Hi ! I need help.. for fueling..

I have been designing fueling system for 5:1 oxy-propane mix and I'm having some trouble finding a way to get correct mixture. I was thinking of using two timed solenoid valves in tandem with a chocked orifice plates after valves. Orifice plates would be sized to have a 5:1 flow of gases so both oxygen and propane would be fueled simultaneously. But, how do I calculate the flow/size of the orifices ?

My basic instinct would size the two orifices to have 5:1 cross sectional area difference for 5:1 flow, but how does the gas density etc. affect the ratio of mass flow rate ? Is it negligible ?

My chamber size is 7 litres, how would I calculate the time needed for valves to be open / what is the flowrate through the orifices ?

My cannon can handle the mix easily, so no need to talk about that for now and solenoid valves will be sealed from blast with my 500bar rated ss /ptfe ball valves. Cannon is actually used as hybrid now, but I'm looking to try atmospheric oxy-propane mix to do some testing.

Thanks for help ! I will post pics here when building the fueling system