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

The low-temperature oxidation of higher molecular mass hydrocarbons an d its relationship with the autoignition has been studied by following the oxidation of n-heptane and n-tetradecane at temperature and press ure conditions closer to the actual conditions occurring inside intern al combustion engines. The oxidation of n-heptane, a typical low-octan e-number component of gasoline, has been studied in a jet stirred flow reactor operating at 0.2 MPa by measuring the compositional changes o f the reaction products as the temperature increases in the low-temper ature regimes typical of the ''end-gas'' in a spark-ignition engine. T he oxidation scheme used for the interpretation of n-heptane data is i n the framework of the low- temperature oxidation of light hydrocarbon s. Oxygenated compounds, that is, aldehydes, and ketones, are preferen tially formed at low temperature and decrease as temperature increases giving rise to CO2 and olefin formation. The autoignition of n-tetrad ecane, a typical component of practical diesel blends, was studied by injecting the liquid fuel in a quiescent high-temperature and high-pre ssure oxidative environment, that is, under diesel-like conditions, si mplified from the aerodynamic point of view. Its chemical evolution wa s followed by sampling the reaction products at different air inlet te mperatures. Chemical data have been determined for the oxidation of a complex fuel, such as n-tetradecane, injected in diesel-like condition s, where physical and fluid-dynamic effects are supposed to control th e oxidation process. This can be interpreted by simple kinetic schemes of low-temperature oxidation, commonly foreseen and validated for sim ple experiments and light fuels.