New engine sends shock waves through auto industry

How about the gt's in racing powerboats gearbox is very small compared to the engine as it was originally part of it.
I wonder how the all up weight is, must be close as they are a bit more horspower and a bit faster..when they run?

 

Tell it to the unlimited hydro builders; I'm sure this would be great news to them. The Allison (Now Rolls-Royce) 250 series engines make 300-800 HP. Their integral gear reduction provides an output shaft speed of ~6000 rpm. This is a fact, not a fallacy. They weigh from about 140 lbs for the 300HP models to just under 200lbs for the 700HP models. Is 6000 RPM an unusable output shaft speed to run a typical marine prop for a fast planing craft? I don't think so.

They are pretty thirsty, though

Jimbo

 

Those million pound class locos were an awesome thing; still not rivaled by any single loco made today.

Jimbo

 

Well, I don't know who did the gearbox that you were using, but a gearbox for that size engine doesn't need to weigh that much at all.

Turbine speed is related to power. Bigger more powerful engines turn slower, but since the prop or a waterjet that absorbs that much power also turns slower. An engine turning in the 17,000 rpm range is generating a bit less than 5,000 hp. The AE2100 engine makes that much power and has a gearbox that brings the 16,000 rpm power turbine shaft down to 1040 rpm. The entire engine and gearbox weighs 1600 pounds.

I would suspect that whoever did that gearbox was used to doing gearboxes for diesels, and the tooth loading for a reciprocating engine gearbox needs to be a lot more stout than a turbine. But a gearbox for a waterjet (since it doesn't require reversing) doesn't to weigh anywhere near that much. We commonly use a single stage reduction followed by a planetary set to provide the total 15.4:1 reduction ratio. It doesn't take much design talent to overdesign something.

You need to find another gearbox house.

 

That’s what we thought too…but all the usual suspects, Twin Disc, ZF, etc etc, all had similar size and weight gear boxes. Thus the salesman pitch evaporated very quickly.

It produced 4.5MW

Sorry, again, to dispel the myth.

Our arrangement came in at 8.5 tonne, engine and gear box.

Then of course the very very heavy air filtration units, then the very heavy exhaust lagging and of course the air assists and extra additions required by Class. This added a further 5 tonne.

All up, for the 4.5MW installation using GTs, the saving in weight was around 5-10% over that of a conventional diesel installation. But with GTs much much more fuel is needed. So, all up…no gain.

Figures for weights etc, as noted here, are generally for those little run abouts. I’m referring to big real boats carrying crews, passengers, cargo etc.

 

This statement about the relative robustness of a gearbox for a reciprocating engine versus a turbine is not just true, it is *Profoundly* true!

Reciprocating aircraft powerplants abound, and they virtually all have pretty dismal weight/power ratios compared with a high performance auto or motorcycle engine. And why is that? It's because most are direct drive. Propellers can't be turned too fast lest the tips exceed mach 1, so this very strictly limits engine RPM. Increasing RPM with constant torque effort is the easiest way to increase power outout, yet this simple expedient is not available to the designer of a direct drive aircraft engine.

So why not just use a gear reduction? The past is littered with the numerous failed attempts to make a light gearbox that will work reliably on a reciprocating aircraft engine. All the major manufacturers have made them and they are universally hated by pilots and mechanics, especially mechanics. The power pulses and harmonics of a typical piston engine work to destroy the gearbox in a short time, unless it is built like a battleship.

It's a completely different story when it comes to a smooth power source like a turbine; light reliable gearboxes are the norm with turbines.

Jimbo

 

6000 rpm for a race boat yes and the unlimited hydros are over 4000hp but all use the original reduction as they were helicopter engines just like the offshore race boats which are from 1500 to 2000hp.

Dont forget Mercury sells a 1350hp Euro/EPA spec engine +tran+drive just under 800kg

So I guess if you need commercial displacement prop shaft speed of under 200rpm the gearbox is going to be big?
30:1 or something after the box in the engine?

 

CFM56, V2500. Please don't shoot

 

I though many had thermal efficiancy like a diesel hence there use in small power stations?
Wasnt that the claim to fame of the old RR Olympus as a stationary engine?

 

No, there are shaft engines in the 1200 hp class that are designed to produce an SFC of less than .4 lbs/hp-hr... Diesels are in the .36 to .38 range so it is close....

