What happened ? ...

[Jim GM4DHJ ...]

unless it is on a smart motorway ....

[nightjar]

Nor did I claim it was.

Only if it is an uncontained failure, which is why aircraft engines now have containment chambers around them.

[Jim GM4DHJ ...]

[Jim GM4DHJ ...]

[Vir Campestris]

I was on a ship recently and asked why they use diesels not turbines.

Too thirsty.

I think the only reason they work in power stations is because of the combined cycle saving the exhaust heat.

Some warships do use turbines, but it's not common.

Andy

[The Natural Philosopher]

Actually not, but gas turbines cant run on bunker oil which is pretty cheap.

No, because they are more efficient than diesels from the get go.

Straight gas turbine about 37% or a tad more. but running on gas. Diesel maybe 27% at best.

Because the fuel is very expensive.

[Paul]

The Americans use them in some of their coastal vessels.

"The Independence-variant LCS uses two GE LM2500 gas turbines that allow the ship to travel at speeds in excess of 40 knots."

The captain wants to water ski.

*******

Even the small ships have some level of redundancy. If the captain wasn't water skiing, they might cruise at a slower pace.

Installed power Electrical: 4 Isotta Fraschini V1708 diesel engines, Hitzinger generator units, 800 kW each Propulsion 2 x Rolls-Royce MT30 36 MW (48,000 hp) gas turbines 2 x Colt-Pielstick 16PA6B 6.8 MW (9,100 hp) diesel engines 4 Rolls-Royce waterjets[8][9]

*******

Paul

[newshound]

Not so sure about that. Modern aero engines are so efficient because of the bloody great fan in the front, and it's not so easy to take those supersonic!

[Steve Walker]

As soon as you go fast enough, you don't need that fan - in fact you don't need any moving parts, as you can use a ramjet or scramjet.

Getting up to speed and power at the lower speeds needed for landing would need either rocket power (it is possible for some ramjets to also function as rockets) or turbojet engines (not turbofans) in the wing (like on the Comet), with doors that close over them at high speeds.

Whether the weight penalty or fuel consumption would be practical, I have no idea.

[williamwright]

Interesting.

Bill

[The Natural Philosopher]

Bollocks

All supersonic fighters today have turbofans. Part of the art of designing them is to create an intake that gets the airflow subsonic for the fan...or make fan that can handle supersonic speeds...

It's true to say that high bypass airliner engines are not *designed* to go supersonic but that's because the fuel per passenger mile would go sky high if they did. Mach 0.8 and 38,000 ft is a sweet spot for cheapo flights..

F15 eagle..."2x Pratt & Whitney F100-PW-220 afterburning turbofans,

14,590 lbf (64.9 kN) thrust each dry, 23,770 lbf (105.7 kN) with afterburner"

Mpg aint so hot tho

[Andrew]

I'm sure I read somewhere that the RB-211 as used in Concorde had to be warmed up carefully because the main shaft had a wobble when cold.

[The Natural Philosopher]

Yes, you do.

There is an efficiency curve that determines fuel economy - turbofans are needed for that well into supersonic regimes.

(sc)ramjets take over around mach 4-5.

No, you use turbofans for everything below about mach 2 if you want more than 15 minute duration (english electric lightning)

Only ancient stuff like the blackbird were pure turbojet/afterburner/scramjet style things

You can be sure others have done the sums and that's why we dont have supersonic airliner

[Andrew]

Another clueless reply. Modern wide bodied passenger jets are effectively Turbofan designs where the external propeller has simply become the front fan that seems to be part of the engine. If it were possible to insert a step-down gearbox behind the front fan then a jet engine with a higher rotational speed would be more efficient. Rolls Royce were involved in this development a few years back.

Jet fighters rely on pure thrust with the added bonus of an afterburner when needed.

[Tim Streater]

Unlikely. It was the Olympus used in Concorde, not the RB-211, which came rather later.

[Vir Campestris]

A quick google for "marine diesel engine efficiency" (no quotes) give me

"Low speed two-stroke turbocharged diesel engines are the most commonly used marine propulsion engines today. These engines are the most efficient, exhibiting 50% efficiency"

Andy

[The Natural Philosopher]

I am not sure I actually believe that.

It implies a combustion temperature that is really rather high

A combined cycle gas turbine with a steam turbine on the back could easily break 60%.

But it would need to run on at least kerosene

[Dave Plowman (News]

The main problem was the fuel consumption was horrendous.

[Max Demian]

I want one with gull wing doors like in UFO.