Adonios N. Karpetis

Pressure and thermochemistry measurements in high speed flows using rotational and vibrational Raman spectroscopy

We present line imaging measurements of rotational / vibrational Raman in high speed, non-isobaric flows. The technique can be used to measure pressure, temperature, and density in in the wake of an underexpanded jet nozzle. Line images of rotational and vibrational Raman spectra are collected for a 8-mm linear laser probe, and are combined onto the same EMCCD detector. Temperature measurements along the laser test section are extracted from the rotational Raman spectra, whereas major species densities are measured by the levels of their respective vibrational Raman lines. Pressure can be calculated using an equation of state, in every location along the linear laser probe. We present detailed spatial measurements in the wake of an underexpanded jet issuing from a converging nozzle.

Miniaturized Combustor for Supersonic Methane–Air Flames

A miniaturized combustor has been designed that can produce open supersonic methane–air flames amenable to laser diagnostics. The combustor is based on a two-stage design. The first stage is a vitiation burner that provides ignition and flameholding. The design of the vitiation burner was inspired by well-known principles of jet engine combustors. The salient parameters of operation were explored experimentally, and flameholding was verified computationally using a well-stirred reactor model. Both experiments and computations were used to verify a traditional scaling used in jet engine combustor design. The second stage of the combustor generated an external supersonic flame, operating in premixed and partially premixed modes. The equivalence ratio of the external supersonic flame was varied, as well as the total mass flow rate, and the overall flame phenomenology was examined, specifically supersonic flame length. The very high Reynolds numbers and strain rates present in the supersonic flames should pro...