Oxidation of Soot Agglomerates in a Direct Injection Diesel Engine

Carbon black particles, which morphologically and chemically simulate a diesel exhaust soot, were mixed with the intake air of a single-cylinder direct injection diesel engine to investigate the efficiency of their removal by oxidation in the combustion chamber. An aerosol generation system, which is capable of generating carbon black aerosol of a size distribution and mass flow rate comparable to those of the soot agglomerates, was developed first. The aerosol was then introduced into the engine which was operating on conventional fuel. Four methods were used to characterize the exhaust particles: an electrical aerosol analyzer, a condensation nuclei counter, a low volume filter, and a micro-orifice cascade impactor. The size distribution and concentration of the diesel soot particles in the lubricants were investigated by methods of photosedimentation and quantitative spectrophotometry, respectively. The net increase of carbon mass in the exhaust and lubricating oil due to the measured addition of carbon black was used to determine the net oxidation efficiency.

It was found that simulated particles (mass median diameter about 2 μm) can be consumed effectively inside the combustion chamber. The oxidation efficiency increases from 81% to 88% as equivalence ratio varies from 0.2 to 0.57 and decreases with increased engine speeds. The emissions of volatile material increased with the carbon addition. Approximately 5.5% by mass of added particles entered the lube oil, independent of engine duty cycles. Mass weighted particle size distributions in the exhaust shifted to the larger diameters due to carbon addition while those in the lube oil were not changed.