Steam Engines

westernman

westernman

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What would the overall efficiency of a steam engine using steam generated from a boiler heated by burning diesel compare to that of a diesel engine in the power range of says 50-100 hp and in 5000 to 10000 hp?

I notice that most of the worlds power stations are steam powered - albeit steam turbines which are presumably the most efficient solution at constant RPM.

Just idly thinking of a steam power classic mobo for my old age.......
 
Dunno, but I wonder if Hook Norton Brewery do. Most of the machinery in their brewery is driven by a small steam engine on the ground floor; I believe the boiler for it is a modern diesel-fired unit.

Pete
 
Mosquito, a modern replica of Otto, will do over 20 knots (shhh).

LakeSept30_13.jpg


Mosquito.jpg


Another boat built in Lancashire with a diesel powered boiler will do a similar speed. (Designed by the bloke with the hat)

Dayonlake05.jpg
 
Steamer

A friend has built a modern version of a Murray River Paddle Steamer. He got a 100yo steam Roller engine and boiler which he runs on firewood. It takes about 4to6 hrs to get up steam and the shallow draft and paddles means it is hard to manage in a strong wind its about 60 ft long.
One thing he has a small steam engine to run a 240VAC alternator for power. The boat is pretty luxurious for 6 people to sleep on.
I occasionally dream of building a small steamer using a similar engine (I believe you can buy them on internet) driving a fibreglass hull perhaps a fin keel type without fin keel.(about 27ft)
I don't know much about boilers however but it could be fun for boating on no wind days. olewill
 
What would the overall efficiency of a steam engine using steam generated from a boiler heated by burning diesel compare to that of a diesel engine
Click to expand...
The maximum theoretical thermal efficiency of a heat engine is determined by the 2nd law of Thermodynamics (q.v.) but all this is outside my comfort zone, especially at 3o'clock in the morning

e = (T2-T1)/T2​

Where T2 and T1 are the temperatures at the beginning and end of the process in °K

This means that the theoretical maximum efficency of a steam engine that would be powering a small boat would be very low because the inlet steam temperature is relatively low.

Large modern power plants operate using superheated steam at temperatures in excess of 800 °K and pressures in excess of 150 bar. These steam conditions enable overall thermal efficiencies approaching 0.4 (40%) to be achieved.

Modern small diesel engines can achieve overall efficiencies greater than these large modern power plants.
 
It stretching my memory a bit (a lot, actually!) but I seem to remember from my days at marine engineering college that the fuel efficiency of a steam turbine plant was around 45% but a diesel engine was around 70%.
 
michaelchapman said:
What would the overall efficiency of a steam engine using steam generated from a boiler heated by burning diesel compare to that of a diesel engine in the power range of says 50-100 hp and in 5000 to 10000 hp?

I notice that most of the worlds power stations are steam powered - albeit steam turbines which are presumably the most efficient solution at constant RPM.

Just idly thinking of a steam power classic mobo for my old age.......
Click to expand...

Efficiency of steam engines depend largely on whether or not the exhaust steam goes to a condenser running a high degree of vacuum. James Watt improved the efficiency of Newcomen engines from 1/2% to 2% in this way. Even with a condenser you would be very lucky to get an overall efficiency much greater than 10% with a small modern engine. That's why most merchant ships, even very large ones, are diesel powered.
 
Why steam turbines for power stations?

Why are most power stations steam turbine powered if the overall efficiency of a diesel engine is higher?

The diesel engine also has the advantage of being able to be stopped and started quickly.
 
michaelchapman said:
Why are most power stations steam turbine powered if the overall efficiency of a diesel engine is higher?

The diesel engine also has the advantage of being able to be stopped and started quickly.
Click to expand...

In the sizes needed for a power station the efficiency of the steam plant is actually pretty good, but there are other issues. Primarily that coal and gas are the main fuels used, and overall cost not not overall effeciency is the key.

To return to the original question the thermal efficiency of small steam plants is low, with almost all steam railway locomotives returning less than 10%.
 
Lots of small guage steam trains have diesel boilers - check them out. The big downer is the time it taes to heat the water up in the first place. You could try a flash boiler or Combi domestic boiler as a pre-heater!

I don't fancy waiting an hour while the engine warms up before I can use it.
 
michaelchapman said:
Why are most power stations steam turbine powered if the overall efficiency of a diesel engine is higher?
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Another influential factor is the availaility of fuel. That's why there are so many power stations around the Selby and Goole area, for example. The power stations are sitting on top of a coalfield.
 
Back in the 1970s I knew George Hargreaves who owned Churr

It had a pressure paraffin burner. He used to pressurise the tank and fire up the boiler as soon as he got on board. IIRC after about 20 minutes he had sufficient steam pressure to get underway.

Designed so that it could be operated by one man... you did not have to take the gardener or a footman along to stoke the boiler. The little cabin was just right to "entertain" a lady friend!

My father worked for J.B Hickey who owned Elfin

That's coal fired. My father, who did not like boats or the water, was frequently the stoker!
 
Funny that. The Mosquito I pictured above was called Elfin when first built.
The bloke who built it has an engineering business and built everything. Hull,boiler and (non condensing) engine.
It says 17mph on the listing but a friend who has a steamboat says that is being modest. (Tenacity is a bit underpowered.)

Shamrock is a beauty on the lake. Restored by Roger Mallinson, who builds steam engines, it is now run by a trust, to ensure it's continued good health.

Mallinson.jpg
 
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Thermal efficiency of a heat engine is theoretically limited by the max. temperature of the working cycle.
In practice, overall thermal efficiency of a diesel engine might typically be say around 35%. To reach that sort of figure with steam plant requires extremely high steam temperatures, ~560 deg. C. which is virtually red hot. Such temps. are used in with large power generating plant, together with pressures of well over 2000psi. and is at the metallurgical limit of steel pipes etc. but such temperatures would be fairly impractical in most mobile plant.
Reciprocating pistons in cylinders also bring about efficiency reductions due to heat loss, hence turbines.
 
Funny that. The Mosquito I pictured above was called Elfin when first built.
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My own recollection is that when Mr. Hickey owned her she was named Elfin II, presumably because there was already an Elfin on the Thames.

Mr Hickey also later owned and restored The Pierrette after finding the hull abandoned in a field

Pictured below on the day she was relaunched at Woottons boat yard at Cookham in 1954. JB Hickey at the helm. Frank Desvignes, son of the original builder George Desvignes, in the stoke hole. Frank delivered the boat to her first owner in 1894

In her day the Pierrette was used as the Umpires boat in the University boat race being one of the few fast enough!

scan0091.jpg
 
parsifal said:
It stretching my memory a bit (a lot, actually!) but I seem to remember from my days at marine engineering college that the fuel efficiency of a steam turbine plant was around 45% but a diesel engine was around 70%.
Click to expand...

Err not sure about steam engine efficiency but do know that the best fuel efficiency achieved by a diesel is in the order of 33%.

If you want to improve the efficiency of a piston type steam engine you need to reuse the steam with pistons of increasing size, hence the term tripple expansion. for a three piston engine of this type. But I dont think they achieve diesel engine efficiency levels in small sizes.
 
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