Abstract
Knocking combustion in SI engines is regarded as an auto-ignition of unburned gas, and it has been widely examined by using rapid compression machines (RCM) or test engines. Recent researches point out the importance of the low temperature reaction and negative temperature coefficient. To investigate the effect, measurements of instantaneous local gas temperature, visualization and pressure were conducted. Measurements using real engines are too difficult to analyze while those with RCM have not been made with flame propagation. Therefore, the authors aimed to make measurements under knock conditions where propagating flame exists during the induction time for auto-ignition using a constant volume vessel. Adopting the two-wire thermocouple method enables us to measure the local temperature until the moment when the flame front passes by without any interference. High-speed images inside the unburned region were also recorded simultaneously using an endoscope. As a result, it was found that when knock occurs, the ignition time seems slightly early compared to results without knock. Interference of hot spots may cause a higher gas temperature region and leading to knock due to a larger heat release by auto-ignition than by flame propagation when the initiation time of auto-ignition was accelerated for some reasons.
