“…Absorption spectroscopy of water was used for temperature measurements in Hcci engines (Ghandhi et al, 2003), Rayleigh scattering 10.5 Fuel film thickness measurement (mm) on the piston top of a direct injection engine using a refractive index matching approach (Drake et al, 2002). imaging has been used for studies on nitric oxide formation (Bräumer et al, 1995;Schulz et al, 1996), and flame propagation (Orth et al, 1994) has been used in research engines that were designed to minimize reflections. To suppress such reflections and Mie scattering from fuel droplets in direct injection engines, filtered Rayleigh techniques could in principle be used (Yalin and Miles, 1999).…”