Starting fuel load question.

[Bernd Felsche]

Con Torrisi tapped away at the keyboard with:

> Cold is ambient of about 15-20 Celsius. In my system the cranking
> value is regardless of hot or cold, the cold enrich works only
> when the engine is cold and begins decaying until it cuts out at
> about engine temp of 60 deg.

That 60 degrees is the coolant temperature, isn't it? Your inlet air
temperature could be as cold as 5 degrees and as hot as 45 before
it's subjected to heating from the engine.

> I have high volume injectors and every engine type is different.
> What would be useful is know is how much extra fuel is required
> for cold cranking compared to (say) hot idle. Then I can work it
> out. Cold where I live (Brisbane Australia) is relatively constant
> and I see that most systems would have to cope with a much wider
> variation of temperatures. However, my system is much simpler and
> suits my application reasonably well.

The amount of necessary cold enrichment depends on two factors;
 1. fuel vapourization at a particular (air) temperature
and
 2. inlet wetting.

The vapourization issue is fairly straightforward to determine;
the fuel manufacturers probably have constants that define the
vapourpressure w.r.t. temperature for the fuel you're using.

Wetting is something specific to the geometry of the engine and
dependent on the engine temperature.

The mixture during cranking is usually set quite rich to increase
the chance of ignition and to cause initial wetting of the inlets.
However; too rich and it won't ignite either due to a lack of O2.
A lambda of around 0.9 is probably as rich as you'd want to go with
warm engine and air.

The initial amount to inject is sufficient to cause wetting of the
manifold, plus that required for ignition. Once wet, the amount of
wetting stays relatively constant with temperature - unless there's
been a lean mixture phase for one reason or another.

One strategy that might work for you, as you don't know the wetting
amount, would be to reduce the injected amount for wetting with each
cycle of the engine. The management system may be able to learn and
"remember" and adapt to the mixtures that work for particular
combinations of air and engine temperature so subsequent warm/hot
starts from around those temperatures would require fewer cycles.

-- 
 /"\  Bernd Felsche - Innovative Reckoning, Perth, Western Australia
 \ /      ASCII ribbon campaign | I'm a .signature virus!       |
  X       against HTML mail     | Copy me into your ~/.signature|
 / \      and postings          | to help me spread!            |
----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org