Exergy Destruction in Gas Turbine Components

ExergyJet Engineering Team · 8 min read · Sep 2026

Fuel enters a jet engine carrying almost pure exergy. Thrust power leaves carrying only a fraction of it. Between those two points, every component takes its cut — but not equally, and not for the same reasons. Knowing which component destroys how much, and why, is the difference between guessing at design improvements and targeting them.

Destruction vs loss: two different ways exergy disappears

Before touring the components, one distinction matters. Exergy destruction is irreversibility generated inside a device — friction, turbulence, mixing, combustion, heat transfer across a finite temperature gap. It is quantified by the Gouy–Stodola relation:

Exergy loss, by contrast, is exergy that simply leaves the system unused — chiefly the exhaust stream's remaining physical and kinetic exergy. Destruction happens within the machine; loss walks out of the nozzle. A serious second-law analysis reports both, component by component, and they respond to different design levers.

Component by component

1. Inlet / diffuser — small but honest

In subsonic cruise the inlet is usually the most innocent component: a well-designed diffuser decelerates air with modest friction, destroying only a few percent of total irreversibility. At supersonic flight the story changes — shock waves are concentrated irreversibility generators, and inlet design becomes a second-law problem in its own right.

2. Compressor — the price of pressure

The compressor destroys exergy through blade friction, tip leakage, and flow separation. Typical share: roughly 5–10% of total destruction in a modern cycle, rising sharply if stages stall or operate off-design. Every point of compressor polytropic efficiency is worth real exergy — this is why turbine inlet temperatures rose only as fast as compressor technology allowed.

3. Combustor — the undisputed champion of destruction

Here is the uncomfortable fact that first-law efficiency hides: the combustor is usually the largest single exergy destroyer in the engine, often around half of the total. The reason is fundamental. Fuel carries highly ordered chemical exergy; combustion converts it into thermal exergy at a finite temperature, and reaction plus mixing generate entropy that no burner design can avoid. The levers that genuinely help:

• Raise turbine inlet temperature (with matching pressure ratio): heat added at higher average temperature destroys less exergy.
• Minimize combustor pressure drop: every lost point of total pressure is paid for in the turbine.
• Approach stoichiometric burning of the core flow where materials allow; heavy dilution is an exergy tax.

4. Turbine — borrowing back what the compressor spent

The turbine's destruction resembles the compressor's — blade friction and cooling-air mixing — typically another 5–10% share. Cooling deserves special mention: bleeding compressor air into hot turbine passages is thermodynamically expensive mixing, and advanced cooling is as much an exergy problem as a materials problem.

5. Afterburner — destruction as a design choice

When reheat is lit, it commonly becomes the largest destroyer in the entire engine, rivaling or exceeding the main combustor: heat is added at low pressure to an already-expanded stream, across enormous temperature differences. Afterburning is a deliberate trade — thrust now, exergy efficiency later. The exergy balance tells you exactly how much that trade costs, per second.

6. Nozzle and exhaust — mostly loss, not destruction

A well-expanded nozzle destroys little exergy internally. Its contribution to the balance is the exhaust stream itself: gas leaving hotter and faster than ambient carries exergy that never became thrust. This is the term the turbofan attacks (see our turbojet vs turbofan comparison).

Typical shares of total exergy destruction

These are typical textbook ranges for a dry turbojet at cruise, not guarantees for any specific engine. Afterburning, supersonic flight, or off-design operation reshuffle the table — which is precisely why you should compute the balance rather than quote it.

Frequently asked questions

Run the balance yourself

Tables like the one above are starting points. Your engine, your flight condition, your numbers: configure a cycle and read the destruction breakdown component by component.