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and the fee set forth in 37 CFR 1.17(e) has been timely paid, the finality of the previous Office action has been withdrawn pursuant to 37 CFR 1.114.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 2/26/2026 has been entered.
Claim Objections
Claims 2, 7 objected to because of the following informalities: claims 2, 7: “gasses” should be changed to be consistent with the spelling of claim 1 –gases--, which was amended on 2/26/2026. Appropriate correction is required.
Claim Rejections - 35 USC § 112
The following is a quotation of 35 U.S.C. 112(b):
(b) CONCLUSION.—The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the inventor or a joint inventor regards as the invention.
Claims 1, 2, 5, 7, 11 are rejected under 35 U.S.C. 112(b) or 35 U.S.C. 112 (pre-AIA ), second paragraph, as being indefinite for failing to particularly point out and distinctly claim the subject matter which the inventor or a joint inventor (or for applications subject to pre-AIA 35 U.S.C. 112, the applicant), regards as the invention.
Claim 1, 2nd ¶ from the end, “the system further comprises an exhaust configured to exit a heated exhaust gas flow that is a combination of the hydrogen fuel received from the outlet of the first heat exchanger and the hydrogen fuel received from the outlet of the second heat exchanger, mixed with the compressed air from the compressor bleed” is unclear. First, “an exhaust configured to exit a heated exhaust gas flow that is a combination of the hydrogen fuel received from the outlet of the first heat exchanger and the hydrogen fuel received from the outlet of the second heat exchanger, mixed with the compressed air from the compressor bleed” is missing essential elements so as to determine where and what the exhaust is. Second, the claim literally requires “the exhaust gas flow” … “is a combination of the hydrogen fuel received from the outlet of the first heat exchanger and the hydrogen fuel received from the outlet of the second heat exchanger, mixed with the compressed air from the compressor bleed.” Is applicant referring to the burner’s 304, 314 exhaust? Note that burner 304 receives all the claimed flows? Is the exhaust instead referring to the exhaust line 309? In both of these cases, the claim is unclear because hydrogen is not exhausted in the exhaust line 309 nor exhausted by the burner 304, 314, which is what the claim appears to literally require. Additionally, applicant also requires “a heated exhaust gas flow.” However, the claim does not make clear how exhaust gas is heated or if the burning process alone is sufficient for the exhaust gases to be considered “heated”. Furthermore, it is unclear whether “an exhaust configured to exit a heated exhaust gas flow” has any relationship to “the first heat exchanger is configured to transfer heat from exhaust gases produced by the burner to hydrogen fuel in the main fuel conduit.”
Claim 2 recites “burner exhaust gasses” but it is not clear what the relationship is to “an exhaust configured to exit a heated exhaust gas flow” from claim 1.
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) 1, 2, 5, 11, as understood, is/are rejected under 35 U.S.C. 103 as being unpatentable over Palmer (2022/0099020) in view of Ranjan et al (2023/0083470) and Owoeye et al (11,753,995) and Hosford (4942733)1. Palmer teaches (1) A fuel system for a gas turbine engine comprising: a fuel offtake 301 configured to divert a portion of hydrogen fuel from a main fuel conduit 217; a burner 303 configured to burn the portion of hydrogen fuel diverted from the main fuel conduit; at least first 303 heat exchanger; wherein the first heat exchanger 303 is configured to transfer heat from exhaust gasses produced by the burner to hydrogen fuel in the main fuel conduit 217; the burner comprises a second hydrogen fuel inlet 301 configured to receive hydrogen fuel from a fuel source, the main fuel conduit configured such that the hydrogen fuel flowing through the main fuel conduit is not mixed with the hydrogen fuel received from the outlet of the first heat exchanger 303 [hydrogen delivered to the burner is used for heating the main fuel conduit 217 and is not mixed therewith as the combustion gases are exhausted from burner 303 at the top in Fig. 3] and the second hydrogen fuel inlet 301 comprises an auxiliary fuel heater 305 that is an electric fuel heater, the system further comprises an exhaust configured to exit a heated exhaust gas flow that is a combination of the … and the hydrogen fuel received from the outlet of the [to be added] second heat exchanger, mixed with the compressed air from the compressor bleed [air to 304 is compressed air, see ¶ 0062] and the first heat exchanger 303 is arranged as cross- flow heat exchanger.
