A compact sensor for measuring temperature and pressure in a combustion chamber has been proposed. Heretofore, independent measurements of high pressures and temperatures in combustion chambers have not been performed. In the original intended application, the combustion chamber would be that of a rocket engine. Sensors like this one could also be used to measure temperatures and pressures in other combustion chambers and other, similar harsh settings. There could be numerous potential applications in the aeronautical and automotive industries.
In the original rocket-engine application, accurate measurements of pressure and temperature are needed for feedback control to suppress combustion instability. Heretofore, none of the available pressure sensors have been capable of surviving the thermal environment of a combustion chamber without the use of sensing lines or helium-filled cavities. Pressure- measurement signals obtained by use of sensing lines or helium-filled cavities have altered power spectra that make the signals unsuitable as feedback signals for control purposes.
The proposed sensor would include two optically birefringent, transmissive crystalline wedges: one of sapphire (Al2O3) and one of magnesium oxide (MgO), the optical properties of both of which vary with temperature and pressure. The wedges would be separated by a vapor-deposited thin-film transducer, which would be primarily temperature-sensitive (in contradistinction to pressure-sensitive) when attached to a crystalline substrate. The sensor would be housed in a rugged probe to survive the extreme temperatures and pressures in a combustion chamber. An externally generated optical input signal would travel through parts of the wedges. The effect of the thin-film transducer on the propagating light beam would provide temperature information. The effect of stress-induced birefringence in the crystalline wedges upon the light beam would provide pressure information.