Combustion reaction - discrepancy between hand calc. and computer sim

[engineer23]

Combustion reaction -- discrepancy between hand calc. and computer sim

I am considering the reaction C2H4O (liquid) --> CO + 0.5CH4 + 0.5H2 + 0.25C2H4
I calculated the flame temperature when the reactant is at 298 K and 20 atm using H(reactants) = H(products) to get Tfinal = 945 K.
I then used a combustion software package and got a flame temp. of 1289 K.

By LeChatelier's principle, it makes sense that dissocation of products decreases with increasing pressure (as the equilibrium shifts toward the reacants). My hand calculation did not take dissociation into account -- less dissociation at higher pressure means a higher flame temperature. But 36% higher? Is this reasonable or too large a discrepancy between simple hand calculation and the direct numerical sim?

The reaction at equilibrium is 2CH4 --> 2H2 + C2H4. Does this figure into the hand calc. or computer calc. somehow?

 

[jaap de vries]

Does the computer calculation take into account that you start of with a liquid? Was it constant pressure combustion which program did u use to model?

I always like this program http://navier.engr.colostate.edu/tools/equil.html to do equil calculations with however I could not get a result for the above reaction maybe you have more luck.