(4) wherein the burner 303 is configured to burn hydrogen fuel 301 with air from the compressor bleed 218. (11) A gas turbine engine comprising a fuel system according to claim 1.
Palmer does not teach (1) a second heat exchanger, the second heat exchanger is provided upstream in hydrogen flow of the first heat exchanger, and is configured to transfer heat from a further heat exchange fluid to hydrogen fuel in the main fuel conduit, and the further heat exchange fluid comprises compressed air provided from a compressor bleed of a gas turbine engine nor the burner comprises … a first hydrogen fuel inlet configured to receive hydrogen fuel from an outlet of the second heat exchanger; the main fuel conduit configured such that the hydrogen fuel flowing through the main fuel conduit is not mixed with … the hydrogen fuel received from the outlet of the second heat exchanger; a heated exhaust gas flow that is a combination of … the hydrogen fuel received from the outlet of the first heat exchanger and the hydrogen fuel received from the outlet of the second heat exchanger; and the first heat exchanger and the second heat exchanger are both arranged as cross- flow heat exchangers
(2) wherein, the fuel system is configured such that, in use, the further heat exchange fluid has a lower temperature at entry to the second heat exchanger than burner exhaust gasses at entry to the first heat exchanger; nor (5) wherein the second heat exchanger is configured to cool the compressor bleed air / further heat exchange fluid to a temperature above 273K at an outlet of the second heat exchanger. Owoeye et al may be applied as a teaching reference that teaches it is well known to place a second heat exchanger 196 upstream of the first heat exchanger 200 in the direction of the hydrogen flow in order to provide for heating of the hydrogen fuel in axial stages [with shared heat loads, e.g. col. 6, lines 1-36]. Ranjan et al teaches (1) … a second heat exchanger 320, the second heat exchanger is provided upstream in hydrogen flow of the first heat exchanger 322, and is configured to transfer heat from a further heat exchange fluid 316 to hydrogen fuel in the main fuel conduit [from 302], and the further heat exchange fluid comprises compressed air 316 provided from a compressor bleed 316 of a gas turbine engine 304; (2) wherein, the fuel system is configured such that, in use, the further heat exchange fluid 316 has a lower temperature at entry to the second heat exchanger 320 than burner exhaust gasses [burner exhaust gases are hot, whereas compressed air 316 temperature is 470 ⁰C, per ¶ 0021, 0053-0054, and this is much lower temperature than typical burner gas temperatures – alternately, it would have been obvious to make this relationship so, as typical conditions of compressed air temperature vs burner exhaust]; (5) wherein the second heat exchanger 304 is configured to cool the compressor bleed air / further heat exchange fluid to a temperature above 273K at an outlet of the second heat exchanger [temperature of air 338 exiting 320 exceeds 515K, per ¶ 0021, 0053-0054, note the air exiting 322 exceeds the temperature exiting 320]. Ranjan teaches that the second heat exchanger facilitates preheating / warming the hydrogen and aids the hydrogen fuel in attaining the required temperatures in the main combustor [¶ 0037] and facilitates weight reduction and thus greater efficiency [see ¶ 0058]. It would have been obvious to one of ordinary skill in the art to employ (1) a second heat exchanger, the second heat exchanger is provided upstream in hydrogen flow of the first heat exchanger, and is configured to transfer heat from a further heat exchange fluid to hydrogen fuel in the main fuel conduit, and the further heat exchange fluid comprises compressed air provided from a compressor bleed of a gas turbine engine; (2) wherein, the fuel system is configured such that, in use, the further heat exchange fluid has a lower temperature at entry to the second heat exchanger than burner exhaust gasses at entry to the first heat exchanger; (5) wherein the second heat exchanger is configured to cool the compressor bleed air / further heat exchange fluid to a temperature above 273K at an outlet of the second heat exchanger, in the manner suggested by Ranjan et al, because using the second heat exchanger facilitates preheating / warming the hydrogen and aids the hydrogen fuel in attaching the required temperatures in the main combustor [¶ 0037] and facilitates weight reduction and thus greater efficiency [see ¶ 0058] and where Owoeye et al may be applied as a teaching reference that teaches it is well known to place a second heat exchanger upstream of the first heat exchanger in the direction of the hydrogen flow, in order to provide for heating of the hydrogen fuel in axial stages / shared heat loads. Note that adding the second heat exchanger to the system of Palmer can be one of two options, either upstream of the offtake 301 or downstream of 301. The location as upstream has been the one selected as there are a limited number of options. As modified by Ranjan et al, the second heat exchanger is added upstream of the first heat exchanger [see annotations]. Making the burner comprise a second hydrogen fuel inlet configured to receive hydrogen fuel from an outlet of the second heat exchanger [after modification by Ranjan et al] is regarded as an obvious location, as that location is upstream of the first heat exchanger, which is consistent with the teachings of Palmer. It would have been obvious to one of ordinary skill in the art to make the burner comprise a second hydrogen fuel inlet configured to receive hydrogen fuel from an outlet of the second heat exchanger, by adding a second heat exchanger in the annotated location by Ranjan et al., as a location that is upstream of the first heat exchanger of Palmer and thus compatible with its heating system.
