AUTOIGNITION OF N-HEPTANE AND N-TETRADECANE IN ENGINE-LIKE CONDITIONS

The low-temperature oxidation of higher molecular mass hydrocarbons and its relationship with the autoignition has been studied by following the oxidation of n-heptane and n-tetradecane at temperature and pressure conditions closer to the actual conditions occurring inside internal combustion engines. The oxidation of n-heptane, a typical low-octane-number component of gasoline, has been studied in a jet stirred flow reactor operating at 0.2 MPa by measuring the compositional changes of the reaction products as the temperature increases in the low-temperature regimes typical of the ''end-gas'' in a spark-ignition engine. The oxidation scheme used for the interpretation of n-heptane data is in the framework of the low- temperature oxidation of light hydrocarbons. Oxygenated compounds, that is, aldehydes, and ketones, are preferentially formed at low temperature and decrease as temperature increases giving rise to CO2 and olefin formation. The autoignition of n-tetradecane, a typical component of practical diesel blends, was studied by injecting the liquid fuel in a quiescent high-temperature and high-pressure oxidative environment, that is, under diesel-like conditions, simplified from the aerodynamic point of view. Its chemical evolution was followed by sampling the reaction products at different air inlet temperatures. Chemical data have been determined for the oxidation of a complex fuel, such as n-tetradecane, injected in diesel-like conditions, where physical and fluid-dynamic effects are supposed to control the oxidation process. This can be interpreted by simple kinetic schemes of low-temperature oxidation, commonly foreseen and validated for simple experiments and light fuels.