Measurement of the Local Gas Temperature at Autoignition Conditions Inside the Combustion Chamber Using a Two-Wire Thermocouple 2006-01-1344

The phenomenon of autoignition is an important aspect of HCCI and knock, hence reliable information on local gas temperature in a combustion chamber must be obtained. 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 traditional 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. 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). In preliminary tests, local gas temperature inside the combustion chamber under compression without combustion was measured to examine the accuracy of two-wire thermocouple.