Evaluation of kinetics mechanisms ability to predict natural gas reactivity using a fuel substitution method

Abstract

Previous homogeneous-charge compression-ignition engine fuel substitution experiments1 were used to test the performance of five different chemical kinetics mechanisms for natural gas fuels. A two-zone model was used to simulate the engine experiments using the five mechanisms tested. Simulations of engine experiments for six distinct operating conditions using based fuel mixtures of methane/hydrogen and methane/propane were performed along with simulations of fuel substitution sweeps with fixed boundary conditions using hydrogen, ethane, ethylene, propane, and n-butane as test fuels. The simulation results were used to quantify the ability of mechanisms to predict both the absolute reactivity of the reference fuels and the reactivity of the test fuels relative to the reference fuels using two metrics: required temperature at intake valve closure (IVC) with fixed fuel concentrations and required reference fuel concentrations with fixed IVC temperature. The five mechanisms used for this study showed substantially different results, most notably related to their propane chemistry. Simulations using the LLNL mechanism resulted in the closest match to propane engine test results, while the Aramco and C5-49 mechanisms showed some disagreement, and the GRI and UBC mechanisms showed much larger discrepancies. Simulations with all five mechanisms showed good agreement with hydrogen engine test results.