel Ratio in gasoline engines is controlled to be near 14.7 to 1 much but not all of the time in direct injection gasoline engine systems and it could NOT be controlled if air flow were to be UN controlled

if air flow is not controlled then AFR must be maintained by varying the amount of fuel to keep AFR at 14.7 to 1 , the net effect of this would be that the engine would only have one load condition
100%
wide open throttle
all the time

the throttle plate (or variable lift intake valves ala BMW) is not an option
on gasoline engines with direct injection
or
on diesel engines with direct injection

I very much enjoy these well explained posts; thank you mwebb.

What if air could be injected into the cylinder at the same time as the fuel instead of drawn in through a throttle. This would turn the engine into a 2 stroke, which would increase the power output relative to displacement. Smaller motors with fewer pistons could then be used, which would cut down on cost and frictional losses.