Technologies for producing an exhaust gas stream with controlled hydrocarbon species are disclosed. In some embodiments the technologies include an apparatus for producing an exhaust gas stream. The apparatus may include a burner for combusting primary fuel and produce an exhaust gas stream, and an exhaust pipe coupled to the burner to receive the exhaust gas stream. One or more supplemental fuel inlets may be coupled to the exhaust gas pipe for the addition of supplemental fuel to the exhaust gas stream. In embodiments, the speciation and total concentration of hydrocarbon compounds in the exhaust gas stream may be adjusted by controlling the relative amount of supplemental fuel added to the exhaust gas stream. Methods for producing an exhaust gas stream are also disclosed.