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Old 30-06-2013, 13:55   #31
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Re: Gas Turbines?

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at what point does sucking in dog hair become problematic?
When the dog is still attached ?
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Old 30-06-2013, 14:00   #32
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Re: Gas Turbines?

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Turbines are simple in theory, the tolerances and materials required make them very expensive, and at the RPM they run, failure is catastrophic.
Actually not all that true any more - I routinely work with pumps turning at 100,000+ RPM, and the impellers are machined on standard 5-axis machine tools from aluminium relatively cheaply. The only special materials are needed for high turbine temperatures to get up to the ~40% thermal efficiencies required by commercial jets. Marine diesels are more like 30%, which can be achieved by fairly conventional nickel alloys.

Failure also isn't all that bad - in my previous job one of my responsibilities was to deliberately destroy the rotors on pumps turning at 60,000 - 100,000 RPM to confirm the containment worked. The only issues we had were with bolts failing - the 1/2" aluminium walls were always strong enough.

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Rotary engines generally are the most compact and lightweight, inexpensive, and are being used in UAVs. I've heard there are developments to use them for hybrid cars.
That does seem to be the way things are going, although I'm far from convinced they're suitable for anything beyond outboards and racing boats. I can't really envisage them getting the compression ratio up high enough, given the nature of the seals within the engine.
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Old 01-07-2013, 11:15   #33
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Re: Gas Turbines?

Something like 20 years ago I was at Solar Turbines' plant in San Diego. While there I saw a small turbine generator unit that was produced for the army's use. It was in a sound reducing container, could be picked up by two men, and would happily run on diesel, gasoline, kerosene, propane, natural gas or about anything else that burns. Was used to power up field operations. Assume that they have been improving these as time has marched on.
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Old 01-07-2013, 12:13   #34
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Re: Gas Turbines?

If you think a deisel is noisy, just try sitting 10 feet from a jet or turbine engine. I used to sleep on an aircraft carrier where the jets would basically stop over my face, with just 16" of steel between me and them. I could sleep fitfully, but it was not a restful, peaceful sleep.

The deisel in the back of my Ericson was much more pleasant to listen to. Not pleasant mind you, but the frequencies are lower and quieter.
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Old 01-07-2013, 13:40   #35
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Re: Gas Turbines?

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If you think a deisel is noisy, just try sitting 10 feet from a jet or turbine engine. I used to sleep on an aircraft carrier where the jets would basically stop over my face, with just 16" of steel between me and them. I could sleep fitfully, but it was not a restful, peaceful sleep.

The deisel in the back of my Ericson was much more pleasant to listen to. Not pleasant mind you, but the frequencies are lower and quieter.
Ericson diesel = ~30 hp
GE F110 (Tomcat, etc.) = 45,000 hp per engine *

In other words, you're saying a pair of engines ~3,000 times larger was a bit more obnoxious. If anything, that's evidence that a well developed gas turbine might actually be quite well mannered.

* GE F110 produces ~28,000 lbs of thrust, which doesn't translate directly to power. However, a Rolls-Royce Avon comes in power generation and aircraft versions - at ~15,000 lbs of thrust or ~22,000 hp. Hence the translation of an engine capable of ~28,000 lbs of trust being capable of ~45,000 hp.
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Old 01-07-2013, 17:27   #36
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Re: Gas Turbines?

The Chrysler turbine was a fuel sucking hog and reputed to be deemed a fire hazard. If memory serves me the Abrams tank engine is a lot bigger, i've built parts for that... roughly 32" diameter....
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Old 01-07-2013, 20:19   #37
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Re: Gas Turbines?

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Ericson diesel = ~30 hp
GE F110 (Tomcat, etc.) = 45,000 hp per engine *

In other words, you're saying a pair of engines ~3,000 times larger was a bit more obnoxious. If anything, that's evidence that a well developed gas turbine might actually be quite well mannered.

