Prospects of application of microwave discharges on a dielectric net excited in the field of a quasioptical electromagnetic beam for plasma-sustained combustion Lev P. Grachev, Igor I. Esakov, Alexander A. Ravaev, Kirill V. Khodataev

FSUE «Moscow Radiotechnical Institute RAS» Moscow, Russia

Thermochemical processes in plasma aerodynamics July 2-6, 2012, Saint-Petersburg, Russia 1

Simplified scheme of ramjet engine Fuel

Burning area

Air M>1

M>1 M~1

M<1

M~1

Some problems: necessity of flow deceleration, stable ignition in a wide range of mix flow parameters, completeness of combustion at various flow speed, stabilization in space and reduction of burning zone, etc.

MRTI

2

Quasi-Optical Microwave Beam S – finite E0 MW discharge Microwave generator

Units forming electromagnetic beam

Quasi-Optical MW Beam

Wavelength (not frequency) λ = 2…12 cm Microwave power PMW = 103…107 W Gas pressure p = 10…750 Torr

MRTI

3

Areas of realization of microwave discharges Area of efficient MW-plasma interaction/absorption

Freely-localized

Tch ~ n·1000 0C

and initiated MW discharge

MRTI

4

First experiments on ignition of fuel mixes Gas mix – propane + air of stochiometric content Wavelength λ = 2.5 cm MW field E0 = 3 kV/cm Pulse duration p = 100 s Air pressure p = 100 Torr Flow speed: M ≈ 2

MW

Laval nozzle

Burning speed: 5·104 cm/s Discharge front: 106 cm/s

MRTI

Gas flow ignition – Yes! High speed of burning Very lean fuel mixes Stable in space

5

Possible scheme of application of initiated sub-critical MW discharges in ramjet engines Initiator

Combustion chamber

М

 E0

Supersonic diffuser Fuel injectors

Supersonic nozzle

 П0

MW discharge

Radiotransparent lens MW generator

Main disadvantage: still high power pulse MW generator is required – up to 106 W

MRTI

6

Microwave discharge on a dielectric surface Fiber-laminated textolite plate 1 mm in thickness

Gas – AIR Wavelength λ = 8.9 cm MW field E0 = 6 kV/cm Pulse duration p = 40 s Air pressure p = 750 Torr

MW

Initiator

MW discharge propagates along the dielectric surface! Discharge front velocity: 5·105 cm/s

MRTI

7

Microwave discharge on a dielectric net Dielectric net is made of capron threads 0.3 mm in diameter

Gas – AIR Wavelength λ = 8.9 cm MW field E0 = 6 kV/cm Pulse duration p = 40 s Air pressure p = 750 Torr

MW

Wire initiator

Again MW discharge propagates along the dielectric fibers!

MRTI

8

Possible scheme of application of initiated sub-critical MW discharges on a dielectric net in ramjet engines Initiator

Area of burning

Net

M > 1 

Radiotransparent window

M>1

Microwave generator

MRTI

9

Conclusion The idea and background for application of electric gas discharges excited on a dielectric net in supersonic ramjet engines in the field of quasi-optical microwave beam are first proposed and analyzed. The following investigations of this type MW discharge are strongly recommended: 

 



Determine discharge features depending on such net parameters as its orientation in space, step, diameter and material of threads, shape of its transversal cross-section, etc. Determine propagation velocity of discharge front along the net in a wide range of microwave and fuel-mix flow parameters. Obtain data on influence of net blow by high-speed air flow and propane-air mixtures at their various percentages on discharge characteristics. Measure extension of propane-air burning zone and degree of completeness of fuel-mix combustion.

MRTI

10

Acknowledgements The work is based on Grants executed under previous financial support of

European Office of Aerospace Research and Development

Thank you for attention!

MRTI

11