What does it take to be a Transport Correspondent?
 

In message , at 13:11:36 on
Sat, 23 Apr 2011, Jonathan Morton
remarked:

It's not just the "Standard". Christian Wolmar, writing in Friday's "Times"
states that an HST "has a locomotive at one end".

Yerse - but it does have a locomotive at one end... and another at the
other end :)

--
Roland Perry

What does it take to be a Transport Correspondent?
 

In article ,
(Jonathan Morton) wrote:

"bob" wrote in message
...
[...]

It's not just the "Standard". Christian Wolmar, writing in Friday's
"Times" states that an HST "has a locomotive at one end". Last time
I checked, it was one at each end.

A pity, since his basic premise that it is nuts to transport dead
diesel engines round under the wires (in bi-mode IEP) was sound.

I suspect he miswrote. The distinction he was making was that the
locomotives are separate vehicles, two in the case of HSTs, one on most
other local-powered passenger stock.

--
Colin Rosenstiel

What does it take to be a Transport Correspondent?
 

On Sat, 23 Apr 2011 11:56:21 +0100
Jeremy Double wrote:
If what is being claimed is true - ie that heat is always required to do
work then this should be impossible.

Heat isn't always required to do work _directly_: hydro-power uses the

Exactly. Which was my point.

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.

B2003

What does it take to be a Transport Correspondent?
 

On Apr 21, 1:07*pm, Paul Corfield wrote:
On Wed, 20 Apr 2011 22:40:29 +0100, "Jack Taylor"
wrote:

The standard of railway-related writing has, for some while, been plummeting
steadily lower and we often lambast the BBC for their reporting but today's
efforts in the London "Evening Standard" by their Transport Correspondent,
Dick Murray, are spectacularly dismal.

It is interesting to note that a fair proportion of the comments under
today's "6 lines closed over Easter" article are strongly critical of
the article and the quality of the journalism.

No longer the case - perhaps a moderator's been along?
The article in question* did annoy me on Thursday, particularly for
its opening sentence:
"Huge sections of London's transport system will shut down over the
four-day Easter break, it emerged today."

Er, no, it didn't emerge on Thursday. It probably emerged weeks, if
not months before on http://www.tfl.gov.uk/livetravelnews...r/default.aspx
- and also the day previously in TfL's weekly closures email.

* http://goo.gl/DXO66 or
http://www.thisislondon.co.uk/standa...er-meltdown.do

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On Mon, 25 Apr 2011 03:51:02 -0700 (PDT)
martin wrote:
"Huge sections of London's transport system will shut down over the
four-day Easter break, it emerged today."

Er, no, it didn't emerge on Thursday. It probably emerged weeks, if

When journos say "it emerged today" what they actually mean is "I just heard
about it today when my sub editor told me to look into it".

That said, it doesn't make LU's **** poor planned works schedule look any
better.

B2003

What does it take to be a Transport Correspondent?
 

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/

What does it take to be a Transport Correspondent?
 

On Tue, 26 Apr 2011 07:36:39 +0100
Jeremy Double wrote:
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).

Ok, you've got me there. However , it doesn't just produce CO2, it produces
steam which is also a gas at those temperatures so you do end up with more
gas that you had before since 1 molecule of O2 gives rise to 2 molecules
of water. Mind you , it requires heat to convert the water into steam which
rather undermines my original argument.

Ah well, can't win them all!

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.

Since the wikipedia entry on it is huge and I don't have time to read it
I'm not going to comment other than to say it can't be that efficient or
powerful or we'd all be using them today.

I suggest you learn some thermodynamics before making further
pronouncements.

Actually I think its more my chemistry I need to brush up on.

B2003

What does it take to be a Transport Correspondent?
 

On Apr 26, 10:38*am, wrote:
On Tue, 26 Apr 2011 07:36:39 +0100

Jeremy Double wrote:
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).

Ok, you've got me there. However , it doesn't just produce CO2, it produces
steam which is also a gas at those temperatures so you do end up with more
gas that you had before since 1 molecule of O2 gives rise to 2 molecules
of water. Mind you , it requires heat to convert the water into steam which
rather undermines my original argument.

Right, let's have some numbers here.

