Water injection (was: Re: fuel cooling intake air)

[Bruce Plecan]

> It is my general perception that diesel engines runs slower than SI
engine.

Our small diesel (least as called by another in another post) is run at
6,000 to 6,500 rpm
My gas engine I spin to 5,500 rpm.

> Also, it seems that the benefits of water on combustion are realized at
high
> rpm "It is important to note that these improvements came at the upper end
> of the power range where sufficient fuel and air was available to have an
> excess of energy that could not be converted to usable pressure in a
timely
> manner." said Mr. Harris.
> So I'm interested in knowing the approximate speed referred to as "the
upper
> end of the power range". If we are talking F1 engines, it may well be
around
> 18000 rpm or more.

It would seem like the upper 25% might be a resonable figure.
Say 14K+ on that app..

on a 9K engine 7+K

2K rpm probably over 1.5K.

Again this is taking in particular response to that one item in an area
where there are more factors.

> It is my understanding that the combustion should take at most 40-50 crank
> degrees or so, thus there must be a speed above which this cannot be
> realized, the crank turning too fast, and power is wasted.
> Water, speeding up the combustion as I've just learned, should help
release
> the energy quick enough.

There are many elements.
If the WI allows for more boost, then retarding the timing *might* make more
HP.  Folks often sem to obsess on advancing, and sometimes miss other items.

> Also, IMHO, the maximum torque speed (as in your statement above) is
> certainly not a speed where any "excess of energy" cannot be "converted in
a
> timely manner" - or it would not be the "maximum torque" speed, indeed.

You've lost me with that statement.

> Then, given that, as noted by Mr. Colon, "the total energy is of course
the
> same" and that you need "sufficient fuel and air" so I still fail to see
how
> you can _gain_ anything by making your engine swallow its air already
> saturated with water vapor.

Saturated?. At what level is that?.  My version is, just experimenting with
the mine amount of timing, lean best performance, plus 1-2 graduations
(depends on fueling adjustments), and min water for best performance (again
plus a couple percent).  I consider reliability, as a very important
concern.

 I argue that you _recover_ a lot of power that
> would otherwise be lost due to abnormal combustion, and I pretend that
you'd
> probably recover more by injecting the water as late as possible. This
claim
> in backed up by information posted on the ERL web site (see Mr. Dennis
Doza
> II's post) where someone saw a power increase of 5-20%, IIRC, by injecting
> water directly inside the combustion chamber.

All kinds of things change with Direct Cylinder injection.  It's just sooo
much more effecient and accurate (ok, can be)..

 They claim the gain comes from
> vapor pressure, so no complex thermochemistry here, according to them.

I can claim all kinds of things.  So all information posted today, just
stops because of their claim?.
That just make sense to me.

> Please note that I mentioned the potential gain due to vapor pressure,
> thanks to in-cylinder evaporation, in my original post.
> Reports and testimonies I've read so far in this thread (and related ones
> recently posted) supports more the "detonation retardant" due to
> "in-cylinder cooling" aspect of things, allowing to safely reach MBT by
> proper spark advance setting,  than the "combustion stimulator" side, so I
> come to suspect that this benefit, while apparently tangible and real, is
> only seen at very high engine speed, probably well above a typical diesel
> operating range, running lean of top of that ( "20 percent (or more) lean
of
> stoichiometric" [at maximum engine power] - Heywood 10.1, p492)

Like I said we tune for performance, so I can't guess at actual ratios, if
not visible at our 6,500 rpm I doubt it would be much on your 8,000 rpm
engine either.  If I correctly understand what your saying.

so there is
> not that much "excess of energy" to be released anyway. Also, what Saab is
> able to achieve in a research lab may not be easy to reproduce at home.
For
> example, I know they use a variable compression engine in their quest for
> maximum efficiency.

Or anyone with less then oem manufacturing analyse.
Grumpy

> The speed issue may explain why I saw nothing on my own engine, which only
> runs up to 8000 rpm, speed at which gasoline seems to burn fast enough
(too
> fast, indeed, as I'm facing detonation when I insist with spark advance).
>
> Axel


----------------------------------------------------------------------------
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