Adiabella

Meet Adiabella, a gas squeezed so fast she heats up before any heat can leave.

In an adiabatic process no heat flows in or out. If you compress a gas that way, all the work you do goes into its internal energy, so it gets hotter. For an ideal gas the rule is TV^(γ−1) = constant, where γ is the ratio of the heat capacities at constant pressure and constant volume, about 1.4 for air.

Example: compressing air from 300 K to one tenth of its volume adiabatically gives T = 300 × 10^0.4 ≈ 754 K, hot enough to ignite diesel fuel. Diesel engines use exactly this: they have no spark plug, and the fuel ignites in air heated by compression.

The reverse works too. Air rising in the atmosphere expands and cools at about 10 °C per kilometre when dry, which is why mountain tops are colder and how clouds form. Bicycle pumps get warm when used hard.

Real compressions are never perfectly adiabatic, and real gases depart from ideal behaviour at high pressure, so engines reach somewhat different temperatures.