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Author Topic: I Got it Wrong!  (Read 1192 times)
hardlec
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« on: September 23, 2014, 03:06:11 am »

The reason Internal combustion took over from steam, I was told, was that Diesel and Gasoline had much better fuel density, i.e. joules/kilogram, than did coal, and that the losses involved in heating water to steam were prodigious.   

I was looking at making a compressed air engine, and realized that the air pressure was the defacto fuel of the engine, but alcohol or kerosene was added to heat the air as it expanded.

The fuel of a steam engine is not then the fuel that heats the water, but rather the heat in the water vapor.  Hotter steam is more power. 

Using a steam engine that moves means building a fuel plant and carrying it with you, a great waste of energy.

Perhaps now ?I know why there are some Corliss engines still in use: Stationary steam engines are still excellent. 

Oh, there is also the nuclear option.  The most efficient way to turn the heat generated by a Nuclear kettle is with a steam engine.  The nuclear reactor creates steam, the steam fuels the steam engine.
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MechanicalMouse
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« Reply #1 on: September 23, 2014, 07:37:07 am »

I don't know if he's still active on the forum but there is a chap called HAC around here.

He's a real bonefide steam enginer having worked on the railway at the end of the steam age of trains.

One of bigger issues was not fuel efficiency, but water usage. A gallon of petrol could get you 50 miles, but a gallon of water would only last 10 miles.
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Rory B Esq BSc
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« Reply #2 on: September 23, 2014, 03:31:33 pm »

The vital factor is the power to weight ratio when an engine and it's supply of fuel etc moves, as it has to overcome the inertia of the mass of the engine, fuel and so on, rather than simply the load of the machinery it drives.  This is why electric motors are common except for cars due to the batteries they must carry, Although electric bikes are now quite common and for low speed local deliveries the 'milk float' has used electric power for many years.
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Victor Rothwood Esq.
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« Reply #3 on: September 23, 2014, 05:10:38 pm »

 I hate to spoil a good post, however the real main reason steam went "out of fashion" was the dirt it created, and the time it took to get going. Steam road haulage went out when laws were introduced regarding axle loading came into being, making the tax too costly to justify keeping a steam vehicle on the road. That coupled with the advancement of the I.C engine, who wants to get up 2 hours earlier to light a fire, when with the I.C engine all you have to do was turn a key...
 Rail steam was a slightly different story in the UK, it ended predominantly due to one Dr Beeching, who it was later found out had some sort of tie with British Petroleum, hence the mad rush to scrap steam locos and convert to diesel, even if some of the early diesels were slower, less reliable and less powerful.
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Narsil
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« Reply #4 on: September 23, 2014, 11:46:19 pm »

There are a few reasons why IC engines predominated in road vehicles. For the sort of power required for road vehicles IC engines tend to represent a more convenient package for a variety of reasons.

As mentioned one of the main factors is mass and bulk, as well as fuel, steam engines need either a substantial quantity of water, which is consumed, you can have closed cycle engines which don't consume much water but they need a lot of extra plant in terms of condensers etc and you need to get rid of a lot of waste heat which tends to mean very big radiators and heat exchangers.

In terms of overall thermal efficiency  the fundamental driver is the difference in temperature between the heat source and the heat sink. Because IC engines burn fuel intermittently and vent the combustion products and working fluid the the environment they are relatively easy to cool (there are plenty of practical air cooled engines and even liquid cooled ones usually only need a few litres of coolant). This means you can have much higher flame temperatures, which would melt the working parts if they were sustained. In steam engines the temperature for the working fluid is significantly lower. This can be offset to a great extent in large plant by the fact that you can reclaim a lot of the energy that you put in by putting waste heat back into the system, however this does need a lot of extra plant which is difficult to package in a vehicle.

You can use gasoline of kerosene as fuel for steam engines just as well as coal, in fact many steam engines were converted to oil fired boilers. The big advantage of steam is that because the combustion is separate from the working fluid you can use almost anything as fuel, coal, wood, waste etc...IC engines by contrast need high quality clean-burning fuels which can easily be vaporised because the combustion is in direct contact with moving parts. The initial adopti9on of IC engines was helped by the fact that, at the time, gasoline was relatively cheap and abundant

However it's important to remember that IC engines didn't really 'replace' steam. Steam trains were in general use long after IC engined road vehicles were common and steam turbines still generate the majority of electrical power. In fact the major change was a move away from local generation of mechanical power at the level of individual factories etc to more centralised generation distributed as electricity with individual machines using electric motors rather than belt drives etc.


« Last Edit: September 25, 2014, 07:48:01 pm by Narsil » Logged







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« Reply #5 on: September 24, 2014, 12:22:05 am »

Electric cars become steam driven since much of the electricity in the grid is generated with steam turning the generators.
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