Spectral extinction measurements of spray combustion in a divided-chamber diesel engine system

Abstract

Sepctral flame extinction measurements from UV to visible with high temporal and spatial resolution were performed in an optically accessible divided-chamber diesel system. This system was developed ad hoc by modifying a real engine to realize a soot-forming premixed spray combustion at high pressure, high temperature, and high swirl. The large optical accesses of the divided chamber allowed us to follow the progress of fuel injection, vaporization, autoignition, and combustion by direc high-speed photography (8000 frames/s). Light extinetion measurements were carried out in 153 different spatial locations for 250 consecutive combustion cycles from the start of injection to the end of combustion. The photographic sequences have shown that spray is strongly distorted and mixed downstream of the high-swirling flow, resulting in a well premixed region in which the combustion starts. Then, the combustion proceeds rapidly, involving the entire chamber volume. Consequently, the flame luminosity increases, denoting fast soot formation-oxidation processes in the region close to the tangential duet in which the mising is higher. The analysis of the extinction spectra in the UV and visible range has allowed us to follow spatially and temporally the soot formation process and to identify the nature of the particulate matter and the agglomeration degree of soot particles, as well as the time history of the soot volume fraction.