Seung Yeon Yang

Effect of Temperature, Pressure and Equivalence Ratio on Ignition Delay in Ignition Quality Tester (IQT): Diesel, n-Heptane, and iso-Octane Fuels under Low Temperature Conditions

This paper was supported by Saudi Aramco FUELCOM Program and Clean Combustion Research Center, King Abdullah University of Science and Technology.

Experimental Investigation on the Oxidation Characteristics of Diesel Particulates Relevant to DPF Regeneration

Diesel engines generally employ diesel particulate filter (DPF) systems to meet increasingly stringent emissions regulations. The development of optimum methodologies for DPF regeneration requires detailed information on the oxidation characteristics of diesel particulate matter (PM) that accumulates on the DPF under realistic engine conditions. An experimental investigation on the oxidation behavior of diesel PM collected from a DPF test system connected to the exhaust stream of a 1.9 L, 4-cylinder, light-duty diesel engine is reported. A thermogravimetric analyzer (TGA) was used to measure the instantaneous sample mass and the rate of mass loss during its oxidation for a wide range of conditions, which include initial sample mass, amount of volatile components of soluble organic fraction (SOF) in the sample, oxygen concentration, and various heat treatment schemes in both the inert and oxidizing environments. The global kinetic parameters, i.e., the reaction orders of soot and oxygen, activation energy, and pre-exponential factor, were determined for the diesel PM and surrogate soot samples. Significant differences are observed in the oxidation behavior of surrogate soot and diesel PM. The oxidation rate of surrogate soot decreases continuously as the soot is oxidized, while that of diesel soot is nearly constant until about 80% of the sample mass is oxidized, and then decreases as the sample is completely oxidized. In addition, the oxidation behavior of surrogate soot is found to be essentially independent of the heat treatment schemes used, while that of diesel soot is strongly influenced by them. These differences may be attributable to changes in soot morphology during heating/oxidation and the presence of surface functional groups and heavier SOF components in the diesel PM. The effects of SOF and thermal aging on diesel PM oxidation have also been characterized. Results indicate that the PM oxidation is only weakly influenced by the presence of volatile components of SOF, whereas it is noticeably affected by thermal aging.

Extinction of interacting nonpremixed flames and existence of stationary retreating edges in twin-jet counterflow

A two-dimensional ‘twin-jet counterflow’ burner, in which two opposing streams from two double-slit nozzles form a counterflow, has been utilised to investigate the effect of the interaction of nonpremixed flames on extinction behavior. Results show that owing to the existence of unique petal-shaped flames, the extinction boundary for the cross-stream arrangement can be extended appreciably, as compared with that for the conventional counterflow arrangement, through the interaction of the curved sections of the interacting flames. The stationary petal-shaped flames had four flame edges, consisting of two retreating edges with negative edge speed in the direction toward the burnt gas region and two propagating edges with positive edge speed in the direction toward the unburned mixture. The OH-PLIF images of the petal-shaped flames demonstrated a strong concentration interaction between the two curved flame sections. Hysteresis in the transition between the petal-shaped flame and the curved flame having planar wing sections were observed. The representative propagation speed of the retreating edges of the petal-shaped flames correlated reasonably with maximum flame luminosity. The extinction characteristics of the retreating edges can be described in terms of the local Karlovitz number, which accounted for the local characteristic reaction time.

MEASUREMENTS OF HEAT RELEASE OF DIESEL PM FOR ADVANCED THERMAL MANAGEMENT STRATEGIES FOR DPF REGENERATION

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.