Global Kinetic Model of a Three-Way-Catalyst-Coated Gasoline Particulate Filter: Catalytic Effects of Soot Accumulation

In the present study, a global kinetic model of three-way-catalyst-coated gasoline particulate filters was developed to understand the relevant kinetic mechanisms taking place both in clean and real soot-loaded filters. The model involves reaction rate expressions for CO, C2H4, and C7H8 conversion over a model Pd/CeZr/Al2O3 catalyst, hydrothermally treated at 650 \ub0C. Particularly, a new rate expression was proposed for ethylene based on the distinctive experimental trends observed for this hydrocarbon. The model predicted satisfactorily the conversion of all three reductants under different experimental conditions. The soot inhibition effect was also modeled by the reduction of the number of active sites. Interestingly, ethylene was less affected compared to other reductants by the presence of soot due to the formation of less stable and more reactive species on the catalyst surface

Energetic Nanoparticles as Fuel Additives for Enhanced Performance in Propulsion Systems

Biofuels are currently being explored as a carbon-neutral fuel alternative to petroleum-based fuels. However, biofuels such as ethanol has lower energy density (~27MJ/kg) relative to petroleum fuels (~ 45 MJ/kg). Adding high-energy density particles (such as boron with heating value of ~ 58.5 MJ/kg) to biofuels can generate fuel slurry with higher energy density than the base fuel, and represents a potential strategy toward making biofuels more viable. However, the combustion of boron is inhibited (specifically, the ignition is delayed) by the initial presence of an oxide layer, and its high evaporation and boiling temperatures. The present study investigates the combustion behavior of commercially available boron nanoparticles and explores the underlying effects of the particle morphology and size on the combustion characteristics. Detailed characterizations of these particles (using XRD, SEM, TGA, BET surface area and porosimetry) have been carried out before (and after) injecting them into a controlled biofuel (ethanol) combustion environment. Measurements were made in the flame and of the particles captured post-flame. Chemiluminescence and spectroscopic measurements clearly showed evidence of intermediate species of boron combustion and these measurements were used to monitor the ignition and combustion characteristics of the boron particles. The results show that particle size plays a major role on the burning behavior of the particles – larger particles have slower burning rate compared to the smaller counter parts. The combustor’s exit temperature data suggest a positive thermal contribution and increased temperatures due to boron combustion and heat release. A near-linear trend in increasing temperature and energy release is observed with increasing particle loading. Efforts at catalytically coating the boron particle with cerium oxide have shown improvement in the boron ignition (reduction in ignition delay). The XRD and TG analysis of the post-combustion particles reveal that product particles contain boric acid or hydrated B2O3 and no un-burnt boron. The droplet combustion experiments conducted on the burning behavior of single ethanol droplet containing energetic nanoparticles of boron or boron-metal (iron, aluminum and titanium) nanocomposites suggest that improved ignition characteristics of boron can be achieved in presence of metal additives

REGENERATION OF CATALYST-COATED DIESEL PARTICULATE FILTERS

In this work, the effect of the soot-catalyst contact on the regeneration performance of a diesel particulate filter (DPF) wash-coated with nano-metric ceria particles was investigated. The catalyst load was suitably chosen to avoid major changes in pore size distribution of the original filter. Different amounts of soot were loaded into the filter, thus varying the catalyst/soot ratio. Filter samples were characterized by N2 physisorption at 77 K, Hg intrusion porosimetry and SEM/EDX analysis. Regeneration tests were performed in a lab-scale plant by temperature programmed combustion of soot. At the lowest soot load explored (corresponding to catalyst/soot ratio 100 w/w), the soot particles deeply penetrate into the macro-pores of the filter walls coming in close touch with highly dispersed ceria. At the highest soot load explored (catalyst/soot ratio 20 w/w), in addition to the soot particles trapped inside the macro-pores, a thick soot cake layer accumulates on top of the catalytic walls of the filter. The former condition results in a large fraction of soot burned via catalytic path (around 80 % - almost purely catalytic regeneration mode) and, thus, in good regeneration performance (e.g., temperature at which 10 % of the initial soot is converted, T10 %, equal to around 350°C). Conversely, due to the poor cake-catalyst contact, the latter condition results in a large fraction of soot burned via thermal path (around 80 % - catalyst-assisted thermal regeneration mode) and, thus, in much worse regeneration performance (e.g., T10 % 475°C). This study highlights the importance of strategies that avoid or minimize the segregation between the cake layer and the catalytic wall of the filter to operate catalyst-coated DPFs in an effective manner

