Combustion EQ of liquid Hydrogen and liquid Oxygen

AI Thread Summary
The discussion revolves around balancing the equation for the combustion of liquid hydrogen (LH2) and liquid oxygen (LOx) in a Space Shuttle Main Engine (SSME). Initially, the participant considered the simple reaction H2 + 0.5O2 > H2O but was informed by their professor that this was incorrect due to the presence of excess hydrogen and high flame temperatures leading to thermal decomposition of water. They later concluded that the balanced equation should be 2H2 + O2 > 2H2O + H2, acknowledging the need for a specific air-fuel ratio (AF) of 6. The conversation highlights the complexity of balancing combustion reactions, especially when accounting for excess reagents and the distinction between mass balance and balanced reaction equations. Ultimately, the participant recognized the importance of the AF ratio in achieving a correct and complete equation for the combustion process.
MechStudent123
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Im working on a problem regarding a SSME and need to figure out the balanced eq for LH2 and LOx.

I thought it was simply.. H2 +0.5O2 > H2O however my professor has confirmed that it is not the case in this situation. I am stumped as to what it could possibly be, maybe excess H2? And am not supposed to include dissociation for the reaction.
 
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No idea what else it could be, this is the correct overall reaction equation. The mixture is definitely not exactly stoichiometric during the reaction, and the flame temperature is so high some of the water produced undergoes thermal decomposition (or, more precisely, the mixture never reacts to the end till it cools down a bit outside of the engine and the output flame), but in the end it is just a water synthesis.
 
Do you have contamination of the reaction by air?

BoB
 
rbelli1 said:
Do you have contamination of the reaction by air?

BoB
I ended up figuring it out

2H2 + O2 >2 H2O + H2 then baa fed for the AF of 6
 
I believe this was the eq I ended up using, not looking at it right now. *balanced
 
MechStudent123 said:
2H2 + O2 >2 H2O + H2 then baa fed for the AF of 6

Huh?
 
Then balanced the equation. I guess the ssme produces h2 as a byproduct
 
If you balance

H2 + O2 → H2O + H2

you will find no hydrogen on the right (coefficient of zero) and you will end with exactly the same equation you listed in your very first post.
 
I have researched a few articles about the combustion in a ssme. There is excess 'energy' in the form of monotomic or diatomic hydrogen. Will link the reference soon.
 
  • #10
If you know there is a AF ratio of 6 on a mass basis then you will get the complete eq
 
  • #11
Balancing the eq you stated above could result in an infinite number of solutions without the AF ratio..then again I could be wrong, haven't received my grade back
 
  • #12
Perhaps that's a bit of nitpicking on my side, but when you include excess reagents (together with the inert compounds) you get a mass balance for the process, not the balanced reaction equation. In some ways they are similar, in other ways they are distinct.
 
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