Utilization of HVO Fuel Properties in a High Efficiency Combustion System: Part 2: Relationship of Soot Characteristics with its Oxidation Behavior in DPF

The present work is a continuation of the earlier published results by authors on the investigation of Hydrogenated Vegetable Oil (HVO) on a High Efficiency Diesel Combustion System (SAE Int. J. Fuels Lubr. Paper No. 2013-01-1677 and JSAE Paper No. 283-20145128). In order to further validate and interpret the previously published results of soot microstructure and its consequences on oxidation behavior, the test program was extended to analyze the impact of soot composition, optical properties, and physical properties such as size, concentration etc. on the oxidation behavior. The experiments were performed with pure HVO as well as with petroleum based diesel and today's biofuel (i.e. FAME) as baseline fuels. The soot samples for the different analyses were collected under constant engine operating conditions at indicated raw NO x emissions of Euro 6 level using closed loop combustion control methodology. The oxidation behavior results of optimized Thermogravimetric Analysis (TGA) correspond well with the previously published (part-1) results of the kinetics of soot oxidation (i.e. activation energy, reaction rate constant and regen. temperature) conducted on a Laboratory Gas Test Bench using a Temperature Programmed Oxidation (TPO). The results suggest that the soot oxidation temperatures of the HVO decreased by -43 C-circle and 37 C-circle with O-2 and NO2 respectively, as compared to petroleum based diesel. Finally, the relationship of the PM physico-chemical properties (i.e. O-2 content, C/O ratio, C/H ratio and microstructure parameters) is compared with the trends of the oxidation behavior. The overall results from the present work suggest that the oxidative behavior of a specific type of soot cannot be estimated based on a singular characteristic but is more dependent on a set of soot properties.