Temperature measurements in a rapid compression machine using mid-infrared H2O absorption spectroscopy near 7.6 μm

A method for measuring the temporal temperature and number density in a rapid compression machine (RCM) using quantum cascade laser absorption spectroscopy near 7.6 mu m is developed and presented in this paper. The ratios of H2O absorption peaks at 1316.55 cm(-1) and 1316.97 cm(-1) are used for these measurements. In order to isolate the effects of chemical reactions, an inert mixture of argon with 2.87% water vapor is used for the present investigation. The end of compression pressures and temperatures in the RCM measurements are P-C = 10, 15, and 20 bar in the range of T-C = 1000 to 1200 K. The measured temperature history is compared with that calculated based on the adiabatic core assumption and is found to be within +/- 5 K. The measured temporal number density of H2O to an accuracy of 1%, using the absolute absorption of the two rovibrational lines, show that the mixture is highly uniform in temperature. A six-pass, 5.08 cm Herriott cell is used to calibrate the line strengths in air and broadening in an Ar bath gas. (C) 2012 Optical Society of America