Boeing's Engine Fan Upgrade Maximizes Efficiency

Boeing continues to tweak the design of its 737 Max to add fuel efficiency to the next-generation jetliner with a change in the size of fan on the plane's CFM LEAP-1B engine.

Boeing and engine manufacturer CFM International -- part of GE Aviation -- have decided to increase diameter size of the engine's fan from 68 inches to 69 inches as part of engine optimization plans that will continue for about the next year, Boeing spokeswoman Lauren Penning told us.

Boeing won't release its final design configuration for the Boeing 737 Max until mid 2013. However, the company has already unveiled a number of design features to meet the jet's overall fuel efficiency goal, which is a 13 percent increase over the previous version of the 737 jet. This fuel-efficient design is a response to the needs of a financially-strapped airline industry facing increases in oil prices, Penning said.

Increasing the fan size allows for a higher bypass ratio, which is the ratio between the mass flow rate of air drawn through a fan disk that bypasses the engine core -- so-called uncombusted air -- to the mass flow rate passing through the engine core. This flow is part of the combustion that produces mechanical energy, giving a jet engine its power.

A higher bypass ratio in general adds to an engine's fuel efficiency. However, Jamie Jewell, spokespeson for CFM, urged caution when making the argument that "bigger is better."

In an interview, she said:

    A bigger fan can increase both aircraft weight and drag, with a negative impact on fuel efficiency. You need to find the optimum size that balances all of the elements that affect fuel burn: engine efficiency, installation, weight, and drag.

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