Pump Pressure
Sanity Challenged
expert_not at hotmail.com
Fri Jun 19 12:11:08 GMT 1998
Wayne, a second set of injectors would work best and easiest.
The issue is span of control. There is only so much flow thru an
injector that can be reasonable controlled. To extend that span
generally involve's greatly complicating defecation as you are beginning
to see.
If you are in control of the design of the Engine Control Unit, you
might as well make life simple. Use a second set of injectors that come
on at a certain power point.
Now, if you really do your math, look at the simple fact that at even
moderate rpm, the injector is on longer than the intake cycle and by
upper rpm is virtually running always on. Above about 3000 rpm it
doesn't make a rats ass difference if you are pulsing or simply
continously flowing.
Simplify. Turn on a fixed jet of fuel thru the nozzles at above a
certain rpm and power. Size the nozzles for the fuel injector line
pressure such that the fixed jets flow 35% to 45% percent of the total
flow at WOT. Place the nozzles as far up the individual runners as
practical - reason - maximum charge cooling at load - remember that
total power goes up 1% for every 10F temp drop.
Now when your ECU exceeds the turn on value for the fixed jets, turn
them on, and reduce your pulsers accordingly. As the load progress's
upwards past this point you simply control as "normal". This almost
doubles your span of control without any micky rat stuff and BTW has
been done successfully by many many machines.
There is no reason why the fixed jet fuel has to be the same as the
primary. It could be anything you want - depending on the racing rules.
For street, it could even be model airplane fuel with up to 60%
nitromethane. Just a fuelish thought for the sanity challenged.
>From: Wayne.MacDonald at zurich.com.au
>To: diy_efi at efi332.eng.ohio-state.edu
>Date: Fri, 19 Jun 1998 15:56:44 +1000
>Subject: Re: Pump Pressure
>Reply-To: diy_efi at efi332.eng.ohio-state.edu
>
>>If I'm reading between the lines correctly, I think what
>>you need is a larger capacity injector. Take a look at this
>>page
>
>No, What I am actually after is a way to better match the pulse length
to
>the intake cycle whilst still putting enough fuel in. The project I am
>working on is a motorcycle engine that revs to 10,500, that only gives
6ms
>per rev and even less when the inlet is open. If we use a high flow
>injector to drop the pulse length required near redline this would
shorten
>the pulse length at low revs to the point that it would be hard to get
>consistent fuel metering. My idea was to drive the injector for a
longer
>period with a lower pressure at low revs and ramp up the pump pressure
>whilst shortening the pulse length at higher revs. Is this a stupid
idea?,
>Is it a waste of time?, If not where do I get a variable pressure fuel
pump
>that I can control from my computer. Or would it be better to install a
>second set of (high-flow) injectors above the butterflies and ramp from
the
>lower (standard) injectors to the higher flow second set as the revs
>increase?.
>
> Wayne.
>
>
>
Habeneros - not just for breakfast anymore!!
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