Hosford teaches the burner comprises a first hydrogen fuel inlet 56 configured to receive hydrogen fuel from an outlet of the first heat exchanger 28, the main fuel conduit configured such that the hydrogen fuel 42 flowing through the main fuel conduit is not mixed with the hydrogen fuel received from the outlet of the first heat exchanger 28 and the hydrogen fuel received from the outlet of the second heat exchanger 32 [32 is upstream of 28 in hydrogen flow], It would have been obvious to have the burner comprises a first hydrogen fuel inlet configured to receive hydrogen fuel from an outlet of the first heat exchanger [with the existing … a second hydrogen fuel inlet configured to receive hydrogen fuel from an outlet of the second heat exchanger of the modified Palmer2], the main fuel conduit configured such that the hydrogen fuel flowing through the main fuel conduit is not mixed with the hydrogen fuel received from the outlet of the first heat exchanger and the hydrogen fuel received from the outlet of the second heat exchanger, as taught by Hosford [in addition to the modified Palmer], in order to utilize a convenient source of heated fuel for the burner and which facilitates enhanced combustion efficiency due to the heating of the hydrogen prior to combustion.
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After Palmer is modified by Ranjan and Hosford [see annotations], the burner comprises a first hydrogen fuel inlet [from Hosford] configured to receive hydrogen fuel from an outlet of the first heat exchanger a second hydrogen fuel inlet [301of Palmer] configured to receive hydrogen fuel from an outlet of the second heat exchanger [see annotations]; the main fuel conduit configured such that the hydrogen fuel flowing through the main fuel conduit [to the right of 301] is not mixed with the hydrogen fuel received from the outlet of the first heat exchanger and the hydrogen fuel received from the outlet of the second heat exchanger, the second hydrogen fuel inlet 301 comprises an auxiliary fuel heater 305 that is an electric fuel heater [Palmer ¶ 0035], the system further comprises an exhaust configured to exit a heated exhaust gas flow that is a combination of the hydrogen fuel [see annotations] received from the outlet of the first heat exchanger [added from Hosford] and the hydrogen fuel 301 received from the outlet of the second heat exchanger [added from Ranjan], mixed with the compressed air from the compressor bleed [air in 304 is compressed air, ¶ 0036, 0062].
Palmer already teach the first heat exchanger 303 of Palmer is arranged as cross- flow heat exchanger [90 degree flows].
As for both the first and the second heat exchanger are both arranged as cross- flow heat exchangers, Ranjan also teaches both of heat exchangers 320, 322 are both arranged as cross- flow heat exchangers [see ¶ 0044] and that the flow of hydrogen from 302 is at 90 degrees with respect to the flow 316. It would have been obvious to one of ordinary skill in the art to make the second heat exchanger or to make both the first and second heat exchangers arranged as cross- flow heat exchangers, as taught by Palmer and/or Ranjan, as a typical heat exchanger geometry utilized in the art.
