Flameless & Low NOx Combustion Patents: Leaders & Trends 2026
- 31.3% sits with five filers. the top five assignees combine for 238 of the 760 records in scope, with a long tail of single- and few-filing entrants behind them.
- Burner and combustion-apparatus classes dominate claim space. F23D and F23C each cover roughly half of all records, while control-specific class F23N sits at just 8.4% — a narrower, more open band.
- Filing has cooled from its 2023 peak. activity ran 2021's 20 filings down to 14 by 2024, a 30% pullback over that span, even before accounting for publication lag in the newest years.
Filing growth compares 2021 (20 records) with 2024 (14) — a three-year span. 2024 is the most recent year we treat as complete: publication lags filing by roughly 18 months, so 2025 onwards are still filling in and any growth rate that ends there would understate the field. Top-5 share is the combined record count of the five largest assignees divided by all 760 records in scope (CR5), not by the ranked leaders only.
What this landscape covers
This dataset tracks 760 published patent records filed between 2015 and mid-2026 that combine flameless combustion, low NOx burner design or furnace combustion control with a secondary technique such as exhaust gas recirculation, oxygen enrichment, peak flame temperature management or reaction zone dilution. The search string deliberately pairs a combustion-control concept with an emissions or thermal-management mechanism, so the corpus is narrower than “combustion” at large and closer to the specific engineering problem of cutting NOx without losing flame stability.
Coverage spans six receiving offices, led by the United States and the European Patent Office, with meaningful WIPO, Japanese, Canadian and Indian filing activity. Because publication trails filing by roughly eighteen months, the final one to two years of the trend understate real activity and should be read as provisional rather than declining.
Filing trend and technology composition
Two views of the same 760 records: how filing volume has moved year over year, and how the field splits across IPC subclasses when a record can carry more than one classification.
Filing trend, 2017-2026
Filings rose from 14 in 2017 to a peak of 25 in 2023, then eased to 14 by 2024 — a 30% decline over the 2021-2024 window using the last fully comparable years. 2025 and 2026 figures are still filling in as publications catch up to filing dates.
IPC subclass composition
Burners (F23D, 54.9% of records) and combustion apparatus (F23C, 48.9%) anchor the field; air and draught supply (F23L, 22.0%) is the next largest. Furnace casings and linings, combustion control, incinerators and gas-turbine plants each sit in single-digit-to-low-double-digit territory, marking narrower but still active bands of claim activity.
Shares are the percentage of the 760 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Flameless and Low NOx Combustion in Furnaces with Eureka
This page is one run against one query. Ask Eureka your own question about flameless and low nox combustion in furnaces and every answer comes back with the patent numbers behind it.
Try EurekaRepresentative and most-cited records
US6039560A — Low NOx burner and method of controlling recirculation of exhaust gas
A low NOx burner having a burner body, to which an electric fan for supplying air for combustion is connected and which includes an exhaust gas recirculation passage for supplying combustion gas from the burner body to air for combustion, the low NOx burner including an exclusive exhaust-gas recirculation fan provided for the exhaust gas recirculation passage and arranged to forcibly recirculate exhaust gas, and a bypass passage formed between the exhaust gas recirculation passage and a passage for air for combustion formed in the burner body.Filed by Sanyo Electric, granted 2000-03-21 — a foundational architecture combining a dedicated recirculation fan with a bypass passage, still cited by later burner-design filings in this corpus.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US5154599A | Method for apparatus for combusting fuel in a combustion chamber | 220 |
| 2 | US7980312B1 | Integrated in situ retorting and refining of oil shale | 195 |
| 3 | US6168709B1 | Production and use of a premium fuel grade petroleum coke | 195 |
| 4 | US20020179493A1 | Production and use of a premium fuel grade petroleum coke | 179 |
| 5 | US20020069648A1 | Novel design of adiabatic combustors | 156 |
| 6 | US20090232729A1 | Steam-Hydrocarbon Reforming Method with Limited Steam Export | 118 |
| 7 | US20060032788A1 | Production and use of a premium fuel grade petroleum coke | 115 |
| 8 | US6773256B2 | Ultra low NOx burner for process heating | 109 |
| 9 | US20070254251A1 | Ultra-low NOx burner assembly | 104 |
| 10 | US8261823B1 | Integrated in situ retorting and refining of oil shale | 96 |
Citation counts reward older filings that have had more time to be cited within this searched set — read them as a signal of influence on the field, not as a ranking of current technical importance.
Each row carries its publication number; clicking a row searches Eureka by that number.
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Browse MCP servers →What the numbers mean for a filing decision
Three read-throughs from the concentration, composition and citation data above.
The top is occupied, the tail is wide open
Five assignees hold 238 of the 760 records in scope, a meaningful but not overwhelming concentration. The other 522 records are spread across a long tail of the remaining ranked companies plus unranked filers, which means most of this space is not locked up by any single player.
Burner hardware claims are the densest single band
Over half of all records touch F23D burner classifications, and nearly as many touch F23C combustion apparatus. New burner-geometry claims are filing into the most contested part of the field; combustion-control-specific claims under F23N, at 8.4%, face far less prior art.
