Brayton Cycle Efficiency Calculator
Computes the thermal efficiency of a gas turbine (Brayton cycle) accounting for real compressor and turbine losses. Use it when sizing gas turbines, jet engines, or power-plant cycles.
About this calculator
The Brayton cycle models gas turbines using isentropic compression and expansion corrected by component efficiencies. The ideal compressor exit temperature is T2s = T1 · rp^((γ−1)/γ), then corrected to T2 = T1 + (T2s − T1) / η_comp. The ideal turbine exit is T4s = T3 / rp^((γ−1)/γ), corrected to T4 = T3 − η_turb · (T3 − T4s). Net specific work is w_net = cp · [(T3 − T2) − (T4 − T1)] and heat input is q_in = cp · (T3 − T2), giving η = w_net / q_in × 100%. Higher pressure ratios and turbine inlet temperatures improve efficiency, while component irreversibilities reduce it significantly.
How to use
Suppose rp = 10, T1 = 300 K, T3 = 1400 K, η_comp = 85%, η_turb = 90%, γ = 1.4. T2s = 300 × 10^(0.4/1.4) = 579.2 K; T2 = 300 + (579.2 − 300)/0.85 = 628.5 K. T4s = 1400/10^(0.4/1.4) = 724.7 K; T4 = 1400 − 0.90 × (1400 − 724.7) = 792.3 K. w_net = 1.005 × [(1400 − 628.5) − (792.3 − 300)] = 1.005 × 279.2 = 280.6 J/g. q_in = 1.005 × (1400 − 628.5) = 775.4 J/g. η = 280.6/775.4 × 100 ≈ 36.2%.
Frequently asked questions
What is a good thermal efficiency for a Brayton cycle gas turbine?
Modern industrial gas turbines achieve simple-cycle Brayton efficiencies of 35–42%, while advanced combined-cycle plants exceed 60% by recovering exhaust heat in a steam bottoming cycle. Aeroderivative engines can reach simple-cycle efficiencies close to 45% due to high pressure ratios and turbine inlet temperatures above 1500 K. Component efficiencies of compressors and turbines (typically 85–92%) are the biggest drivers of real-cycle performance.
How does pressure ratio affect Brayton cycle efficiency?
Increasing the pressure ratio raises the ideal isentropic efficiency because the compression and expansion temperature swings grow, extracting more work per unit of heat added. However, there is an optimal pressure ratio beyond which compressor outlet temperature approaches turbine inlet temperature, shrinking net work output. For a fixed turbine inlet temperature of ~1400 K and γ = 1.4, the maximum-efficiency pressure ratio is typically in the range of 15–25. Real component losses shift this optimum lower than the ideal analysis predicts.
Why does compressor efficiency matter more than turbine efficiency in a Brayton cycle?
The compressor consumes a large fraction of turbine output—often 40–60%—so even a small drop in compressor isentropic efficiency causes a disproportionate reduction in net work and overall cycle efficiency. A 1% drop in compressor efficiency typically degrades cycle efficiency by roughly 0.5–1 percentage point, whereas the same drop in turbine efficiency has a slightly smaller but still significant effect. This is why multi-stage axial compressors with carefully profiled blades are critical in high-performance gas turbines.