[Diy_efi] Knock sensing - water injection

[Greg Hermann]

At 9:28 PM 2/24/05, Gary wrote:
>> "slowing down the burn rate' is about the opposite of what you want to
>> avoid end gas detonation---

Getting rid of squish increases detonation. Adding/tightening squish
generally reduces it. Squish most definitely increases the rate of flame
propogation.

End gas detonation is a function of time the mixture spends at high temp
and pressure. Reduce the time, and the tendency to detonate is reduced.
Ref: Obert, 'Internal Combustion Engines and Air Pollution'.

Yes, higher octane fuel is more resistant to detonation, and, as a
by-product, has a slower burn rate. But, see above.

Adding an internal coolant--water, methanol, or even more fuel -- reduces
the temp/pressure side of the detonation equation.

Water ALSO 'facilitates' combustion. Ref: Irwin Glassman, 'Combustion'.

There are other tricks, as well--try looking at what Waukesha did with a
second spark plug located so as to light and burn the end gas well before
the flame front raised its pressure/temp sufficiently for it to get into
the detonation area !! And--THIS was done on a FLATHEAD, of all things !!!

BTW-- Obert and Glassman are guys who did original, basic research--NOT
parrots !

Greg
>
>There are those that believe running a richer mixture delays the onset
>of detonation, due to a cooling effect of the extra fuel.  Actually, fuel is
>a
>rather inefficient means of cooling the combustion mixture, especially
>when compared to H2O.  Although running with a richer mix can result
>in cooler operation, it is really a secondary effect, and not the true
>cause.
>
>Combustion speed reaches it's max at around 50-75*F RICH of peak
>exhaust gas temp.  Either by adding additional fuel, or taking a step in
>the opposite direction, by operating the engine 50-75*F LEAN of peak
>exhaust gas temp, will SLOW the combustion rate, and DELAY the point
>at which peak chamber pressure occurs, and go to great lengths in
>eliminating the risk of detonation.  Combustion is most efficient when
>the point of peak combustion pressure occurs at 16-18* ATDC.
>Therefore the true reason for the delay of detonaton from richer mixture,
>(or better yet, from a leaner mixture) appears to be due to the peak
>combustion pressure occuring LATER.  So Bear.... AFAIC, this suggests
>the frame front is being SLOWED down.   The research was performed
>by General Aviation Modification, Inc. located in OK.
>
>GAS
>
>
>----- Original Message -----
>From: "Greg Hermann" <bearbvd at mindspring.com>
>To: "A list for Do-It-Yourself EFI" <diy_efi at diy-efi.org>
>Sent: Thursday, February 24, 2005 8:22 PM
>Subject: Re: [Diy_efi] Knock sensing - water injection
>
>
>> At 10:32 AM 2/25/05, Geoff Harrison wrote:
>> >Hi all.
>> >IIRC, knocking = pre-ignition = detonation,
>>
>> NOPE.
>>
>> Pre-ignition does NOT equal detonation.
>>
>> The other things which you are stating as 'sort-of' facts are also pretty
>> wildly distorted.
>>
>> If you look through the archives, there is PLENTY of info on what H2O
>> injection can do, and why it does it. Your so-called 'rate of expansion'
>> ain't it at all--but water's very high latent heat of vaporization has
>> quite a lot to do with it--as does its ability to facilitate hydrocarbon
>> combustion.
>>
>> "slowing down the burn rate' is about the opposite of what you want to
>> avoid end gas detonation---
>>
>> Greg
>
>
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