Hot flame detection in a completely automated autoignition temperature measurement apparatus

Abstract

The auto-ignition temperature (AIT) is essential for assessing the hazard of flammable liquids in relation to hot surfaces. An international ISO/IEC standard describes the method and protocol of AIT measurement as well as ignition detection by the eye. It also allows automatic flame detection if the same results are obtained during apparatus verification. As the intensity, temperature and color of the flame phenomenon can depend on the substance class and quantity, the question arises as to how reliably ignitions can be detected when additional sensor parameters affect the detection signal. This particularly applies to substances that tend to produce cold flames. The standard does not give detailed guidelines on sensor types and the given flame detection parameters seem questionable. Nevertheless, there are AIT test rigs available, which use semi-automated flame detection, but the criteria are set by the manufacturers. This study focuses on developing a largely automated apparatus for AIT measurements. This includes temperature control, dosing of the liquid and cleaning of the flask. Specific emphasis lays on hot flame detection during an ignition test in the first step. Future work will be related to cool flames. This paper aims to specify the sensors used, their positioning, and the flame detection parameters to enable nearly unsupervised operation of the apparatus. New recommendations for hot flame detection are provided. Both VIS/NIR and UV photodiodes are used successfully for hot flame detection. Thermocouple measurements based on the rate of temperature rise were found to be reliable, when Delta T/Delta t > 80 degrees C/s.