Which flame has slightly more acetylene than the 1:1 ratio and features inner cone, acetylene feather, and outer cone?

• A. Neutral flame
• B. Carburizing flame
• C. Oxidizing flame
• D. Reducing flame

Answer: (B)

Understanding how flame types relate to gas ratios helps you read what you see in the flame. With acetylene and oxygen, about a 1:1 ratio forms a neutral flame: a stable inner blue cone with a balanced outer envelope and clean combustion. If you introduce a bit more acetylene than the 1:1 ratio, you enter a carburizing (reducing) flame. In this mode, the flame still shows the inner cone and the outer cone, but you also see an acetylene feather—the pale blue wisps around the flame that indicate excess fuel not fully reacting. This acetylene feather is a telltale sign of a slightly acetylene-rich flame, i.e., carburizing. So, the flame described by an inner cone, acetylene feather, and outer cone is carburizing.