Oilers/Plant Tenders (HHC) Civil Service Practice Exam

What is the impact of high temperatures in diesel engine cylinder jackets?

1. Improved lubrication

2. Decreased mechanical efficiency

3. Increased risk of engine knocking

4. Enhancement of fuel combustion

The correct answer is: Increased risk of engine knocking

High temperatures in diesel engine cylinder jackets have a significant impact on engine performance, particularly regarding the risk of engine knocking. Knocking occurs when the air-fuel mixture in the combustion chamber ignites prematurely, leading to a knocking or pinging sound and potentially damaging the engine. When the temperature in the cylinder jackets is excessively high, it can lead to increased cylinder pressure and more rapid combustion rates. This creates an environment where the compression ignition process, which is essential for diesel engines, may become unstable and result in knocking. Excessive heat can also degrade lubrication properties, reduce the density of the air-fuel mixture, and create fewer optimal conditions for combustion, which further exacerbates the risk of knocking. While improved lubrication and enhancement of fuel combustion might seem beneficial at first glance, extreme temperatures generally compromise lubrication quality and control over combustion. Increased mechanical efficiency can occur under ideal temperature conditions, but high cylinder jacket temperatures typically detract from overall engine efficiency. Thus, the increased risk of engine knocking is the most direct and critical consequence of high temperatures in diesel engine cylinder jackets.