Detonation, What's it all about?
 

Hello everyone,
There has been a lot of talk on here about detonation. Since people come to this site to gain knowledge, I figured I would post an article that I found on Detonation. The article describes what it is, what are the main causes, and basic prevention. The article is a bit long with minimal pictures, but I think it is important for people to read who are new or do not understand detonation.

Here is the link to the article.
http://zhome.com/ZCMnL/PICS/detonation/detonation.html

All opinions/facts stated in the article are for informational purposes only.

NACA (old name for NASA) did a lot of research on this matter, most of which remained hidden until recently. It's very interesting and questions a lot of the "modern" theories on knock with interesting results.

NACA TR 912 is perhaps one of the most interesting as it qualitatively seperates the phenomenon of "pin-point autoignition" and "knock"; two phenomena which are still confused with eachother in technical papers even to this day: http://naca.larc.nasa.gov/reports/1948/naca-report-912/

Also of interest are these NACA reports:
http://naca.larc.nasa.gov/reports/1946/naca-report-855/

http://naca.larc.nasa.gov/reports/1946/naca-report-856/

http://naca.larc.nasa.gov/reports/1946/naca-report-857/

http://naca.larc.nasa.gov/reports/1942/naca-report-727/

Another particularly interesting one:
http://naca.larc.nasa.gov/reports/1943/naca-report-761/
Interesting indeed.

Apparently, NASA observed in hundreds of experiemnts, that the knocking reaction actually takes place in the burning, or already burned, gasses and not in the end-zone. Since NASA conducted this reseach some 60 years ago, little research has taken place to determine the actual locational origin of knock. We know lots about what knock does, and how to avoid it, but we still don't understand where it comes from or what chemical reactions precipitate it.

Previous theories from the 1920's or earlier had indicated, falsely, that knock originated in the end-gas. With the exception of NASA, it's just been "assumed" to be in the end-zone and, as a result, everyone points their research cameras there. Not suprisinginly, the actual chemical reaction responsible for knock has not been revealed.

When NASA changed it's name (it was originaly NACA) and began focusing on aerospace research, the research into internal combustion engines was stopped. It's likely that, as it was war-related research at the time, much of it was classified. It must have been filed in some cabinet somewhere for years as very few people are yet aware of it. :dunno:

At any rate, read what you can. NASA asks some very interesting questions and gets very suprising answers, many of which may be usefull to anyone doing research in this field today. :)

-Adrian

p.s. NASA also did a bunch of research on "internal coolants" (IE: water/meth injection) ... and there's a lot to be learned there as well, though it's not as interesting as their knock research. Just search the NACA site for "internal coolants": http://naca.larc.nasa.gov/

Detonation is the last thing your motor experiences before parts break through the bottom end. Caused by temperature, pressure, and low flash point (low octane).

FWIW, flash point is not octane; it can affect the knocking tendencies of certain fuels, but it does not define them. Fuels with a low octane do often have low Auto-Ignition Temperatures, but that's not always the case.

Here's an example:

-Cyclohexane has an RON rating of 110, but an AIT of only 245*C.

-Benzene, on the other hand, has an RON rating of 98, but an AIT of 560*C.

-Iso-octane (2,2,4 trimethylpentane) has an RON rating, by definition, of 100, but an AIT of 415*C.

Not that it matters to most people ... :p

What I refered to in a lay way was that low oct fuels combust at lower pressures

SaabTuner, you know too much about this for your own good. Great information you have dug up!

OT: You don't happen to be a mechanic at a local shop there in Davis do you? A couple years ago a guy with a turbo saab helped me out with my honda, worked at a local import mechanic shop there. Wondering if that is you?

Nah. Just a humble engineering/physics student here at UCD.