Hmmm, fuel controled RPM?

Free and Open Source Engine Management discussions excluding more specific things on this board.
Post Reply
User avatar
jharvey
1N4001 - Signed up
Posts: 1607
Joined: Tue Jun 10, 2008 5:17 pm

Hmmm, fuel controled RPM?

Post by jharvey »

I've been thinking of the pro's and cons of using fuel only as a RPM limiter, no butter fly, no idle bypass, ect. I'm sure there are good reasons for decreasing intake pressure for idle, but I don't know them off the top of my head.

I seem to recall redundant system(s) are handy for limiting power in the event an injector is stuck open. Also controlling the air is easier than controlling the fuel charge (partly Xtau issues, partly fuel metering tolerance issues).

I also seem to remember that burning lean can be harder to ignite and burning lean can cause erosion. Both leading to engine damage.

However, and humor me, if you drilled a hole down the center of a spark plug, then installed it in an engine with a center mounted spark plug, couldn't you inject fuel through the plug? Placing your charge in a tower in the center of the cyl cavity. Then when you spark, you would spark in an area with a higher concentration of fuel, (where it's not considered lean) which would then increasing the chances of combustion? As well as reducing the ping on the side walls, preventing erosion and emissions due to the extra air cushion around the charge.

I think VW does a similar thing, called GDI. Any how, I think about it because I've got a small engine with a center mounted spark plug. The plug on these engines is also quite short, making it easier to drill a hole down the center.

Thoughts?
User avatar
Fred
Moderator
Posts: 15431
Joined: Tue Jan 15, 2008 2:31 pm
Location: Home sweet home!
Contact:

Re: Hmmm, fuel controled RPM?

Post by Fred »

Lowest vac = least fuel wasted idling.

As for the rest, yeah, like you said, just go and buy any modern DI stratified charge engine and be happy :-)

It works because when you ignite it's rich and won't knock, and when the flame gets past the richness, the piston is well beyond tdc and it won't knock.

The result is 13:1 compression and 91RON/86AKI gas and good performance with no knock.

However, they aren't all that reliable yet and the fuel systems run enormous pressure etc etc.

Fred.
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!
Post Reply