InAsSb Photodiode-Based Infrared Radiation Thermometer for the Investigation of Droplet Surface Temperature Dynamics Within an Enclosed Combustion Chamber.

This study presents a novel approach to analysing the early stages of the combustion process by measuring the surface temperature of a kerosene droplet from its point of ignition through to its evaporation. An indium arsenide antimonide (InAsSb) photodiode-based infrared radiation thermometer (IRT), operating between 3 μm and 11 μm in wavelength, was designed to enable non-contact, low-temperature sensing with an acquisition time of 500 μs. Integrated with a data acquisition unit (DAQ), the instrument captures the transient combustion stages occurring below the droplet's boiling point of 300 °C. The instrument was assessed against industry standards and demonstrated a measurement uncertainty of ±2 °C, confirming suitability within the performance bounds of commercial instrumentation. The IRT was deployed to measure the temperature of a kerosene droplet within an enclosed combustion chamber upon ignition, in direct comparison with a contact thermocouple. The instrument demonstrated its capability to measure the droplet's surface temperature changes throughout its early-stage combustion. Furthermore, the wavelength specificity of the IRT eliminates thermal interference from the subsequent flame, a capability which contact thermocouples lack, thereby enabling measurement of the droplet's temperature in isolation. This study focuses on single-droplet Jet A kerosene combustion under controlled conditions, using a transferable methodology adaptable to other fuels and environments. It supports the use of IRT for non-contact temperature measurement of fuel droplets and early-stage combustion, aiding fuel characterisation and the development of future fuels such as SAF.