London Banter - View Single Post - What does it take to be a Transport Correspondent?

Jeremy Double · April 26th 11, 06:36 AM posted to uk.transport.london,uk.railway

On 25/04/2011 09:25, d wrote:
On Sat, 23 Apr 2011 11:56:21 +0100
Jeremy wrote:
allowing them to do work and move the piston. Almost all of the
expansion of the combustion gases is due to the heat liberated by
combustion, not due to the increased number of moles of gas (for
instance, 1 mole of carbon burning uses 1 mole of oxygen to give 1 mole
of carbon dioxide). Remember that most of the gas in the cylinder of an
engine is nitrogen from the charge air (air is about 79% nitrogen).

That doesn't matter - 1 mole of CO2 at room temperature takes up vastly
more volume than 1 mole of liquid a hydrocarbon. If all the reaction did was
to heat the air in the cylinder up by 500 hundred degrees and didn't produce
any extra gas then very little would happen. The same applies to a steam
engine - you don't heat air up and shove hot air into the cylinders, you need
to convert a liquid (water) into a gas (steam) to get work out.

You're talking complete b*******.

1. The volume of one mole CO2 gas is no greater than the volume of the
one mole carbon (from either solid or liquid fuel) plus the one mole of
oxygen from the air needed to burn it (at the same temperature).

2. If you keep the volume the same, a quantity of air at 500 deg C has
nearly three times the pressure of the same quantity of air at ambient
temperatures. (This is easily estimated using the Ideal Gas Law or a
more sophisticated equation of state such as Van der Waals). And the
adiabatic combustion temperature of hydrocarbon fuel is _a lot_ higher
than 500 deg C.

3. There is a well-known external-combustion hot-air engine, called the
Stirling engine. This was invented by a clergyman, Robert Stirling,
father of the 19th century steam locomotive engineers Patrick and James
Stirling. It's not as commonly used as the steam engine, but that
doesn't mean it's impossible.

I suggest you learn some thermodynamics before making further
pronouncements.
--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/