Jet engine performance

A jet engine converts fuel into thrust. One key metric of performance is the <a href="/facts/Thermal_efficiency/fR0ysNpr">thermal efficiency</a>; how much of the chemical energy (fuel) is turned into useful work (thrust propelling the aircraft at high speeds). Like a lot of <a href="/facts/Heat_engine/t1gq4r5d">heat engines</a>, jet engines tend to not be particularly efficient (<50%); a lot of the fuel is "wasted". In the 1970s, economic pressure due to the rising cost of fuel resulted in increased emphasis on efficiency improvements for commercial airliners. 
Jet engine performance has been phrased as 'the end product that a jet engine company sells' and, as such, criteria include thrust, (specific) fuel consumption, <a href="/facts/Time_between_overhauls/RGgtaJHQ">time between overhauls</a>, <a href="/facts/Power-to-weight_ratio/NykmM0pr">power-to-weight ratio</a>. Some major factors affecting efficiency include the engine's <a href="/facts/Overall_pressure_ratio/dFVVlj2X">overall pressure ratio</a>, its <a href="/facts/Bypass_ratio/rpsDPRHL">bypass ratio</a> and the turbine inlet temperature.
Performance criteria reflect the level of technology used in the design of an engine, and the technology has been advancing continuously since the jet engine entered service in the 1940s. It is important to not just look at how the engine performs when it's brand new, but also how much the performance degrades after thousands of hours of operation. One example playing a major role is the creep in/of the rotor blades, resulting in the aeronautics industry utilizing <a href="/facts/Directional_solidification/Db18txxJ">directional solidification</a> to manufacture turbine blades, and even making them out of a <a href="/facts/Single_crystal/UMG5pFp9">single crystal</a>, ensuring creep stays below permissible values longer. A recent development are <a href="/facts/Ceramic_matrix_composite/zvty2Svr">ceramic matrix composite</a> turbine blades, resulting in lightweight parts that can withstand high temperatures, while being less susceptible to creep.
The following parameters that indicate how the engine is performing are displayed in the cockpit: <a href="/facts/Engine_pressure_ratio/uzzEqGDd">engine pressure ratio</a> (EPR), <a href="/facts/Exhaust_gas_temperature/kLpq1eUX">exhaust gas temperature</a> (EGT) and fan speed (N1). EPR and N1 are indicators for thrust, whereas EGT is vital for gauging the health of the engine, as it rises progressively with engine use over thousands of hours, as parts wear, until the engine has to be overhauled.

The performance of an engine can calculated using thermodynamic analysis of the engine cycle. It calculates what would take place inside the engine. This, together with the fuel used and thrust produced, can be shown in a convenient tabular form summarising the analysis.

Jet engine performance open-in-new

Jet engine performance