Answer and Explanation:
The diesel engines are employed in heavy vehicles as they are capable of producing high torque value at low speed.
As they have high compression ratios they can't be used in light vehicles like bikes and compact cars.
As a result of high compression ratios of diesel engines, noise and vibrations are produced which only heavy vehicles can withstand.
Another reason being that heavy vehicles require more fuel and in this case diesel is efficient because petrol burns at a faster rate than diesel.
Otto engines are used for light vehicles and provides high speed and can be regulated and tuned for more torque production.