The engine piston is locked in
position and heat flows into the
gas. What happens to the
pressure, volume, and
temperature?
Volume constant (piston locked)
Temperature increases
Pressure increases proportionally
20.5 - Engine processes
In this section, we will review an engine cycle. It
involves the three processes described below. To
understand these processes, watch the gauges that
display the pressure, volume, molar quantity and
temperature of the gas. We assume that the pressure
and temperature are uniform throughout the gas.
We start with one mole of gas with a volume of
2.44×10í^2 m^3 at 292 K and a pressure of
1.00×10^5 Pa. The piston is locked and no heat is
allowed to flow in or out. This state of the engine is
depicted in the illustration at the top of the page.
First process. Now, 1350 joules of heat are allowed to flow into the gas. The energy inflow increases the internal energy of the gas, which is
reflected by its increased temperature. Since the piston is locked, the gas’s volume cannot change. This means its pressure must increase.
You see this directly above. Its pressure has increased from 1.00 to 1.36×10^5 Pa and its temperature has increased from 292 to 400 K.
Initial state of heat engine.First process
Volume held constant
Heat flows in
Pressure and temperature increase