Understanding the Relationship between Cetane Number and the Ignition Delay in Shock Tubes for Different Fuels Based on a Skeletal Primary Reference Fuel (n-Hexadecane/Iso-cetane) Mechanism

Abstract

A new skeletal oxidation mechanism for the primary reference fuel (PRF) was established with a decoupling methodology. The mechanism is composed of n-hexadecane and iso-cetane submechanisms, containing 44 species and 139 reactions. Using the present mechanism, the relationship between cetane number and the ignition delay in shock tubes was investigated. First, based on the ignition delay data in shock tubes, the cetane number of various fuels was estimated using the present PRF mechanism and a weighted least-squares method. The prediction of cetane number investigated in this study primarily focused on the operating conditions of practical diesel engines (i.e., the equivalence ratio of 1.0 and pressures from 19–80 atm), which encompass the cetane number from 15 to 100. Under the test operating conditions, the mean absolute deviation of the predicted cetane number is within 3.327. Furthermore, according the cetane number of different fuels, the ignition delays in shock tubes were reproduced by the present mechanism focusing on a wide range of equivalence ratios (0.5–3.0) and pressures (20–50 atm). The results indicated that the predicted IDs of alkanes were more accurate than those of other types of fuels and blended fuels because of the consistent molecular structure of the n-hexadecane/iso-cetane used in the present mechanism. Because of the compact size of the skeletal mechanism, its application can considerably reduce the computational time for 3D combustion simulations, especially for practical fuels with complicated compositions.