Generally, a 12% to 14% content of carbon dioxide in boiler flue gases indicates __________.

Correct Answer: Option C — proper combustion of the fuel oil

Flue gas analysis measuring 12% to 14% carbon dioxide reflects complete combustion with optimal excess air, ensuring high boiler efficiency. Excessive oxygen indicates too much excess air, while low CO2 points to unburned hydrocarbons or poor fuel-air mixing, validating proper furnace operation under marine operating standards.