Within this 47-family dataset, Rolls-Royce and its German affiliate form the strongest filing group, linked by the dataset's largest co-assignee pair with 16 shared families. Chinese research institutes such as AECC Shenyang Engine Research Institute and universities like Beihang appear as smaller, more recent filers. No single organisation holds a dominant share of the full set, and the field reads as a handful of legacy programmes plus a long tail of single-institution filings.

Filing activity peaked in 2021 at 10 records and had already dropped to 3 by 2022, with recent-year momentum by assignee mostly flat or at zero. That pattern suggests the core lean burn and liner cooling claim space filled up during a design cycle tied to specific engine programmes rather than continuing to grow. New filings are still occurring, but at a lower rate, and any new application will be examined against a denser prior-art base than it would have faced five years ago.

F23R, covering combustion chambers, accounts for 43 of the 47 families in this dataset and is the class to search first. F02C (gas-turbine plants) and F23C (combustion apparatus) are secondary but still meaningful, while F23D burners, F02K jet propulsion, F23K fuel feeding, B64D aircraft equipment and F23M furnace linings each register only a handful of records. A thorough freedom-to-operate search should still cover the smaller classes, since low volume there can mean either genuine white space or simply that the language used in those filings differs from the search terms used here.

US11353215B1, assigned to Rolls-Royce, claims a lean burn combustor built around fuel injectors with a pilot injector arranged coaxially inside a main injector, plus a defined injector head tip diameter and a combustor chamber geometry set by a meter panel. It does not claim lean burn combustion generally, so a design that uses a different injector arrangement, a different tip geometry, or a different means of defining primary combustion zone size is unlikely to be blocked by this specific claim set. Anyone designing a coaxial pilot-main injector with similar tip dimensioning should review the full claim language rather than rely on the abstract.

The clearest gaps sit in subclasses adjacent to the dominant F23R combustion-chamber class: burner design under F23D, jet and reaction propulsion integration under F02K, and furnace-casing thermal linings under F23M all show single-digit record counts in this dataset. Multi-microswirler injection heads and fine-grained liner cooling hole geometry also appear thinly claimed relative to the volume of combustor-chamber filings overall. Low volume in a niche search does not guarantee the space is legally open, so any filing decision there should be paired with a broader keyword and classification check.