A few years back I have seen that Pratt and Whitney 's Geared Turbofan Engine(GTF) has reduced it's noise levels to about 50%. But recently I was having a discussion with a friend and he told me that there is an engine which has the noise levels reduced to about 10%.I tried searching on the net couldn't find any such engine .Is that even possible? Considering the fact that the most of the noise is from the engine main exhaust. Thanks in advance
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$\begingroup$ Manufacturers have noise reduction objectives and commitments with civil aviation international bodies (e.g. ICAO Annex 16). See this summary. The document confirms the jet noise is the largest one at take off (so the GTF is relevant), but not on approach. $\endgroup$– minsFeb 5, 2019 at 10:39
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Turbofans already produce much less noise than the turbojets used in the 1960s. In general, the higher the bypass ratio, the lower the noise level.
It's difficult to silence a jet engine: any silencer impedes the airflow which means a significant power loss.
Noise levels are usually expressed in dB rather than %, a reduction by 90% is a 20 dB difference, which is huge. To give an impression: from 1992 to 2000 NASA ran a technology development program aimed at reducing noise by 6 dB.
This chart shows various noise sources in an engine:
Here is an overview of the noise regulations currently in effect:
So Stage 3 is a reduction by 10 dB compared to Stage 2, Stage 4 is a reduction by 7 dB. The quietest aircraft are already at 17 dB below the Stage 4 limit.
So an engine that 'has the noise levels reduced to about 10%' seems plausible (depending on what you're comparing to), and the graphic identifies a few candidates.
