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Noisy bacon
Guest
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 Posted:
Thu Nov 10, 2005 4:20 am Post subject:
Diesel v petrol fuel economy |
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On the subject of fuel economy I wonder if anybody on the ng can answer this
question. Do diesels give more mpg because there's simply more energy per
unit volume in diesel fuel compared with petrol, or is a diesel engine
intrinsically more efficient at turning hydrocarbons into kinetic energy (or
perhaps I should phrase it "less inefficient")?
--
___________________
Homer: D'oh!
Bart: A deer!
Marge: A female deer!
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Hairy One Kenobi
Guest
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| Posted:
Thu Nov 10, 2005 5:46 pm Post subject:
Re: Diesel v petrol fuel economy |
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"Noisy bacon" <NeillYoung@crazyhorse.com> wrote in message
news:XCucf.11849$f_5.5832@newsfe6-gui.ntli.net...
| Quote: | On the subject of fuel economy I wonder if anybody on the ng can answer
this
question. Do diesels give more mpg because there's simply more energy per
unit volume in diesel fuel compared with petrol, or is a diesel engine
intrinsically more efficient at turning hydrocarbons into kinetic energy
(or
perhaps I should phrase it "less inefficient")?
|
In thermodynamic terms, they're totally different things. Best of all would
be the Carnot Cycle (I'm not even going to get started - just Google ;o)
Funnily enough, Diesel engines use the Compression Ignition Cycle, which
isn't quite as good as the Diesel Cycle. AFAIK, the "proper" Diesel engine
remains pretty much theoretical.
Depending upon how you look at it, Diesel was either a visionary or a bit of
an engineering idiot: he designed something to utilise waste coal and cotton
dust, but, given the state of materials technology at the time, the only
thing his engines powered were themselves - at high speed, and over an
expanding area of real estate. 400 bar and wrought iron just.. doesn't.
His design improved on steam engines of the day, in terms of fuel
efficiency, but lacked the power to weight ratio required for use in a car.
That took several decades' of development by slightly more switched-on
engineers.
--
Hairy One Kenobi
Disclaimer: the opinions expressed in this opinion do not necessarily
reflect the opinions of the highly-opinionated person expressing the opinion
in the first place. So there! |
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Chris Bartram
Guest
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| Posted:
Fri Nov 11, 2005 3:33 am Post subject:
Re: Diesel v petrol fuel economy |
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Noisy bacon wrote:
| Quote: | On the subject of fuel economy I wonder if anybody on the ng can answer this
question. Do diesels give more mpg because there's simply more energy per
unit volume in diesel fuel compared with petrol, or is a diesel engine
intrinsically more efficient at turning hydrocarbons into kinetic energy (or
perhaps I should phrase it "less inefficient")?
Well, there was a rumour that at the time of it's launch, the VW-Audi PD |
130 TDi was the most thermally efficient production car engine
available, if that's any help. I've read somewhere that it's acpable of
transferring 43% of the fuel energy into power, so "less inefficient"
may apply here, but that's much more efficient than, for example, an
ordinary lightbulb.
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Hairy One Kenobi
Guest
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| Posted:
Fri Nov 11, 2005 6:27 am Post subject:
Re: Diesel v petrol fuel economy |
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"Chris Bartram" <news@delete.me.piglet-net.net> wrote in message
news:81Pcf.5207$Lw5.4701@text.news.blueyonder.co.uk...
| Quote: | Noisy bacon wrote:
On the subject of fuel economy I wonder if anybody on the ng can answer
this
question. Do diesels give more mpg because there's simply more energy
per
unit volume in diesel fuel compared with petrol, or is a diesel engine
intrinsically more efficient at turning hydrocarbons into kinetic energy
(or
perhaps I should phrase it "less inefficient")?
Well, there was a rumour that at the time of it's launch, the VW-Audi PD
130 TDi was the most thermally efficient production car engine
available, if that's any help. I've read somewhere that it's acpable of
transferring 43% of the fuel energy into power, so "less inefficient"
may apply here, but that's much more efficient than, for example, an
ordinary lightbulb.
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Sounds like someone's dream - the mere age of the fuel would make several
percent difference in conversion efficiency, let alone the fact that they're
using the same thermodynamic cycle as everyone else!
It's been a couple of decades since College, but 43% sounds like the Carnot
Cycle (i.e. theoretically perfect), rather than something produced by a
typical petrol engine. The hs tables are undoubtedly in the loft, but, well,
um ;o)
Standing-by to be corrected...
