What type of flames will be observed when primary air is insufficient?

When primary air is insufficient in a combustion process, it leads to an incomplete combustion of the fuel. This typically results in the production of yellow-tipped flames. The yellow color in the flames is due to the presence of unburned carbon particles that are heated to a luminous state, giving the flames a characteristic yellow appearance.

In contrast, blue flames indicate that a more complete combustion is taking place, as sufficient primary air allows for efficient burning of the fuel, resulting in a cleaner flame with less emissions. White flames often occur at very high temperatures and may not relate directly to primary air levels, while green flames are usually indicative of the presence of copper compounds rather than combustion conditions. Thus, the observation of yellow-tipped flames serves as a clear indicator of insufficient primary air in a gas combustion scenario.