[Gasification] THERMAL EFFICIENCY

[gfwhell at aol.com]

The heat engine efficiency theorems were applied to the 4 stroke Humphrey engine,and  were given an efficiency rating of over 90%.by the engineering examining body.
The exhaust gas temperature leaving the engine was less than 15 Deg F above ambient.
Does this mean, 90% of the fuel was converted into work?
GF


-----Original Message-----
From: Benjamin Domingo Bof <benjaminbof at yahoo.com.ar>
To: Discussion of biomass pyrolysis and gasification <gasification at listserv.repp.org>
Sent: Thu, 7 Feb 2008 11:33 am
Subject: [Gasification] THERMAL EFFICIENCY



Heat engines When transforming thermal energy into mechanical energy, the 
hermal efficiency of a heat engine is the percentage of heat energy that is 
ransformed into work. Thermal efficiency is defined as

 

 
[edit] Carnot efficiency The second law of thermodynamics puts a fundamental 
imit on the thermal efficiency of heat engines. Surprisingly, even an ideal, 
rictionless engine can't convert anywhere near 100% of its input heat into 
ork. The limiting factors are the temperature at which the heat enters the 
ngine, , and the temperature of the environment into which the engine exhausts 
ts waste heat,, measured in the absolute Kelvin or Rankine scale. From Carnot's 
heorem, for any engine working between these two temperatures:

 
   

This limiting value is called the Carnot cycle efficiency because it is the 
fficiency of an unattainable, ideal, lossless (reversible) engine cycle called 
he Carnot cycle. No heat engine, regardless of its construction, can exceed 
his efficiency.

Examples of  are the temperature of hot steam entering the turbine of a steam 
ower plant, or the temperature at which the fuel burns in an internal 
ombustion engine.  is usually the ambient temperature where the engine is 
ocated, or the temperature of a lake or river that waste heat is discharged 
nto. For example, if an automobile engine burns gasoline at a temperature of  
nd the ambient temperature is , then its maximum possible efficiency is given 
y:

 
   

In practice, because no practical implementation of the Carnot cycle exists 
oupled with other irreversibilities such as the combustion process itself and 
riction, real engines fall far short of the Carnot efficiency. Real automobile 
ngines are only around 25% efficient, combined cycle power stations have 
fficiencies much higher however will still fall at least 15% points short of 
he Carnot value. As Carnot's theorem only applies to heat engines, devices that 
onvert the fuel's energy directly into work without burning it such as fuel 
ells, can exceed the Carnot efficiency.
       
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