In a diesel engine, how is the fuel introduced into the combustion system?

• A. Fuel is injected into the intake manifold
• B. Carburetor mixes fuel with air
• C. Fuel is injected after ignition
• D. Direct injection into the combustion chamber

Answer: (D)

In a diesel engine, fuel must be introduced in a way that takes advantage of compression ignition. Air is drawn in and highly compressed, reaching a temperature high enough to ignite fuel without a spark. Injecting fuel directly into the combustion chamber under high pressure allows the fuel to atomize finely and mix with the hot air precisely when combustion should start. This timing and direct delivery into the chamber are what enable efficient, controlled ignition and power.

Injecting fuel into the intake manifold would premix fuel with air before compression, which diesel engines don’t do and would lead to poor control, excessive smoke, and lower efficiency. A carburetor is a gasoline-engine technology used to mix fuel with air before it enters the cylinder, not something used in diesels. Injecting fuel after ignition wouldn’t work because ignition in a diesel is caused by the hot compressed air, so delaying fuel addition would disrupt the intended combustion process.

Therefore, the correct approach is direct injection of fuel into the combustion chamber.