DETAILED ACTION
Notice of Pre-AIA or AIA Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Continued Examination Under 37 CFR 1.114
A request for continued examination under 37 CFR 1.114, including the fee set forth in 37 CFR 1.17(e), was filed in this application after final rejection. Since this application is eligible for continued examination under 37 CFR 1.114, and the fee set forth in 37 CFR 1.17(e) has been timely paid, the finality of the previous Office action has been withdrawn pursuant to 37 CFR 1.114. Applicant's submission filed on 8/19/2026 has been entered.
Res
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
Claim(s) 20-21, 24-26, 29-32, 35-37 is/are rejected under 35 U.S.C. 103 as being unpatentable over Palmer (2023/0092811) in view of Porter (3575521) and Cryovation “Cryogenic Pumps & Control Packages” and any of Dittman (7251942), Smith (3238993) and/or Firey (5031397). Palmer [particularly, Fig. 6] teaches (20) A method of starting a liquid hydrogen fueled gas turbine engine of an aircraft propulsion system, the aircraft propulsion system comprising: a hydrogen storage tank 104 configured to store liquid hydrogen; a liquid hydrogen pump 301 or 607 configured to pump hydrogen in at least a liquid state; a core combustor 207 configured to receive hydrogen fuel from the hydrogen fuel pump 301 or 607; a pre-heater combustor 302, 207 404 [Fig. 4] downstream in hydrogen fuel flow of the liquid hydrogen pump 301 or 607; a core compressor 202 or 204 configured to provide pressurized air to the core combustor 207 and to the pre-heater combustor [air to 405 in Fig. 4; air 653 to 302 in Fig. 6]; and a hydrogen fuel vent [e.g. 633, 634, 635, 636; alternate vent is 631 - when pump is 607] provided downstream of the liquid hydrogen pump 301 or 607, and configured to selectively vent hydrogen fuel; the method comprising: in a liquid priming step, flowing hydrogen from the hydrogen storage tank 104 through the liquid hydrogen pump 301 or 607 [see e.g. ¶ 0167-0171] and the pre-heater combustor 302, 207 404 [done prior to startup and during startup, see ¶ 0118, 0121-0126], then, in a liquid pumping step, operating the liquid hydrogen pump to pump liquid hydrogen to the core combustor 207 at a required flow rate and pressure for engine ignition in an engine ignition step [¶ 0171-0172]. (31) An aircraft propulsion system comprising a hydrogen fueled gas turbine engine, the propulsion system comprising: a hydrogen storage tank 104 configured to store liquid hydrogen; a liquid hydrogen pump 301 or 607 configured to pump hydrogen in at least a liquid state; a core combustor 207 configured to receive hydrogen fuel from the hydrogen fuel pump 301 or 607; a pre-heater combustor 302, 207 404 [Fig. 4] downstream in hydrogen fuel flow of the liquid hydrogen pump 301 or 607; a core compressor 202 or 204 configured to provide pressurized air to the core combustor 207 and to the pre-heater combustor [air to 405 in Fig. 4; air 653 to 302 in Fig. 6]; and a hydrogen fuel vent [e.g. 633, 634, 635, 636; alternate vent is 631 - when pump is 607] provided downstream of the liquid hydrogen pump, and configured to selectively vent hydrogen fuel; an engine start controller 613 configured to: in a liquid priming step, flow hydrogen from the hydrogen storage tank 104 through the liquid hydrogen pump 301 or 607 and the pre-heater combustor 302, 207 404 [done prior to startup and during startup, see ¶ 0118, 0121-0126] then, in a liquid pumping step, operate the liquid hydrogen pump to pump liquid hydrogen to the core combustor 207 at a required flow rate and pressure for engine ignition in an engine ignition step. (21, 32) wherein the liquid hydrogen pump comprises one of a positive displacement pump wherein the positive displacement pump is a piston pump, and a variable displacement pump wherein the variable displacement pump