Volume has pulled back from its 2023 peak
Filing peaked at 25 in 2023 before easing to 14 by 2024, a 30% drop across the last fully comparable three-year window. That is a real signal of cooling investment pace in the corpus, though the very newest years will revise upward as publications complete.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to flameless and low nox combustion in furnaces, with the prior art for and against each one.
| Assignee | Co-assignee | Shared families |
|---|---|---|
| Zeeco, Inc. | ZINK DARTON J | 3 |
| Zeeco, Inc. | ROBERTS RYAN | 3 |
| Zeeco, Inc. | MCDONALD JOHN | 3 |
| Zeeco, Inc. | MARTY SETH | 3 |
| Zeeco, Inc. | LITTLE CODY L | 3 |
| Zeeco, Inc. | ISAACS REX K | 3 |
| Zeeco, Inc. | GUARCO JOHN PHILIP | 3 |
| Zeeco, Inc. | BEALE FR E | 3 |
Only ten co-assignee pairs appear in the corpus, with the strongest pairings repeating at three joint filings — combustion patents here are overwhelmingly filed by a single assignee rather than through joint ventures or co-development structures.
Who is filing, and where the gaps sit
The ranking covers 100 companies drawn from patent families across the full 760-record corpus. It is the complete list the dataset returns, not a curated top tier.
A clear leader, then a steep drop
The top-ranked assignee holds 64 records, more than double the fifth-place company's 27. That gap suggests one filer has built a genuinely broader combustion-hardware portfolio rather than a narrow set of related continuations.
Even leaders have gone quiet in the latest year
The top-ranked assignee shows only a single filing in the most recent year captured, and several other ranked leaders show none. Read this cautiously given publication lag, but it is consistent with the broader cooling seen in the 2021-2024 trend.
Filing is concentrated in the US and Europe, with real Asian and Indian volume
The United States and the European Patent Office lead receiving-office counts, followed by WIPO PCT filings and then Japan, Canada and India. That spread indicates this is a technology being protected across major industrial furnace markets rather than in a single jurisdiction.
| Assignee | Recent year | YoY |
|---|---|---|
| Air Products and Chemicals, Inc. | 1 | — |
| Praxair Technology, Inc. | 0 | — |
| Zeeco, Inc. | 0 | — |
| ClearSign Technologies Corporation | 0 | — |
| Edwards Ltd | 0 | — |
| Babcock Hitachi K.K. | 0 | — |
| ExxonMobil Chemical Patents Inc. | 0 | — |
| Honeywell International Inc. | 0 | -100% |
Where to take this analysis
The dataset points to specific next steps depending on whether you are scoping freedom-to-operate or looking for a filing angle.
Check claim overlap before filing in F23D or F23C
With more than half of all records touching burner classifications and nearly as many touching combustion apparatus, a new burner-geometry or apparatus claim needs a careful prior-art read against the leading assignees' portfolios before drafting.
Run a freedom-to-operate check in EurekaTrack the leading assignee's next moves
A single assignee holds 64 of the 760 records with a steep drop to the rest of the field — worth monitoring for continuations or new filings even though its latest-year activity has slowed.
Set up assignee monitoring in EurekaExplore combustion-control and gas-turbine adjacencies
F23N combustion control and F02C gas-turbine classes each sit under 10% of records, well below the burner and apparatus classes — a comparatively open band for a first claim.
Explore white space with EurekaCommon questions about this landscape
One assignee leads the ranked field with 64 of the 760 records in scope, well ahead of the fifth-place company at 27. The top five assignees combined hold 238 records, or 31.3% of the total corpus, which is a real but not dominant concentration. The remaining records are spread across a long tail of smaller and single-filing entrants, so the field is not locked up by a handful of players.
Filing peaked in 2023 at 25 records and had eased to 14 by 2024, a 30% decline across that three-year window. That said, publication typically lags filing by around eighteen months, so 2025 and 2026 figures in this dataset are still incomplete and should not be read as confirmation the field is dying. The honest read is a pullback from a 2023 peak, not a collapse.
F23D, covering burners, appears in 54.9% of the 760 records, and F23C, covering combustion apparatus generally, appears in 48.9%. Air and draught supply (F23L) is next at 22.0%, with furnace linings, combustion control, incineration and gas-turbine classes each in single digits to low double digits. Because a single record can carry several classifications, these shares add up to more than 100% and should not be summed.
Combustion-control-specific claims under F23N cover only 8.4% of records, and gas-turbine-adjacent flameless designs under F02C cover 4.9%, both far below the burner and apparatus classes that dominate the corpus. Incinerator-specific NOx suppression under F23G also sits at a comparatively thin 8.2%. These narrower bands are where new claims face less crowded prior art, though thinner filing density does not by itself guarantee patentability — it simply means fewer competing claims to design around.
US6039560A, assigned to Sanyo Electric and granted in 2000, claims a low NOx burner architecture that pairs a dedicated exhaust-gas recirculation fan with a bypass passage between the recirculation line and the combustion-air passage. It is a foundational design still cited by later filings in this corpus, which signals continuing technical relevance rather than current enforceability, since the patent is decades old. New designs should still map their recirculation and bypass architecture against it, but any live blocking risk is more likely to come from newer, unexpired filings that build on the same mechanism.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.