Nonequilibrium Thermodynamics Laboratories The Ohio State University

Chemi-Ionization and Visible/UVEmission 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

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

Nonequilibrium Thermodynamics Laboratories The Ohio State University

Schematic of a Rocket Plume Flow

Dominant Emitting Species

Ultra-Violet: -CO 4th Positive, NO Bands, OH

Visible: - CH, C2 Swan

Infrared: - CO, CO2, H2O

Mixing Layer

CombustionChamber

NozzleExpansion(Supersonic)

Mixing Layer

Rocket Engine

Oxidizer+ Fuel

Flow

Nonequilibrium Thermodynamics Laboratories The Ohio State University

Background: “Lights Out” experiment in CO-N2 optically pumped plasma

No DC voltage applied 2 kV DC voltage applied

(CO/N2=1/100, T = 300K, P=500 torr, CO laser power 15 W)

CN and C2 Swan bands emission disappears when electrons removed

CO + hυ => CO (v) v ~ 10

(CO)2+ + e Ionization

CO (v) + CO (w)

CO (v-1) + CO (w+1) v, w ~ 40

CO2 + C

CO (v) + e => CO (A 1Π) + e

Nonequilibrium Thermodynamics Laboratories The Ohio State University

Schematic of the Experiment Setup

Plenum: P0 = 1 atm

Fuel: C2H4

Oxidizer: air, O2/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

MgF2 Optical Access Windows

Flow3 Sparkplugs

Air orO2/Ar

Flushed Electrodes

Angle step Diffuser

Stagnation Pressure Port

To Vacuum system

Flameholder

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*, C2*, 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)

Nonequilibrium Thermodynamics Laboratories The Ohio State University

Combustion Chamber

M = 3 flow M = 3 flow

Emission Spectra from Combustion Chamber and M = 3 Flow(C2H4 / air)

H and O atomic lines also detected

Similar results for C2H4/O2/Ar

290 295 300 305 310 315 Wavelength (nm)

OH 3064oAsystem

410 420 430 440 450 Wavelength (nm)

CH 4300oAsystem

500 505 510 515 520 525 530 Wavelength (nm)

C2 Swan System

Nonequilibrium Thermodynamics Laboratories The Ohio State University

0 100 200 300 400 500

Voltage, V

0

50

100

150

200

250

Current, µA

Current-Voltage characteristicC2H4 / O2/Ar combustion products, M = 3

Similar results in C2H4/air

ne = (1 - 2) x 109 cm-3

Nonequilibrium Thermodynamics Laboratories The Ohio State University

C2H4 / O2/Ar: Current and Visible Emission in M =3 Flow

Voltage = 200 V (current saturated)

C2 Swan (516 nm) CH (430 nm)

1 3 5 7 9 11 130

100

200

300

400

500

Current (A)

Time (s)

EmissionCurrent

1 3 5 7 9 11 130

200

400

600

800

Current (A)

Time (s)

EmissionCurrent

Nonequilibrium Thermodynamics Laboratories The Ohio State University

No detectable change in CH and C2 emission intensity when electrons are removed

C2H4 / O2/Ar: Current and Visible Emission in M =3 Flow

(continued)

C2 Swan (516 nm) CH (430 nm)

0 2 4 6 8 10 12 Time (s)

Voltage OffVoltage On

0 2 4 6 8 10 12 Time (s)

Voltage offVoltage on

Nonequilibrium Thermodynamics Laboratories The Ohio State University

C2H4/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 C2 Swan band emission (516 nm)

50 100 150 200 2500

0.2

0.4

0.6

0.8

1

Time (msec)

Current (mA) Emission Intensity (Arbitrary Units)

EmissionCurrent

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 C2 Swan band and CH emission when electrons are

removed

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, N2, CO, and NO into supersonic flow to study energy transfer from combustion products to these species