is a centrifugal or axial flow pump [see ¶ 0113]. (24, 35) wherein the pre-heater 302 comprises a heat exchanger configured to heat hydrogen fuel flow with heated exhaust flow. (25, 36) wherein the vent [e.g. 634, 635] is provided downstream in hydrogen fuel flow of the pre-heater 302, and upstream in hydrogen fuel flow of the core combustor 207. (26, 37) wherein the hydrogen storage tank 104 is configured to store hydrogen at an above-ambient pressure, and is configured to store hydrogen at a pressure between 1 and 4 Bar [¶ 0108]. (29) wherein the method comprises, during the liquid pumping step, prior to the ignition step, operating the liquid hydrogen pump to provide liquid hydrogen to the core combustor 207 at a pressure greater than the compressor delivery pressure prior to the ignition step [inherent, fuel pressure to the combustor 207 must be greater than compressor delivery pressure supplied by the combustor 207 in order for fuel to flow into the combustor 207]. (30) wherein the method comprises operating the gas turbine engine at a minimum overall pressure ratio at idle greater than a hydrogen storage tank 104 pressure, wherein an overall pressure ratio at idle of 4 bar or greater [note that the disclosed hydrogen storage pressure may as low as 1 bar, which is around atmospheric pressure, and any compression from the high pressor compressor at idle is many times higher than atmospheric pressure / 1 bar by the nature of compression; alternately, even the italicized range is virtually inherent, the examiner takes official notice that the high pressure compressors typically operate at much higher pressures than 4 bar at idle, e.g. above 30 bar are common ranges in aircraft gas turbines. To the point not already inherent, it would have been obvious to one of ordinary skill in the art to employ an overall pressure ratio at idle of 4 bar or greater, as an obvious matter of using the workable ranges in the art]. Note that Palmer teaches flowing / flow hydrogen from the hydrogen storage tank through the liquid hydrogen pump but do not teach in the liquid priming step, venting / vent hydrogen through the hydrogen fuel vent until the hydrogen pump is primed with liquid hydrogen. However, Porter teaches in the liquid priming step, flowing / flow liquid from the liquid storage tank 11 through the liquid pump 16-18 and teach venting / vent through the vent 45 until the liquid pump 16-18 is primed with liquid where the vent 45 provided is downstream of the liquid pump. Porter teaches that the vent valve is open during the priming to vent any gases during the priming [col. 3, line 69 - col. 4, line 35] which facilitates having only liquid flow through the pump. It would have been obvious to one of ordinary skill in the art to apply this liquid priming technique to Palmer, by venting / vent hydrogen through the hydrogen fuel vent until the hydrogen pump is primed with liquid hydrogen, as taught by Porter, as venting through the vent until the pump is primed with liquid facilitates priming of the pump and having only liquid flow through the pump. Note that Palmer does not teach when the hydrogen pump is primed with liquid hydrogen and temperature in the pump is stabilized. Cryovation teaches from the excerpt below that the cryogenic pump (note liquid hydrogen is cryogenic) that during priming that the temperature is monitored and controlled to below a temperature set point to provide protection for the pump, i.e. it maintains the prime / is stable and that the temperature is stabilized to prevent cavitation. It would have been obvious to one of ordinary skill in the art to operate such that the hydrogen pump is primed with liquid hydrogen and temperature in the pump is stabilized, in the manner taught by Cryovation, in order to maintain the pump prime and maintain the temperature of the pump as well prevent cavitation.
