Temperature Measurements of Combustion Gas in a Spark Ignition Engine by Infrared Monochromatic Pyometry

Instantaneous temperature of in-cylinder gas provides a lot of useful and local information for analyzing the combustion process in an internal combustion engine, so many optical pyrometries have been proposed and developed. Among others, the infrared monochromatic radiation pyrometry is considered to be more applicable to a practical engine due to requirement of only a single optical window, whereas two optical windows are indispensable for the conventional infrared absorption pyrometry.

In this paper, the former pyrometer is used to measure the mean gas temperatures averaged on an optical path (or cylinder diameter) of a spark ignition engine, of which a prechamber is connected to the main chamber by a torch nozzle of various area sizes. The temperature-crankangle diagrams so-measured not only clarify the influences of torch jet flow on the combustion processes, but also the correlation between the rate of temperature change and the heat release rate calculated from the pressure diagrams. Furthermore, the temperature diagrams are found to be in reasonable agreement with the brightness curves ensemble-averaged on the image-processed pictures of flame propagation and also with the gas temperature diagrams calculated numerically by a thermodynamic model.

In conclusion, the infrared monochromatic pyrometry is confirmed to be capable of measuring the gas temperatures in the combustion chamber of a practical engine with only one optical window.