Mid-infrared gas sensing for combustion applications

Progress is reported in the use of room-temperature, wavelength-tunable, solidstate mid-infrared (mid-IR) laser sensors for combustion and propulsion applications. Two such laser technologies have recently become commercially available: DFB tunable diode lasers near 2.7 μm and difference frequency generation (DFG) lasers near 3.3 μm. These lasers access the strong transitions in the fundamental O-H and C-H stretching vibrations as well as the ν1+ν3 and 2ν2+ν3 combination bands of CO2. These new laser sources provide the potential for sensitive detection of hydrocarbon fuels and combustion products H2O and CO2 in a wide variety of environments. Recent results in pulse detonation engines, laboratory flames, and shock-heated ignition experiments illustrate the potential of these tunable mid- IR laser sources for a wide variety of practical combustion applications.