Methane And Oxygen Combustion - info source 1

[Speedy]

Hi Folks,

I am looking for a good source (ideally a handbook reference) of information on the combustion properties of both methane and hydrogen in oxygen at different pressures pre-ignition (up to 40 bar).
This is basic stuff I know but when I work through calculations I find I am making assumptions about ideal gases etc.

I did the basics years ago in college, but it has been a while.

Thanks in Advance,
Speedy
[Atom] [Atom]

 

[Montemayor]

Speedy:

You are right; this is so elementary that you will find it in any high school Chemistry text book at your local library. I know, because I've taught Chemistry and I learned this basic combustion information in high school.

Please don't take this response as condescending, because it certainly is not meant to be. My point is that the solution to your need is a simple and inexpensive one - and this should be good news.

Good luck in researching the oxidation properties of Hydrogen and Methane.

 

[Speedy]

Thanks Montemayor,

The reason I ask this is, I have an application that involves the combustion of both Hydrogen an Methane at twice stoichiometric, that is twice the oxygen needed.

For identical conditions, vessel size, pre-ignition pressure etc, the Hydrogen is producing twice the temperture peak of the methane.)There are on 2 different test rigs). The thermocouple is placed well within the wall of the vessel so temperature rise is only about 70C (for hydrogen).

I have worked tru the calculations and I reckon the hydrogen should only be slightly higher, not twice as it is.

I assume that this is down to slight variations in the mounting of the thermocouple, air insulating gaps etc.

I have used 285.8Kj/mol for H2 and 890 for Ch4.

Could it be due to differences in the amount of heat tied up in the heat of vapourisation of the water. (Hydrogen is producing 20% more water).

Any comments appreciated.

Cheers,

Eamonn

 

[25362]

Eamonn

Just for clarity. What are the peak temperatures you are getting ? Are you using air or oxygen for combustion ? Are you comparing equal volumes of hydrogen and methane ? There is always the possibility of a false temperature reading.

 

[Montemayor]

Eamonn:

I'm trusting that you made the calculations appropriately, taking into consideration some things you haven't stated:

1) What is the basis for the two different combustions? Are you basing it on the same moles of fuel? the same volume of fuel? the same mass of fuel?

2) Are you doing the combustion in a heated calorimeter? If not, a lot of the heat will go into heating the calorimenter instead of having an adiabatic combustion reaction. The result will be cooler products of combustion.

3) The combustion of pure H2 will produce pure water + excess Oxygen; the combustion of Methane will produce water + CO2 + excess Oxygen. Depending on your basis for comparison, you may or may not have more water produced.

4) Are the two combustions taking place under the same pressure? Are both yielding superheated water vapor (steam) and no condensed water vapor?

25362 has some good, educated questions. It makes a lot of difference if you are using pure Oxygen or air as your O2 source. All these questions have to be answered in order to offer some degree of constructive opinion.

 

[Speedy]

To answer your questions;
Peak Temps are 58C for Hydrogen, 27C for Methane.
Using pure O2 (although the chamber is full with air initially).
The gases are supplied from regulators to pre-compression type pistons. The ratios of the CSA's of the pistons are 4:1 and 1:1 (hence twice stoichiometric). The pressure settings are equal pre-compression, 4Bar/4Bar for Hydrogen/oxygen and 9/9 for methane. Mixed gas pressures pre-ignition are the same, 11.5 Bar in both cases. This 11.5 was the bases for comparison.
I know there are slight variations in the compressibility of the gases and the temperatures pre-ignition may be different but this doesn't explain everything. Also these are industrial type machines and not calorimeters as such.
The purpose of the thermocouple is to recognise ignition. Opening of the chamber pre-ignition, as you can imagine poses a significant health and safety risk.
I imagine that when peak temp is recorded, all water is in superheated form. If you look tru the equations for equal moles of gases, the Hydrogen does produce 20% more water (in any form). To me this looks like where the heat goes, and thus teh lower peak temp.

Speedy.