Multi-walled carbon nanotube (MWNT) was synthesized through flame in a diesel engine, in which normal dodecane/ethanol mixing fuel was employed as carbon and heat sources instead of gas oil. Ferrocene was used as a floating catalyst for MWNT formation and additives such as sulfur and molybdenum were employed as a promoter of MWNT formation. Mean adiabatic combustion temperatures of various experimental conditions were evaluated by measuring CO and CO2 amounts in the exhaust gas and carrying out a mass and heat balance at the inlet and outlet of an engine. These measurements revealed that not only a mean adiabatic combustion temperature but also CO amount during combustion may play a significant role in synthesizing CNT in a diesel engine.