Kyeong O. Lee

Morphological investigation of the microstructure, dimensions, and fractal geometry of diesel particulates

Strong support from Dr. Sidney Diamond at the US DOE-OHVT is greatly appreciated. The authors also thank Dr. Russell Cook of Argonne’s Electron Microscopy Center for his valuable advice on microscopy.

Detailed Characterization of Morphology and Dimensions of Diesel Particulates via Thermophoretic Sampling

This project is supported by the Office of Heavy Vehicle Technologies of the U.S. Department of Energy. The constant support of Dr. Sidney Diamond is greatly appreciated. Authors also thank Mr. Gregory Hillman for his dedication to engine dynamometer operations and Dr. Russell Cook for his valuable advice on microscopy.

Effect of Nozzle Geometry on the Common-Rail Diesel Spray

The authors would like to acknowledge the support of National Research Laboratory scheme, Korean government.

Effects of Exhaust System Components on Particulate Morphology in a Light-duty Diesel Engine

The detailed morphological properties of diesel particulate matter were analyzed along the exhaust system at various engine operating conditions (in a range of 1000 - 2500 rpm and 10 - 75 % loads of maximum torques). A 1.7-L turbocharged light-duty diesel engine was powered with California low-sulfur diesel fuel injected by a common-rail injection system, of which particulate emissions were controlled by an exhaust gas recirculation (EGR) system and two oxidation catalysts. A unique thermophoretic sampling system first developed for internal combustion engine research, a high-resolution transmission electron microscope (TEM), and a customized image processing/data acquisition system were key instruments that were used for the collection of particulate matter, subsequent imaging of particle morphology, and detailed analysis of particle dimensions and fractal geometry, respectively. The data analysis showed that the average primary particle sizes significantly changed in a range of approximately 15 nm to 30 nm as a function of engine operating condition, while overall decreasing along the exhaust pipe. Aggregate particle sizes also significantly changed in a range of approximately 50 nm to 100 nm, in terms of radius of gyration, through the entire engine operating conditions. These particle sizes were affected mainly by the oxidation catalysts and tail pipe as well as engine operating conditions. Particle geometry was changed along the exhaust pipe, most significantly by the first catalyst, while overall becoming more spherical in shape toward the tail pipe. Fractal dimensions were measured in a range of approximately 1.4 to 1.8 through the entire engine operating conditions, which identified the change of particle geometry. A distinct increase of fractal dimension appeared after the first catalyst. The spherical particle shape, represented by the larger fractal dimension, was justified by soot morphology observed at the sample collected immediately after the catalyst.

Evolution in Size and Morphology of Diesel Particulates Along the Exhaust System

The physical and morphological properties of the particulate matter emitted from a 1.7-liter light-duty diesel engine were characterized by observing its evolution in size and fractal geometry along the exhaust system. A common-rail direct-injection diesel engine, the exhaust system of which was equipped with a turbocharger, EGR, and two oxidation catalysts, was powered with a California low-sulfur diesel fuel at various engine-operating conditions. A unique thermophoretic sampling system, a high-resolution transmission electron microscope (TEM), and customized image processing/data acquisition systems were key instruments that were used for the collection of particulate matter, subsequent imaging of particle morphology, and detailed analysis of particle dimensions and fractal geometry, respectively. The measurements were carried out at four different positions along the exhaust pipe. The rapid insertion of sampling probe into the exhaust stream, whose residence time resolves as short as 10 msec, provided near interference-free sampling of diesel particulates. From analyses for the soot samples collected at 2500-rpm and 25%-load, it was revealed that the primary particle diameter decreased from 28.6 nm to 19.1 nm and the corresponding radius of gyration of aggregate particles also decreased from 101.6 nm to 49.6 nm along the exhaust pipe. This reduction of particle sizes implies that particle sizes are significantly affected by aftertreatment components in the exhaust system. The detailed fractal analysis supported this finding; a fractal dimension of particles was slightly higher right after the first catalyst than those evaluated at other sampling positions, which indicates that particles became more spherical in shape during passing through the first catalyst. The fractal dimensions varied in a range of 1.5 to 1.7 along the exhaust pipe. It is speculated that the catalytic oxidation and aerodynamics of exhaust streams were major parameters influencing the distributions of measured sizes and fractal geometry. A chemical analysis using energy dispersion spectroscopy revealed that diesel particulates consist of elemental carbons in most portions.

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.

Effects of exhaust gas recirculation on diesel particulate matter morphology and NOx emissions

Abstract Diesel particulate morphology and nitrogen oxides (NO x ) emissions were investigated in detail to reveal the effects of exhaust gas recirculation (EGR). The different rates of EGR were precisely controlled by using a customized engine control unit in a 1.7 l turbocharged common-rail direct-injection diesel engine. The tests, which combined two different EGR modes (i.e. constant boost pressure (CBP) and constant oxygen-to-fuel ratio (COFR)), were designed to decouple the effects of EGR thermal and dilution processes. Particulate samples were collected directly from the raw engine exhaust by using a novel thermophoretic soot-sampling system. The samples were examined and imaged with a high-resolution transmission electron microscope and quantitatively analysed by using a customized image-processing/data-acquisition system. Results showed that the particulate dimensions, number density of primary particles, and soot yield all changed significantly under various EGR rates. The NO x emissions also varied significantly as the EGR rate changed, showing a typical trade-off with respect to the data measured for particulate emissions. At low EGR rates, the thermal effect was the dominant phenomenon that affected the changes of the measured morphological characters, while at higher EGR rates the dilution effect became more important. However, the fractal geometry of diesel particulates did not change significantly between the two EGR modes, suggesting that the influence of EGR dilution was less than that of the thermal process. EGR operation providing a COFR at the same EGR rate yielded a significant benefit in particulate emissions and engine power output, while still maintaining the reduction of NO x emissions at a satisfactory level.

