Knock in spark-ignition engines: eng-gas temperature measurements using rotational CARS and detailed kinetic calculations of the autoignition process

摘要

Cycle-resolved end-gas temperatures were measured using dual-broadband rotational CARS in a single-cylinder spark-ignition engine. Simultaneous cylinder pressure measurements were used as an indicator for knock and as input data to numerical calculations. The chemical processes in the end-gas have been analyzed with a detailed kinetic mechanism for mixtures of iso-octane and n-heptane at different Research Octane Numbers. The end-gas is modeled as a homogeneous reactor that is compressed or expanded by the piston movement and the flame propagation in the cylinder. The calculated temperatures are in agreement with the temperatures evaluated from CARS measurements. It is found that calculations with different RONs of the fuel lead to different levels of radical concentrations in the end-gas. The appearance of the first stage of the autoignition process is marginally influence by the RON, while the ignition delay of the second stage is increased with increasing RON.