Implications of the Use of Biodiesel on the Longevity and Operation of Particle Filters

While biodiesel is one of many necessary steps forward in a cleaner transportation future, alkali metal residuals, including Na and K (in the form of oxides, sulfates, hydroxides, and carbonates) originating from fuel production catalysts were found to be detrimental to emissions control components. Na + K and Ca + Mg (also biodiesel production byproducts) are regulated by ASTM-D6751 standards (American Society for Testing and Materials) to be less than 5 ppm for B100; however, the literature gives examples of physical and chemical degradation of automotive emissions catalysts and their substrates with these Na and K residuals. The purpose of this study is to investigate the impacts of ash from Na-doped biodiesel fuel (B20) on a diesel particulate filter (DPF). Investigations found that the Na-ash accumulated in the DPF has several unique properties which help to fundamentally explain some of the interactions and impacts of biodiesel on the particle filter. The biodiesel-related Na-ash was found to (1) have a significantly lower melting temperature than typical ash from inorganic lubricant additives and Ultra Low Sulfur Diesel (ULSD) fuel resulting in ash particles sintered to the DPF catalyst/substrate, (2) have a primary particle size which is about an order of magnitude larger than typical ash, (3) produce a larger amount of ash resulting in significantly thick wall ash layers and (4) penetrate the DPF substrate about 3× deeper than typical ULSD and lubricant-related ash. This study utilizes numerous characterization techniques to investigate the interactions between biodiesel-related ash and a DPF, ranging from visualization to composition to thermal analysis methods. The findings suggest the need for tighter control of the thermal environment in the DPF when using biodiesel, additional/improved DPF cleaning efforts, and avoidance of unregulated biodiesel with high Na/K levels

Multiscale methods for the fundamental understanding of diesel soot mitigation

Current regulations for diesel exhaust emissions cannot be met by engine improvements alone, and for this reason the diesel particulate filter (DPF) is a widely used aftertreatment component for the control of diesel particulate matter (PM). The DPF functions by trapping PM and destroying it by oxidation. The oxidation of the solid portion of PM, or soot, is a complex and non-linear process which can occur either with or without catalysts. In addition, lubrication-derived, incombustible ash accumulates in the DPF and over time accounts for a majority of the trapped mass in the DPF on average. As soot and ash accumulate in the DPF, the pressure drop over the filter increases, which negatively affects the fuel economy. Improved understanding of the fundamental properties of soot and ash leads to more efficient aftertreatment components. The work in this thesis consisted of two related focus areas, including diesel soot oxidation and the effects of ash accumulation on the DPF. An experimental method was developed to study the kinetics of the non-catalytic oxidation of carbon by O2, while a theoretical model was constructed to describe the relationship between carbon microsctructure and reactivity. The catalytic oxidation of carbon by O2 was studied by means of a recent nanofabrication technique where the carbon-catalyst contact could be accurately controlled. In addition, a system of both novel and established experimental techniques was used in this thesis to add to the fundamental understanding of lubrication-derived ash accumulation in the DPF

Multiscale methods for the fundamental understanding of diesel soot mitigation

Current regulations for diesel exhaust emissions cannot be met by engine improvements alone, and for this reason the diesel particulate filter (DPF) is a widely used aftertreatment component for the control of diesel particulate matter (PM). The DPF functions by trapping PM and destroying it by oxidation. The oxidation of the solid portion of PM, or soot, is a complex and non-linear process which can occur either with or without catalysts. In addition, lubrication-derived, incombustible ash accumulates in the DPF and over time accounts for a majority of the trapped mass in the DPF on average. As soot and ash accumulate in the DPF, the pressure drop over the filter increases, which negatively affects the fuel economy. Improved understanding of the fundamental properties of soot and ash leads to more efficient aftertreatment components.The work in this thesis consisted of two related focus areas, including diesel soot oxidation and the effects of ash accumulation on the DPF. An experimental method was developed to study the kinetics of the non-catalytic oxidation of carbon by O2, while a theoretical model was constructed to describe the relationship between carbon microsctructure and reactivity. The catalytic oxidation of carbon by O2 was studied by means of a recent nanofabrication technique where the carbon-catalyst contact could be accurately controlled. In addition, a system of both novel and established experimental techniques was used in this thesis to add to the fundamental understanding of lubrication-derived ash accumulation in the DPF

