Which of the following is an indication of proper combustion in an oil burner?

A clear blue flame is an indication of proper combustion in an oil burner. This type of flame suggests that the oil is burning efficiently and completely, with sufficient air supplied for combustion. When combustion is optimal, it results in a flame that is well-defined and predominantly blue in color, which indicates that the hydrocarbons in the oil are burning thoroughly without significant production of carbon particles or other combustion by-products.

In contrast, a yellow flame generally indicates incomplete combustion, which can occur due to insufficient air supply, resulting in a cooler flame and the production of soot and other harmful emissions. An intermittent flame may suggest issues with burner operation, such as inconsistent fuel supply or air flow, and does not reflect stable combustion. High soot production is an indication of improper combustion, where the fuel is not burning cleanly, leading to carbon buildup and potential system damage or inefficiencies. Therefore, the clear blue flame is the mark of a well-functioning oil burner, denoting effective combustion.