Looking for NVH test experts who can shed some light on the underlying root cause for Vibration and Harshness (at the engine level only, rather than at the vehicle level)
From what I know a significant part of the engine noise comes from the high pressure release coming from the combustion. Diesel engine experience a higher pressure increase, explaining the higher noise of this type of engine.
That's a reason for using some advanced injection strategies, such as pilot injection, as it contributes to reduce the pressure increase, and so the noise produced by combustion.
So basically anything which as an influence on combustion will have an influence on the noise. As when you're asking for more power (a higher charge), you are asking the engine to produce a higher pressure increase in less time, and thus increasing the combustion noise.
I don't know if there is other significant source of noise, but hopefully, somebody will be able to complement the topic.
Hope it will help!
Hi
Exhaust/Intake noise is part of regular NVH design for motors, so is sound radiated from block vibration and structure-borne sound emitted from motor supports.
Apart from combustion noise, you will find mechanical sources like unbalance, rattling and gear whine.
If you are into flow and asking whether it is the flow, the answer is that flow and kinetic pressure are not major contributors to NVH. It usually is the elastic part of the pressure, i.e. the sound that matters for NVH.
Sincerely
Claes
Thank you Claes
Can you clarify what you mean by "It is usually the elastic part of the pressure"? If I understand you correctly, the combustion and fluid flow itself will not have an effect on vibration. In other worlds, if we had a hypothetical perfectly balanced engine with absolutely no mechanical vibrations, then the vibration resulting from the fluid flows is essentially negligible. Is this a safe assumption? I am mostly concerned about the vibrational effects rather than the noise effects
Hi Simon
There is pressure, pressure and pressure. Take a look here
http://qringtech.com/2010/09/15/wave-steepening-increase-peak-pressure-piping-pumps/
http://qringtech.com/2014/01/28/how-to-measure-pulsation/
A brief introduction to aeroacoustics is found here.
http://qringtech.com/2014/04/04/flow-induced-noise-explained/
Hope this helps
Claes
" cylinder by cylinder variation of combustion" could be a possible reason of vibration.
so if you are sure about engine supports, and still having serious problem about vibration, cylinder by cylinder variation of parameters affecting combustion, like fuel injection and spark,should be checked.
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