H1K |
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Albert T Cone
Guest
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| Posted:
Fri Nov 11, 2005 5:59 pm Post subject:
Re: Diesel v petrol fuel economy |
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Hairy One Kenobi wrote:
| Quote: | Well, there was a rumour that at the time of it's launch, the VW-Audi PD
130 TDi was the most thermally efficient production car engine
available, 43% of the fuel energy into power
Sounds like someone's dream - the mere age of the fuel would make several
percent difference in conversion efficiency, let alone the fact that they're
using the same thermodynamic cycle as everyone else!
It's been a couple of decades since College, but 43% sounds like the Carnot
Cycle (i.e. theoretically perfect), rather than something produced by a
typical petrol engine. The hs tables are undoubtedly in the loft, but, well,
um ;o)
Standing-by to be corrected...
H1K
|
Hmmm. A diesel-cycle, with an expansion ratio of 5, a CR of 19 and
using eta=1.4 gives a theoretical efficiency of 57%, even ignoring the
increased effective CR due to the turbo.
IIRC modern low NOx diesels have flame temperatures of under 2000K, and
exhaust temperatures of around 500K, so the equivalent Carnot cycle
efficiency would be around 75% |
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Spooky
Guest
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| Posted:
Sat Nov 12, 2005 1:03 am Post subject:
Re: Diesel v petrol fuel economy |
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Hello Hairy. Don't you hang around uk.telecom.mobile too? Think I've seen
your name in there somewhere. |
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Hairy One Kenobi
Guest
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| Posted:
Sat Nov 12, 2005 3:45 pm Post subject:
Re: Diesel v petrol fuel economy |
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"Spooky" <nobodyofthatname@hatmail.com> wrote in message
news:0W5df.12106$lJ.603@newsfe5-win.ntli.net...
| Quote: | Hello Hairy. Don't you hang around uk.telecom.mobile too? Think I've seen
your name in there somewhere.
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Nope, sorry...
H1K |
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Hairy One Kenobi
Guest
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| Posted:
Sat Nov 12, 2005 3:49 pm Post subject:
Re: Diesel v petrol fuel economy |
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"Albert T Cone" <me@yahoo.com> wrote in message
news:3tjfcgFsgkqsU1@individual.net...
| Quote: | Hairy One Kenobi wrote:
Well, there was a rumour that at the time of it's launch, the VW-Audi PD
130 TDi was the most thermally efficient production car engine
available, 43% of the fuel energy into power
Sounds like someone's dream - the mere age of the fuel would make
several
percent difference in conversion efficiency, let alone the fact that
they're
using the same thermodynamic cycle as everyone else!
It's been a couple of decades since College, but 43% sounds like the
Carnot
Cycle (i.e. theoretically perfect), rather than something produced by a
typical petrol engine. The hs tables are undoubtedly in the loft, but,
well,
um ;o)
Standing-by to be corrected...
H1K
Hmmm. A diesel-cycle, with an expansion ratio of 5, a CR of 19 and
using eta=1.4 gives a theoretical efficiency of 57%, even ignoring the
increased effective CR due to the turbo.
IIRC modern low NOx diesels have flame temperatures of under 2000K, and
exhaust temperatures of around 500K, so the equivalent Carnot cycle
efficiency would be around 75%
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Wowsa.. things have changed since 1988 ;o) For some reason, 43% rang a
bell.. I stand/sit corrected!
The age of the fuel still makes a difference, though - enough so that F1
fuel is overrated when transported, but down to pump values when used a few
days later.
H1K |
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Noisy bacon
Guest
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| Posted:
Sun Nov 13, 2005 12:10 am Post subject:
Re: Diesel v petrol fuel economy |
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Hairy One Kenobi wrote:
| Quote: | "Spooky" <nobodyofthatname@hatmail.com> wrote in message
news:0W5df.12106$lJ.603@newsfe5-win.ntli.net...
Hello Hairy. Don't you hang around uk.telecom.mobile too? Think I've
seen your name in there somewhere.
Nope, sorry...
H1K
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Well how about ntl.discussion.broadband then? |
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Hairy One Kenobi
Guest
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| Posted:
Sun Nov 13, 2005 5:48 am Post subject:
Re: Diesel v petrol fuel economy |
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"Noisy bacon" <NeillYoung@crazyhorse.com> wrote in message
news:Beqdf.8556$mF5.4974@newsfe4-gui.ntli.net...
| Quote: | Hairy One Kenobi wrote:
"Spooky" <nobodyofthatname@hatmail.com> wrote in message
news:0W5df.12106$lJ.603@newsfe5-win.ntli.net...
Hello Hairy. Don't you hang around uk.telecom.mobile too? Think I've
seen your name in there somewhere.
Nope, sorry...
Well how about ntl.discussion.broadband then?
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Been there, but not recently.. the servers have to be working, first ;o)
H1K |
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