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Diesel's (Why so loud)?

41K views 19 replies 18 participants last post by  tryNto 
#1 ·
Why do Diesels, especially Cummins make so much noise? Why do they rattle, and shake, vibrate, and move so much? And what is that distinct sound a Cummins makes at idle that no other diesel engine really makes? Is it the valves opening and closing (valve clatter)? Or the injectors injecting fuel? Whichever it is, it sounds awesome!!

Thought this would make for a cool topic of discussion. :confused013:
 
#2 ·
In general a diesel is loud due to the fact that the fuel is exploding under compression without a ignition source like a gas motor which uses those nasty things called spark plugs. so basically what happens in the cylinders is the diesel is exploding under high compression and thats the general reason for the shaking and loud motor. I'm sure that someone could explain it in a lot more detail, i just gave a bumper sticker version.
 
#4 ·
You just can't beat the growl of a Cummins at idle. On the other hand, my F350 sits at idle and sounds like a jet, which is kinda cool, but I'd rather have the Cummins growl....... If I had the funds.......... my truck would become a fummins real quick like. I love the truck, but I hate the motor. I know.... I didn't answer your question........ Sorry. LOL!
 
#5 ·
Compression Ignition. Squeeze, squeeze, squeeze, squeeze, squeeze. Then BOOM.

When you compress air it becomes superheated, to the point that it readily ignites flammable liquids (diesel) on contact.
 
#7 ·
A lot has to do with the injection systems and injectors along with the the fuel being ignited by compression. Also most diesels are almost all gear driven...crank, cam, pump, etc.....you see a lot of change to other systems such as belt or chain to do away with the sound...which i think is stupid...a diesel is suppose to be loud.
 
#9 ·
i had always wondered this too i thought it was the compression but i never was for sure and then you add the exhaust on like most of guys have and they get even LOUDER! lol
 
#11 ·
what you usualy hear is the sound of the explosion.

But how do they make the newer trucks quieter, simple inject the diesel in sets, ie

89-2002 diesels used 1 injection pulse per power stroke, once you move to the common rail era the pumpers move up to 3 injection pulses. then you get to the 6.7's where i believe there are 5 injection pluses , 2 before 1 at tdc and 2 after (for emissions), the more pluses the more controlled the explosion, thus the quieter in operation..



i think its the sound of my engine eating its self lol.
 
#15 ·
1. If you have ever heard an incorrectly-tuned gasoline engine knock--rare these days with electronic ignition with knock sensors--diesels are not that much louder than a knocking gas engines, comparing apples (cu.in.) to apples. Those of us old enough to remember a good ol' (say 1960's era) 350 c.i. V-8 gas-engine "dieseling" can attest to that.
2. Solid lifter/tappet (don't flame me on this one) config's. of diesels produce more metal-on-metal contact points increasing noise. Ditto chain &/o gear driven vs. belt driven components.
3. At idle, frequencies are lower so they are more noticeable. That's why the boom-boxes in rice burners p.m.o. vs.little ol' ladies listening to Montavani CD's.
4. Why Cummins? Dodge did not do much [any? :spank:] NVH damping on 1st and 2nd Gen models.

More, from: Diesel engine - Wikipedia, the free encyclopedia

Noise
The characteristic noise of a diesel engine is variably called diesel clatter, diesel nailing, or diesel knock.[45] Diesel clatter is caused largely by the diesel combustion process, the sudden ignition of the diesel fuel when injected into the combustion chamber causes a pressure wave. Engine designers can reduce diesel clatter through: indirect injection; pilot or pre-injection; injection timing; injection rate; compression ratio; turbo boost; and exhaust gas recirculation (EGR).[46] Common rail diesel injection systems permit multiple injection events as an aid to noise reduction. Diesel fuels with a higher cetane rating modify the combustion process and reduce diesel clatter.[45] CN (Cetane number) can be raised by distilling higher quality crude oil, by catalyzing a higher quality product or by using a cetane improving additive. Some oil companies market high cetane or premium diesel. Biodiesel has a higher cetane number than petrodiesel, typically 55CN for 100% biodiesel.[citation needed]

As pepsiocean said...
A combination of improved mechanical technology such as multi-stage injectors which fire a short "pilot charges" of fuel into the cylinder to initiate combustion before delivering the main fuel charge, higher injection pressures that have improved the atomisation of fuel into smaller droplets, and electronic control (which can adjust the timing and length of the injection process to optimise it for all speeds and temperatures), have mostly mitigated these problems in the latest generation of common-rail designs, while improving engine efficiency.
 
#13 ·
The older the truck the less stuff on the motor and under the hood to absorb the sound.
 
#14 ·
Two stroke diesels i.e. early Detroits are quiet compared to four strokes. Fire every other stroke, superchargers instead of turbos and less moving parts.
 
#17 ·
Yes the lack of a valve train helped. Granted I would never consider a two stroke diesel a "quiet" engine. An old trucker told me the only reason the trucks with those engine had radios was so you had something to listen to when the truck was broke down. Because you could never hear the radio if the engine was running.
 
This post has been deleted
#20 ·
Fixed that.
 
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