If a combustion analysis reveals 0% oxygen and 10% CO in the flue gas, what can be inferred about the fuel burn?

When a combustion analysis reveals 0% oxygen and 10% carbon monoxide (CO) in the flue gas, it indicates that combustion is occurring with a significant excess of fuel relative to the amount of air being supplied. The presence of 0% oxygen means that there is no unburned oxygen available in the exhaust, suggesting that the combustion process is not receiving enough air to fully burn the fuel.

The high level of carbon monoxide, at 10%, further supports this conclusion because CO is a byproduct of incomplete combustion. When there is insufficient oxygen present during combustion, carbon in the fuel partially oxidizes to form carbon monoxide rather than fully oxidizing to carbon dioxide (CO2). This results in a rich fuel mixture, where there is a predominance of fuel compared to the available oxygen, leading to inefficient combustion and the production of CO.

In contrast, a lean condition would be indicated by higher levels of oxygen and lower CO levels, thus confirming that the correct inference here is that the combustion is too rich.