Why does efficiency rise with pressure ratio in the simple formula?

Higher compression raises the mean temperature of heat addition relative to heat rejection in this idealization, similar in spirit to the Carnot limit trend—real engines trade off component losses, material limits, and non-constant cp.

Where are regenerators and intercooling?

Not modeled. Regeneration preheats air before the combustor using turbine exhaust; intercooling splits compression to reduce work—both change the effective cycle on real diagrams.

Brayton Cycle (Gas Turbine)

The **Brayton cycle** is the idealized **open** or **closed** gas-turbine loop: **compress** the working fluid (often air) nearly **isentropically**, **add heat** at nearly **constant pressure** (combustor or heat exchanger), **expand** through a **turbine** **isentropically**, then **reject heat** at low pressure—again modeled as **isobaric** cooling before the compressor inlet. Jet engines add a **nozzle** after the turbine; the **core** thermodynamics still echo Brayton. This page uses a **normalized** **PV** sketch with **γ = 1.4** to show the four legs and compares a **cold-air** efficiency estimate **η ≈ 1 − r_P^{(1−γ)/γ}** to a **path** efficiency from **∮P dV** divided by a simple **isobaric Q_in** proxy—both are **pedagogical**, not cycle deck software.

Who it's for: Engineering thermodynamics after Otto/Diesel; aerospace and power-plant survey courses.

Key terms

Brayton cycle
Gas turbine
Pressure ratio
Isentropic compressor
Isobaric heat addition
Jet engine core
Cold-air standard

How it works

The Brayton cycle is the archetype of **steady-flow** power: **compress** cold air, **add heat** at roughly constant pressure (combustor), **expand** through a turbine (or nozzle in a jet). The enclosed **PV** area is net **specific work** in this lumped model.

Key equations

η_cold ≈ 1 − r_P^{(1−γ)/γ} · PV^γ = const on isentropes · isobars: P = const

Frequently asked questions

Why does efficiency rise with pressure ratio in the simple formula?: Higher compression raises the mean temperature of heat addition relative to heat rejection in this idealization, similar in spirit to the Carnot limit trend—real engines trade off component losses, material limits, and non-constant cp.
Where are regenerators and intercooling?: Not modeled. Regeneration preheats air before the combustor using turbine exhaust; intercooling splits compression to reduce work—both change the effective cycle on real diagrams.