From Newsgroup: uk.d-i-y

As the subject, really.

I once read that the pressure generated by the combusting gasses in a
piston cylinder is the measure for an I.C. engine's efficiency, but I've
no idea if that is correct.

In a gas turbine is it how hot the combustion chamber (or whatever it is properly called) gets? Is it the speed of the exhaust flowing through
the turbines?

Any information gratefully received.

David Paste.
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From Newsgroup: uk.d-i-y

On 09/05/2026 20:56, David Paste wrote:

As the subject, really.

I once read that the pressure generated by the combusting gasses in a
piston cylinder is the measure for an I.C. engine's efficiency, but I've
no idea if that is correct.

In a gas turbine is it how hot the combustion chamber (or whatever it is properly called) gets? Is it the speed of the exhaust flowing through
the turbines?

Any information gratefully received.

David Paste.

I seem to recall from my A level physics that the efficiency of an
internal combustion engine was related to the Carnot cycle.

https://en.wikipedia.org/wiki/Carnot_cycle
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From Newsgroup: uk.d-i-y

On Sun, 10 May 2026 10:14:26 +0100, SH wrote:

On 09/05/2026 20:56, David Paste wrote:

As the subject, really.

I once read that the pressure generated by the combusting gasses in a
piston cylinder is the measure for an I.C. engine's efficiency, but
I've no idea if that is correct.

In a gas turbine is it how hot the combustion chamber (or whatever it
is properly called) gets? Is it the speed of the exhaust flowing
through the turbines?

Any information gratefully received.

David Paste.

I seem to recall from my A level physics that the efficiency of an
internal combustion engine was related to the Carnot cycle.

https://en.wikipedia.org/wiki/Carnot_cycle

Or

https://en.wikipedia.org/wiki/Atkinson_cycle

Which is used in the ingenious Toyota hybrid powertrain.
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From Newsgroup: uk.d-i-y

On 09/05/2026 20:56, David Paste wrote:

As the subject, really.

I once read that the pressure generated by the combusting gasses in a
piston cylinder is the measure for an I.C. engine's efficiency, but I've
no idea if that is correct.

In a gas turbine is it how hot the combustion chamber (or whatever it is properly called) gets? Is it the speed of the exhaust flowing through
the turbines?

Any information gratefully received.

Thermodynamics determines that the maximum efficiency of a heat engine
is the input minus the output temperatures expressed as a percentage of
the input temperature using an absolute temperature scale such as Kelvin.
--
Max Demian
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From Newsgroup: uk.d-i-y

On 10/05/2026 14:34, Max Demian wrote:

On 09/05/2026 20:56, David Paste wrote:

As the subject, really.

I once read that the pressure generated by the combusting gasses in a
piston cylinder is the measure for an I.C. engine's efficiency, but
I've no idea if that is correct.

In a gas turbine is it how hot the combustion chamber (or whatever it
is properly called) gets? Is it the speed of the exhaust flowing
through the turbines?

Any information gratefully received.

Thermodynamics determines that the maximum efficiency of a heat engine
is the input minus the output temperatures expressed as a percentage of
the input temperature using an absolute temperature scale such as Kelvin.

Where does the 'maximum' come into that determination?


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From Newsgroup: uk.d-i-y

On 10/05/2026 14:48, jkn wrote:

On 10/05/2026 14:34, Max Demian wrote:

On 09/05/2026 20:56, David Paste wrote:

As the subject, really.

I once read that the pressure generated by the combusting gasses in a
piston cylinder is the measure for an I.C. engine's efficiency, but
I've no idea if that is correct.

In a gas turbine is it how hot the combustion chamber (or whatever it
is properly called) gets? Is it the speed of the exhaust flowing
through the turbines?

Any information gratefully received.

Thermodynamics determines that the maximum efficiency of a heat engine
is the input minus the output temperatures expressed as a percentage
of the input temperature using an absolute temperature scale such as
Kelvin.

Where does the 'maximum' come into that determination?

It means that no matter how hard you try there is a
predictable upper limit to efficiency based on the input
and output temperatures.
John

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From Newsgroup: uk.d-i-y

SH <i.love@spam.com> wrote:

I seem to recall from my A level physics that the efficiency of an
internal combustion engine was related to the Carnot cycle.

https://en.wikipedia.org/wiki/Carnot_cycle

As the page says, the Carnot cycle provides an upper bound
on the possible efficency (asssuming various standard and
uncontroversial thermodynamic assumptions).

#Paul
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From Newsgroup: uk.d-i-y

On 10/05/2026 10:14, SH wrote:

On 09/05/2026 20:56, David Paste wrote:

As the subject, really.

I once read that the pressure generated by the combusting gasses in a
piston cylinder is the measure for an I.C. engine's efficiency, but
I've no idea if that is correct.

In a gas turbine is it how hot the combustion chamber (or whatever it
is properly called) gets? Is it the speed of the exhaust flowing
through the turbines?

Any information gratefully received.

David Paste.

I seem to recall from my A level physics that the efficiency of an
internal combustion engine was related to the Carnot cycle.

https://en.wikipedia.org/wiki/Carnot_cycle

Like most things enfgineerinfg there is more than one way to make a mathematical model.,

Bernouilli/Newtonian.

Carnot/energy analysis.

It is pretty easy to see that energy extracted cannot exceed energy in combustion minus energy leaving the tail pipe.

You don't need to analyse that with Carnot,

Gas turbines would be efficient if the exhaust was not so damned hot,
since combustion temperatures are in fact very high.

The combined cycle turbvine that uses those exhaust gasses to heat a
steam boiler is the most efficient internal combustion derived heat
engine we have.

Turbocharged diesel and petrol engines with very high combustion
temperatures - generally achieved with high effective compression
ratios and very weak fuel air mixes - are getting close though.
--
rCLThere are two ways to be fooled. One is to believe what isnrCOt true; the other is to refuse to believe what is true.rCY

rCoSoren Kierkegaard

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From Newsgroup: uk.d-i-y

On 10/05/2026 14:48, jkn wrote:

On 10/05/2026 14:34, Max Demian wrote:

On 09/05/2026 20:56, David Paste wrote:

As the subject, really.

I once read that the pressure generated by the combusting gasses in a
piston cylinder is the measure for an I.C. engine's efficiency, but
I've no idea if that is correct.

In a gas turbine is it how hot the combustion chamber (or whatever it
is properly called) gets? Is it the speed of the exhaust flowing
through the turbines?

Any information gratefully received.

Thermodynamics determines that the maximum efficiency of a heat engine
is the input minus the output temperatures expressed as a percentage
of the input temperature using an absolute temperature scale such as
Kelvin.

Where does the 'maximum' come into that determination?

You can always waste energy in other ways than through the exhaust pipe

--
"It is an established fact to 97% confidence limits that left wing conspirators see right wing conspiracies everywhere"

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