Diesel Sound Quality

[fscliment]

Hi Experts,

In an automotive technical center, diesel engine NVH section we are, just now starting SQ activities in order to add it to our development target sheets. Now only absolute interior noise are required, but we know that it might not be enough.

Firstable, we are trying to choose better SQ indexes for Diesel engine.
We are thinking in choose indexes that shows the fluctuant, rough, impulsive character of the noise as sharpness, roughness... and we are going to use an index related with diesel combustion noise.

I would like to know if from your experience, you have good tips and mistakes that ye could avoid from the begginning.

Many thanks!!

 

[GregLocock]

I /never/ found sharpness or roughness filters to be of the slightest use when judging engine noise quality.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[fscliment]

Hi GregLocock,

Just remark that our objective is to 'smooth' diesel knocking noise. Probably SQ is more related to sportiveness, powerfulness, etc...

But that we are looking for is some index that judges the 'awful' diesel noise, not only the SPL.

We are quite interested in Loudness, 1/f freq ratio, sharpness, fluct strenght....

Do you have experience in that field?

Thanks,
Francisco

 

[GregLocock]

Yes. None of the standard filters worked.

For a given engine it was possible to develop rules of thumb, but almost all of my engine noise quality work relied on a critical ear and a bit of filtering.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SomptingGuy]

I agree with Greg. Much money has been spent by many trying to invent subjective noise indices for diesels based on objective measures. None was as good as panel testing. Knock was largely "knocked out" with pilot injection. Sound quality is more likely to be tweaked via the air path (intake/exhaust) than by the actual engine.

- Steve

 

[fscliment]

Of course by means modifying pilot injection timing, dPrail/dt, and other factors we improve knocking noise. Indeed, this is the most efficient way. (Although today fuel cons & emissions limitations make it hard to play).

But for instance: dont you prefer the disel sound of VWGolf than others?
I feel it as the most diesel pleasant sound, and I think that the question is regarding the 1/f freq ratio...

Many thanks,

Francisco.

 

[SomptingGuy]

I can't say I've compared VAG diesels back to back with their direct competitors (e.g Ford/PSA). But the Merc E320 sounds like it's going somewhere in a hurry.

Back to your original point though. The engine itself is no longer part of the equation. Today's T/C diesels are quiet and refined (if you exclude cold start). Bad noises are gone. The problem is making the sporty models sound sporty - making the good noises lounder. Sportiness is normally associated with intake noise and T/C diesels don't really have any (the compressor kills most engine pulsation noise).

So some companies are going to great (and wierd) lengths to make T/C diesels sound like N/A gasolines. Check this out:

http://www.savills.co.uk/residentia...identialSearch/propertyDetail.aspx?pID=178268

There are other similar devices made by other tier 1's, but the whole idea seems a bit hokey to me.

- Steve

 

[SomptingGuy]

I would blame Bill Gates, but he's stepped down. I still HATE windoze though. This was my intended link:

http://www.mann-hummel.com/company/index.html?iKeys=3.1.176.1.1&cScr=23&rec_no=316

Sorry...

- Steve

 

[fscliment]

Pretty interesting Steve.. Thanks!