Rocket Propellant Injection

Here are some tables with calculations for propane and oxygen. I think if you are going to do something like this, propane is what you want to use. It has a huge liquid range, and so can be subcooled very deeply. Oxygen is the most likely oxidizer - but note that it is far less useful, because of it's narrower liquid range.

Perhaps the best option would be propane and hydrogen peroxide - though peroxide has it's own issues, and a peroxide injector could be quite dangerous!

Anyway, the key to good injection is subcooling! (Well, don't superheat the steam too far either - you want it to exit the nozzle just above boiling.)

Substance	Propane	Propane	Propane	Propane
Gas Heat Capacity	1.67	1.67	1.67	1.67
Liquid Heat Capacity	2.23	2.23	2.23	2.23
Latent heat of evaporation	425	425	425	425
Boiling point (C )	-42.1	-42.1	-42.1	-42.1
Gas Velocity (m/s)	300	300	300	600
Gas Temperature (C )	0	0	0	0
Liquid Temperature (C )	-180	-180	-180	-180
Liquid Density (kg/m3)	582	582	582	582
Mass Mixture Ratio	0.9	0.8	0.55	0.55
Mixed velocity (m/s)	30	60	135	270
Mixed temperature (C )	-146.23	-116.89	-62.99	-62.99
Stopped Pressure (Atm)	2.59	10.37	52.51	210.04

Substance	Oxygen	Oxygen	Oxygen	Oxygen
Gas Heat Capacity	1.84	1.84	1.84	1.84
Liquid Heat Capacity	2	2	2	2
Latent heat of evaporation	426.25	426.25	426.25	426.25
Boiling point (C )	-182.95	-182.95	-182.95	-182.95
Gas Velocity (m/s)	300	300	600	1200
Gas Temperature (C )	-150	-180	-180	-180
Liquid Temperature (C )	-215	-215	-215	-215
Liquid Density (kg/m3)	1140	1140	1140	1140
Mass Mixture Ratio	0.9	0.85	0.85	0.85
Mixed velocity (m/s)	30	45	90	180
Mixed temperature (C )	-189.89	-182.67	-182.67	-182.67
Stopped Pressure (Atm)	5.08	11.43	45.71	182.85