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1st message | this message only posted: 30 Dec 2018 13:13
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from:
DerekStuart
United Kingdom

 

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Hi all
Knowing there are some damned clever chaps on this forum, I wonder if anyone can answer this question from a technical perspective.

When a diesel engine changes speed, especially when the change is sudden, there is a distinctive sound- The HST's Valenta being probably the best example I can think of, but it also affects the smaller road diesels I work on.

What is actually happening to cause this sound? The best I can think of is that this is the 'natural' engine sound before it is drowned out by the turbo (that works on the large Valenta but doesn't explain the 4l-8l I work on, where the turbo is quieter). I did ask once in 'the other place' but all I had by way of answer was the question repeated back to me...

Best wishes for 2019 everyone.

Derek

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2nd message | this message only posted: 3 Jan 2019 18:56
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Rob Manchester
Manchester



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Hi Derek,

Happy New Year. Can I ask the reason for your posting ?

Possibly the best place to ask would be with one of the companies that specialises in re-programming Loksound and Zimo chips for the diesel engines. There is a lot going on inside the hood of an HST for example.

Rob


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3rd message | this message only posted: 5 Jan 2019 08:04
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from:
madscientist
 

 

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It’s actually a very complex answer as there are lots of contributing factors

Obviously you have firstly simple increases in frequency , nature and volume of the rotating parts and other mechanical interconnects , then you have sounds changes due to the introduction of more fuel , more air as the throttle is opened , changes in combustion pattern, as well as changes due to the load on the engine , you have ancillary noise changes due to resonances in the exhaust , exhaust scavenging , turbo noise , air induction noise and overall NVH noise ( Noise vibration , harshness) not to mention noise contribution from the many ancillary engine driven accessories 

There’s no simple answer , in different engines different noises predominate
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4th message | this message only posted: 17 Jan 2019 16:46
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from:
DerekStuart
United Kingdom

 

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Thanks Rob. Sound engineers are experts at recording and characterising the sounds, but probably not what is causing them. However, you've given me an idea. I wonder if any of them will have a recording that they can filter out the sound of the turbo and see what is left- it might be, as I speculated, the natural sound that is just drowned out by the turbine.

Hello MS, thanks for the observations. I am of course aware of that. It could be something as obscure as the change of rotational speed of various components momentarily causing standing waves.

Thanks chaps
Derek
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