Question 18 QMED03 - Oiler

The Correct Answer is B. ### Explanation for Option B (Ignite the fuel) The primary goal of the compression stroke in a diesel engine is to rapidly and significantly increase the pressure and, critically, the temperature of the air inside the cylinder. Diesel engines rely on **compression ignition**. Unlike gasoline engines, which use a spark plug, the diesel engine injects fuel only after the air has been compressed to such an extent that its temperature exceeds the autoignition temperature of the diesel fuel. Therefore, attaining sufficient compression conditions directly leads to the high temperature required to **ignite the fuel** upon injection. ### Why Other Options Are Incorrect **A) turn the flywheel:** While the initial starting mechanism (like an electric starter or compressed air) is used to turn the flywheel and begin the cyclic process, turning the flywheel itself is the *means* to start the cycle, not the *goal* of the compression process. The compression process's goal is thermal preparation for combustion. **C) overcome inertia:** Overcoming the inertia of the stationary engine components is necessary to get the engine turning (the initial starting action), but it is a prerequisite to compression, not the ultimate purpose of achieving high compression conditions. **D) reduce friction:** Lubrication is used to reduce friction. Compression conditions (pressure and temperature) are designed for combustion, and have little direct relation to the engine's friction management system.