(KA-4) Optical Diagnostics in Engines

Abstract

The science of optics has always played an important role in the measurement and understanding of combustion phenomena, including not only laboratory flames but also practical combustion devices such as the internal combustion engines. In particular, being the combustion in direct injection systems a two-phase, turbulent mixing-controlled process that includes short time scale phenomena such as turbulence production and dissipation, spray breakup and evaporation, and pollutants formation it is appropriate to make investigation by non intrusive diagnostic techniques for their intrinsic high temporal and spatial resolution. The paper reviews the optical techniques currently under application to investigate the in-cylinder fluid dynamics, combustion, pollutant formation processes as well as to characterize the exhaust emissions of current internal combustion engines. The review starts with the laser Doppler based techniques for measuring the fluid dynamic field both on air flow test rig and in engines operating under motored conditions as well as the droplet size and velocity of high pressure jet for direct injection engines. Then, it proceeds discussing the potential of polychromatic light scattering, extinction and absorption techniques (Fig. 1) as diagnostic tool for engine investigation alternative to laser induced incandescence (LII) and laser induced fluorescence (LIF). In the second part, polychromatic light extinction and absorption for liquid and vapor distribution measurements in an engine with large optical access is discussed. In the third part, simultaneous extinction, scattering and flame chemiluminescence measurements from ultraviolet (UV) to visible for obtaining detailed information about combustion precursors species during early soot formation and chemical properties of nanometric carbonaceous particles are introduced. In the last part, the potential of broadband (190-500 nm) extinction and scattering spectroscopy is demonstrated to detect and evaluate in real time the size and the number concentration of the exhaust soot particles.