Abstract
This work contributes to improve the understanding of the link between the well-known integral method and the kinetics involved for predicting ignition delay time and knock occurrence crank angle. Extensions of the Relative Concentration of Chain Carriers method, originally developed for predicting ignition delay time under variable thermodynamic conditions of surrogate liquids fuels, were proposed. These extensions are composed of four formulations, which were deduced from the Glassman's kinetic model for predicting knock occurrence crank angle in spark-ignition engines fueled with gaseous fuels. Cases of study of engines fueled with CH4/H2, H2/CO/CO2 and iC8H18/nC7H16 mixtures under Spark Ignition and Homogeneous Charge Compression Ignition mode were considered to assess the performance of the formulations working with hydrogen peroxide (H2O2), formaldehyde (CH2O), hydroperoxyl (HO2) and hydroxyl (OH) as chain carriers. According to the experimental measurements of knock occurrence crank angle for mixtures of CH4/H2, the formulation 1 defined as CC/CCcrit=1, had the best performance working with H2O2 as a chain carrier. Moreover, to understand the role of the so-called chain carrier, a thermal sensitivity analysis, based on the relative contribution of key elementary reactions of the GriMech3.0 chemical kinetic mechanism on the total volumetric heat release rate was carried out. The analysis revealed that the elementary reactions that play an important role in the autoignition of a stoichiometric mixture of CH4/H2/50/50 were the chain propagating reactions R36, R116, and R168, the third body reactions R85 and R33, and finally, the chain branching reaction R119.
Published Version
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