Once you ignite the motor, pressure in the chamber will increase very quickly, so unless you have a monster vacuum pump (or a fairly large hypobaric chamber), you won't be able to reliably assess the burn (e.g. does the motor burn properly, or does it fizzle enough to raise the pressure in the chamber and only then burn properly).
Two things spring to mind:
- a large-ish tank of some variety, connected to the test chamber via a pipe to effectively increase the available vacuum (similar to the expansion tank on your central heating system)
- a pressure sensor under the motor to measure the engine thrust, particularly during the first one or two seconds - to be compared against a similar burn performed with the chamber at normal pressure.
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The pressure issue
Once you ignite the motor, pressure in the chamber will increase very quickly, so unless you have a monster vacuum pump (or a fairly large hypobaric chamber), you won't be able to reliably assess the burn (e.g. does the motor burn properly, or does it fizzle enough to raise the pressure in the chamber and only then burn properly).
Two things spring to mind:
- a large-ish tank of some variety, connected to the test chamber via a pipe to effectively increase the available vacuum (similar to the expansion tank on your central heating system)
- a pressure sensor under the motor to measure the engine thrust, particularly during the first one or two seconds - to be compared against a similar burn performed with the chamber at normal pressure.