What are the problems with Steam Engines?

[Xyius]

For some reason, steam power fascinates me very much. I had a couple questions about steam power and I figured this place was the best place to ask!

Would it be naive of me to believe that any engine engineered correctly can be useful? What are the advantages and disadvantages of a steam engine? I asked a few people this and a lot of them said the efficiency of a steam engine is only around 30%. This confused be because a 4 stroke internal combustion engine has around the same efficiency of about 30%.

Can anyone shed some insight on this for me?

Thanks!

 

[Danger]

Hi, Xyius.
There are two main advantages that I can think of for steam engines. They can't stall in the way that an internal combustion engine will under excessive loading. They might stop turning, but will get right back to business-as-usual when the load is lessened. The second is extreme fuel flexibility. If it burns, it can be used to power the thing. Anything from sawdust to napalm will get you going. (Uranium, too, but I assume that you don't have a lot of that stashed in your garage.)
Nuclear power plants use steam turbines for electrical generation, so it obviously isn't obsolete. Since I assume that you are specifically referring to reciprocating engines, I'm restricting my comments to those.
A disadvantage is that you have to inject lubricant which is constantly destroyed, rather than have a circulating steady supply. That's no worse than a 2-stroke IC engine, though.
There are some neat things to be mentioned about it, but I'll hold off until next post.

 

[xxChrisxx]

Steam engines are also physically enormous.

 

[Danger]

Steam engines are also physically enormous.

Not necessarily. The engines in the old locomotives were a lot smaller than the diesel/electric units in use today. Almost all of that bulk that you see was water storage.

 

[Xyius]

Thanks for your replies! So would the disadvantages be enough to make it completely impractical to run a car on? What about a Steam/Electric Hybrid, maybe using an induction heater to heat the water or something.

 

[AlephZero]

There were some neat designs for small steam trucks, about 100 years ago. I used to know a couple of guys in the UK who restored one from the 1920s and used it regularly for "real" delivery work, not just as a toy to show off at steam rallies. The main modification they made was to tweak the suspension to run better on modern tires and modern road surfaces.

It had a recirculating oil fired boiler, so no big water tank required and the fuel tank was similar to any other truck (but it ran on cheap heating oil). The 2-cylinder engine was no bigger than a modern truck engine, and a lot simpler. It had two gears, with max speed about 40 mph in first and 80 in second (and the same gearing in reverse, which was a trap for "non-regular" drivers!). Unlke an IC engine it was almost completely silent, and the acceleration from a standing start could leave car drivers wondering what just happened. There was something of a "Marie Celeste" feeling when it was driving silently alongside you in the next lane at 50 or 60 mph!

The only real disadvantage was that it took a few minutes to get some steam pressure before driving off on the first trip of the day. For general delvery work around town within 10 or 20 miles of their base, it was just as effective and reliable as a modern truck - and much better value as a mobile advertisement for their business.

 

[Danger]

The only real disadvantage was that it took a few minutes to get some steam pressure before driving off on the first trip of the day.

This brings up one of the "neat things" that I mentioned earlier. Back in the mid-70's, either "Hot Rod" or "Car Craft" magazine (they're sister publications, and I always get mixed up) had an article about one awesome steam car. It was based upon a fibre-fab kit car, perhaps a Bradly GT. The designer converted a 35hp 2-stroke outboard boat motor to steam and stuffed it into the car. In any weather, this thing was ready to go within 10 seconds of turning the key. The trick to that was that there was no boiler (in the normal sense of the word). A coil of 5/8" (or 3/8", I can't remember) copper tubing occupied the trunk of the car. For steamage (yeah, I made up that word), a tiger torch blew down the centre of the coil. Two of the fuels that they tested were coal dust and nitroglycerine (I have no idea why the hell they tried the latter), and it ran without a glitch. (I must say, though, that I sure as hell wouldn't want to undergo a collision while toting along a fuel tank full of nitro. )
Anyhow, the vehicle pulled 0.9 g's acceleration and ran the 1/4 mile track in something like 10 seconds. That ain't bad for obsolete technology.

 

[Jobrag]

The big plus for steam engines is high torque at low revs, the big minus is you either need a condensor, or carry around lots of water.

 

[Xyius]

These are very interesting replies! I want to learn all I can about modern steam engines because as I said before, for some reason they fascinate me so much!

Thanks everyone for your insight :]

 

[Danger]

Thanks everyone for your insight :]

You're more than welcome. As a side-note, Sterling engines are somewhat similar in some ways, so you might want to check those out as well.

 

[Bob S]

I recall about 50 years ago going out on a nice quiet early Sunday morning drive, only to run into a fog bank. I finally discovered that I was driving behind an old Stanley Steamer. Maybe nowdays, vapor condensers (in lieu of catalytic converters) might be required on all steam car exhausts.

 

[Danger]

I recall about 50 years ago going out on a nice quiet early Sunday morning drive

Jeez, and I consider myself old... Your dentures must be about my age.

 

[Pkruse]

To answer your original question, there is nothing wrong with a steam engine. It just lost out to the internal combustion engine because that type turned out to be a more cost effective means of meeting the designers' design objectives. As technologies improve and/or availability of resources changes, we might see them come back in one form or another. But not for the time being.

A friend of mine who recently died of old age made a steam powered motorcycle about three decades ago. It worked out very well. He had a lot of fun with it until he wore it out, and then went on to his next interest. It used propane and had a boiler similar to the copper tube idea described above.

 

[Danger]

Another advantage is that if you get tired after driving all day, you can use your car as a still to brew up a nightcap...

 

[phyzguy]

I was told that a steam engine is inherently less efficient than an internal combustion engine for the following reason. The thermodynamic efficiency of a heat engine is 1-Tlow/Thigh. Since Tlow is usually set by the environment, the only way to get better efficiency is to raise Thigh. You also have a materials limit in that the material (presumably metal) that your engine is built out of will melt if it gets too hot. In a steam engine, you cannot get the working fluid (steam) any hotter than the temperature limit of the material, since the heat has to pass through the walls of the boiler. In an internal combustion engine, The working fluid combusts inside the chamber, so it can be a lot hotter than the melting point of the walls of the combustion chamber, assuming you cool the walls of the chamber. So, in theory at least, an internal combustion engine can be higher efficiency than an external combustion engine.