Investigation of clean diesel combustion with oxygenated fuels in a constant-volume combustion chamber using forward illumination light extinction technique.

摘要

A fully automatically controlled constant-volume spray chamber was designed and fabricated to provide a stable and controllable environment to study diesel combustion. The chamber also has a larger ambient temperature and ambient oxygen concentration range than a diesel engine. Therefore, the chamber facilitates the investigation of soot formation mechanism and ultimately helps to achieve high efficient clean diesel combustion.; A Forward Illumination Light Extinction (FILE) technique was developed to achieve quantitative 2D soot measurement. The incident light is attenuated as passing through the soot cloud twice with the adoption of a light diffuser behind the soot cloud. The line of sight soot volume concentration is obtained by comparing the light intensity with and without the presence of soot cloud. Transient 2D soot distributions were obtained with the adoption of high-speed camera and pulsed laser.; A better understanding of diesel combustion process was obtained when applying FILE, flame luminosity, liquid jet penetration and lift-off length measurements together. It was found that the total soot mass has a rapid increase after appearing in the premixed combustion period and reaches its peak around the end of injection with the peak soot mass about 1.3% of total fuel mass at the baseline condition. Since the end of injection, soot oxidation becomes dominant and the total soot mass begins to decrease till most soot get burnt out. Further understanding of soot generation mechanism was obtained by studying soot formation at different ambient temperatures and ambient oxygen concentrations.; The mechanism of soot reduction from oxygenated fuels was explored. DBM and TPME oxygenated fuels with 7% oxygen by weight were studied and have shown different soot reduction performances at different diesel combustion modes. In the premixed combustion mode, the higher oxygen efficiency from TPME due to its molecular structure advantage contributes to the less soot generation. While at mixing controlled combustion mode, DBM oxygenated fuel has less soot formation due to its capability to entrain more ambient air. The influences of both fuel physical and chemical properties on soot formation were further demonstrated with the study of tetradecane and two commercial diesel fuels.