 

And if it lasted more than a couple of hundred hours at full power it would be a miracle. You can get big power out of a supercharged recip, but it won't last long. A gas turbine can have a life of thousands of hours and it will still have a far superior power to weight ratio.

What happens is that, for a turbine, even though the speed ratio is large, the weight is generally lighter than a gearbox for a comparable diesel. There are a couple of reasons for this. First is the afforementioned lack of torque pulses, but second is that the first stage of the gear train doesn't weigh much. That is because power is torque times speed, and if speed is high, torque is down, and torque drives the weight of the gears, the box itself, and the size of the shafts. As you enter the final stage of reduction, (where most of the weight is) you are generally still spinning two or three times as fast as a diesel. As a result you end up with a larger diameter final dirve gear, but, since the torque coming into it isn't large, the tooth width doesn't have to be that big and the gear doesn't have to be heavy. To keep the weight down the key is to not use large helical angles, which keeps the thrust load on the gears down and keeps the weight of the gears reasonable.

If you use the "rules of thumb" for power torque and helix angles from a recip gearbox for a turbine gearbox it will weigh, literally, tons. But reliable gearboxes for turbines are common and they don't have to weigh all that much.

 

What you have to compare is the cost per kW of electricty and in that is the cost of fuel. Generally even industrial gas turbines don't have quite the fuel efficiency of a diesel, close but not quite.

But in a ground power application, you can burn natural gas. The cost per BTU of natural gas is far less than diesel fuel, so if you want to make power cheaply, you burn natural gas.

If you convert a diesel to natural gas, the engine produces less power (from the lower compression ratio and poorer volumetric efficiency), so the cost of the installed engine, per kW is worse. Moreover, the fuel burn is worse because of the lower compression ratio. Big gas turbines are more efficient than reciprocating natural gas engines, they make more power and cost less per kW of power produced, in first cost, maintenance cost, and fuel cost. For those reasons, natural gas burning powerplants are, for the most part gas turbine territory.

 

It's worth viewing these stats.

2006 Miss GEICO Mystic #113

Builder: Mystic Powerboats
Materials: Carbon, Kevlar, S Glass
Length: 50 feet
Weight: 10,000 lbs
Type: Jet-A
Engines: Whispering Turbines Inc. T-53 703 series
Horsepower: 2100 x 2
Top Speed: 210+ mph

http://www.missgeicoracing.com/

Watch the videos.

Bottom middle "New Mystic C5000-R sea trial" shows the compact size of the turbines.


http://en.wikipedia.org/wiki/Miss_GEICO

P

 

This might be the best thing since sliced bread, but the originators do themselves no favours by making such wildly inaccurate claims. Typical gasoline car engines are around 28% efficient, with the better ones being over 30% efficient, so claiming that they are 15% efficient is plain wrong. Similarly, they are very, very few ordinary car engines that weigh anything like 1000lbs, most modern car engines will come in at half that weight or less, so quite how this engine could knock that much weight off the total weight of a car is a mystery.

My guess is that all the figures being quoted by these people have to be at best untrustworthy, at worst complete BS, based on the obviously false statements they've made.

It's on old idea that has been looked at a few times in the past, but like all rotary engines there are challenges to overcome with sealing and seal lubrication, as has already been mentioned.

Jeremy

 

If you count the extra fuel that smaller gas turbines consume, there is no weight savings at all. Only really large gas turbines (like used on commercial aircraft) are anywhere near efficeint enough to be viable. The smaller ones are light and compact, but not efficient at all.

This engine concept is more of a couriosity I think than viable. the claims are so completely outrageous I would say they are coming from someone who knows nothing about engine, efficiency and thermodynamics. The wiki articals says 3.5 times more effienct, and normal car engines are only 15 percent efficinet. Just not true and not possible. Modern car engines are closer to 25-30 percent or more efficient. Despite the mechanical simplicity (fewer moving parts) the combustion chamber shape if far from ideal, so there is no way it can be any more efficient. the same physics apply to this engine as any other.

It might be more compact and lighter, if they can actually make it work at all, not likely it is more efficient. In moving craft like boats, cars and aircraft, there are a lot of other considerations besides just efficiency. Like reliablity, size, throttle responce, emissions, cost, safety, etc.

They have over a century of development on the conventional piston engine to catch up on with this invention, I seriously doubt it will replace modern engines any time soon.