Thesis (Ph.D.)--Drexel University, 2009. / Includes abstract and vita. Includes bibliographical references (leaves 226-234).

In order to improve understanding of diesel soot oxidation, an experimental rig was designed and set up, in which the soot oxidation conditions, such as temperature, oxygen partial pressure, and CO2 partial pressure, could be varied independently of each other. The oxidizing gas flow in the oxidizer was under laminar condition. This test rig comprised a naturally-aspirated single cylinder engine which acted as the soot generator, and a separate premixed oxidation burner system in which soot extracted from the engine was oxidized under controlled conditions. Diesel soot was extracted from the engine exhaust pipe and from the engine pre-combustion chamber, and the soot-laden gas was then conveyed to the burner where it was oxidized. The burner was positioned vertically and it had a flat flame whose thickness was only a few millimetres. The hot gases from the flame flew upwards through a quartz transparent tube which acted as the soot oxidation duct. The soot-laden gas from the engine was premixed with the feedgas (itself a premixed mixture of methane, air, oxygen, and nitrogen) to the burner. The soot particles passed vertically through the flame front and continued burning in the post-flame gas flowing through the quartz tube oxidation duct. The oxygen concentration and temperature of the post-flame soot oxidation gas were controllable by adjusting the flowrate and composition of the burner feedgas. Diesel soot particles were sampled at different heights along the centreline of the quartz tube above the burner. Profiles of oxygen concentration, temperature, and soot particle velocity in the oxidation zone were thus measured. Morphology and size distributions of the sampled diesel soot particles were analyzed by means of Transmission Electron Microscopy (TEM) and a computer software called ImagePro Plus. Subsequently, the specific surface oxidation rates of the soot particles were worked out based on soot particle size distributions. The TEM micrographs obtained in this study showed that the diesel soot agglomerates existed in forms of clusters and chains, each containing between a small number and thousands of individual, mostly spherical tiny particles. Of order 97% of the individual spherical particles (spherules) had a size range from 10 to 80 nm. Occasionally, individual spherules of about 150 nm in diameter could be observed. The diesel soot particles sampled from the pre-chamber of the engine had different size distributions from those sampled from the exhaust of the engine, indicating that the soot underwent an oxidation process in the combustion chamber. Soot oxidation experiments were performed in the burner post-flame gas under oxygen partial pressures ranging from 0.010 to 0.050 atm and temperatures from 1520 to 1820 K. The test results showed that the oxidation rates of the diesel soot extracted from the diesel engine were generally lower than those predicted by the well-known Nagle and Strickland-Constable formula; however, the measured oxidation rates were higher than the predictions made with another well-known formula - the Lee formula. The soot extracted from the engine pre-chamber appeared not to oxidize as fast as the soot extracted from the exhaust of the engine. CO2 gas injection to the post-flame oxidation gas at constant oxygen partial pressure and oxidation temperature seemed to have accelerated the diesel soot oxidation rate. Based on the experimental results of this study and the results of other researchers, modifications to the Nagle and Strickland-Constable formula and to the Lee formula were accomplished. Also, an empirical expression, as an alternative to semi-empirical formulae, was worked out and presented in the thesis.

Les enjeux écologiques liés au réchauffement climatique, et plus généralement la lutte contre la pollution, ont occasionné une révolution sans précédent dans le domaine des transports. De nombreuses recherches portant sur l’identification de voies d’amélioration du rendement mécanique des moteurs à combustion interne ont été menées au cours de ces dernières décennies. Dans les moteurs Diesel, le contact Segments-Piston-Chemise (SPC) représente à lui seul près de 40 % des pertes d’énergie par frottement mécanique totales du moteur. Ce travail de thèse s’inscrit dans le cadre général de la lubrification des moteurs Diesel en présence de suies et s’intéresse plus particulièrement au poste SPC pour des contacts Diamond-Like Carbon (DLC) lubrifiés. Ce travail de thèse s’appuie sur des outils de tribométrie originaux pour reproduire les cinématiques particulières des contacts impliqués au niveau de la segmentation. Cette thèse s’attache à identifier l’influence d’un lubrifiant vieilli en fonctionnement sur les mécanismes de lubrification et les mécanismes de frottement associés de couches minces dures de type DLC, en balayant l’ensemble des régimes de lubrification pour des conditions stationnaires et transitoires. Les revêtements DLC développés dans le cadre de ce travail de thèse ont permis de diminuer significativement le frottement limite en conditions stationnaires et transitoires. La déstructuration du lubrifiant via la formation d’agrégats, générés par le passage des suies, ou par une annulation temporaire de la vitesse d’entraînement représentative des cinématiques de contact observées en zone SPC, sont gouvernés par le triptyque, lubrifiant, surface et cinématique de contact. Enfin, l’analyse de la réponse tribologique de l’interface lubrifiée en conditions stationnaires et transitoires permet à la modélisation théorique du frottement lors d’un cycle complet de glissement à vitesses variables. / Ecological issues related to global warming, and more generally the reduction of pollution, have lead to a major revolution in the field of transport. Considerable research work has been carried out during the past decades in order to improve the mechanical efficiency of internal combustion engines. In Diesel engines, almost 40 % of total engine energy losses due to mechanical friction occur in the Piston rings-Piston-Cylinder contact (PPC). The overall framework of this PhD thesis is Diesel engine lubrication in presence of soot and this work focuses more particularly on Diamond-Like Carbon (DLC) lubricated contacts for PPC region. Unique tribometry tools are used to reproduce the particular contact kinematics involved in the piston assembly. This thesis aims to identify the influence of an aged lubricant on the lubrication and friction mechanisms of DLC hard coatings for all lubrication regimes in steady-state and transient conditions. DLC coatings developed during this thesis significantly reduce the boundary friction in steady-state and transient conditions. The lubricant destructuring due to aggregate formation, generated by the passage of soot, or by a temporary vanishing of the entrainment speed, are governed by the triplet, lubricant, surface and contact kinematics. Finally, the analysis of the tribological response of the lubricated interface in steady-state and transient conditions leads to the theoretical modeling of the friction during a complete cycle of sliding at variable velocities.

