Stirling Engines - Page 3 - PeachParts Mercedes-Benz Forum

73MB280SEL · #31 07-23-2006, 06:42 PM

No Monty Python skits to type out from memory (I'm impressed) but....

Stirling engines are also reversable so if you motor them, they will act as a refrigerator. While Stirling POWER is probably not that practical except in a few applications, Stirling refrigeration is used in cryogenic plants.

http://www.sce-online.de/dbs_p_e.html

While they may not replace our freezers and refrigerators, for very low temperatures they work very well.

Sholin

cmac2012 · #32 07-23-2006, 06:50 PM

Quote:

Originally Posted by ForcedInduction

The problem with stirlings is they are external combustion engines. It's almost impossible to make them thermally efficient as even a cheap gas engine.

They need a high temperature differential to make good, usable power.

Using the hot exhaust from a stationary generator/steam turbine/coal powerplant/nuclear cooling towers would be good sources of heat energy that would otherwise be wasted into the atmosphere.

A stirling alone, like a piston steam engine, is not a viable power source in the modern world.

That might explain why they're good for subs -- cold water for cooling.

I'm telling you, I have this crazy fantasy that someone would pay good money to have a motor drive yacht developed that ran on quiet Stirling generated electricity. Flex fuel in the bargain.

The generator shown in the first link in the 1st post puts out 55 Kw. I found this conversion ratio ditty in a chat room:

3 KW = 4 HP

That comes from a little thumbrule we use in the nuclear submarine Navy that goes "3, 4, 5, 12 Kick Hymie's Ass Daily". "Hymie" being short for Hyman G. Rickover, the father of the nuclear Navy, of course. The K H A D represent KW, HP, AC amps, and DC amps (assumes 450Vac and about 270Vdc, the common voltages used in submarine electrical systems). So 165hp is about 123KW. 1200 DC amps is about 300KW. The amps to KW or HP conversions are pretty rough, but the KW to HP ratio is almost perfect.

So 55 Kw translates to 73 hp. Not huge but not peanuts either. I've been trying to find info on the Swedish sub powerplant. No luck but I haven't tried that hard. Here goes...

cmac2012 · #33 07-23-2006, 06:55 PM

Strengths of Stirling engines

The heat is external and the burning of a fuel-air mixture can be more accurately controlled.

They can run directly on any available heat source, not just one produced by combustion, so they can be employed to run on heat from solar, geothermal , biological or nuclear sources.

A continuous combustion process can be used to supply heat, so emission of unburned fuel can be greatly reduced.

Most types of Stirling engines have the bearing and seals on the cool side; consequently, they require less lubricant and last significantly longer between overhauls than other reciprocating engine types.

The engine as a whole is much less complex than other reciprocating engine types. No valves are needed. Fuel and intake systems are very simple.

They operate at relatively low pressure and thus are much safer than typical steam engines.

Low operating pressure allows the usage of less robust cylinders and of less weight.

They can be built to run very quietly and without air, for use in submarines.

They hold promise as aircraft engines. They are quieter, less polluting, gain efficiency with altitude (internal combustion piston engines lose efficiency), are more reliable due to fewer parts and the absence of an ignition system, produce much less vibration (airframes last longer) and safer, less explosive fuels may be used.

cmac2012 · #34 07-23-2006, 06:57 PM

Problems with Stirling engines

Some Stirling engine designs require both input and output heat exchangers, which must contain the pressure of the working fluid, and which must resist any corrosive effects due to the heat source. These increase the cost of the engine, especially when they are designed to the high level of "effectiveness" (heat exchanger efficiency) needed for optimizing fuel economy. Fuel economy may not be an issue with the advantages of using unlimited but unusual fuel sources that a Stirling engine can make use of.

Stirling engines that run on small temperature differentials are quite large for the amount of power that they produce, due to the heat exchangers. Increasing the temperature differential allows for smaller Stirling engines that produce more power.

Dissipation of waste heat is especially complicated because the coolant temperature is kept as low as possible to maximize thermal efficiency. This drives up the size of the radiators markedly, which can make packaging difficult. This has been one of the factors limiting the adoption of Stirling engines as automotive prime movers. (Conversely, it is convenient for domestic or business heating systems where combined heat and power (CHP) systems show promise.

