Answer: This is an incomplete combustion reaction.
Step-by-step explanation:
Combustion reaction is defined as the reaction in which a hydrocarbon produces carbon dioxide gas and water molecule when reacted with oxygen gas. General equation for this reaction is:

Incomplete combustion is also a reaction between oxygen and hydrocarbon in which the products obtained are carbon monoxide, water and carbon. This type of combustion happens when there is insufficient supply of oxygen gas. General equation for this reaction is:

Hence, the hydrocarbon is undergoing an incomplete combustion reaction.