Question 16

The Correct Answer is B **Explanation for B (Excessive cylinder lubrication):** Blue exhaust smoke in a diesel engine is the result of lubricating oil being burned in the combustion chamber. Normally, the oil is scraped off the cylinder walls by the piston rings. If there is excessive lubrication (often due to worn rings, damaged liners, or issues with oil control seals/turbos), the oil enters the combustion chamber and burns. Because lubricating oil is heavier and burns differently than diesel fuel, it produces a distinctive, acrid-smelling, bluish-white smoke. **Why the other options are incorrect:** * **A) a light load:** A diesel engine operating under a light load often runs cooler, which can lead to incomplete combustion of the **fuel**. This condition typically results in white or light grey smoke, not blue smoke (which indicates burning oil). * **C) cold intake air:** Cold intake air, especially when combined with a cold engine, can hinder the ignition process and lead to poor combustion of the **fuel**. Like running a light load, this usually results in white smoke (unburned fuel particles). * **D) excessive compression pressure:** Excessive compression pressure generally improves combustion efficiency, leading to more complete burning of the **fuel**. This would typically result in clearer exhaust or potentially black smoke if fuel delivery is optimized for the higher pressure, but it would not cause blue smoke, which is related to the burning of **oil**.