[Gasification] Hydrogen combustin defficit?

[Thomas Reed]

*Dear All:

The world runs on good engineering, and we are spreading from 
gasification to automotive engineering.  This is not totally 
inappropriate, since running smaller power gasifiers on wood during WWII 
was the principle demonstration of biomass gasification use.  We have 
not come close to repeating that  -  yet.

I spent two years running an automotive fuel research lab recently and 
had time to consider the relationship of the fuel to the engine.  Here 
is one insight that I haven't heard from others.
*
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*Yes, Mr. heat is the primary driving force for most fuels.  However, at 
the thermodynamic level, the maximum power is related to both heat and 
entropy, as expressed in the Gibbs Free Energy equation:

Maximum Power Available in a chemical reaction is given by the enthalpy 
change, DH, - T times the entropy change, or

  DG = DH - TDS
**
(In a more formal setting the capital D should be D but it is too hard 
to change, read D = delta). 

The entropy change, DS of any reaction depends primarily on the number 
of moles of gas appearing or disappearing in the reaction, Dn. 

For methane combustion,

CH4 + 2 O2 ==> CO2 + 2 H2O              Dn = 0

However, for hydrogen combusti0n,

2 H2 + O2 = 2 H2O                                 Dn = -1

so you only produce 2/3 as much hot product as you consume and the 
expansion is 2/3 of what you would predict on a flame temperature basis. 
*
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*Fortunately, the presence of 79% nitrogen with the combustion oxygen 
makes this effect quite small when you include the nitrogen on both 
sides of the equation.  Still, it needs to be taken into account for 
hydrogen combustion in engines. 

Tony:    Is this effect worse or better in hydrogen fuel cells?

Onward,

TOM REED      BEF
*Jeff Davis wrote:

>On Saturday 13 May 2006 07:38 pm, Michael Redler wrote:
>  
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>>PV=nRt. 
>>    
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>Mean old Mr. T
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>>...my $.02
>>
>>Mike
>>
>>carlos.gurgel at pesquisador.cnpq.br wrote:
>>  I would prefer: the pressure moves the piston!!!!
>>Work=F.dx
>>F=P.A
>>The heat is responsible for the pressure rise...
>>
>>Quoting Jeff Davis :
>>    
>>
>>>Dear Col and list,
>>>
>>>Some would say that mean old Mr Heat moves the Piston.
>>>
>>>On Thursday 11 May 2006 10:55 am, col wrote:
>>>      
>>>
>>>>While the flame velocity may be important in fuel efficiency,surely
>>>>it is the explosion of the burnt gas in the cylinder that drives the
>>>>piston,not the flame velocity .
>>>>        
>>>>
>>>--
>>>Jeff Davis
>>>      
>>>
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>>    
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