Pre-chamber combustion is well known for the effective way to improve thermal efficiency in internal combustion engine. An active pre-chamber can accomplish super lean burn while a passive pre-chamber can easily improve combustion with low-cost. Therefore, various studies have been carried out. However, since its combustion characteristics are very complicated, the sequence of events for torch ignition and flame propagation in main-chamber from ignition and flame propagation inside pre-chamber have not been well clarified. Especially, investigation on the process from torch ejection to ignition of mixture in main-chamber has been carried out using combustion vessels and rapid compression machines, but this phenomenon has not been clarified.
In this study, three types of optically accessible passive pre-chamber with different orifice patterns (normal six orifices, asymmetric five orifices and tangential five orifices) were designed and installed to a single-cylinder gasoline spark ignition engine. Also, an optical-scope was designed uniquely and installed to main-chamber. The flame propagation inside pre- and main-chambers was taken simultaneously by using two high speed cameras. In addition, the temperature distribution around the torch ejection in main-chamber was taken by high speed IR (Infrared) camera. As a result, cyclic variation in flame propagation direction inside pre-chamber and variation in timing of torch ejection in main-chamber were observed. In the cycles when torch ejected to the intake side first, the flame propagation was shifted to the same side inside pre-chamber. This variation of flame propagation direction changed by the orifice pattern of pre-chamber, the flame propagation direction of pre-chamber with tangential orifices were the most stable inside both pre-chamber and main-chamber. Visualizing the temperature distribution during torch ejection showed that the mixture in main-chamber was ignited locally around the torch.