* GE F110 produces ~28,000 lbs of thrust, which doesn't translate directly to power. However, a Rolls-Royce Avon comes in power generation and aircraft versions - at ~15,000 lbs of thrust or ~22,000 hp. Hence the translation of an engine capable of ~28,000 lbs of trust being capable of ~45,000 hp.
I saw a small one on Bang goes the Theory, it was on TV, so I could not hear how loud it actually was. It was still noisy and high pitched. The demonstrator was wearing the same ear protectors we used on the flight deck. I would still prefer either my 4hp outboard or the old 4hp diesel I used to have to one of these under the lazerette.



The Jet engine is on the right, This is a demo of how a little rocket engine packs more punch than a slightly larger jet engine.
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Old 01-07-2013, 21:14   #38
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Re: Gas Turbines?

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Believe it was Chrysler built a few prototype turbine cars back in the '60s. Nothing came of it probably because the cost of the turbine among other things.
Rover in the UK also looked into it, the P6 was designed with a free engine bay and an innovative front suspension to make room for a turbine. It wasn't engineering or construction costs that collapsed that project and caused the P6 project to be fitted with the V8 and given the production name of P6B. What killed it was the metallurgy of the 60's and 70's wasn't up to the grades and purity required at the allowable costs. Modern metals and ceramic composites are available in much purer alloys and for cheaper. Modern metals science has moved on and made producing the raw materials much cheaper and more accurate, and if 70's tech was up to construction, how much better is modern construction!
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Old 02-07-2013, 00:56   #39
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Re: Gas Turbines?

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I saw a small one on Bang goes the Theory, it was on TV, so I could not hear how loud it actually was. It was still noisy and high pitched. The demonstrator was wearing the same ear protectors we used on the flight deck. I would still prefer either my 4hp outboard or the old 4hp diesel I used to have to one of these under the lazerette.
If you're using a turbojet for thrust (as they appear to be), the gas leaves the engine at supersonic speeds. That causes a huge amount of noise, both from turbulent mixing and shockwaves. If you're using it to drive a turbine, it isn't supersonic so the volume will go way down.

Incidentally, I'm more optimistic than I was about how easy these would be to silence. A small amount of digging turns up this silencer which has some fairly impressive silencing for moderate weight (~120 lbs).


Given that the Capstone unit is rated at 65 dB(A) and that silencer is rated at 25-30 dB(A) for the synchronous speed of the turbine, that takes us to ~40 dB(A), far quieter than just about any marine engine going. So it's possible to do it quietly, the problem appears to be cost rather than anything else.
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Old 02-07-2013, 03:40   #40
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Re: Gas Turbines?

To develop the idea a bit (since I'm really bored), I thought I'd take a look at charter catamarans since they are the best chance of replacing many engines with one/have the highest likely house electrical loads. That puts the Lagoon 420 the obvious place to start as it comes in both versions.

Hybrid is 13,380 kg loaded, max speed is 8.4 kts*
Diesel is 12,170 kg loaded, max speed is 9.2 kts

That looks about right - the various owner comments on here seem to say it's about a knot slower. Of this difference, going by the model about a third is due to lower hull speed and the rest due to lower available power.

A Yanmar 40 hp diesel is ~173 kg, the 11kW generator most of them seem to be fitted with is ~315 kg and the house batteries appear to be 6 x 74 kg. That's a total of 1105 kg (!), implying the "hybrid" system weighs 2,315 kg.

Assuming the batteries are only there for harbour use and to minimise running the generator, that means the generator needs to be sized for top speed. Since Capstone seem to be the only people selling them right now, that means a C30 unit at 405 kg for the standard version. incidentally, this is rated to be the same noise level as the generator currently fitted.

That in turn implies 15 kW drive units - around 40kg each. Incidentally, 15 kW is a bit of a goldilocks number - it allows you to keep to 48V systems which don't require any special safety precautions.

