3rd Class Stationary Steam Engineer License Practice Test 2025 – All-in-One Resource for Exam Success!

The combustion control system on a boiler primarily regulates the air-fuel ratio, which is essential for efficient and safe operation. The air-fuel ratio is the proportion of air to fuel that is mixed during the combustion process. Proper regulation of this ratio is crucial because it directly affects the efficiency of the combustion, the production of steam, and the overall performance of the boiler.

A balanced air-fuel ratio ensures complete combustion, minimizing the formation of harmful pollutants and preventing the buildup of unburned fuels. If the ratio is too rich in fuel or air, it can lead to inefficient combustion, increased emissions, and potential operational issues such as flame instability or excess carbon monoxide production.

While water temperature, fuel type, and exhaust emissions are important aspects of boiler operation, they are not directly regulated by combustion control systems. Water temperature is typically managed by the boiler’s feedwater control and temperature sensors, while fuel type is determined by the design and capabilities of the boiler itself. Exhaust emissions are monitored and managed through different stages of operation but are ultimately a result of the combustion process itself, influenced by the air-fuel ratio that combustion control regulates.