Measurements of Heat Release of Diesel PM for Advanced Thermal Management Strategies for DPF Regeneration

Abstract

Diesel engines typically require diesel particulate filter (DPF) systems to reduce particulate matter (PM) emissions in order to meet increasingly stringent emission regulations. While there have been noticeable advances in DPF technology, significant efforts are still needed to develop optimum DPF regeneration strategies and achieve efficient removal of diesel PM. In particular, the development of an effective thermal management system is essential to prevent the potential failure of the DPF system by the thermal runaway during soot oxidation in DPF regeneration. In an effort to develop optimum thermal management strategies, this experimental investigation is concerned primarily with measuring the instantaneous rate of heat generation as well as the total amount of heat released during the oxidation of diesel PM containing different concentrations of soluble organic fraction (SOF). The experimental approach was to measure directly, by means of a differential scanning calorimeter (DSC), the amount of heat release during the thermal reactions of diesel PM with air and to elucidate differences in the heat release characteristics of diesel PM and surrogate (model) soot. The diesel samples were collected from a cordierite particulate filter, where PM emissions bypassing the exhaust pipe of a light-duty diesel engine were deposited. Furthermore, a thermogravimetric analyzer (TGA) was used to obtain dry diesel soot samples with no volatile components present. The DSC experiments revealed that the amounts of heat released from the oxidation of SOF-containing diesel PM sample, dry diesel soot, and surrogate soot were approximately 14.67 kJ/g, 17.3 kJ/g, and 14.02 kJ/g, respectively, indicating that the largest heat release was obtained from the dry diesel soot sample. Results also indicated significant differences in the temporal rates of heat release in the oxidation of SOF-containing diesel PM, dry diesel soot, and surrogate soot. In particular, significant differences were found on the results for dry diesel soot samples with respect to the oxidation temperatures of 550°C and below 550°C in air. The heat release rate profile for the 550°C case exhibited a continuous sharp decrease after the peak value, while those for the 535°C and 525°C cases indicated first a sharp decrease, followed by slow and then sharp decrease again. The present experimental data are expected to lead to better predictive tools for thermal energy distribution during DPF regeneration, and thus the development an optimum thermal management system for DPF systems.

Keywords:

• Diesel particulate matter
• DPF regeneration
• Heat release rate measurements

ACKNOWLEDGMENT

This work is supported by the combustion and emissions program of the U.S. Department of Energy, Office of Vehicle Technologies.

Notes

A passive regeneration is a catalytic regeneration technique in which either the fuel doped with catalytic additives or the DPF coated with a catalyst is used to lower the soot oxidation temperature. In active regeneration, additional device such as fuel burner, resistive heating coils, or microwave energy is used to provide heat to the diesel exhaust system.

In the present study, the terms surrogate soot and model soot refer to the same thing.

In experiments with model soot, the residual mass is zero (i.e., M_r = 0), since the soot sample undergoes complete oxidation with no ash remaining.

This is consistent with the results of previous studies which indicate that the specific heat release increases if the internal structures of carbon material becomes more ordered and contains less SOFs.