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Assume I have the product (exhaust gas) from a combusted air/petrol mix. The mixing ratio was richer than stoichiometric (i.e., air:fuel < 14.67 in this case), so there was no excess of oxygen.

I know the $\ce{CO2}$ and $\ce{O2}$ concentration of the combustion product, say 11% and 2% respectively. I also know that the combustion product only consists of $\ce{CO2}$, $\ce{H2O}$, $\ce{CO}$ and leftover $\ce{O2}$. (All fuel combusts to $\ce{H2O}$ and either $\ce{CO2}$ or $\ce{CO}$.)

Is it possible to approximate the $\ce{CO}$ concentration of the combustion product with that information?

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    $\begingroup$ No, that wouldn't work since there are too many unknowns. Combustion is a very complex process. In most chemistry problems "complete" combustion is typically assumed. $\endgroup$ – MaxW Nov 5 '17 at 20:17
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    $\begingroup$ You’re ignoring uncombusted and partially combusted hydrocarbons in the equation. $\endgroup$ – Jan Nov 6 '17 at 1:58
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    $\begingroup$ If you knew the H2O concentration you could estimate CO from an oxygen balance. If you knew the uncombusted fuel concentration you could estimate CO from a carbon balance. $\endgroup$ – Curt F. Nov 6 '17 at 13:22
  • $\begingroup$ @MaxW What unknowns would have to be known then? I know that real combustions are more complex, but i'm looking for an approximation, so the calculation can be kept simple. $\endgroup$ – Bart Nov 6 '17 at 14:38
  • $\begingroup$ @Jan I know, I said that in my question; that the combustion only results in CO2, H2O and CO. I assume al HC to be combusted to either CO or CO2 to keep things simple. $\endgroup$ – Bart Nov 6 '17 at 14:40

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