PNG
media_image1.png
188
448
media_image1.png
Greyscale
As for crank(ing) the core compressor to generate sufficient compressed airflow and pressure to support combustion within the pre-heater combustor, before or during flowing / flow hydrogen from the hydrogen storage tank through the liquid hydrogen pump and the pre-heater combustor, it is noted that the flowing / flow hydrogen from the hydrogen storage tank through the liquid hydrogen pump and the pre-heater combustor occurs prior to start-up was already taught, Palmer already teaching flowing / flow hydrogen from the hydrogen storage tank 104 through the liquid hydrogen pump 301 or 607 [see e.g. ¶ 0167-0171] and the pre-heater combustor 302, 207 404 [done prior to startup and during startup, see ¶ 0118, 0121-0126]. As for crank(ing) the compressor 102 to generate sufficient compressed airflow and pressure to support combustion within the pre-heater combustor 104, before flowing fuel to the pre-heater combustor 104, it noted that Dittmar et al teach crank(ing) [108 in motor mode turns the compressor 102, see col. 7, lines 15-32; col. 4, lines 43-45] the compressor 102 to generate sufficient compressed airflow and pressure to support combustion within the [pre-heater] combustor 104, and flowing fuel to the [pre-heater] combustor 104. Smith teaches cranking the core compressor 34 to generate sufficient compressed airflow and pressure to support combustion within the [pre-heater] combustor 30, and flowing fuel from the fuel storage tank 38 through the liquid fuel pump 40 and [pre-heater] combustor 30. Smith teaches that the fuel injection is after the initiation of the cranking of the core compressor, so as to prevent explosions from excessive fuel – see col. 1, lines 12+. While the combustors 104, 30, respectively, of Dittmar et al et al and Smith are core combustors, their teachings are applicable to the pre-heater combustor of Palmer, which also utilizes compressed air to operate and start. Alternately, Firey teaches crank(ing) the core compressor 1 to generate sufficient compressed airflow 13 and pressure to support combustion within the pre-heater combustor 12 [col. 7, lines 36-55] prior to steady state operation of the core “combustors” 5, 6 [see col. 3, lines 3-17] and flowing fuel from the fuel storage tank [implied or obvious, compare with other applied art which uses a tank to supply the liquid fuel, e.g. Smith, Palmer, etc.] through the liquid fuel pump 23 and the pre-heater combustor 12 [col. 8, line 49-col. 9, line 5. Firey teaches this sequence is the typical starting sequence during liquid fuel priming step. It would have been obvious to one of ordinary skill in the art to employ crank(ing) the core compressor to generate sufficient compressed airflow and pressure to support combustion within the pre-heater combustor, during the liquid priming step, as taught by any of Dittmar et al, Smith, and/or Firey, as they teach the cranking of the compressor is done to ensure sufficient compressed air is for combustion of the [pre-heater] combustor and where Smith and Firey specifically teach compressor cranking is required prior to fuel delivery to the [pre-heater] combustor as the typical sequence utilized in the art for safety and for priming / supplying the liquid fuel. It would have been obvious to be cranking the compressor prior to flowing the hydrogen through the liquid fuel pump and pre-heater combustor, during the liquid priming step, in order to ensure that the compressed air is available for combustion within the pre-heater combustor before the fuel is delivered thereto.
Response to Arguments
Applicant's arguments filed 08/19/2026 have been fully considered but they are not persuasive.
Applicant argues the new limitations added by amendment. To address this, the Cryovation reference has also been applied to teach temperature stabilization is typical of priming of cryogenic pumps.
Contact Information
Any inquiry concerning this communication or earlier communications from the Examiner should be directed to TED KIM whose telephone number is 571-272-4829. The Examiner can be reached on regular business hours before 5:00 pm, Monday to Thursday and every other Friday.
The fax number for the organization where this application is assigned is 571-273-8300.
If attempts to reach the examiner by telephone are unsuccessful, the examiner’s supervisor, Devon Kramer, can be reached at 571-272-7118 Alternate inquiries to Technology Center 3700 can be made via 571-272-3700.
Information regarding the status of an application may be obtained from Patent Center https://www.uspto.gov/patents/apply/patent-center. Should you have questions on Patent Center, contact the Electronic Business Center (EBC) at 866-217-9197 (toll-free). General inquiries can also be directed to the Inventors Assistance Center whose telephone number is 800-786-9199. Furthermore, a variety of online resources are available at https://www.uspto.gov/patent
/Ted Kim/
Telephone
571-272-4829
Primary Examiner
Fax
571-273-8300
August 21, 2026
Prosecution Insights