Challenged by the industry to advance the fire protection of hoses used in aircraft engine applications, engineers at the Parker Aerospace Stratoflex Products Division have used standard, low-cost materials to create a high-temperature flexible hose (HTFH) that redefines hose life expectancy. HTFH replaces traditional solutions, including both standard flexible hose and rigid pipe, to provide more durable fire protection, vibration damping, and thermal expansion flexibility to the feeder lines that supply the nozzles spraying fuel into the combustion chamber of jet engines.
Current state: increased vibration, problematic technologies
Vibration is a growing challenge for today’s engine manufacturers. While new lean-burn engines deliver a more complete combustion of fuel that results in lower NOx and particulate emissions, they can cause more vibration or rumble in the engine. Additionally, lighter and thinner components used to reduce engine weight are more susceptible to vibration.
Traditional technologies used to connect fuel manifolds to nozzles can be problematic, even potentially dangerous:
- A stainless-steel wire-reinforced polytetrafluoroethylene (PTFE) hose with a slip-over silicone sleeve and/or integral silicone fire sleeve, is a forty-year-old technology with a temperature limit of 450˚ F (232˚ C). While it provides good vibration damping, its temperature resistance is inadequate and its silicone cover is susceptible to thermal aging, requiring replacement in as little as five to ten years.
- Rigid CRES or Inconel pipe is currently the technology most used due to its higher temperature rating of 1,200° F (650° C). However, the pipe is prone to high cycle fatigue vibration issues, resulting in limited life and replacement of the manifold. In addition, there are more stringent tolerance requirements associated with the precise and time-consuming manufacturing of the all-rigid manifold to ensure proper installation with the fuel nozzles and other manifold connections.
High-temperature innovation: Parker HTFH
Our high-temperature flexible hose is a win-win for engine manufacturers. With a temperature rating of 800°F for ambient conditions with minimal fuel flow of 0.07 gpm, the kink-resistant innovation has inherent damping capability, reducing vibration sensitivity. Plus, it is easier to install, less sensitive to tolerance stack up, offers equal fire-resistance performance to integral fire sleeve hose, and eliminates the problem of thermal aging of fire protection material.
Constructed with a robust, stainless steel outer braid that is superior to a silicone fire sleeve for abrasion and chafing, HTFH has an insulating layer that acts as a fire sleeve. This insulating layer:
- Withstands 1,800°F (982°C) continuous exposure and short-term exposure of up to 3,000°F (1,650°C).
- Is used as thermal insulation in many applications.
- Provides minimal shrinkage at higher temperatures.
- Offers no evidence of abrasion after impulse or vibration.
- Has low absorption of fluids.
The end result of this advanced engineering is a product that is much less costly to maintain due to ease of replacement and significantly longer service intervals, projected to be minimum of 15 years.
Qualified in -4 and -5 sizes (1/4 inch and 5/16 inch diameters respectively) and adaptable to a wide variety of fitting styles and configurations, HTFH is redefining the market.
Six years of service on Rolls-Royce engines
Rolls-Royce utilizes Parker HTFH on four of its engine platforms: the Trent XWB (Airbus A350XWB), Trent 1000 (Boeing 787), BR725 (Gulfstream G650), and Trent 7000 (A330neo). The move to HTFH reflects Rolls-Royce’s recognition of the HTFH technical benefits.
HTFH performance to date has been impressive, without any sign of cycle fatigue or thermal related failures for more than six years.
For additional information on Parker Aerospace systems and capabilities, please visit our website.
This post was contributed by Tracy Rice, strategic chief engineer – engines for Parker Aerospace Stratoflex Products Division.