In order to increase the efficiency of diesel particulate filter regeneration more knowledge about diesel soot and its reactivity is required. This thesis compares soot created during accelerated filter loading by lowered rail pressure, with soot from normal filter loading. Soot properties and their correlations to oxidation reactivity are also examined through thermogravimetric analysis, scanning electron microscopy, energy dispersive x-ray spectroscopy, BET nitrogen sorption, and FTIR spectroscopy. The usefulness of these analysis methods was also evaluated. The soot samples consisted of two carbon blacks for reference (Printex U and Vulcan XC 72), four accelerated soot samples and two non-accelerated samples. The results showed that the accelerated samples contained less volatile organic compounds than the non-accelerated soot and required slightly higher temperatures to oxidize in air. Soot with a high oxygen/carbon ratio and high levels of volatile organic compounds was found to be the most reactive. The most useful method for analyzing the soot was the thermogravimetric analysis. The scanning electron microscopy and energy dispersive x-ray spectroscopy were useful additions but the FTIR spectroscopy provided very little useful information. The usefulness of BET nitrogen sorption was not decisively concluded. / För att kunna förbättra regenereringen av dieselpartikelfilter krävs en ökad kunskap om dieselsot och dess reaktivitet. I detta examensarbete jämförs sot som skapas vid accelererad sotinlagring genom sänkt railtryck, med sot från normal sotinlagring. Hur sotets egenskaper påverkar dess reaktivitet undersöks också genom termogravimetrisk analys, svepelektronmikroskopi, energidispersiv röntgenspektroskopi, BET-kväveadsorption och FTIR-spektroskopi. Hur väl dessa analysmetoder lämpar sig för analys av sot utvärderades också. Sotproverna utgjordes av två så kallade ”carbon black” för referens (Printex U och Vulcan XC 72), fyra accelererade sotprov och två icke-accelererade prov. Resultaten visade att de accelererade proverna innehöll mindre flyktiga organiska föreningar än icke-accelererade sot och krävde något högre temperaturer för att oxideras i luft. Sot med ett högt syre/kol-förhållande och höga nivåer av flyktiga organiska föreningar visade sig vara mest reaktivt. Den mest användbara metoden för att analysera sot var den termogravimetriska analysen. Svepelektronmikroskopi och energidispersiv röntgenspektroskopi var användbara som komplementerande metoder men FTIR-spektroskopi gav väldigt lite användbar information. Ingen konkret slutsats drogs gällande nyttan av BET-kväveadsorption.

The objective of this study was onboard testing of a mixed metal oxide diesel soot oxidation catalyst composing of oxides of lead and cobalt previously developed in our lab, by mounting a diesel particulate filter (DPF), which is coated with this catalyst, to the exhaust stream of a diesel vehicle. Commercial wall flow type DPF&rsquo / s (Corning EX-80) were coated with the catalyst by a slurry wash-coating procedure and then mounted on the exhaust stream of a diesel light duty vehicle (LDV) provided by TOFAS (FIAT Doblo 1.9 JTD). These vehicles were driven on the rollers of the chassis dynamometer at constant speed and gear for two different loading conditions and on a standard driving cycle (NEDC) in the Test and Emission Laboratory of TOFAS-FIAT. The exhaust gases were analyzed for NOx, CO, CO2, THC and PM. The pressure drop caused by the filter was monitored during these tests as an indication of soot accumulation on the filter with the help of pressure sensors placed before and after the filter. Also temperatures before, inside and after the filter were monitored by means of thermocouples. Three different filters were tested in this manner: (1) Monocoated (CoOx), (2) Sequential PbOx coated over CoOx (PbOx/CoOx), (3) Simultaneously coated (PbCoOx). Also tests with the uncoated filter were performed to determine the pressure drops as a result of non-catalytic soot oxidation. The performances of the catalytic filters were evaluated by determining the temperature at which the soot oxidation rate on the filter equals the soot production rate in the engine (balance point temperature-Tbal). This temperature was used for comparing the catalytic activity of the supported catalyst with that of the powder form tested in the laboratory, i. e. Tpeak. The results of the onboard test were in parallel with the previous laboratory studies with similar catalytic activity temperatures. The continuous regeneration temperatures (Tbal) obtained in onboard tests with PbOx/CoOx and PbCoOx filters of about 370oC, which was close to the values attained in the lab study with the same mixed metal oxide catalyst having a Tpeak value of 385oC. Also the PM emissions during the tests were complying with the current EURO-IV emission limits.

