The combustion of fuels in the raceway and the resultant raceway depth were investigated using an experimental blast furnace simulated to the lower part of a commercial furnace. The results obtained are as follows:
1) The combustion of a great majority of cokes takes place near the boundary of the raceway. When fuel is not injected, CO and H₂ are hardly observed in the raceway, although their concentration increases rapidly by the carbon solution reaction which takes place near the boundary of the raceway.
2) With heavy fuel oil injection, the combustion zone approaches to the tuyere nose and the temperature rises at the furnace wall around the tuyere. At the same time, the region where CO and H₂ arc generated shifts near to the tuyere.
3) The raceway depth under the condition of combustion is possibly estimated by taking account the properties of coke, the changes of gas volume and temperature in front of tuyere into Wagstaff's equation.