Broadband ultrafast-laser-absorption spectroscopy for multi-hydrocarbon measurements near 3.3  µm in flames

This paper presents the development and application of a broadband ultrafast-laser-absorption-spectroscopy (ULAS) technique operating in the mid-infrared for simultaneous measurements of temperature, methane (C H ₄), and propane (C ₃ H ₈) mole fractions. Single-shot measurements targeting the C-H stretch fundamental vibration bands of C H ₄ and C ₃ H ₈ near 3.3 µm were acquired in both a heated gas cell up to ≈650K and laminar diffusion flames at 5 kHz. The average temperature error is 0.6%. The average species mole fraction errors are 5.4% for C H ₄ and 9.9% for C ₃ H ₈. This demonstrates that ULAS is capable of providing high-fidelity hydrocarbon-based thermometry and simultaneous measurements of both large and small hydrocarbons in combustion gases.