Soot is a carbonaceous materials produced as a result of incomplete combustion of fuels (gasoline, diesel, etc). At the present level of automobile technology, emission of soot from combustion in diesel engine appears to be an inevitability. The disadvantage in the diesel combustion is that it is not homogeneous throughout the cylinder. So the fuel-air ratio cannot be maintained constant throughout the flame zone and hence rich combustion zone leads to the formation of soot. Diesel engine combustion processes produce a large amount of soot, which is one of the major pollutant emissions of the exhaust systems. The fraction of combustion particulate, which is soot, is often estimated by finding the insoluble portion of the particulate. Hydrocarbons or other available molecules may also condense on or beads orbed by soot depending on the surrounding conditions. Other particulate matter constituents include partially burned fuel/lubricant oil bound water, wear metal and fuel derived sulfate. In diesel engine lubrication, soot has long been recognized as the major contaminant that is detrimental to engine lubrication, particularly in friction and wear. Different techniques for soot abatement have been investigated by researchers from the field of combustion and fuel. In spite of the large numbers of investigations of soot formation conducted till date, there is relatively little quantitative information is available about the mechanisms and governing rate processes. Some of the studies focused on the combustion chemistry of soot formation while some emphasized on engine design. On the other hand comparatively a few research works are coming out from the tribological point of view. Considering that internal combustion engines play such an important role in industry, investigative research of the parametric influences of particle size, agglomeration, oil viscosity, additives and surfactant as well as chemistry and electrical properties of particles on wear as well as into the wear mechanisms have not perhaps been as extensive as it is detrimental. Existence of a large numbers of variables in tribological contacts makes the situation very complex and difficult to analyze it quantitatively. In this complex scenario, where many opposed effects are playing their roles in soot tribology, the influence of the physical, structural and mechanical properties of soot on engine tribology has limited attention. We focus our study on one of the end effects of engine soot; friction and wear of the engine components. Since a diesel engine is not particularly suitable for use in a laboratory study of the fundamental processes and parameters of combustion due to its inherent difficulties on control and safety as well as data analysis uncertainty, so the most useful studies of soot fundamentals have emerged from studies of processes which have used simplified environments such as diffusion flames. We focus on soot tribology in steel-on-steel interaction in the presence of soot material suspended in relatively simple paraffinic hydrocarbons, hexadecane; with and without an additive. The physical, structural, chemical and mechanical properties of the particle and their changes as a function of tribological parameters are monitored throughout this study. Three type of soot are used in this work. Firstly, commercial grade carbon blacks has been used as soot simulant. Secondly, to enable controlled variations of the physical, mechanical, chemical and geometrical parameters of the particles, soot is generated in-situ by burning ethylene gas and the particles are extracted thermophoretically from different thermal zones of the flame. Thirdly, to establish the validity of the study, two types of diesel soots are extracted from an engine and studied. The objective is to use such an understanding to elucidate the basic mechanisms of friction and wear in the presence of soot which may limit the performance of a diesel engine. From our study we find that these soots have widely different morphologies, crystallographic orders and reactivity. At tribological contact the soot agglomerates fragment to primary level particles. The physical and chemical properties of such particles determine the friction between and wear of mating components. If the soot is strongly graphitic, the friction and wear are moderate. If the soot is made of chemically active organic groups, the friction and wear are high. The hardness, friction and resistance to material removal of the soot collected near the flame tip and diesel soot are found to be high compared to the other types of soot. Besides, the high hardness, irregular primary particle shape, large inter-particle adhesion leading to agglomeration and more abrasive nature of diesel soot influence the metal wear adversely. This trend of soot tribology is profound when these soots are suitably dispersed in the oil by the addition of dispersants, in our case it is polyisobutylene succinimide. Different functional groups present on the soot surface play important role in defining the interaction between surrounding medium and contacts which, in turn define the contact conditions, particle/agglomerate behavior and soot tribology. Finally, agglomeration is simulated using the features of a dissipative particle dynamics package as the simulation technique. Simulations are performed on a sizeable number of particles to observe agglomeration behavior, on simple environment, in future which can be further extended.