Consider an Air Standard Otto Cycle. This is a conceptual cycle used
for teaching engine thermodynamics, is an approximation to the
characteristics of a petrol engine. In this cycle, air is compressed
by a certain volume ratio, then heat is added at constant volume
(reflecting the fact that combustion is fast compared with the
rotating speed of engines), then the resultant mix is expanded by the
same volume ratio back to the initial volume, and heat is rejected to
restore the initial conditions. There is no change in the chemistry
of the working fluid.

If we take initial conditions of 288 K (about 15 celsius) and 10^5 Pa
(1 bar). Let's let the maximum combustion temperature be 1600 K (to
reflect material limitations in our engine), and assume a compression
ratio of 10 (ie the ratio of compressed volume to uncompressed
volume). Assuming air to have a specific gas constant of 287 kJ/kg K
and gamma of 1.4, and idealised compression/expansion, and a cp of
1006 kJ/kg K (reasonable values, you can look them up), then after
compression, before combustion, the gas conditions are 24.5x10^5 Pa
and 748.5 K. After the heat addition, the conditions are 53.14x10^5
Pa and 1600 K, with the conditions at the end of expansion being 637 K
and 2.09x10^5 Pa.

The heat addition here is (1600-748.5)*(1006-287)=61.2 kJ/kg (ie per
kg of air in the cylinder), producing a pressure increase of 2.14
times.

Now, petrol has a lower calorific value of 44.4 MJ/kg (but the values
for hydrocarbon fuels are all in the mid 40s, changing between methane
and heavy oil makes no big difference), so to get 61.2 kJ we would
need to burn 1.3 grammes of petrol for every kg of air. In molar
terms, that's 0.011 moles of fuel burning in 34.5 moles of air.

If we assume petrol to be octane (C8H18), then the combustion reaction
will be
C8H18 + 12.5O2 - 8CO2 + 9H2O
For 0.011 moles of petrol, we consume 0.011 moles of fuel (the fuel is
in the gas phase at this temperature and pressure) and 0.1375 moles of
O2 and create 0.187 moles of combustion products.

So we have 34.511 moles in the gas phase to start with and 34.5495
moles after combustion.

The fact is, the heat release from the fuel is so enormous that the
effect of the heat release is several orders of magnitude greater than
the effect of changes in mole numbers.

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.

Since the wikipedia entry on it is huge and I don't have time to read it
I'm not going to comment other than to say it can't be that efficient or
powerful or we'd all be using them today.

Stirling engines can be both efficient and powerful. The problem with
them is that they require heat to be transferred from metal to air in
the heat addition and rejection stages, and gases generally have poor
heat transfer properties, meaning very large heat exchangers.
Liquids, on the other hand, have massively better heat transfer
characteristics, so heating water in a boiler and cooling it in a
condenser gives rise to a much smaller (cheaper) peice of kit, in the
form of a steam cycle, for similar performance.

Robin

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In uk.transport.london message , Mon, 25
Apr 2011 08:25:53, d posted:


That doesn't matter - 1 mole of CO2 at room temperature takes up vastly
more volume than 1 mole of liquid a hydrocarbon.

A little knowledge is a dangerous thing; but you have not yet reached
that stage.

A mole of CO2 gas at room temperature takes up essentially the same
volume as the oxygen that it was in part made from.

Fuel is, in essence, a polymer of (CH2); for each CO2 there will be an
H2O, but H2O gas only takes twice the volume of the oxygen that went
into it.

Don't forget that at least 80% (by volume) of the input gas is nitrogen,
which plays no useful part in the chemistry.

--
(c) John Stockton, near London.
Web http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, and links.
Correct = 4-line sig. separator as above, a line precisely "-- " (RFC5536/7)
Do not Mail News to me. Before a reply, quote with "" or " " (RFC5536/7)

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On Tue, 26 Apr 2011 11:22:42 -0700 (PDT)
bob wrote:
The fact is, the heat release from the fuel is so enormous that the
effect of the heat release is several orders of magnitude greater than
the effect of changes in mole numbers.

Ok, fine. I'm big enough to admit when I've got it wrong unlike a lot of
people on here.

B2003