Distributed temperature profile in hydrogen flame measured by telecom fiber and its durability under flame by OFDR

The distributed temperature profile of hydrogen flame based on optical frequency-domain reflectometry (OFDR) was experimentally demonstrated for the first time. Spatial temperature field at different flow rate of H-2 flame was monitored by OFDR via a telecom fiber (Corning SMF-28, CPC6) inside the flame over seconds, and the highest temperature is on the sides of center flame separated by similar to 1.4mm with difference of 140 similar to 190 degrees C over the flame dimension of 2.5 mm above 900 degrees C. Uniformity level of temperature is studied by varying the distance between fiber and tube entrance, and the largest uniform region over 1-millimeter length of fiber is obtained. Rayleigh scatters correlation coefficient decreases with temperature to 90% around 400 degrees C, further reduces to 70% about 800 degrees C, and 50% roughly at 1000 degrees C. It indicates that a nonlinear thermal sensitivity of SMF is expected for temperature higher than 400 degrees C with OFDR measurement. The durability of single-mode fiber under H-2 flame is studied via decorrelation time at various temperature. It maintains 20s at 880 degrees C with correlation coefficient around 68% and drops to 50% decorrelation at 1000 degrees C over 20s. This information is important for high temperature measurement using telecom fiber over 800 degrees C based on OFDR. A maximum temperature of 1100 degrees C was measured by OFDR, and it is possible for higher temperature measurement beyond of 1100 degrees C with quicker system response time (<1s). (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement