Validation of Kinetic Mechanisms against Various Ignition Delay Data and the Development of Ignition Delay Correlations for Ethanol, Natural Gas, and Primary Reference Fuel Blends under Homogeneous Charge Compression Ignition Conditions

Homogeneous Charge Compression Ignition (HCCI) is a promising advanced combustion concept with high efficiencies and low emissions. Chemical kinetic mechanisms and ignition delay correlations (IDCs) are often applied to simulate HCCI combustion. However, a large number of mechanisms and correlations are not developed specifically for HCCI conditions, i.e., lean mixtures and usually with significant residual gas fractions (RGF). To address this issue, a two-part study is conducted. First, experimental ignition delay time (IDT) data from literature under typical HCCI conditions is collected. Then, thirteen widely applied mechanisms for ethanol, natural gas, and primary reference fuel (PRF) blends of isooctane and n-heptane are validated by running constant-volume simulations. Their performance and accuracy are evaluated. Second, the mechanism with the highest accuracy for each fuel is used to generate IDCs for HCCI conditions. For each fuel, simulations were performed to cover a wide range of pressure (5-50 bar), temperature (800-1400 K), equivalence ratio (0.15-0.8), and RGF (0-60%). The newly generated IDCs have better accuracies than the existing correlations not designed for HCCI conditions. In addition, extra terms are added to the IDC of each fuel for more universal application. A water term is added into the ethanol correlation since wet ethanol is a promising new fuel for HCCI and Thermal Stratified Compression Ignition (TSCI). The effect of ethane and propane is included in the natural gas correlation. A PRF correlation can predict the main ignition event for PRF 80-100 blends with a simple mathematical form. In summary, this study will be valuable for researchers to perform fast and accurate simulations of advanced combustion.