Question 39 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is C ### Why Option C ("Dense black smoke") is correct: The observed flame condition—a **reddish color** accompanied by a **panting/pulsating furnace**—is a classic indication of incomplete combustion due to insufficient air (excessively low air/fuel ratio). 1. **Reddish Flame:** A proper, high-efficiency oil flame should be bright yellow to slightly orange. A deep red or cherry-red flame signifies that the fuel oil is not fully oxidizing (burning) due to oxygen starvation. This results in the formation of significant quantities of unburned carbon particles (soot). 2. **Panting/Pulsating Furnace:** This symptom is caused by cycles of fuel-rich burning followed by temporary pressure buildup and minor explosions, often due to poor mixing or air insufficiency. 3. **Correlation to Stack Gas:** When the combustion process produces large amounts of unburned carbon (soot) because of a severe lack of oxygen, this soot is carried directly up the stack. **Dense black smoke** is the visual manifestation of a high concentration of uncombusted carbon solids leaving the stack. ### Why the other options are incorrect: * **A) Light brown haze:** A light brown or sometimes yellow/brown haze often indicates the presence of nitrogen oxides ($\text{NO}_x$) or very finely dispersed particulate matter, typically associated with optimized combustion at high temperatures, but not the severe lack of air implied by a reddish, panting flame. * **B) Clear stack:** A clear stack is the goal of efficient combustion, indicating that the fuel is fully burned, leaving only water vapor, $\text{CO}_2$, and excess nitrogen/oxygen. This condition requires adequate excess air, which contradicts the described reddish, oxygen-starved flame. * **D) White smoke:** White smoke is primarily water vapor condensing after exiting the stack. While some white smoke is normal in cool or humid weather, persistent, heavy white smoke often indicates the presence of unburned or atomized fuel oil mixed with water vapor, or sometimes poor atomization. While potentially linked to poor combustion, the severe air shortage causing a red flame and pulsation leads primarily to heavy soot (black smoke), not predominantly white vapor.