[Diy_efi] Knock sensing - water injection

[Greg Hermann]

At 4:36 AM 2/25/05, hugh at sol.co.uk wrote:
>Greg,
>
>Assuming you agree with the concept that pre-ignition is caused by the
>cylinder pressure in general reaching a critical pressure and detonation is
>caused by local hot spot / high pressure area.
>
>It then follows that squish will go forom becoming a combustion improving
>device to one that causes a local increase in pressure and can therefore be
>a point of detonation.
>
>How many big power drag engines do you see with squish still in place?
>
>Hugh

Burning nitro is a WHOLE different deal---

Greg
>
>Original Message:
>-----------------
>From:  bearbvd at mindspring.com (Greg Hermann)
>Date: Thu, 24 Feb 2005 23:22:12 -0700
>To: diy_efi at diy-efi.org
>Subject: Re: [Diy_efi] Knock sensing - water injection
>
>
>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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