What type of burner mixes fuel gas and air only at the burner port?

The correct choice is that the type of burner which mixes fuel gas and air only at the burner port is known as a nozzle mixing burner. This burner type is designed to allow for the mixing of fuel gas and air right at the point where combustion occurs, which typically offers better control over the combustion process and can enhance efficiency.

This method of mixing can result in more complete combustion, as it ensures that air and fuel interact closely right where they are ignited. This implies that the air and gas do not mix extensively before reaching the burner port, allowing for a more directed and concentrated burn.

In contrast, a pre-mixed burner blends the air and fuel before it reaches the burner, leading to a different combustion process. Similarly, a pilot burner is used to initiate the combustion of a main burner, while a conventional burner may mix fuel and air in a more generalized manner, not specific to the burner port. Understanding the specific workings of each type of burner helps clarify why the nozzle mixing burner is distinct in its operational methodology.