Claim(s) 1, 2, 5, 11, as understood, are rejected under 35 U.S.C. 103 as being unpatentable over the Palmer combination as applied above, and Peters et al (3,237,401). The Palmer combination, as applied above, teach a first construction of “the system further comprises an exhaust configured to exit a heated exhaust gas flow that is a combination of the hydrogen fuel received from the outlet of the first heat exchanger and the hydrogen fuel received from the outlet of the second heat exchanger, mixed with the compressed air from the compressor bleed”. For an alternate treatment of this limitation, Peters et al teach the system further comprises an exhaust configured to exit a heated exhaust gas flow [exhaust gas flow downstream of 56] that is a combination of the hydrogen fuel received from the outlet 44, 22 of the first heat exchanger 40 and the hydrogen fuel received from the outlet 52, 54 of the second heat exchanger [regenerator 52 ignites the fuel from regenerator and it burns at flameholder 54], mixed with the compressed air [from 16] from the compressor 16 bleed [see col. 1, lines 31-35]. This promotes reduced weight and/or increases fuel efficiency [col. 1, lines 22-26] It would have been obvious to one of ordinary skill in the art to employ an exhaust configured to exit a heated exhaust gas flow that is a combination of the hydrogen fuel received from the outlet of the first heat exchanger and the hydrogen fuel received from the outlet of the second heat exchanger, mixed with the compressed air from the compressor bleed, as taught by Peters et al, for reduced weight and/or increased fuel efficiency.
Claim(s) 7 is/are rejected under 35 U.S.C. 103 as being unpatentable over the Palmer combination with or without Peters, as applied above, and further in view of Kesseli et al (2012/0096869). Palmer does not teach (7) wherein the fuel system comprises a third heat exchanger provided downstream of the second heat exchanger and upstream of the first heat exchanger in hydrogen fuel flow and configured to exchange heat between exhaust gasses from the burner downstream of the second heat exchanger, and hydrogen in the main fuel conduit. Owoeye et al further teach (7) wherein the fuel system comprises a third heat exchanger 198 provided downstream of the second heat exchanger 196, to exchange heat the upstream of the first heat exchanger 200 in hydrogen fuel flow, to exchange heat with hydrogen in the main fuel conduit, in order to provide for heating of the hydrogen fuel in axial stages / shared heat loads. Kesseli et al teach (7) wherein the fuel system comprises a third heat exchanger configured to exchange heat between exhaust gasses [from 8] from the burner 5 downstream of the second heat exchanger 4, and hydrogen 102 in the main fuel conduit [see ¶ 0017-0018 which teaches the fuel 91, 96 may be hydrogen]. The heat of the burner 5 is recovered and utilized to heat multiple heat exchangers 4 and 42 [Fig. 6] as is typically done in the art to extract as much heat as possible from the burner for thermal efficiency [abstract, ¶ 0007]. It would have been obvious to one of ordinary skill in the art to exchange heat between exhaust gasses from the burner downstream of the second heat exchanger, and hydrogen in the main fuel conduit, i.e. send the exhaust gases from the burner of Palmer, to the third heat exchanger, as added from Owoeye et al, in order to maximize the energy recovery from the burner exhaust as is typically done in the art for thermal efficiency [abstract, ¶ 0007].
Response to Arguments
Applicant's arguments filed 2/26/2026 have been fully considered but they are not persuasive. Applicant’s terminal disclaimer obviates the double patenting rejection.
Applicant’s arguments concerning the amended limitations are not persuasive as the limitations are problematic under 35 USC 112(b) and lack clarity. As for the arguments concerning Palmer, Hosford and Ranjan, these suggest that the underlying combination of references and how they are put together were not well understood. Applicant emphasizes that the “second hydrogen fuel inlet has an auxiliary electric heater.” Palmer already teach that feature, especially after adding an upstream second heat exchanger. Accordingly, Palmer has been annotated with the modifications by Hosford and Ranjan to better understand the combination. The cross-flow heat exchangers were already taught by the art of record and are extremely conventional.
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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.
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/Ted Kim/
Telephone
571-272-4829
Primary Examiner
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April 1, 2026
1 Hence, the Palmer combination
2 i.e. modified by Ranjan