Next, assume we're using LiFePO4 batteries. Most of them (if I'm understanding this correctly) can be charged at 1C - i.e, if it's a 100Ah battery, you can charge at 100A.
Assuming a nominal run time of 1 hour to charge batteries fully, that gives a 30 kWh battery bank.
The Mastervolt ones are 58 kg for 5 kWh, so 290 kg in total. Add in a handwaved 100 kg for battery management/inverter

That gives a total of 875 kg, for a total boat weight of 11,940 kg. Applying the same method as before gives a boat speed of 9.4 kts - slightly faster than the standard diesels. This should also be a lot lower maintenance than the current 3-diesel system.
In real life nobody is going to take the risk (especially with the rumoured price of $1,000/kW for the Capstone units), but if I won the Euromillions I'd be very tempted to try it...

* using the calculator here, assuming 3 hp = 1kW, which seems to be a common rule of thumb to compensate for the more efficient propellers
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Old 02-07-2013, 06:08   #41
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Re: Gas Turbines?

Are we not talking about an APU as usually found on commercial aircraft? Used ones appear for sale periodically. They are very expensive to maintain, are very noisy, burn a huge amount of fuel, but are very small and light for the amount of elec produced.

I have never heard of anyone using one on a boat, but if there is anyone, tell us about your experience.
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Old 02-07-2013, 06:22   #42
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Re: Gas Turbines?

Not really - the examples I'm thinking of seem mainly to be used as emergency/backup generators on land, with a handful of other uses (burning landfill gas is a common one, since piston engines have problems with that). Fuel efficiency and noise levels seem to be broadly similar to a diesel generator, but with much better time between overhauls and vibration levels.

APUs are all about light weight, and nobody really cares about fuel consumption or noise. With generators, that isn't really true and so they're much more suitable for marine applications.

This is the only marine example I can find, on a liquefied natural gas barge for the Rhine. I'm guessing they aren't used for propulsion though...
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Old 02-07-2013, 07:08   #43
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Firstly, if you think fitting a turbine engine will save you money on fuel, forget it. They use loads of fuel as sea level and only reach high efficiency when they have a good supply of ram air and are operating at high altitude ( why do you think jets fly at 40,000ft?) as a side note, they can and will run on just about any flammable substance you can atomise properly in the can. Some ag plane operators run their planes on normal diesel/Avgas/Jet A1 whichever is close by.

They can be made very quiet if you design them properly. A turbo fan would be best as you could bypass a lot of the air around the engine to help diffuse the noise of the internal workings and exhaust gases.

Just as an example of how efficient they are: a garrett TPE331-10 turboprop produces around 3000hp but uses 2000 of those HP to drive the engine and gearbox and the other 1000 for driving the prop. Full power you are looking at around 420-450lbs/hr fuel and idle is about 120-140lbs/hr. that being said, they can produce almost max power at high altitude (27000ft) at only 250-300lbs/hr.

Maintenance wise they are awesome though. Very few controls or electric bits if you get a simple engine (lots of electrics if you have a fancy one). You can run them for hundreds or even thousands of hours before you have to change any filters or inspect anything (maybe not if you run them on dodgy fuel) some modern passenger jet engines don't even get an oil change between overhauls.

Finally, they are not designed to be started and stopped often. This is when most damage will be done as different parts of the engine cool at different rates and sometimes the blades can rub on the diffuser etc. basically they are designed to be started once and left to run forever (in a perfect turbine world)

They are actually in UAV's too. The yanks use them a lot as they are quiet and relatively trouble free (perfect for sneaking about the skies)

But if they can invent one that works, then cool, they will be rich quick and I'll stand corrected.


Ben

Ps turbines are heaps of fun to play with
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Old 02-07-2013, 08:57   #44
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Re: Gas Turbines?

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Firstly, if you think fitting a turbine engine will save you money on fuel, forget it. They use loads of fuel as sea level and only reach high efficiency when they have a good supply of ram air and are operating at high altitude ( why do you think jets fly at 40,000ft?)
Actually that has very little inherently to do with the engines - they have been optimised for that particular role because that is the best place to fly. Skin friction drag is a lot lower in the thinner air, and the ride is incomparably smoother/safer. As soon as jet engines made it possible to fly at those altitudes, airlines wanted to.

