Thermodynam.
an idealization of the thermodynamic cycle of the internal combustion engine with air as the working substance: intake of air at atmospheric pressure, then adiabatic compression, then ignition with an increase of pressure and temperature at constant volume, then adiabatic expansion and performance of work, then a drop to atmospheric pressure at constant volume and a rejection of heat to the environment, then the exhaust of air at constant pressure.
[ 1885-90; named after Nikolaus August Otto, 1832-91, German engineer and inventor ]