On Mon, Sep 01, 2003 at 07:15:27AM +0800, David Palmer wrote: > On Sun, Aug 31, 2003 at 09:57:26AM -0500, Ron Johnson wrote: > > The DEs I've seen trundling past my house create very little exhaust. > > Steam engines create a *lot*, and need to be regularly replenished > > with consumables. DEs just look to be more fuel efficient, and less > > offensive to the neighborhood. > > Just because you can't see it, don't mean it ain't there.
Diesel engines are several times better in terms of thermal efficiency than steam. For the same useful energy output, a diesel will consume much less fuel than a steamer and produce correspondingly less exhaust. Also, steamers generally burn coal, which generates more CO2 per unit energy than oil. (The picture changes where burning renewable fuels is concerned; the CO2 emissions don't matter, and the ability to burn any old crap is an advantage. Sugar plantations have used steam locos fuelled by burning the processed plant waste, for example.) As far as the visible particulate emissions from a steamer are concerned, they are universally built to a design which received government approval as able to consume its own smoke, dating from the very beginnings of steam locomotive traction. How well this is actually achieved depends a lot on the skill of the fireman. (And maintenance levels, but this applies to diesels too of course.) British 1950s-design DMUs had an interesting particulate emissions bug; at a particular (fairly low) engine speed, a resonance would develop in the exhaust system that prevented the cylinders from inducing a full charge of pure air. As they accelerated away from a station, suddenly the exhausts would make this blattering noise and black smoke would pour out until they got beyond the critical speed. -- Pigeon Be kind to pigeons Get my GPG key here: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x21C61F7F
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