Effects of Exhaust Gas Recirculation on Particulate Morphology for a Light-Duty Diesel Engine

Exhaust gas recirculation (EGR) is a commonly used technique for the reduction of Nitrogen oxide (NO x ) emissions from internal combustion engines. However, it is generally known that the use of EGR will cause an increase in emissions of particulate matter (PM). The effects of EGR operating mpde on particulate morphology were investigated for a 1.7-liter light-duty diesel engine. This engine was equipped with a turbocharged and inter-cooled air induction system, a common-rail direct fuel injection system, and an EGR system. A rapid prototyping electronic control system (RPECS) was developed to operate this engine at various EGR rates under different conditions (i.e. constant boost pressure, constant oxygen-to-fuel ratio (OFR)). A unique thermophoretic sampling system was employed to collect particulates directly from exhaust manifold after exhaust valves. The collected samples were later analyzed by using a high-resolution transmission electron microscope (TEM) and an image processing/data acquisition system. Diesel particulates were characterized in their morphological characteristics, such as primary particle size, aggregate particle size and fractal geometry. From analyses for the soot samples collected at 2500 rpm and 50% load, it was revealed that primary particle sizes (dp) increase with the increasing EGR rate, in general. The EGR dilution effect has more influence on primary particle sizes than thermal effect at low EGR rate. The aggregate particle sizes (radius of gyration, Rg) were measured within a narrow size range at different EGR rates. The fractal dimensions, which represent the complex geometry of diesel particulates, were measured in the range of 1.78 to 1.95. These results revealed that particulate geometry is sensitive to the changes of engine EGR rates. From this investigation, comprehensive information was obtained for effects of EGR on particulate morphology. These results will offer essential data to designers of diesel engines and aftertreatment systems.

An Investigation of Particulate Morphology, Microstructures, and Fractal Geometry for ael Diesel Engine-Simulating Combustor

The particulate matter (PM) produced from a diesel engine-simulating combustor was characterized in its morphology, microstructure, and fractal geometry by using a unique thermophoretic sampling and Transmission Electron Microscopy (TEM) system. These results revealed that diesel PM produced from the laboratory-scale burner showed Similar morphological characteristics to the particulates produced from diesel engines. The flame air/fuel ratio and the particulate temperature history have significant influences on both particle size and fractal geometry. The primary particle sizes were measured to be 14.7 nm and 14.8 nm under stoichiometric and fuel-rich flame conditions, respectively. These primary particle sizes are smaller than those produced from diesel engines. The radii of gyration for the aggregate particles were 83.8 nm and 47.5 nm under these two flame conditions. These results were compared with particulate mobility diameters measured by using a Scanning Mobility Particle Sizer (SMPS). Fractal dimensions were also measured to standardize the geometry of the particulates collected from both diesel engines and the combustor. The result for combustor soot showed that the fractal geometry of particulates formed at a stoichiometric condition resembles that of heavy-duty diesel particulates and the fractal geometry of particulates at a fuel-rich condition that of light-duty diesel particulates.

Sooting Behavior of Ethanol Droplet Combustion at Elevated Pressures Under Microgravity Conditions

Liquid ethanol is widely used in practical fuels as a means to extend petroleum-derived resources or as a fuel additive to reduce emissions of carbon monoxide from spark ignition engines. Recent research has also suggested that ethanol and other oxygenates could be added to diesel fuel to reduce particulate emissions. In this cursory study, the combustion of small ethanol droplets in microgravity environments was observed to investigate diffusion flame characteristics at higher ambient pressures and at various oxygen indices, all with nitrogen as the diluent species. At the NASA Glenn Research Center 2.2-second drop tower, free ethanol droplets were ignited in the Droplet Combustion Experiment (DCE) apparatus, and backlit and flame view data were collected to evaluate flame position and burning rate. Profuse sooting was noted above 3 atm ambient pressure. In experiments performed at the Japan Microgravity Center 10-second (JAMIC) drop shaft with Sooting Effects in Droplet Combustion (SEDC) apparatus, the first data that displayed a spherical sootshell for ethanol droplet combustion was obtained. Because of the strong sensitivity of soot formation to small changes in an easily accessible range of pressures, ethanol appears to be a simple liquid fuel suitable for fundamental studies of soot formation effects on spherical diffusion flames. The results impact discussions regarding the mechanism of particulate reduction by ethanol addition to fuels in high-pressure practical combustors.