# Predicting incomplete combustion?

I understand the concept of incomplete combustion and that it occurs when oxygen is not a large enough supply to allow for complete combustion. My question is: how can we model combustion properly in terms of predicting the ratio of complete to incomplete combustion? Is it possible to use basic kinetic with reaction rate constants to model the rate of each reaction and then obviously model how the changing concentration from both affects each individual rate etc.

• Very interesting question - I would be very interested if there has been a study based on this. – user15489 May 26 '15 at 10:45
• This sounds possible in principle, but quite hard in practice. Wonder if anyone has some good input on it. – Nicolau Saker Neto May 26 '15 at 11:27

## 1 Answer

Before entering the kinetics realm, it is advisable to check the equilibrium. Besides the straightforward combustion reactions, you have two more, Boudouard reaction, which favors formation of $\ce{CO}$ from $\ce{CO_2}$ and Water-gas shift reaction.

The actual reactions which contribute to the equilibrium depend on the fuel. In case of pure carbon, you at least get rid of the Water-gas shift reaction.

You might need to solve the system iteratively, as the temperature of the equilibrium mixture is result of the combustion reactions, but also affects the position of equilibrium.

• so what you're saying is that I could simply model complete combustion and then use these equilibriums to model conversion of original products into those of incomplete combustion? – J-S May 27 '15 at 9:02
• What exactly do you mean by incomplete combustion? For me, simply speaking it is combustion, where there is not enough oxygen. – ssavec May 27 '15 at 9:18
• Incomplete combustion is the process of combustion in which carbon dioxide and water isn't produced but rather carbon monoxide and water – J-S May 27 '15 at 10:34
• @user2353082: yes, indeed. Is the reason for this that there is not enough oxygen? Or because the fuel leaves the combustion chamber so fast, that it cannot burn fully? – ssavec May 27 '15 at 10:49
• I'm looking at instances mainly where the fuel is stationary but the surrounding oxygen levels are not high enough to allow 100% complete combustion or at least it becomes energetically more favourable to take incomplete combustion paths instead of 'waiting' for complete combustion. For some fuels such an environment is the normal environment. – J-S May 31 '15 at 7:19