A "pure" Stirling engine cannot start instantly; it literally needs to "warm up". This is true of all external combustion engines, but the warm up time may be shorter for Stirlings than for others of this type such as steam engines. Stirling engines are best used as constant run, constant speed engines.

Power output of a Stirling is constant and hard to change rapidly from one level to another. Typically, changes in output are achieved by varying the displacement of the engine (often through use of a swashplate crankshaft arrangement) or by changing the mass of entrained working fluid (generally helium or hydrogen). This property is less of a drawback in hybrid electric propulsion or base load utility generation where a constant power output is actually desirable.

Hydrogen's lowest molecular weight makes it the best working gas to use in a Stirling engine, but as a tiny molecule, it is very hard to keep it inside the engine and auxiliary systems need to be typically added to maintain the proper quantity of working fluid. These systems can be as simple as a gas storage bottle or as complicated as a gas generator. In any event, they add weight, increase cost, and introduce some undesirable complications. Some engines use air as the working fluid which is less thermodynamically efficient but avoids loss problems. Most technically advanced Stirling engines like those developed for United States government labs use helium as the working gas, because it functions close to the efficiency of hydrogen with fewer of the material containment issues.

peragro · #35 07-23-2006, 08:03 PM

Quote:

Originally Posted by cmac2012

Take it FWIW.

I do. It's summer, it's hot, it happens.

cmac2012 · #36 07-23-2006, 08:16 PM

It sho' is happenin' a LOT right about now.

peragro · #37 07-23-2006, 08:20 PM

Quote:

Originally Posted by cmac2012

It sho' is happenin' a LOT right about now.

Is it really or are you just more sensitive to the reporting of it?

cmac2012 · #38 07-23-2006, 10:35 PM

Who knows. I'm feelin' it. We'll have a clearer idea in 10 to 20 years. In the meantime, I proceed as though it (AGW) is a given because there are so many other good reasons to drastically cut fossil fuel burning anyway.

About 10 good reasons. I'm going to get the jump on you and have products in place that make the most of new realities. Sort of like how Toyota is eating GM's lunch and dinner because they developed their product in an economic environment that more accurately reflected the true, scarce nature of petroleum.

cmac2012 · #39 07-23-2006, 10:48 PM

I hold onto a suspicion that steam could still be useful in cars or trucks. The Stanley steamers could go over 100 mph and had great, smooth torque. Plus, the external combustion arrangement allows about 1/10th or better the pollutants. It might be more practical for trucks because a piston steam vehicle could be essentially direct drive, even with a clutch and tranny. The clutch wouldn't be needed in initial acceleration where a lot of the wear and tear comes on a clutch. A piston steam car starts from rest, with sufficient steam available. The clutch could be used to disengage from one gear to another. The Stanley had no tranny and a 1906 model still holds the record for a steam car at 127 mph.

One often hears, or used to hear, people say, "well, if Bill Lear (inventor of the Lear Jet and the 8 track tape) couldn't make a steam car work, no one can." I don't buy it. Lear was an a$$ in the project from what I heard and I found someone who concurs with that at a steam enthusiasts web site:

Yes, the Lear turbine did work well, it was the rest of the powerplant that caused endless problems. They just tried too many high tech ideas out at the same time, had no time for real development and while the bus ran for a short time, the other components failed far too often. Coupled with Bill Lear's massive ego and yelling at everyone also getting in the way. His idea was that it was his money and he could dictate everything connected with the project. He didn't even know what he was looking at.

Also, as with the Monte Carlo sedan conversion, if it didn't work perfectly the first time, out it came and another whole idea was inserted.

First that silly Deltic engine, then staged screw expanders, then a gas turbine, then the Learium ( we called it DeLerium, a total fraud), and finally the turbine, which was supposed to use DeLearium as the working fluid; but wound up using plain water.

Lear's chief engineer in the beginnning was a fraud and a con artist of the highest caliber. He led them down the wrong path again and again until Lear fired him. Coupled with the basic problem that not one person at Lear Motors knew one damn thing about steam cars, nor did they want to be educated. It was engineering by decree. The whole thing was doomed to failure and it did, after they spent $17 million dollars.

From: http://www.steamautomobile.com/ForuM/read.php?1,1424