Characterization of radiative heat transfer in a spark-ignition engine through high-speed experiments and simulations

A combined experimental and Large-Eddy Simulation (LES) study of molecular radiation was performed for combustion in a homogeneous pre-mixed spark-ignition engine. Molecular radiation accounted for ~10% of the engine heat loss and demonstrated a substantial impact on the local conditions within the combustion chamber. The Transparent Combustion Chamber engine, a single-cylinder two-valve research engine with a transparent liner and piston for optical access, was applied. High-speed infrared emission spectroscopy and radiative post-processing of LES calculations were carried out to study the timescales and magnitude of radiative emissions of molecular gases during the combustion process. Both the measurements and simulations revealed significant Cycle-to-Cycle Variations of radiative emission. An agreement in the instantaneous radiative spectrum of experiment and simulation was observed, but the crank-angle development of the radiative spectrum showed disagreement. The strengths and limitations of the optical experiments and radiative simulations were observed in the results and pathways for future efforts in characterizing the influence of molecular radiation are provided with emphasis on the relative changes of the spectral features as they contain information about the thermochemical properties of the gas mixture.