Question 319Steam Plants - Assistant Engineer

The correct answer is B) the blue portion of the flame spectrum. A photoelectric cell in an oil-fired boiler safeguard system is primarily sensitive to the blue portion of the flame spectrum. This is because the blue portion of the flame spectrum corresponds to the highest temperature region of the flame, which indicates proper combustion and the absence of incomplete or improper burning. The photoelectric cell is designed to detect this blue portion of the flame to ensure the boiler is operating safely and efficiently. The other answer choices are incorrect because they do not accurately describe the primary sensitivity of the photoelectric cell in this application. The cell is not specifically sensitive to the incandescent brickwork or the orange portion of the flame spectrum, which would not provide the same indication of proper combustion.