I recently watched a show about a Swedish submarine powered by a Stirling engine. It was a fairly large attack sub that could stay submerged for three weeks in spite of being "conventionally" powered. The engine ran on kerosene and was so quiet that the sub was virtually undetectable. The sub was so effective it was being inspected by the U.S. Navy.
I can't help but wonder if a Sterling engine can perform so well in a submarine, how would one do in a locomotive?
Having an external heat source could allow flexibility in combustion and choice of fuel.
The Sterling engines that I am familiar with are small models that hobbyists build, like the low temp. difference engine that runs on the heat from the palm of your hand or sitting in the sunlight, and the ones that look like a chunk of pipe over a bunson burner.
I suspect Sterling engines don't react quickly to large changes in load, and that would be fine for a large engine in a submarine where slow speed and constant load aid in stealthiness.
Could a large Sterling engine be built to efficiently handle large changes in load? I know in the past there have been Sterling engines built comperable to automobile engines, could such an engine function in a genset-battery setup?
Also, after having read about the problems facing Tier IV four stroke engine developement, I have some suggestions:
Bring back the Inline engine. Current power per cylinder is already justifying engines with fewer cylinders. Inline engines are more robust and can handle higher power per cylinder, and an inline configuration will solve packaging problems with external environmental control systems.
Slower speed. Lowering RPM is the simplest way to increase combustion time, helping to control temperature and combustion process.
Rod ratio. Increasing rod ratio will give greater dwell time over top dead center allowing more time for combustion.
Decreasing bore. Decreasing bore will help piston sealing and help eliminate dead air space along with other current trends like raising hight of top ring land.
Increase stroke. Increasing stroke can allow higher peak pressures while controlling temperature by giving greater distance to piston travel.
I guess the last three suggestions are contradictory - you can only fit so long a rod in so narrow a bore for a given stroke, but hey engine design is a balancing act right?
Space constraints put a pretty tight limit on what can be done with a diesel engine in railroad service. Also, the track record of large-bore, slow-turning inline engines in rail service has not been good, the maintenance expense of a De La Vergne engine was appreciably higher than a 567 or even a 244. A slower-turning inline engine would need a new main alternator designed to the performance curve of that engine. Consider the problems that EJ&E had when they repowered their Baldiwn centercabs with V-12 567 engines but kept the Westinghouse main generator.
A new engine designed along the above parameters, assuming it would fit in the loading gauge, would need a new main alternator and other auxiliaries, driving up the development cost.
More info on the use of a Stirling engine in the Swedish submarine is at
http://www.deagel.com/Submarine-Propulsion-Systems/Stirling-AIP_a001357001.aspx
What they are doing is burning liquid oxygen and fuel to run the Stirling engine, and then they dissolve the combustion gasses in seawater in order to discharge them without giving away their location with a trail of gas bubbles.
If you think about it, instead of using a storage battery to store energy, you store energy in tanks of fuel and tanks of liquid oxygen. Instead of using a fuel cell to convert that to electricity to run a motor, you power a high efficiency Stirling engine. Maybe a fuel cell would be more efficient and have longer range, but not by much if your Stirling engine is pretty good.
I suppose you could even surface and use a Diesel engine to run a liquid oxygen plant to recharge the supply of liquid oxygen, but I don't know if they do that.
One thing you have to remember about a Stirling engine is that it needs a largish radiator to discharge the waste heat. With a gasoline or Diesel engine, you still need a radiator, but most of the waste heat goes out the tailpipe and the radiator only discharges the heat that leaks through the cylinder walls. With the Stirling engine, all the waste heat goes out the radiator as you are running a closed cycle on the working fluid and can't discharge waste heat as exhaust.
In the submarine, you have all of that ocean water to cool the radiator, but in a locomotive, you may need big air-cooled radiators. Maybe not as extreme as those South African steam engines with the enormous condensing tenders -- the Stirling has much higher fuel economy and the radiator can be proportionately smaller -- but you need much bigger radiators than on a DIesel.
Needing a big radiator is not an insurmountable engineering problem, but if the question comes up "why do they have Diesels on locomotives instead of Stirling engines", one of the answers is the Diesel needs a much smaller radiator, and you know that the radiator is one of the big components of a high-horsepower Diesel locomotive to begin with.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Back in the 50's, GM / Cleveland Diesel / EMD built and experimented with a Sterling engine hoping to achieve high thermal efficiency. They even resorted to hydrogen as the working fluid but couldn't solve the leaking problem. I guess the improvement in efficiency over diesels wasn't enough to stand the hassles and they put it aside.
At the Kitsap County Antique Engine show they usually have some Ryder engine version of the Sterling cycle and the only noise is the hiss of the fire but they are very bulky for the power they produce.
Ironically if you drive a sterling cycle engine (thermodynamically backwards - power in and heat out) you can use it to liquify air. They are also used to drive refrigeration on truck units because they are so quiet.
I guess Sterling engines are more common than I thought.
The link is cool, I'm surprised to learn that the submarine plant has been around since 1980.
Combustion in the presence of sea water, I wonder what the combustion chamber looks like.
It seems to me that in a very general view, since the early nineties, that horsepower increases in truck sized engines almost challenge the paradigm of locomotive sized engines, and a way foreward may be with something that combines characteristics from both classes; for example, an inline 2 or 4 stroke engine with individual cylinder heads and a displacement in the neighborhood of three hundred cubic inches per cylinder.
I guess the question is whether the leap to a completely new engine is justified. It seems to me a more compact engine would allow more flexibility in placement and room for auxiliary equipment. Maybe an inline engine using existing components is a solution.
I guess there is also the question of horsepower per unit, seeing there are already plenty of choices for lower horsepower applications, a locomotive in the 4000 hp range would be a challenge with an engine limited to six or eight cylinders. A six cylinder engine over six hundred horsepower per cylinder would be a challenge.
I also wonder if battery technology could be used not so much for storage capacity as for smoothing power pulses - a hybrid battery-inverter would allow flexibility of other components.
It was pointed out in the EMD rising thread that there are poeple earn'en the bucks who know more about this stuff, but I hold the belief that wondering aloud may be of use to someone somewhere.
- infinite wisdom is transient, pass it on! -
- for every action there is an equal and opposite malfuntion -
My understanding is that while Sterling engines are very efficient in certain applications their low power-to-weight ratio make them not a very attractive option for powering large land vehicles.
In the submarine air -independent -propulsion system you mention they work quite well, although keep in mind the subs using that technology could be considered very underpowered compared to a US Nuclear Steam Turbine powered vessel (one reason that the US has an all Nuclear sub fleet). Basically the Sterling engine acts as a range extender on the traditional battery electric setup (charged by diesel gensets while the boat is on or near (via snorkel) the surface).
As far as inline diesels, GE is currently offering inline 6 & 8 cylinder versions of the GEVO engine as a repower option for medium horsepower (22000-3000 HP) locomotives. So far they have no orders...
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
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