Investigation of soot processes in an optical diesel engine

Abstract

This study is dedicated to investigation of soot formed during combustion in diesel engine. Measurements were performed in a high speed direct injection optical diesel engine. Initially soot particle size, size distribution and soot volume fraction were investigated using time resolved laser induced incandescence (TR-LII) technique. For this study standard diesel fuel was used and measurements were performed for various injection timing and two different engine loads. Investigation showed that TR-LII is a powerful tool that can be used for characterization of in-cylinder soot in the engines. Subsequently TR-LII technique was developed to measure in-cylinder soot in two dimensional plane (planar laser induced incandescence PLII) and technique was combined with high speed imaging to investigate soot processes for ultra-low sulfur diesel (ULSD) and bio-fuel (RME). Two injection strategies of single and double injection were applied during these measurements. A high speed imaging technique was used to study the soot formation and oxidation during the combustion process within the cylinder and PLII was applied later in the stroke to study qualitatively the relative amount of un-oxidised soot that was left in the combustion chamber. In addition to PLII, TR-LII technique was used simultaneously to explore crank angle resolved variation of primary soot particle size and their size distribution during the expansion stroke. The same measurements were repeated for fuels with different composition investigating the relationship between the fuel properties and soot emission. Finally mathematical model for soot particle size and distribution width was modified by introducing assumption of multi-lognormal in-cylinder soot particle size distribution.