Propane

The propane molecule

Propane is probably the most common fuel used by builders of higher-end combustion launchers - and with good reason too. It is powerful, easily metered, clean burning, widely available and inexpensive.

Propane can be injected the same way an aerosol fuel would, but it is common to devise a method to carefully control the amount metered into the chamber; often a conventional fuel meter or large syringe is used, although using the pre-mixed fuel mixture from an unlit propane torch is convenient for fueling very small launchers.

It is important that the fuel/air mixture be near 4.2% by volume, because you lose power if your fuel/air mix is wrong.

Propane leaves no soot when burned, so it does not require one to clean their chamber frequently, and leaves practically no offensive odor.

Propane is sold in bulk tanks and disposable canisters at most hardware stores, and most large stores, and is often the primary propellant in aerosols.

Propane is a member of the alkane family of hydrocarbons, having the general formula, C_nH_2n+2.
Molecular Formula: C₃H₈
Condensed Formula: CH₃CH₂CH₃
Combustion: C₃H₈ + 5O₂ ==> 3CO₂ + 4H₂O

Temperature (oF)	Vapor Pressure (psig)
-44 1)	0
-30	6.8
-20	11.5
-10	17.5
0	24.5
10	34
20	42
30	53
40	65
50	78
60	93
70	110
80	128
90	150
100	177
110	204

From: engineeringtoolbox.com