Implications of Hydrated Ash on Filtration Efficiency and Performance of Particulate Filters (DPF, GPF, and SCRF)—a Perspective

Abstract Particulate filters are used to meet current and future emission-control standards for particle mass and particle number requirements. However, with vehicle operation, non-combustible material (termed as “ash”) collects in the filter leading to an increase in ∆P, lower fuel economy, reduced soot storage space, and lower conversion rates for exhaust gases such as HC, NO, and NO2. In most cases, CaSO4 originating from detergent formulations in the lubricant forms the major component of inorganic ash; CaSO4 undergoes hydration cycles forming gypsum, along with semi-/hemi-hydrates through a series of transformations that are a function of temperature, time, and humidity. The exact nature of these transformations and the interaction of hydrated species with the filter substrate are poorly understood. The current work highlights the recent serendipitous discovery of hydrated ash structures and their deleterious effects on the filter and informs the automotive emission control community about the strategies for effective management of the filter

The Role of Active Sites in the Non-Catalytic Oxidation of Carbon Particulate Matter: A Theoretical Approach

The oxidation of carbon particulate matter is a complex process involving many different surface compounds; however, it is clear that there is a direct relationship between the inherent structure of the carbon and the oxidation reaction rate. This reaction occurs on surface sites which are on the periphery of the crystallites that make up carbon particles. These surface sites can be described as active sites where the reaction occurs and spectator sites that do not participate in the reaction. A model has been constructed that calculates the distribution of these types of surface sites during oxidation to show their dynamic behavior, and is compared to experimental data

Soot and ash deposition characteristics at the catalyst-substrate interface and intra-layer interactions in aged diesel particulate filters illustrated using focused ion beam (FIB) milling

The accumulation of soot and lubrication-derived ash particles in a diesel particulate filter (DPF) increases exhaust flow restriction and negatively impacts engine efficiency. Previous studies have described the macroscopic phenomenon and general effects of soot and ash accumulation on filter pressure drop. In order to enhance the fundamental understanding, this study utilized a novel apparatus, that of a dual beam scanning electron microscope (SEM) and focused ion beam (FIB), to investigate microscopic details of soot and ash accumulation in the DPF. Specifically, FIB provides a minimally invasive technique to analyze the interactions between the soot, ash, catalyst/washcoat, and DPF substrate with a high degree of measurement resolution. The FIB utilizes a gallium liquid metal ion source which produces Ga+ ions of sufficient momentum to directionally mill away material from the soot, ash, and substrate layers on a nm-μm scale. As the FIB cuts into the sample, uncovering intra-layer details, the coupled high resolution SEM imaging and energy dispersive x-ray (EDX) analysis provide both morphological and chemical data. This tool was applied to investigate soot and ash accumulation in the DPF, with a specific focus on characterizing interactions between the soot/ash/DPF interfaces, such as soot penetration into the ash layer, as well as soot and ash accumulation in the DPF surface pores. In particular, ash and soot particle size, layer pore structure, and the extent of penetration or intra-layer mixing, are all parameters directly impacting DPF pressure drop, which may be quantified using this technique. The work in this study leveraged existing databases of aged DPFs containing various levels of soot and ash, originating from field trials and controlled laboratory testing. Results obtained with this technique provide a fresh and complementary perspective, as well as additional details useful to understand the macroscopic observations of the combined ash and soot effects on diesel particulate filter pressure drop

Directional radiative cooling thermal compensation for gravitational wave interferometer mirrors

The concept of utilizing directional radiative cooling to correct the problem of thermal lensing in the mirrors of the LIGO/VIRGO gravitational wave detectors has been shown and has prospects for future use. Two different designs utilizing this concept, referred to as the baffled and parabolic mirror solutions, have been proposed with different means of controlling the cooling power. The technique takes advantage of the power naturally radiated by the mirror surfaces at room temperature to prevent their heating by the powerful stored laser beams. The baffled solution has been simulated via COMSOL Multiphysics as a design tool. Finally, the parabolic mirror concept was experimentally validated with the results falling in close agreement with theoretical cooling calculations. The technique of directional radiative thermal correction can be reversed to image heat rings on the mirrors periphery to remotely and dynamically correct their radius of curvature without subjecting the mirror to relevant perturbations