Question

Why thermal efficiency degrade due to ageing of engines?​

Answer 1

Explanation:

I am looking for peer reviewed articles or technical reports that attempt to quantify the effect of ageing on engine efficiency.

So far I only found a study that quantifies this effect for marine propulsion engines [x] which quantifies typical degradation as accounting for a 15% reduction compared to when the engine was new. Does this sound plausible?

Do you think that diesel engines in other applications (drive systems, road transport) have degradation effects of the same magnitude?

[x] Determination of performance degradation of a marine diesel engine

by using curve based approach, Kökkülünk et al. 2016