Temperature and Concentration Measurements by CARS Spectroscopy in a Firing Single-Cylinder Engine

Coherent Anti-Stokes Raman Spectroscopy (CARS) has been applied to a laboratory benchtop engine. Post-combustion spectra were obtained which allowed determinations of the local gas temperature with 50°C accuracy. These spectra also provided species concentration information on the combustion intermediates carbon monoxide and molecular hydrogen. Broadband spectra were collected in a single laser pulse, lasting 10^-8 seconds, and arose from a sampled volume of less than 1 mm³. In light of the cycle-to-cycle fluctuations and spatial inhomogeneities found in piston engines, the excellent time and space resolution displayed by the broadband CARS effect are shown to be advantageous for engine work. CARS and other laser techniques are compared as to their potential for nonintrusive measurements in I.C. engines. Finally, recent advances in CARS experimentation are presented.