Compressed air energy storage
Cylinder pressure p1		MPa
Ambient pressure p2		MPa
Cylinder volume v1		10-3 m3
Cylinder temperature T1		K
Specific heat capacity cp		kJ/(kg·K)
Specific heat capacity cv		kJ/(kg·K)
Gas constant R=cp-cv		kJ/(kg·K)
Isentropic coefficient k=cp/cv		-
mass weight m=p·V/(R·T)		kg
	Isothermal expansion	Adiabatic expansion
Expanded volume v2	m3	m3
Energy released W	kJ	kJ
Temperature T2	K	K
Compared to batteries, compressed air is favorable because of a high energy density, low toxicity, fast filling at low cost and long service life. These issues make it technically challenging to design air engines for all kind of compressed air driven vehicles (http://en.wikipedia.org/wiki/Compressed-air_energy_storage).
www.engineering-abc.com