🔍 Key Concepts

• combustion efficiency in an auxiliary boiler (where the fuel should burn completely: in the furnace, not in the uptake) • relationship between air supply (too little vs too much) and stack temperature • what secondary combustion in the uptake means and how it affects where heat is released

💭 Think About

• Think about where, inside a properly operating boiler, the main heat transfer to the water/steam surfaces is supposed to occur, and what happens to stack temperature if more heat is released further up the gas path instead. • Consider what "insufficient air for combustion" would normally do to flame quality, smoke/soot, and heat transfer, and whether that condition alone would necessarily drive stack temperature high or low. • Ask yourself which option describes a situation where some of the fuel energy is not released in the furnace but is instead released later in the gas path, closer to the stack, and how that would change stack temperature readings.

✅ Before You Answer

• Be clear on the difference between complete combustion in the furnace and combustion occurring later in the uptake or gas passages. • Verify which condition would cause unburned fuel or combustibles to travel into the uptake and then burn there, raising the temperature of gases near the stack thermometer. • Check which options would mainly affect viscosity/atomization (fuel temperature) versus which directly affect where and how combustion occurs.