Development of spontaneous Raman spectroscopy for optical diagnostics in detonation engines
Abstract
Approved for Public ReleaseDetonation waves enable compact and efficient combustion in a supersonic flow and are an enabling technology for future hypersonic flight vehicles. Basic research into the fundamental chemistry remains to be elucidated so that engineering design models can be developed and applied to engine design. With these models, engineers can predict ignition, attenuate instabilities, and mitigate blowout in real engines that will meet the Navy#s interests in scalable lethality and force projection that hypersonic propulsion technology will support. Dr. Steven Tuttle at the US Naval Research laboratory has constructed a unique experimental facility where a stationary shock wave is stabilized above an over-expanded supersonic jet. The configuration gives test times of the order of tens of seconds and has excellent optical access to enable the use of non-intrusive laser diagnostics. We propose a three-year effort to collaborate with Dr. Tuttle and implement spontaneous Raman scattering diagnostics in the NRL facility with the objective of making spatially resolved measurements of temperature, major species concentrations, and quantifying any vibrational non-equilibrium in the flow.We have recruited an outstanding student, Ms. Riley Jacobs, to work on this project. She is a US citizen and will spend extended periods at NRL to work more closely with the technical staff at NRL and transfer the expertise on spontaneousRaman measurement techniques developed at UT to the staff at NRL. She will begin with measurements at UT Austin where we have a unique high dispersion Raman set-up with high collection efficiency. We will make measurements of gas phase fuels at high pressure to investigate the effect of line mixing on the Raman spectra. Measurements will be made at room temperature in our existing high-pressure Raman cell, and at elevated temperatures in a redesigned cell, to evaluate the effects of line-mixing on quantitative Raman measurements of species concentrations. We will also make Raman measurements on gaseous fuel and air mixtures as well as liquid fuel-air mixtures in atmospheric pressure flames. We will conduct experiments with premixed ethylene/air and ethane/air in a high-pressure burner to validate the Raman measurements under steady flow laboratory conditions. As a stretch goal we will attempt to make measurements in a vaporized jet fuel-air flame at high pressure.Measurements at NRL will be guided by the needs of our collaborators there. We anticipate making preliminary measurements of temperature and possible vibrational non-equilibrium in the high-speed flow in theirfacility. We will also examine the relaxation rate to vibrational equilibrium in the post-shock region. As the project at NRL progresses we anticipate making concentration and temperature measurements along the axis of the jet and across the shock, indicating thedecomposition of the fuel, the appearance of fuel decomposition products such as C2H4 and C2H6,and combustion products such as CO, CO2, and H2O if ignition occurs. This project will provide fundamental data on Raman spectra of important fuel intermediates at highpressure which will be needed to apply Raman diagnostics to detonation engines and other high-pressure engines fueled by typical liquid fuels of interest to the US Navy. It will also facilitate the transfer of expertise in spontaneous Raman diagnostics to the staff at NRL. It has the support of Dr. Steven Tuttle at NRL (letter attached).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2023
- Source ID
- N000142312596
Entities
People
- Philip L. Varghese
Organizations
- Office of Naval Research
- United States Navy
- University of Texas at Austin