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Kirk,
Jan's comments are closest to the real
situation. 35% would be the average thermal efficiency of Internal
Combustion Engines determined by the amount of work done (power output) divided
by ther amount of energy available in the fuel. Current petrol engines
have a thermal efficiency of about 30% and diesel engines about
40%.
The Carnot Efficiency is the maximum efficiency
possible for a heat engine operating between an upper and lower cycle
temperature limit. It is a reference value that actual efficiency is
compared with. The Carnot Efficiency for petrol engines operating on the
Otto Cycle is about 70% so the efficiency ratio of an engine at 30% compared to
the ideal Carnot cycle at 70% would be 42.8%.
Fuel cells are not heat engines so there would be
not Carnot Cycle reference value. As fuel is consumed you can still
determine a thermal efficiency value by comparing the work output with the
energy value of the fuel consumed.
See relevant textbooks on heat engines and
operating cycles for further clarification.
Graeme
----- Original Message -----
Sent: Tuesday, September 20, 2005 1:27
AM
Subject: [Biofuel] Carnot -- was Can this
man save the world? (Hydrogeninjection)
The 35% is 35% of the theoretical Carnot, not 35% of the potential
energy of the fuel. And yes, the rest of the energy is in the exhaust pipe and
water jacket although it is almost all heat as unburned hydrocarbons is
usually not true any more.
This little measurement twist is why most don't realize that a 35%
efficient fuel cell and a 35% internal combustion engine are not the same
although I've seen some attempts at using Carnot to diddle fuel cell
numbers.
As for Carnot calculate the available work using Charles law. Then you
will see Carnot is useless for low temperature engines.
Kirk
Jan Warnqvist
<[EMAIL PROTECTED]> wrote:
Furthermore,
when the energy efficiency of a
combustion engine is 35% it means the relationship between added energy
(fuel) and the power that comes as a result. The rest of the energy is heat
energy, which becomes transported by the cooling system as well as
creating hot exhaust fumes. If you could use that heat for some purpose, you
will find that almost 100% of the added energy is accounted
for.
Jan Warnqvist
AGERATEC AB
+ 46 554 201 89
+46 70 499 38 45
----- Original Message -----
Sent: Monday, September 19, 2005 3:05
AM
Subject: Re: [Biofuel] Can this man
save the world? (Hydrogen injection)
"Most internal combustion engines operate at about 35 per
cent efficiency. This means that only 35 per cent of the fuel is fully
burned. The rest either turns to carbon corroding the engine or goes out
the exhaust pipe as greenhouse gases."
Wow, according to this in
theory if we make a 100% efficient internal combustion engine then we will
have a car with zero greenhouse gases emission and zero carbon corroding
to the engine!
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