Steam engine fuel efficiency

[massmanute]

First post here by this newbie.

I realize that the reason for building steam boats is for fun, not necessarily for fuel economy. Nevetheless, I can't help wondering about steam engine efficiency, particularly the level of technology of interest here. Is the thermodynamic efficiency much worse than gasoline or diesel engines?

Thanks.

[massmanute]

... smelly long-chain hydrocarbon engines?

Thanks.

That's kind of fund and funny how the system did a word substitution for that hydrocarbon fuel that resembles jet fuel.

[steamboatjack]

YES
regards Jack

[Bob Cleek]

You worried about fuel efficiency?

Oh yea, it's worse... lots and lots of worse. Then again, it's more fun. Lots and lots of more fun.

Most of the guys in here have forgotten more about steam plant efficiency than I know, but conserving heat is what steam plant efficiency is all about. If you can feel the heat, you're losing it. Insulation is your friend.

Depending upon the fuel you use, steam may be less expensive per mile, but an efficient use of energy it's not.

[fredrosse]

Typical Engine Efficiencies: A Compression Ignition Internal Combustion Engine - Diessel (I had to spell it wrong so the website would not automatically change the word) has a full load thermal efficiency ranging in the 30% to 50% range, the engines of a few horsepower to a few hundred horsepower are typically in the 30-40% range, 50% efficiency is for the very large marine engines in the 40,000 horsepower range.

A Spark Ignition Internal Combustion Engine - Otto Engine or more typically a "Gasoline" Engine has a full load thermal efficiency ranging in the 20% to 30% range, the engines of a few horsepower are typically in the 10-15% range, such as lawnmower engines.

Simple steam plants generally have much lower efficiency, although the biggest steam plants (1,000,000+ Horsepower) can manage efficiencies in the high 40% range. Large reciprocating steamships (triple expansion) could get about 16% efficiency at best. Typical steam locomotives (simple engines, non condensing), only managed, on average, about 4% efficiency, and our steam launches are very much smaller machines, with very much smaller efficiencies. Typically a small steam launch will manage conversion efficiencies in the vicinity of 1% only, maybe a few percent for a good condensing machine with a compound engine. There are exceptions, but this is probably close to the performance of typical steam launches.

To put it into perspective, several hundred pounds (about 300 - 500 pounds) of wood in a steam launch is required to do the same work of one gallon no 2 oil (Diessel) running a reasonably efficient diessel engine.

The technical advantage of the steam plant is that it is an "external combustion" engine, and hence does not need special fuels, you can burn wood or coal or virtually anything and get the power, very little noise and vibrations, time to enjoy the ride rather than rushing about in a speedboat.

In small launch applications, the power to speed relationship allows very low power to provide a reasonable turn of speed, if moderate cruising is your goal.

Looking at a displacement launch, 16 feet long, with a design speed of 5 knots, with 1 horsepower required to make design speed:

Then power requirements follow these relationships approximately:

% Speed Knots Horsepower Reqd.

50 2.5 .125

75 3.75 .422

90 4.5 .729

100 5.0 1.000

125 6.25 3.05

150 7.5 7.6

175 8.75 16.4

200 10.0 32.0

[steamboatjack]

The thermal efficiency of a steam plant relates to the whole plant not just the engine part, the losses are large as there is lots of places to loose heat, a lot goes up the boiler flue but by far the most goes "over the side" in the condenser as very low grade heat but lots of it. (a puffer does use some of this heat in helping the draft).
regards Jack
p.s. its hard to cook sausages on a diesel engine and they would probably taste bad!

[farmerden]

I burn about 2 1/2 gal of fuel per hour at 6+ knots Approx 1/2 of that at 4 knots but that's another story! BUT I have never paid for any fuel-ever! Let's try that in one of those infernal combustion engines!! As earlier stated- steam boilers will burn anything! Cept maybe gasoline -not in my boat anyway! My fuel of choice is used automobile oil but if you're thinking of a romantic evening out on the water ,then burn a nicely scented wood! The taste of the sausages will definitely improve! Den

[Midship]

Hello,

I am interested to know how you have adapted your boiler to burn used oil,

pictures welcome

kind regards

[farmerden]

I'm running an atomizing steam burner [drooling burner is another name I've heard it called] All it is ,is a superheated spray of steam blowing into the firebox with oil [any oil] dripping onto the steam which instantly atomizes the oil. This setup requires some steam pressure to begin with and I simply light a wood fire in the boiler. One could start with propane or coal.I've even heard of compressed air and oil until steam has built up.There have been lots of articles in the old steam magazines of the various types of burners.I once asked Jake Turner for a sketch of a burner he used that even pulled the fuel in without the aid of any fuel pumps. Well I asked for a sketch and that's what I got! [/img]

[Midship]

thanks

do you control the steam pressure, how is adjusted the mix oil/steam, I suppose that to keep it constant you ahve to increase the oil flow as the steam pressure goes up?