η = 1 − TC/TH • Carnot • Otto • Diesel • Brayton — Simulate • Explore • Practice • Quiz
Thermodynamic cycles are the foundation of heat engines and refrigeration systems that power modern civilisation. A thermodynamic cycle is a series of processes that return a working fluid to its initial state, producing net work output (engine) or transferring heat against a temperature gradient (refrigerator). The four most important ideal cycles are the Carnot cycle, Otto cycle, Diesel cycle, and Brayton cycle. Each is visualised on a pressure-volume (PV) diagram where the enclosed area represents the net work produced per cycle. Understanding these cycles is essential for mechanical engineers, automotive engineers, aerospace engineers, and anyone studying thermodynamics or energy systems.
The Carnot cycle consists of two isothermal and two adiabatic processes and sets the maximum possible efficiency for any heat engine: η = 1 − TC/TH. The Otto cycle models spark-ignition (petrol/gasoline) engines with two adiabatic and two constant-volume processes; its efficiency depends on the compression ratio: η = 1 − 1/rγ−1. The Diesel cycle replaces constant-volume heat addition with constant-pressure heat addition, modelling compression-ignition engines used in trucks, ships, and generators. The Brayton cycle uses two adiabatic and two constant-pressure processes and is the ideal cycle for gas turbines and jet engines, with efficiency determined by the pressure ratio.
In Simulate mode, select a cycle type and adjust the hot and cold temperatures, compression ratio, pressure ratio, or cutoff ratio. The left side of the canvas draws a physically accurate PV diagram with colour-coded process lines, state points, and shaded work area. The right side shows an animated piston that cycles through the four processes. Toggle process labels and energy flow arrows for deeper understanding. Use presets like Car Engine (Otto) or Jet Engine (Brayton) to load realistic configurations. Switch to Explore to study 12 thermodynamics concepts across Laws, Cycles, and Applications. Practice mode generates calculation problems, and Quiz tests your knowledge with 5 questions per session.
Thermal efficiency measures how effectively a cycle converts heat into work: η = Wnet / Qin. For a Carnot engine, this is purely a function of the temperature ratio. For Otto and Diesel cycles, the compression ratio r = V1/V2 is the key parameter. The coefficient of performance (COP) measures the effectiveness of refrigeration cycles. All calculations use γ = 1.4 for air (ideal diatomic gas), following standard engineering conventions.
This simulator is designed for mechanical engineering students, thermodynamics trainees, automotive engineering students studying internal combustion engines, aerospace engineering students studying gas turbines, physics students learning about heat engines, and instructors teaching thermodynamic cycles, PV diagrams, or energy conversion. It provides a visual, interactive experience without requiring laboratory equipment or expensive software.