Laser initiated non-linear fuel droplet ignition

• US 5,404,712 A
• Filed: 10/06/1992
• Issued: 04/11/1995
• Est. Priority Date: 10/06/1992
• Status: Expired due to Fees

• Current Assignee: The University Of Tennessee Research Corporation (University of Tennessee)
• Original Assignee: The University Of Tennessee Research Corporation (University of Tennessee)
• Inventors: Lewis, James W. L., Few, Jimmy D.
• Primary Examiner(s): Thorpe, Timothy S.
• Application Number:
  US07/957,613
• Time in Patent Office: 917 Days
• Field of Search: 60/39.06, 60/39.821, 60/39.826, 60/39.828, 123/143 B, 123/143 R, 431/1, 431/2, 431/6, 431/258
• US Class Current: 60/39.821
• CPC Class Codes: F02C 7/264 Ignition
• CPC Class Codes: F02P 23/04 Other physical ignition means, e.g. using laser rays
• CPC Class Codes: F23Q 13/00 Igniters not otherwise provided for
• CPC Class Codes: F23R 2900/00006 Using laser for starting or improving the combustion process
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft

Abstract

Method and apparatus for igniting an air/fuel spray (26) comprised of fuel droplets. The apparatus includes a coherent optical source (12) for introducing at least one pulse of coherent radiation into the air/fuel spray. The pulse generates free electrons and initiates a development of a plasma within the air/fuel spray. The coherent source maintains the pulse of coherent radiation and pumps the developing plasma to higher energies. The pulse is terminated at a time after the plasma has reached a predetermined energy and before ignition of the air/fuel spray. The non-linear ignition system of the invention employs a gas/vapor interface region at a fuel droplet surface and an electric field that extends from and exists outside of a fuel droplet. Free electrons are accelerated to higher energies by the electric field surrounding the fuel droplet. The accelerated electrons initiate a breakdown near adjacent fuel droplets and the liberation of further free electrons. In a short period of time an avalanche process occurs that creates a high density of free electrons and ions which results in the formation of a plasma.

Claims

1. Apparatus for igniting an air/fuel spray comprised of fuel droplets, the air/fuel spray being provided within a combustion chamber of a gas turbine engine, the apparatus comprising:

coherent optical source means that includes means for introducing at least one pulse of coherent radiation into the air/fuel spray, the pulse initiating a development of a plasma within the air/fuel spray;

means for maintaining the pulse of coherent radiation for pumping the plasma; and

means for terminating the pulse of coherent radiation at a time after the plasma has reached a predetermined energy that results in the plasma being self-sustained, and before a time that an ignition of the air/fuel spray occurs, the ignition using ignition precursors that are created from the self-sustained plasma after the termination of the pulse.

2. Apparatus as set forth in claim 1 and further including means for focussing the at least one pulse to a region within the air/fuel spray.

3. Apparatus as set forth in claim 1 wherein the pulse of coherent radiation has a wavelength within a range of approximately 0.3 micrometers to approximately 1.1 micrometers, a pulse width within a range of approximately 5 nanoseconds to approximately 50 nanoseconds, and a power density within a range of approximately 10⁷ to approximately 10⁸ W/cm².

4. Apparatus as set forth in claim 1 wherein the coherent optical source means includes optical fiber means for coupling the pulse to the air/fuel spray.

6. Apparatus as set forth in claim 1 wherein the coherent optical source means has a fundamental wavelength output of 1.06 micrometers, or a frequency doubled (0.532 micron) or frequency tripled (0.355 micron) wavelength output.

5. Apparatus for igniting an air/fuel spray comprised of fuel droplets, the air/fuel spray being provided within a combustion chamber of a gas turbine engine, the apparatus comprising:

coherent optical source means that includes means for introducing at least one pulse of coherent radiation into the air/fuel spray, the pulse initiating a development of a plasma within the air/fuel spray;

means for maintaining the pulse of coherent radiation for pumping the plasma;

means for terminating the pulse of coherent radiation at a time after the plasma has reached a predetermined energy and before ignition of the air/fuel spray; and

feedback means responsive to a presence of a flame within the combustion chamber for operating the optical source means when the flame is not present.