Quote:
Originally Posted by redpoint5
What are some other engine types and peak efficiencies? Very curious to see the efficiency of rocket motors...
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Liquid fuel burning rocket motors are essentially pumps which supply fuel and oxidizer into a high pressure chamber. The pressure is released through a de Laval nozzle. So like any engine there are 3 components to efficiency:
1. The thermodynamic efficiency, which is lower than the Carnot efficiency for the operating temperatures of the engine.
2. The mechanical efficiency of the conversion from heat and pressure to motion.
3. The peripheral losses, such as coolant, lubricant, and fuel pumps, valve mechanisms, etc.
For a gasoline ICE the Carnot efficiency can be as high as 50%, the mechanical efficiency of a piston for extracting power is around 99%, but ancillary losses (pumps and friction) are generally about 10% to 15% so over all peak efficiency is about 35% to 40% Throttled efficiency, say 10% of maximum output, is much lower 10% to 15%
For a liquid fueled rocket, the Carnot efficiency can be very high, 80% for a rocket burning hydrogen and oxygen in the cold vacuum of earth orbit. The nozzle, which turns temperature into thrust, is designed for one specific external pressure, exhaust speed and vehicle speed - efficiency is lower under any other conditions. At the design point nozzles are about 98% efficient. Fuel and oxidizer pumps use between 10% and 15%
Solid fuel rocket motors have practically no ancillary losses. But Carnot efficiency is generally lower than liquid fuel rockets because the combustion temperature is limited to keep the nozzle from disintegrating.
Peak efficiency for rocket motors is 65% to 70%
-mort