Gas Turbine Generator for Hybrid Trawler?

Thank you everyone, I am hopeful to use a microturbine electric hybrid in my retirement home, currently planed to be a 75' wavepiercer. This is still many years away. Capstone is doing great things with electric hybrid automobiles right now, and there are a great many different things on the internet. But I think this is going to take someone with the desire to see it done actually do it and then have everyone copy along in good engineer fashion.

 

," but I think most mechanics would love you for it: go to boat, remove broken unit, insert spare unit, take broken unit back to spacious well-lit shop for repair."


This is exactially the concept used today for tour or dinner boat HVAC systems.

Heated or chilled water is circulated to every cabin or zone , but the freon unit is one of 3 to 5 modules that are self contained.
The modules are yanked and ONLY circ water is touched by the crew , all the refrigeration and heat are in each module , that a licensed freon service repairs. Having working onboard spairs is done by simply making the system have more units.

No replacing from stores while a unit merely needs to be switched on.

The BIG boat main engines currently have fuel burns that are over 50% efficient.
With enough engineering perhaps this could be done (not cheap they all use turbos) in either an air cooled version or water cooled version that becomes cheap by large production runs.

Today a 50% turbine is not in sight , but 50% diesel's are working worldwide .

FF

 

50% efficient diesels are very big, and very heavy...
In fact, Warstilla is over 60% right now, very impressive if you consider they are on the theorical limits of the diesel cycle, but the engine is 6m high...

But you are speaking of low speed engines (<200rpm), and I haven't seen yet a "boat" with such engines.

I don't have precise data, but I thought that the diesel we are using are just above 30% of efficiency...

Considering that, small turbines seem to be a convincing solution, especially for vibrations and noise.

 

To me a gear box would be the problem ,$$$$$, turbines run at high!!! speeds and 100 to 500 is a nice shaft speed.

Even 1000rpm boat shaft would be a 30-1 to 70-1 reduction.

An old truck turbo or two with a simple carb in the intake , and a spark plug, (kerosene or diesel) and you have the turbine , but actually using the power would be a problem.

FF

 

Maybe...
I am used to diesel electric propulsion on the ships I design, so I didn't see the problem here. The efficiency of electric propulsion is impressive nowdays. The losses are below 5%, and that is compensated by the accuracy of the choice on the propellers speed with a constant speed on diesel engines.

But the cost issue will clearly be the problem on a trawler...

 

Tyical high speed diesels have a Specific Fuel Consumption of about .36 to .38 lbs/hp hour. That equates to a thermal efficiency of about 38-36%. Not bad at all.

It depends on what you are driving as to what kind of gear ratio you want. If you look at a typcal small 500 hp turbine you are looking at power turbine speeds of about 36,000 rpm. If you look at a waterjet that absorbs 500 hp you are looking at 2600 rpm or thereabouts. That means a gear ratio of about 14:1.

If the boat is running a prop with high cruising speeds, the prop might run a good bit faster, so it depends on what type of drive you want to use and how fast it runs as to how much reduction you need. While the shaft speeds are higher, remember, the gears are smaller and aren't as expensive. We recently did a two stage gearbox for a 500 hp tubine marine application and it was a bit more expensive than a single stage box for a diesel, but remember the gears for a diesel have to be wider and more beefy to take the pulsation forces that the reciprocating engine makes and that makes the everything in the gearbox like the bearings and shafts heavier for a diesel.

 

If you are going with an electric drive, a gas tubine could be a pretty interesting alternative. A high speed alternator is going to be a lot lighter than a diesel powered machine. On a trawler it might not be that important. but a typical 40 kw gen set weighs about 1200-1500 pounds, a comparable small gas turbine gen set would weigh about 200 pounds and take up not much more room than a big suitcase, and fuel consumption would be close to that of a diesel. Problem is it would cost probalby twice as much as the diesel. We tend to think that might be a good trade, one stateroom for the extra $15,000 you would spend on the turbine as compared to a diesel as a gen set on say a 80 foot yacht...

 

Ok, so "doable" with existing technology

From what I can see, the cost in a turbine is in the blades. So how about a Tesla turbine? Ya know he had a working generator powered by one of his bladeless turbines (steam). Seems that it would also be pretty much imune to the marine environment also.

And again, I bring up the CHP (combined heat and power) concept as I feel any thoughts on efficeincy should include the reductions in those systems enabled by using a device that has as a byproduct so much heat. Even cooling can be produced from it.

Steve in alaska

 

Heating is a good point for Alaska...

 

CHP is very good, but it costs a good bit if you want to get useful work out of it. Gas tubines with heat recovery are efficient (about 33%), but the temperature coming out of the exhaust isn't hot enough (around 600 degrees F) to do anything more than space heating unless you use organic rankine cycles and ORC's aren't very efficient. If you are space heating, a 1,000 hp turbine can heat or cool a Wal Mart, so unless you need process heating there isn't a lot you can do with waste heat in a marine application. Better to try to get higher power efficiency from the system.

If we are talking ground based sytems, then CHP makes a lot of sense. We are doing a DoE program with a goal of 50% thermal efficiency from a combined (gas turbine with a Rankine bottoming cycle) cycle system. The waste heat is at about 300 degrees F so you can still use it for heating or a one stage chiller. The cost goals are pretty impressive, similar to a 1,000 hp diesel.

 

The Tesla Turbine is pretty interesting, in theory, but there's no such thing as a free lunch. In order to get high power density you want high rotational speed. Since the outer diameter of the disk is hotter than the inside the thermal growth near the rim reduces the stress in the outer part of the disk and increases the stress near the bore. In order to keep the stress down the disks need to be thicker at the bore than at the outside. This limits how many rotors you can have in your system, and increases the windage losses on the outside of the disks. The Tesla concept has thin gaps between the disks and you need a lot of disks with nothing in between them. That brings us to the next topic.

Also you have to take into consideration the shaft dynamics. You have to get the first shaft bending mode above the operating range (you can take the first bounce and the first rocking mode below the operating range with soft shaft supports). What this means is that you can't have too long a shaft and this again limits how much work you can do.

No question that the theory works, but it isn't easy to make a practical machine out of it.

Smaller turbines typically cast the blades as part of the disk, the cost of these rotors isn't bad, but you are limited to uncooled parts and that limits operating temperatures. Much of the reason that turbines are expensive is that they don't make many of them. If the production rates were higher and more automated machining and higher production rate processes were brought to bear, then the cost would come down a lot. At GM they did a lot of work in the 80's to get the cost of a small automotive gas turbine down to near that of a V8. They got pretty close, but never quite got to parity or lower cost then the recip. Turbines, once they are running are very clean, but on startup there is usually a good bit of unburned fuel that goes out of the exhaust. Startup emissions were never going to be as good as a piston engine if you wanted to start quickly, and the increasingly tighter controls on that aspect is part of what killed the program.