Combustion-Gas Sampling System.

A molecular beam gas sampling apparatus was designed and fabricated to extract combustion gases from high pressure, high temperature environments. The device is intended to transfer the gases with minimal change to a detector such as a mass spectrometer. In this program, a system was designed using molecular beam techniques for sampling 500 psia, 4000K gases. Much of the system is water cooled including the critical first skimmer. The gas sample expands from the sampling orifice in a free jet. The sampling orifice is large enough to minimize boundary layer effects on the sample received at the detector. The skimmer is placed in the free jet so that continuum flow persists downstream of the skimmer unlike other molecular beam systems described to date. Orifice-to-skimmer and skimmer-to-collimator distances are variable to permit molecular beam optimization for a variety of reactants, and a range of reactor pressures and temperatures. Test results showed the variation of beam intensity with orifice-skimmer distance to be similar to known results for much lower pressures. The collimator in the beam system has an axial adjustment mechanism permitting movement during operation. The location found to give the maximum beam intensity was as close as possible to the skimmer without restricting off-axis gas flow. Combustion tests were limited, involving only a successful demonstration of cooled nozzle operation. Vacuum pumping requirements are discussed for the various stages. Author