Microwave ignition of electrically operated propellants

Patent metadata

Field	Value
Publication number	US-10808649-B2
Application number	US-201615240932-A
Country	US
Kind code	B2
Filing date	Aug 18, 2016
Priority date	Aug 18, 2016
Publication date	Oct 20, 2020
Grant date	Oct 20, 2020

Abstract

Microwave energy is used to ignite and control the ignition of electrically operated propellant to produce high-pressure gas. The propellant includes conductive particles that act as a free source of electrons. Incoming microwave energy accumulates electric charge in an attenuation zone, which is discharged in the form of dielectric breakdowns to create local randomly oriented currents. The propellant also includes polar molecules. The polar molecules in the attenuation zone absorb microwave energy causing the molecules to rapidly vibrate thereby increasing the temperature of the propellant. The increase in temperature and the local current densities together establish an ignition condition to ignite and sustain ignition of an ignition surface of the attenuation zone as the zone regresses without igniting the remaining bulk of the propellant.

First claim

We claim:

1. A gas generation system, comprising:
a combustion chamber;
a source configured to generate microwave energy in a defined microwave band between 0.3 GHz and 300 GHz and to provide said microwave energy as an electrical input; and
an electrically operated propellant in which an ignition condition of the electrically operated propellant is defined by satisfying both a thermal ignition threshold and an electrical ignition threshold, wherein said electrically operated propellant has a self-sustaining threshold pressure at which the electrically operated propellant once ignited cannot be extinguished and below which the electrically operated propellant can be extinguished by interruption of the electrical input in an extinguishment condition, said electrically operated propellant further including,
one or more conductive additives including conductive particles suspended within the electrically operated propellant that increase a conductivity of the electrically operated propellant; and
one or more polar additives including polar molecules suspended within the electrically operated propellant,
wherein the one or more conductive additives and the one or more polar additives reduce an amount of the microwave energy otherwise required to satisfy the ignition condition and to sustain combustion of the electrically operated propellant, and
a controller configured to control the source such that in the ignition condition, the microwave energy accumulates electric charge in the electrically operated propellant in an attenuation zone, with said electric charge being discharged in the form of dielectric breakdowns between the conductive particles through the electrically operated propellant such that a local current density J surpasses the electrical ignition threshold, and wherein in the ignition condition, the microwave energy also rapidly vibrates the polar molecules to increase a temperature of the electrically operated propellant in the attenuation zone to surpass the thermal ignition threshold, whereby the controller controls the source such that the electrical ignition threshold and the thermal ignition threshold are met only at an ignition surface of the attenuation zone whereby only the ignition surface is ignited without igniting a remaining bulk of the electrically operated propellant, to thereby generate gaseous byproducts that pressurize the combustion chamber while maintaining a combustion chamber pressure of the combustion chamber at less than the self-sustaining threshold pressure,

wherein the controller is further configured to control the source to vary a phase or frequency of the microwave energy such that an anti-node of the microwave energy tracks the ignition surface as the attenuation zone regresses,
wherein in the extinguishment condition the source interrupts generation of the microwave energy to interrupt the electrical input and extinguish the electrically operated propellant.

2. The gas generation system of claim 1 , wherein the defined microwave band is a center frequency Fc between 0.3 GHz and 300 GHz plus or minus at most 10% of the center frequency.

3. The gas generation system of claim 2 , wherein the center frequency Fc is between 1 and 10 GHz.

4. The gas generation system of claim 1 , wherein the conductive particles include metal particles that provide fuel for the electrically operated propellant.

5. The gas generation system of claim 1 , wherein said conductive particles constitutes at least 5% by mass of the electrically operated propellant and said polar molecules constitute at least 5% by mass of the electrically operated propellant.

6. The gas generation system of claim 1 , wherein said one or more conductive additives and said one or more polar additives are configured such that at least 5% of the microwave energy coupled into the electrically operated propellant is discharged in dielectric breakdowns and at least 5% is absorbed by the polar molecules to satisfy the electrical ignition threshold and the thermal ignition threshold, respectively.

7. The gas generation system of claim 1 , wherein a depth of the attenuation zone varies as the attenuation zone regresses.

8. The gas generation system of claim 1 , further comprising a nozzle coupled to the combustion chamber to exhaust the gaseous byproducts to produce thrust.

9. The gas generation system of claim 1 , wherein said self-sustaining threshold pressure is at least 500 psi.

10. The gas generation system of claim 9 , wherein the electrically operated propellant comprises:
50 to 90 percent by mass an ionic perchlorate-based oxidizer;
10 to 30 percent by mass a binder;
5 to 30 percent by mass a metal or polymer based fuel;
5 to 40 percent by mass a metal additive; and
5 to 40 percent by mass the polar molecules.

11. The gas generation system of claim 1 , wherein the ignition surface burns as the attenuation zone regresses.

12. The gas generation system of claim 1 , wherein the conductive particles provide a free source of electrons for the dielectric breakdowns.

13. A method of generating a gaseous byproduct to pressurize a combustion chamber, the method comprising:
providing an electrically operated propellant in which an ignition condition of the electrically operated propellant is defined by satisfying both a thermal ignition threshold and an electrical ignition threshold, said electrically operated propellant having a self-sustaining threshold pressure of at least 200 psi at which the electrically operated propellant once ignited cannot be extinguished and below which the electrically operated propellant can be extinguished by interruption of the an electrical input, said electrically operated propellant including metal particles and polar molecules suspended within the electrically operated propellant to reduce an amount of energy supplied by the electrical input required to satisfy the ignition condition;
supplying microwave energy as the electrical input to the electrically operated propellant to rapidly vibrate the polar molecules to increase a temperature of the electrically operated propellant above the thermal ignition threshold;
supplying the microwave energy as the electrical input to the electrically operated propellant to accumulate and then discharge electric charge in the form of dielectric breakdowns into randomly oriented local currents that exhibit a local current density J above the electrical ignition threshold thereby satisfying the ignition condition thereby igniting and sustaining ignition of an ignition surface as the electrically operated propellant burns, wherein the metal particles and polar molecules reduce the an amount of the microwave energy otherwise required to satisfy the ignition condition and to sustain the burning of the electrically operated propellant;
wherein combustion of the ignited electrically operated propellant generates the gaseous byproduct that pressurizes the combustion chamber; and
varying a phase or frequency of the microwave energy such that an anti-node of the microwave energy tracks the ignition surface as the attenuation zone regresses; and
extinguishing the electrically operated propellant by interrupting the microwave energy while the electrically operated propellant is subject to a pressure less than the self-sustaining threshold pressure.

14. The method of claim 13 , wherein the self-sustaining threshold pressure is at least 500 psi, wherein the electrically operated propellant comprises a perchlorate based oxidizer.

Assignees

• Raytheon Co

Inventors

• Villarreal James K
• Danforth Jeremy C
• Summers Matt H
• Johnson Daniel K
• Langhenry Mark T

Classifications

• F02K9/94

  Re-ignitable or restartable rocket- engine plants; Intermittently operated rocket-engine plants · CPC title

• C06B23/00

  Compositions characterised by non-explosive or non-thermic constituents {(in combination with specific explosives C06B25/20, C06B25/26, C06B29/04, C06B29/08, C06B31/06, C06B31/40, C06B33/02)} · CPC title

• C06B45/10

  the organic component containing a resin · CPC title

• F02K9/08

  using solid propellants (F02K9/72 takes precedence; using semi-solid or pulverulent propellants F02K9/70) · CPC title

• F02K9/95 Primary

  characterised by starting or ignition means or arrangements (safety devices F02K9/38) · CPC title