1. Nonequilibrium Thermodynamics Laboratories The Ohio State University Chemi-Ionization and Visible/UV Emission from Supersonic Flows of Combustion Products Saurabh Keshav, Yurii G. Utkin, J.William Rich and Igor V. Adamovich Dept. of Mechanical Engineering The Ohio State University AFOSR, Space Power and Propulsion Program Support

2. Nonequilibrium Thermodynamics Laboratories The Ohio State University Motivation Objective  Control of UV / visible emission from high altitude rocket plumes  Study combustion diagnostic by chemi-ionization  Study energy transfer, chemi-ionization, and emission in supersonic flows of combustion products

3. Nonequilibrium Thermodynamics Laboratories The Ohio State University Schematic of a Rocket Plume Flow Dominant Emitting Species Ultra-Violet: -CO 4 th Positive, NO  Bands, OH Visible: - CH, C 2 Swan Infrared: - CO, CO 2, H 2 O Mixing Layer Combustion Chamber Nozzle Expansion (Supersonic) Mixing Layer Rocket Engine Oxidizer + Fuel Flow

4. Nonequilibrium Thermodynamics Laboratories The Ohio State University Background: “Lights Out” experiment in CO-N 2 optically pumped plasma No DC voltage applied2 kV DC voltage applied (CO/N 2 =1/100, T = 300K, P=500 torr, CO laser power 15 W) CN and C 2 Swan bands emission disappears when electrons removed CO + hυ => CO (v) v ~ 10 (CO) 2 + + eIonization CO (v) + CO (w) CO (v-1) + CO (w+1)v, w ~ 40 CO 2 + C CO (v) + e => CO (A 1 Π) + e

5. Nonequilibrium Thermodynamics Laboratories The Ohio State University Schematic of the Experiment Setup Plenum: P 0 = 1 atm Fuel: C 2 H 4 Oxidizer: air, O 2 /Ar Spark ignition Test section: M=3.2 – 3.4, P=15-20 torr Fuel Injection Port Stagnation Pressure Port M=3 Nozzle Static Pressure Ports Ballast Power Supply MgF 2 Optical Access Windows Flow 3 Sparkplugs Air or O 2 /Ar Flushed Electrodes Angle step Diffuser Stagnation Pressure Port To Vacuum system Flameholder

6. Nonequilibrium Thermodynamics Laboratories The Ohio State University Background theory on Chemi- Ionization and Electron Removal Combustion Chamber  CH + O => CHO + + e  Electronically excited, radiating species (CH *, C 2 *, OH *, O *, H * ) are created  Do electrons help excited species generation? Removal of Electrons from M = 3 flow  Applying voltage to electrodes to draw off electrons (Thomson discharge)

7. Nonequilibrium Thermodynamics Laboratories The Ohio State University Combustion Chamber M = 3 flow Emission Spectra from Combustion Chamber and M = 3 Flow (C 2 H 4 / air) H and O atomic lines also detected Similar results for C 2 H 4 /O 2 /Ar

8. Nonequilibrium Thermodynamics Laboratories The Ohio State University Current-Voltage characteristic C 2 H 4 / O 2 /Ar combustion products, M = 3 Similar results in C 2 H 4 /air n e = (1 - 2) x 10 9 cm -3

9. Nonequilibrium Thermodynamics Laboratories The Ohio State University C 2 H 4 / O2/Ar: Current and Visible Emission in M =3 Flow Voltage = 200 V (current saturated) C 2 Swan (516 nm)CH (430 nm)

10. Nonequilibrium Thermodynamics Laboratories The Ohio State University  No detectable change in CH and C 2 emission intensity when electrons are removed C 2 H 4 / O2/Ar: Current and Visible Emission in M =3 Flow (continued) C 2 Swan (516 nm) CH (430 nm)

11. Nonequilibrium Thermodynamics Laboratories The Ohio State University C 2 H 4 /air flame: CH (431 nm) emission in plenum and chemi-ionization current in M=3 flow Flame “bursts” due to combustion instability Very good correlation between emission and current Same result for C 2 Swan band emission (516 nm)

12. Nonequilibrium Thermodynamics Laboratories The Ohio State University Summary  Self sustained combustion and flameholding achieved  Electron density measured in supersonic flows of combustion products, correlated with flame emission  No effect on C 2 Swan band and CH emission when electrons are removed

13. Nonequilibrium Thermodynamics Laboratories The Ohio State University Future work  Further measurements in M = 4 flows and different equivalence ratios in both steady and unsteady flames  Injection of air, N 2, CO, and NO into supersonic flow to study energy transfer from combustion products to these species