A detailed chemical kinetic reaction mechanism for the oxidation of iso-octane and n-heptane over an extended temperature range and its application to analysis of engine knock

A detailed chemical kinetic reaction mechanism is developed to describe the oxidation of n -heptane, iso-octane, and their mixtures over a wide range of operating conditions. In addition to a high temperature submechanism, reaction paths are included to describe the lower temperature regimes in which the rate and intermediate products of oxidation are controlled by addition of molecular oxygen to alkyl and isomerized alkylperoxy radicals, internal H atom abstractions, and reactions involving O-heterocyclic species. This overall reaction mechanism is validated through comparisons between computed results and experimental data from shock tubes, turbulent flow reactor, and low temperature static and stirred reactors. The mechanism is then used to study the influence of fuel composition on knocking in internal combustion engines. Autoignition of mixtures of iso-octane and n -heptane is examined, in which experimentally measured variations of engine pressure with time were used to simulate the conditions encountered by the end-gases responsible for knocking operation. The computations reproduce the variations of autoignition delay time with octane number and these variations are interpreted in terms of detailed differences in the structure of the two primary reference fuels. Sensitivity analyses of the computations are presented, indicating those portions of the reaction mechanisms which have the greatest influence on the model results.

[1]  J. A. Cole,et al.  Chemical aspects of the autoignition of hydrocarbonair mixtures , 1985 .

[2]  S. Benson,et al.  The kinetics and thermochemistry of chemical oxidation with application to combustion and flames , 1981 .

[3]  Ja Jacques Rijks,et al.  Steam cracking of hydrocarbons 1. Pyrolysis of heptane , 1979 .

[4]  C. Morley,et al.  A Fundamentally Based Correlation Between Alkane Structure and Octane Number , 1987 .

[5]  C. Westbrook,et al.  A kinetic modeling study of n-pentane oxidation in a well-stirred reactor , 1988 .

[6]  Michael J. Pilling,et al.  Direct determination of the equilibrium constant and thermodynamic parameters for the reaction. C3H5+ O2⇌ C3H5O2 , 1982 .

[7]  E. Ratajczak,et al.  Study of the thermochemistry of the ethyl + molecular oxygen .dblharw. ethylperoxy (C2H5O2) and tert-butyl + molecular oxygen .dblharw. tert-butylperoxy (tert-C4H9O2) reactions and of the trend in the alkylperoxy bond strengths , 1986 .

[8]  A. K. Oppenheim,et al.  Auto-ignition of hydrocarbons behind reflected shock waves , 1972 .

[9]  Jürgen Warnatz,et al.  The Mechanism of High Temperature Combustion of Propane and Butane , 1983 .

[10]  E. Reverchon,et al.  Dynamics of n-heptane and i-octane combustion processes in a jet stirred flow reactor operated under pressure , 1986 .

[11]  Robert Shaw,et al.  A compilation of kinetic parameters for the thermal degradation of n‐alkane molecules , 1980 .

[12]  J. Mackie,et al.  Kinetics of pyrolysis of octane in argonhydrogen mixtures , 1983 .

[13]  J. Barnard,et al.  Slow combustion and cool-flame behavior of iso-octane , 1973 .

[14]  C. Westbrook,et al.  Chemical kinetic modeling of hydrocarbon combustion , 1984 .

[15]  J. Barnard,et al.  The spontaneous combustion of n-heptane , 1973 .

[16]  S. Benson.  Effects of Resonance and Structure on the Thermochemistry of Organic Peroxy Radicals and the Kinetics of Combustion Reactions1 , 1965 .