Burner mixing classification in furnaces: When the fuel and the combustion air are fully mixed before ignition at the burner head, the device is called a ________ burner.

Introduction / Context:
Burners are commonly classified by where and how fuel and oxidant mix. This affects flame stability, emissions, turndown capability, and safety. In many low-pressure gas systems, full mixing before the flame front produces characteristic premixed flames.

Given Data / Assumptions:

• Fuel and air are mixed upstream of the flame.
• Ignition occurs at or near the burner tile/port.
• Stable, typically blue, premixed flame.

Concept / Approach:
A premix burner forms a combustible mixture ahead of the nozzle, contrasted with diffusion (non-premixed) burners where fuel and air meet and mix at the flame. Outside mixing type is a generic description akin to diffusion. Rotary refers to mechanical atomisation/dispersion and does not by itself define premixing.

Step-by-Step Solution:

Verification / Alternative check:
Premix gas burners in ovens and kilns show distinct flame speed limits and require flashback protection, consistent with the definition.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing premix with staged or partially premixed designs; here the statement indicates full premixing.

Final Answer:
premix