A Yanmar 3YM30 burns 3 l/hr at 3000 RPM and produces 12kW at the propeller. That's 0.25 l/kWh, or 208 g/kWh - which is really very good for a small diesel. However, at 2000 RPM that drops to 290 g/kWh.

A large marine gas turbine like the WR-21 will manage ~190 g/kWh. The Capstone units I've been using as examples are around 290 g/kWh - so in reality the fuel consumption will be 10-20% worse for a gas turbine series hybrid than for a diesel.

However, fuel consumption isn't the only cost here. Diesels are comparatively complex machines and need a lot of servicing. The gas turbine I'm using as an example has an air filter change recommended every 8,000 hours and a factory rebuild every 40,000 (although I would assume it's less in a marine environment). Contrast that with the Yanmar example - you have work to do at 50, 100, 150, 250 and 1,000 hour intervals. If you're replacing 3 engines, particularly in the charter market where you have to pay someone to do the checks, that stars to get expensive. Add in that most people on here seem to think 10,000 hours a normal life for a marine diesel and the picture gets more complex.

Given that this forces you down the route of one high-power generator for the whole boat, you get other run time efficiencies as well. Assuming no air conditioning, the sort of battery bank this demands could run most boats for a week before being recharged in an hour from the main engines (in turn driving you towards electric cooking, but that's another thread). You exchange 10-15 generator run hours for one turbine run hour - and note that generator fuel consumption tends to be fairly high, around 300g/kWh.

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They can be made very quiet if you design them properly. A turbo fan would be best as you could bypass a lot of the air around the engine to help diffuse the noise of the internal workings and exhaust gases.
I think you're better off paying attention to good sound isolation/attenuation. In any case the C30 I'm using as a reference does something else:

The big thing around the GT unit is a recuperator. Basically it's a heat exchanger that uses the hot exhaust gas to heat the newly compressed incoming air to save fuel. Not practical on aircraft engines since it's big and heavy, but a good idea on stationary applications. In fact, I suspect it might also be an ideal candidate for spray intercooling - with a recuperator you should see a noticeable efficiency improvement.

Incidentally, it doesn't look to me like they're trying very hard to get the size or noise down - lots of empty space, redundant framing and no exhaust or inlet silencer on this example:


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Maintenance wise they are awesome though. Very few controls or electric bits if you get a simple engine (lots of electrics if you have a fancy one). You can run them for hundreds or even thousands of hours before you have to change any filters or inspect anything (maybe not if you run them on dodgy fuel) some modern passenger jet engines don't even get an oil change between overhauls.
Better than that, the Capstone design I've been using as a reference has an air bearing and is air cooled. That means no coolant or lubricant to worry about - just air, fuel and electricity.

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Finally, they are not designed to be started and stopped often. This is when most damage will be done as different parts of the engine cool at different rates and sometimes the blades can rub on the diffuser etc. basically they are designed to be started once and left to run forever (in a perfect turbine world)
I suspect this is design specific. In any case, to account for tolerances a smaller engine will have about the same radial gap but will expand by less (same %), and will warm up/cool down faster due to smaller thermal inertia.

p.s. can you tell I'm an engineer who did gas turbines at university and high speed machines since?
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Old 02-07-2013, 09:22   #45
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Re: Gas Turbines?

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Are we not talking about an APU as usually found on commercial aircraft? Used ones appear for sale periodically. They are very expensive to maintain, are very noisy, burn a huge amount of fuel, but are very small and light for the amount of elec produced.
I have never heard of anyone using one on a boat, but if there is anyone, tell us about your experience.
Yeah, an APU is not real large. I dont know what you do with all that hot exhaust on a smaller boat. Be a good fast swamp boat though with the turbine up and exposed!
There are a lot of turbine engine boats..... but all fairly large craft. The Seattle to Victoria BC catamaran ferry has turbines. Pratt and Whitney sells a line of marine turbine engines.
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