Abstract
The phenomenon of autoignition is an important aspect of spark ignition engine´s knock, hence reliable information on the relationship between the local gas temperature and the autoignition delay in a combustion chamber must be obtained to avoid knock. However, the measurement of local gas temperature, especially near the wall where knock occurs is difficult. Recently, several studies have been conducted by using laser techniques such as CARS. It has a high spatial resolution, but has proven difficult to apply in the vicinity of combustion chamber wall and requires special measurement skills. Meanwhile, a thermocouple is useful to measure local gas temperature even in the vicinity of wall. However, a conventional one-wire thermocouple is not adaptable to measure the in-cylinder gas temperature due to slow response. The issue of response can be overcome by adopting a two-wire thermocouple. The two-wire thermocouple is consisted of two fine wire thermocouples with different diameter hence it is possible to determine the time constant using the raw data from each thermocouple.
In this study, measurements such as local gas temperature inside a constant-volume combustion chamber, pressure and visualization were achieved with and without autoignition. Thereby, the relationship between the ignition delay and the gas temperature was clarified. This is a very important result to analyze the knock phenomenon. As a result, negative temperature coefficient was found to mostly affect autoignition in this experimental condition. This technique was applied at more engine-like conditions, by developing a new RCM (Rapid Compression Machine). Local gas temperature inside the combustion chamber under compression with and without combustion was measured to examine the heat loss and propagating local flame structure.
Keywords:SI ENGINE, KNOCKING, GAS TEMPERATURE, NTC REGION, RCM