Dubai Airshow

CFM Still Working on Leap Fuel-Nozzle Coking Issue

 - November 17, 2019, 1:01 AM
Engine maker CFM is using big data to collect parameters and trace patterns that it anticipates will help predict when Leap-1A and -1B turbofans might be vulnerable to fuel-nozzle coking.

CFM International is employing engine-sensor data analytics to predict if and when any given Leap-1A or Leap-1B engine may experience depositions of hardened carbon on its fuel nozzles, as it continues to seek a permanent fix for the issue.

Gaël Méheust, CFM’s president and CEO, told AIN that the joint venture’s engineers have found patterns in the streams of condition and performance data produced by each Leap engine’s internal sensors which indicate if any individual engine is likely to experience fuel-nozzle coking in service. The OEM used Leap sensor-data analytics in a similar fashion in 2018 to identify the thermal barrier coating degradation issue which affected the ceramic matrix composite parts comprising the shroud around the first high-pressure turbine rotating stage of Leap-1A and Leap-1B engines, he said.

CFM’s continuous monitoring of the health of every Leap engine in operation has shown it that the fuel-nozzle coking issue affects some engines but not others. As a result, CFM knows “there has to be a link with the operating parameters” experienced by each individual Leap engine and its potential vulnerability to fuel-nozzle coking, said Méheust. It is still working to understand exactly what those operating conditions are and exactly how they influence the potential coking tendency for any given engine.

What CFM (Stand 1065) does know is that the coking happens after engine shutdown, when unburned fuel in the fuel nozzles evaporates in the still extremely hot temperatures prevailing in the combustor’s interior, causing solid carbon to be deposited on the nozzles. As CFM explained to AIN before this year’s Paris Air Show in June, all aircraft engines experience some form of coking and OEMs and operators need to manage the issue so it doesn’t result in undue engine performance deterioration or potentially compromise flight safety.

CFM is using the data analytics it has developed to detect potential Leap fuel-nozzle coking to instruct each operator well in advance of coking potentially becoming a serious issue in an engine to schedule an inspection of that engine, said Méheust. If the inspection indicates preventative maintenance is desirable, it can be performed as line maintenance overnight and with the engine still on-wing, so there need not be any disruption to an aircraft’s operating schedule. Operators also have the option of conducting physical checks of their Leap fuel nozzles on a regular basis and, according to Méheust, “a lot of operators are doubling [CFM’s monitoring of engine] analytics with physical checks on nozzles” to ensure they catch potential coking early.

“Now we have analytics in place to tell [if coking is starting to happen] and if it does happen the operator can either replace the fuel nozzles overnight or clean the nozzles,” said Méheust. “We have just finished the process” of developing a quick, on-wing cleaning procedure for the fuel nozzles using specific cleaning tools developed by CFM, “so we are able to minimize the impact for our customers.”

Méheust confirmed that CFM is “still working to find a way of eliminating the build-up” on Leap fuel nozzles, to prevent coking from being an issue in the future. One area of research it is continuing to look at is whether modifying the Leap shutdown process could reduce or prevent the possibility of coking. In that regard CFM has been studying if changes to the Leap’s FADEC engine-control software could produce the desired result.