Why diesel engine makes more noise than petrol engine ?

 I was watching through the window yesterday.

I observed that some auto rickshaws make more noise than other auto rickshaws.

It is not about the vehicle. Be it an auto, car, bus any vehicle.

It is about the engines. 

Diesel engines make a lot of noise than petrol engines while burning the fuel..

There are reasons behind this. 

1. Diesel molecules are much bigger than petrol molecules. Engines run on high  compression.

2. Petrol engines have spark plugs in the cylinders which initiates the combustion. 

But in diesel engines, fuel is ignited by compression only.

Here no source of external combustion.

Hence the combustion in diesel engines is more violent and spontaneous producing higher vibration.

Diesel engines are more heavy and built stronger than petrol engines to sustain the higher pressure involved.