Temperature, Pressure, Velocity, and Water Vapor Mole Fraction Profiles in a Ramjet Combustor using Dual Frequency Comb Spectroscopy and a High Temperature Absorption Database

TL;DR

This study employs dual frequency comb spectroscopy with a new high-temperature water vapor database to accurately measure 2D profiles of key parameters in a ramjet combustor, improving diagnostics and benchmarking CFD models.

Contribution

It introduces a novel high-temperature water vapor absorption database enabling precise spectroscopic diagnostics in ramjet combustors, enhancing measurement accuracy over previous models.

Findings

The new database yields the lowest fit residuals.

CFD simulations overpredict heat release and water vapor.

Spectroscopic measurements provide detailed 2D profiles.

Abstract

Accurate diagnostics of the combustor region of ramjet engines can improve engine design and create benchmarks for computational fluid dynamics models. Previous works demonstrate that dual frequency comb spectroscopy can provide low uncertainty diagnostics of multiple flow parameters in the non-combusting regions of ramjets. However, the high temperatures present in the combustor present a challenge for broadband spectroscopic absorption models that are used to interpret measurements in these regions. Here, we utilize a new water vapor absorption database created for high temperature water-air mixtures to fit spectra measured in a ground-test ramjet engine with a broadband near-infrared dual comb absorption spectrometer. We extract 2D profiles of pressure, temperature, water mole fraction, and velocity using this new database. We demonstrate that the new database provides the lowest fit residuals compared to other water vapor absorption databases. We compare computational fluid dynamics simulations of the combustor with the measured data to demonstrate that the simulations overpredict heat release and water vapor production.