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Author Topic: Why Does A Diesel Engine Make A Rattling Sound ?  (Read 24693 times)

Offline neilep

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Why Does A Diesel Engine Make A Rattling Sound ?
« on: 01/09/2008 01:45:50 »
Dearest Dieselologists,

As a sheepy I am of course always a high performance finely tuned steely eyed sheeping machine !!

....see Frieda the diesel engine here ?




..nice eh ?...as far as engines go, she's a babe alright !...if I was a blokey engine I'd be well happy to put my key in her ignition !.... ;D.............but at what cost ?...

...at the cost of a characteristic rattling noise that has one thinking that Frieda............ is half rattle snake !!

...why's that then ?...why does Frieda and other diesel engines share the same kind of rattling sound !!?
I want to know....do ewe know ?....


Your schematically aural explanations of an engineering kind will be most welcome.



Thank ewe


hugs and shmishes



Neil
Do-er of Dolly Diesels !
xxxxxxxxxxxxxxxxxxx

mwah mwah mwah mwah




« Last Edit: 01/09/2008 01:49:08 by neilep »


 

lyner

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Why Does A Diesel Engine Make A Rattling Sound ?
« Reply #1 on: 01/09/2008 11:43:52 »
That banging noise is the explosion of the fuel. Diesels use higher compression ratio and all the fuel ignites at the same time - hence the bang. Diesel engines need more beefy bearings than petrol engines (in which the flame front moves 'slowly' through the combustion chamber) for this reason.
 

Offline teragram

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Why Does A Diesel Engine Make A Rattling Sound ?
« Reply #2 on: 01/09/2008 17:02:56 »
From my days as an engine fitter many years ago:-
The Diesel engine noise is largely a result of the pressure needed to inject fuel into the cylinder, this pressure also resulting in atomisation of the fuel. The pressures can be 200bar or more. The engine is better than a petrol engine because the fuel is injected progressively into the cylinder over a period starting just before top center of crankshaft (top of piston stroke), finishing maybe ten or fifteen degrees crankshaft movement after top. This means that combustion takes place in a more linear fashion than in the petrol engine, where it is triggered by the ignition spark. It also results in substantial combustion pressure being still available when the crankshft reaches its position of best leverage (approx 90degrees to the connecting rod). This is the reason why Diesels tend to provide greater torque than petrol engines.

Many discussions describe the combustion process in an engine (petrol or Diesel) as an "explosion". This is not true, as fuel in both engines has a well defined "flame from propogation front", in fact a period of time is involved as opposed to a sudden bang.
 

lyner

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Why Does A Diesel Engine Make A Rattling Sound ?
« Reply #3 on: 02/09/2008 10:53:22 »

The Diesel engine noise is largely a result of the pressure needed to inject fuel into the cylinder, this pressure also resulting in atomisation of the fuel. The pressures can be 200bar or more.
The engine is better than a petrol engine because the fuel is injected progressively into the cylinder over a period starting just before top center of crankshaft (top of piston stroke), finishing maybe ten or fifteen degrees crankshaft movement after top. This means that combustion takes place in a more linear fashion than in the petrol engine, where it is triggered by the ignition spark.

Many discussions describe the combustion process in an engine (petrol or Diesel) as an "explosion". This is not true, as fuel in both engines has a well defined "flame from propogation front", in fact a period of time is involved as opposed to a sudden bang.
I went and read my Uni Thermodynamics book again and you're so right.  The two 'cycles' are very different and the better efficiency of the Diesel is shown by the greater area enclosed on the PV diagram. The spark engine has a sharp increase in pressure with little change in volume during the burn whereas the Diesel engine has constant pressure during the burn and the volume is increasing. That would suggest that there should be more of a bang for the petrol engine, if what I said was right. So it must be, as you say, the diesel injector which makes all the racket.
The bigger bearings are just because of the higher compression ratio required for the Diesel engine.
 

Offline teragram

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Why Does A Diesel Engine Make A Rattling Sound ?
« Reply #4 on: 02/09/2008 19:07:59 »
Thanks, Sopiecentaur
 

Offline Karen W.

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Why Does A Diesel Engine Make A Rattling Sound ?
« Reply #5 on: 02/09/2008 21:16:01 »
Cool information guys! Good job!
 

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Why Does A Diesel Engine Make A Rattling Sound ?
« Reply #5 on: 02/09/2008 21:16:01 »

 

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