Ignition of fuel in a diesel engine is by

ANS:B - hot compressed air

Ignition of fuel in a diesel engine is by hot compressed air. Explanation: In a diesel engine, ignition of the fuel is achieved through the process of compression ignition. Here's how it works:

1. Compression: In a diesel engine, air is compressed to a very high pressure and temperature by the piston as it moves upwards during the compression stroke. This compression raises the temperature of the air significantly.
2. Fuel Injection: Once the air is compressed, diesel fuel is injected into the combustion chamber at high pressure. The fuel is atomized into small droplets and mixes with the hot compressed air.
3. Autoignition: Due to the high temperature and pressure of the compressed air, the diesel fuel ignites spontaneously without the need for a spark plug. This process is known as compression ignition or autoignition.