You might have noticed that petrol engines are less noisy and vibrate less compared to diesel engines. This is because
the combustion process in a pre-mixed mixture is smooth and propagates well.
But in a diesel engine, the combustion could begin anywhere in the combustion chamber, and it turns out to be an uncontrolled process.For this reason, to reduce the excessive vibration and noise problem, diesel engines require a more rugged structural design than petrol engines.
Fundamentally, a diesel engine makes more power than a gasoline engine of similar displacement- This is due to the fact a diesel engine is a compression ignition engine, and so must utilize a compression ratio roughly twice that of the gasoline engine in order to ignite its fuel. Now, in an internal combustion engine the compression ratio is directly related to the amount of power created; therefore in similar sized engines, the diesel is creating much more power than the gas engine. So, the diesel engine simply has to be built of sturdier construction than a similar displacement gasoline engine to handle these extra forces created. And this is done by manufacturing all the diesel engine components from denser, more substantial materials. The gas engine will be built lighter because the extra strength is not needed, the extra weight not desired, and it is cheaper to build it lighter. Consequently, the diesel engine is heavier than a similarly sized gasoline engine.
To normalize the heavy unbalanced power production of diesel engines a heavy fly wheel is often required. This is why petrol engines are always preferred for light-weight applications, such as in 2-wheeler or portable devices.