Brayton Cycle Efficiency Calculator
Calculates the thermal efficiency of a Brayton (gas turbine) cycle from pressure ratio, specific heat ratio, and component efficiency. Use it for gas turbine engine design, jet propulsion studies, and power plant performance analysis.
Last updated: September 2026
Brayton Cycle Efficiency
33.43 %
Formula below · 2 sources (grc.nasa.gov, web.mit.edu) · Updated Sep 2026
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About this calculator
The Brayton cycle describes gas turbines and jet engines: compression, constant-pressure combustion, expansion and exhaust. For an ideal cycle, thermal efficiency depends only on the pressure ratio r_p and the specific heat ratio γ: η_ideal = 1 − r_p^((1−γ)/γ). Real compressors and turbines lose energy, and then efficiency also depends on the cycle temperatures. With isentropic temperature ratio τ = r_p^((γ−1)/γ), compressor efficiency η_c and turbine efficiency η_t: T₂ = T₁ + T₁(τ − 1)/η_c, T₄ = T₃ − η_t × T₃(1 − 1/τ), and η = [(T₃ − T₄) − (T₂ − T₁)] / (T₃ − T₂). The component option sets η_c = η_t = 100%, 90% or 85%. T₁ (compressor inlet) defaults to 288 K and T₃ (turbine inlet) to 1400 K if left blank. Higher pressure ratios raise ideal efficiency, but with real components the best pressure ratio depends on T₃.
How to use
Consider a gas turbine with a pressure ratio of 15, γ = 1.4, realistic components (85%), T₁ = 288 K and T₃ = 1400 K. Step 1 — τ = 15^(0.4/1.4) = 2.168, so the ideal efficiency is 1 − 1/2.168 = 53.9%. Step 2 — compressor exit T₂ = 288 + 288 × 1.168 / 0.85 = 683.7 K. Step 3 — turbine exit T₄ = 1400 − 0.85 × 1400 × (1 − 1/2.168) = 758.9 K. Step 4 — net work per unit cp = (1400 − 758.9) − (683.7 − 288) = 641.1 − 395.7 = 245.4 K; heat input per unit cp = 1400 − 683.7 = 716.3 K. Efficiency = 245.4 / 716.3 = 34.3%. With 90% components it rises to 41.3%. Simply multiplying the ideal 53.9% by 0.85 would give 45.8%, which overstates real performance.
Frequently asked questions
What pressure ratio gives the best Brayton cycle efficiency for a gas turbine?
For the ideal cycle, efficiency rises with pressure ratio without limit. With real compressor and turbine efficiencies, efficiency peaks at a pressure ratio that depends on the turbine inlet temperature: the higher T₃, the higher the best ratio. Modern industrial gas turbines use pressure ratios of 15–40. Specific work output (net work per kilogram of air) peaks at a lower pressure ratio than efficiency. Very high pressure ratios also need multi-stage compressors and raise blade stress and cost.
How does turbine inlet temperature affect Brayton cycle performance?
Turbine inlet temperature (TIT) is the single most important parameter for maximizing Brayton cycle work output and thermal efficiency. Higher TIT widens the gap between the peak and minimum cycle temperatures, increasing the work extracted per unit of compressed air. Modern gas turbines operate at TITs of 1400–1700 °C, requiring ceramic thermal barrier coatings and internal blade cooling passages. Raising TIT by 100 K typically improves specific power output by 5–10%. This is why advances in high-temperature materials have driven most of the efficiency gains in gas turbines over the past 50 years.
What is the difference between the Brayton cycle and the Rankine cycle in power generation?
Both are heat engine cycles used in power plants, but they differ fundamentally in working fluid and phase. The Rankine cycle uses water/steam, which undergoes phase changes (liquid to vapor), enabling large energy transfer during boiling and condensation. The Brayton cycle uses a permanently gaseous working fluid (air or combustion gases), relying on sensible heat changes throughout. Brayton cycles are lighter and start faster, making them ideal for aircraft engines and peaker power plants. Rankine cycles achieve higher efficiencies at steady-state base-load operation. Combined-cycle plants pair both: a Brayton gas turbine exhausts into a heat recovery steam generator feeding a Rankine steam turbine, achieving system efficiencies above 60%.
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