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Propulsive efficiency comparison for various gas turbine engine configurations The calculation is somewhat different for reciprocating and turboprop engines which rely on a propeller for propulsion since their output is typically expressed in terms of power rather than thrust.
Nevertheless, high-bypass engines have a high propulsive efficiency because even slightly increasing the velocity of a very large volume and consequently mass of air produces a very large change in momentum and thrust: thrust is the engine's mass flow (the amount of air flowing through the engine) multiplied by the difference between the inlet ...
For any chemical rocket engine, the momentum transfer efficiency depends heavily on the effectiveness of the nozzle; the nozzle is the primary means of converting reactant energy (e.g. thermal or pressure energy) into a flow of momentum all directed the same way. Therefore, nozzle shape and effectiveness has a great impact on total momentum ...
The thermodynamic and propulsive efficiencies are independent. For the turbojet though, any improvement which raised the cycle pressure ratio or turbine inlet temperature also raised the jet pipe temperature and pressure giving a higher jet velocity relative to aircraft velocity. As the thermal efficiency went up the propulsive efficiency went ...
The efficiency of internal combustion engines depends on several factors, the most important of which is the expansion ratio. For any heat engine the work which can be extracted from it is proportional to the difference between the starting pressure and the ending pressure during the expansion phase.
Schematic diagram showing the operation of a turboprop engine Propulsive efficiency for different engine types and Mach numbers. Exhaust thrust in a turboprop is sacrificed in favor of shaft power, which is obtained by extracting additional power (beyond that necessary to drive the compressor) from turbine expansion.
A typical turbocharged V8 diesel engine might have an engine power of 250 kW (340 hp) and a mass of 380 kg (840 lb), [1] giving it a power-to-weight ratio of 0.65 kW/kg (0.40 hp/lb). Examples of high power-to-weight ratios can often be found in turbines. This is because of their ability to operate at very high speeds.
Diesel engines soon offered greater efficiency than the steam turbine, but for many years had an inferior power-to-space ratio. The advent of turbocharging however hastened their adoption, by permitting greater power densities. Diesel engines today are broadly classified according to Their operating cycle: two-stroke engine or four-stroke engine