Help understanding manometric metering
Posted: Mon May 07, 2012 5:23 pm
Can someone explain to me what manometric metering is. Or link me to a post about manometric metering 
Manometric metering is the concept of determining the amounts of gases injected into the chamber by monitoring the chamber pressure and applying the equation of state to find density from the known pressure and temperature.
This can be contrasted with volumetric metering like a syringe (or its equivalent for liquefied gases), or a combination of the two, which uses a "meter pipe" to determine the amount of gas, by the method in the above paragraph. The latter is largely obsolete for everything but atmospheric pressure combustion launchers.
It is worth noting that, due to the approximate nature of equations of state, accurate manometric metering becomes an increasingly difficult endeavour as the fill pressure increases.