Fall of piston pulls in air/gas mixture

1
The Otto Cycle for a 4 stroke gasoline engine.
Ignition of fuel causes rapid increase in temp
and pressure at constant volume.
Fall of piston pulls in air/gas mixture
Return of piston adiabatically compresses air/gas
mixture.
2
Momentum of rising piston expels gas out of
exhaust valve.
Exhaust valve opens when piston reaches bottom
and this drops the pressure to atmospheric.
Power stroke Adiabatically expanding gas does
work on piston.
QH
QC
exhaust
Wnet QH - QC