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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: iScience on October 12, 2013, 07:43:46 PM

Title: does oxygen spontaneously combust in high heat?
Post by: iScience on October 12, 2013, 07:43:46 PM
at high temperatures in a combustion engine oxygen spontaneously combusts which limits the efficiency of an internal combustion engine. But i just wanted to be sure, is it the oxygen that's doing something with itself (spontaneously "combusting" by itself) or is it that the heat breaks apart the O-O bond and the single oxygen then reacts with the hydrocarbon?
Title: Re: does oxygen spontaneously combust in high heat?
Post by: billnotgatez on October 12, 2013, 08:02:24 PM
can you post a link that says this
Title: Re: does oxygen spontaneously combust in high heat?
Post by: iScience on October 12, 2013, 09:34:19 PM
what do you mean?
Title: Re: does oxygen spontaneously combust in high heat?
Post by: billnotgatez on October 12, 2013, 11:03:39 PM
where did you get your information from
Quote
high temperatures in a combustion engine oxygen spontaneously combusts
Title: Re: does oxygen spontaneously combust in high heat?
Post by: curiouscat on October 12, 2013, 11:56:10 PM
Quote from: iScience on October 12, 2013, 07:43:46 PM
at high temperatures in a combustion engine oxygen spontaneously combusts which limits the efficiency of an internal combustion engine. But i just wanted to be sure, is it the oxygen that's doing something with itself (spontaneously "combusting" by itself) or is it that the heat breaks apart the O-O bond and the single oxygen then reacts with the hydrocarbon?

They probably mean knocking.

Combusts without a spark plug initiation.
Title: Re: does oxygen spontaneously combust in high heat?
Post by: magician4 on October 13, 2013, 12:02:48 AM
the thermal dissociation of oxygen will take place, yes
... starting at approx 3500 K , give or take, to be more precise

temperature in the combustion engine will reach approx . 2500 K max. (except of the initial plasma formed by the ignition plug: this is much hotter)


think


regards

Ingo
Title: Re: does oxygen spontaneously combust in high heat?
Post by: iScience on October 13, 2013, 01:26:09 AM
Quote
where did you get your information from

my thermo class: we were talking about how the compression ratio affects the efficiency and how the compression ratio is limited by how hot the chamber is allowed to be before the oxygen spontaneously dissociates and leads to combustion
Title: Re: does oxygen spontaneously combust in high heat?
Post by: Borek on October 13, 2013, 03:13:05 AM
Oxygen doesn't combust, period. What you mean is that the mixture of fuel with air (containing oxygen) spontaneously detonates when heated.
Title: Re: does oxygen spontaneously combust in high heat?
Post by: magician4 on October 13, 2013, 03:24:19 PM
in addition:

depending on the very type of engine (i.e. the compression factor) , the compression will lead to temperatures in the ballpark of 300°C to 700°C before ignition. this is way beneath any relevant thermally triggered oxygen dissociation.

what happens however (with for example diesel engines) is, that oxygen will crash into an alkane , and abstract a hydrogen:
R-H + O2   :rarrow: R. + HOO.

... and these two radicals will start the chain reaction


regards

Ingo