3 ms·
The bit about the naval use and efficiency isn't quite accurate. The issue isn't that they're not efficient. It's that they are only efficient at high power le
by KennyBlanken 3y ago
The bit about the naval use and efficiency isn't quite accurate.
The issue isn't that they're not efficient. It's that they are only efficient at high power level, and the minimum power level they're efficient at (and even their minimum power level, period) - is quite high. To compare: Britain's current aircraft carrier has four diesels that total 40MW...combined those diesels equal one of its two 40MW turbines.
This minimum power level is why jet airplanes have an APU, and often taxi with just one engine running, with the second started up with enough time to get up to operating temperature for takeoff.
Example: https://en.wikipedia.org/wiki/Rolls-Royce_MT30 https://en.wikipedia.org/wiki/Rolls-Royce_MT30
~40MW, minimum efficient power level 25MW.
25MW, even if it's very efficient in terms of turning kerosene into shaft power, means the ship is moving really fast, and thus there's enormous fuel consumption and drag.
- usrusr 3y agoI don't think that it's just inefficiency at certain power levels: The big table on https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio... has the Marine Trent rated less efficient than some car engines. And that table is peak efficiency, not efficiency at some arbitrary inconvenient power level. But you are right in so far as efficiency at the low end of the power range is very important in commercial shipping. Because the energy demand (at the drive shaft) of a given trip is highly dependent on the desired speed and if going show ruins your engine's efficiency any dip in demand will ruin you economically (because others on the market are much better at compensating the dip by "slow steaming")
- taneq 3y agoThen wouldn’t they just have a 5MW turbine and run it at its peak efficiency?