engleski

Optimization of Diesel Autoignition Tabulation Procedures for AVL Code "Fire"

The modifications of existing Diesel auto-ignition tabulation for CFD code AVL "FIRE" will be presented in this paper. Current n-heptane tabulation (used to simulate Diesel behaviour in IC engines) did not include the phenomenon of cool flame ignition. This phenomenon is important since the temperature of the air/fuel mixture is significantly higher after its occurrence and the simulation results could be improved if this is also taken into consideration when simulating combustion in Diesel engines. Current methods of auto-ignition computation in AVL FIRE are based on the extraction of ignition delay times from tabulated data dependent on four parameters: temperature, pressure, air excess ratio and EGR mass fraction. The new tabulation procedure was developed using the same parameters as starting points for two-step chemical combustion. Temperature changes were observed and a compilation of several criteria was used to determine the start of both cool flame and main ignition. The above parameters were varied and the calculations were performed for each parameter set. Chemical software was used for two-step combustion calculations, using reduced then complex chemical mechanisms, and the results of calculations were stored in a binary file. Results included the values for cool flame ignition delay, main ignition delay, and cool flame and main ignition heat releases. This paper will present the methods used to determine the ignition delays (cool flame and main ignition), as well as results comparing the data acquired using three different chemical mechanisms (three levels of complexity). The data acquired from the calculations would be used to optimize the tabulation procedure using more complex (accurate) chemical mechanisms in a way which will also be described.

autoignition; n-heptane; SENKIN

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