Noisy diesel

[stevie21]

Why is it that diesel engines are louder than petrol ones? I know sod all about the technicalities of engines - is there an explanation that would make sense to a luddite like me?

If it's to do with diesel burning more slowly than petrol, how does this affect cars than run on gas, coal or vegetable oil?

[Clanad]

Since diesel engines do not have spark plugs to ignite the fuel on the compression stroke, they rely entirely on pressure for fuel ignition.  This requires substantially higher compression ratios than gasoline engines, which produces noise and the peculiar "rattling" sound...

[KebabMeister]

To expand on what Clannad wrote.

 

Petrol engines draw in a mixture of fuel and air and then compresses them at which point it is ignited by a spark plug.

 

On a diesel engine only air is compressed, but has to be compressed to a very high temperature so it is red hot - diesel is then injected into the red hot air and ignites causing expansion and the noise you describe.  The air to be able to reach 'red hot' requires a higher compression ratio.  This means that the air from inside the cylinder is squashed (compressed) up to 20 times its volume.  A petrol car is up to 10 times its volume.

 

I hope this helps explain matters?