Exhaust aftertreatment modeling for efficient calibration in diesel passenger car applications

Interest in utilizing advanced lean-burn gasoline and diesel engines has increased in the last decades due to their reduced greenhouse gas emissions and increased fuel economy. One impediment to the increasing use of these engines, however, is the need to develop corresponding catalytic systems for controlling pollutant emissions. In particular, although still far from the fuel neutral United States (US) approach, European (EU) legislation limits for Nitrogen Oxides (NOx) emissions are becoming more and more severe and also type approval procedures are going to radically change with the introduction of Worldwide harmonized Light vehicles Test Cycle (WLTC) and Real Driving Emission (RDE) tests. Considering that test bench and chassis dyno experimental campaigns are costly and require a vast use of resources for the generation of data; therefore, reliable and computationally efficient simulation models are essential in order to identify the most promising technology mix to satisfy emission regulations and fully exploit advantages of diesel and lean-burn gasoline when minimizing the side effect of their emissions. Therefore, the aim of this work is to develop reliable models of the individual aftertreatment components and to calibrate the kinetic parameters based on experimental measurements which can be further used as a virtual test rig to evaluate the effectiveness of each technology in terms of reducing pollutant emissions. In the current work, a brief introduction regarding the passenger car emissions, regulations and control technologies, including in-cylinder control techniques and aftertreatment systems, is provided in Chapter 1. In addition, simulation modelling approaches for aftertreatment applications are discussed. More details about specific aftertreatment components are discussed in the next chapters. As an example, the modeling of a Selective Catalytic Reduction coated on Filter (SCR-F), on the basis of Synthetic Gas Bench (SGB) reactor data is presented in Chapter 2; focusing, in particular, on estimation of ammonia storage capacity, NOx conversion and soot reduction due to passive regeneration. LNT is analyzed in Chapter 3, focusing on the reactor-scale Synthetic Gas Bench (SGB) experiments and calibration of the 1D simulation model for two case studies with the aim to characterize Oxygen Storage Capacity (OSC), NOx Storage and Reduction (NSR) and light-off. The calibrated 1D simulation model is thereafter validated, in Chapter 4, for one of the case studies using engine-out emissions, mass flowrate and temperature traces over Worldwide harmonized Light vehicles Test Cycle (WLTC) as the boundary condition for the inlet of LNT for full-size component. Afterwards, the LNT model calibrated in Chapter 3 is, in Chapter 5, further reduced and linearized with reasonable assumptions to be used as a plant-model with very low computational requirement and in real time applications such as Electronic Control Unit (ECU)/ Hardware-in-the-Loop (HiL) systems. Finally, after discussing NOx control systems in previous chapters, modeling of Diesel Oxidation Catalyst (DOC), which plays a fundamental role not only for the CO and HC conversion, but also for promoting the oxidation of NO into NO2, is discussed in Chapter 6. It is worth noting that depending on the complexity of the kinetic model, different optimization tools are implemented for the calibration; as an example, Brent method is used for calibration of SCR-F kinetic model, likewise, Genetic Algorithm (GA) is used for the calibration of the DOC kinetic parameters; however, for more complex kinetic schemes like LNT both manual and automatic optimization is required to evaluate the most suitable reaction pathways and kinetic parameters. Accordingly, after development of the kinetic model for each aftertreatment component and validation of the full-scale model, further investigations could be devoted to combining the models in order to simulate the whole aftertreatment system and assess the performance over different driving cycles

Particulate matter emissions characteristics, dynamics and control in compression ignitions engines

Combustion engines’ exhaust emissions have impacted the environment with greenhouse gas emissions on a large scale and this will reach a global catastrophe limit in the coming decades. It has been an important issue of consideration for many years and substituting fossil fuels to decarbonise the environment has been of utmost importance. With the increase in knowledge and research to understand and control particulate matter emissions, the fundamental research still holds unanswered questions. The study carried out in the following thesis is primarily focussed on the particulate matter’s inception, evolution, control and its characterisation from a compression ignition engine. The thesis proceeds with the initial study on the evolution and course of particulate matter inside the exhaust tailpipe using a zero-dimensional numerical model. The model aims to investigate the nucleation of water and sulphuric acid from the engine out, and its impact on the particulate matter as it is transported autonomously along a 3.5-metre exhaust pipe. The research is also concerned with explaining the effects of exhaust temperatures on particulate matter and gas emissions, by characterising them into size, mass, and concentrations at consecutive testing positions. The simulated and analysed data are used for a comparative analysis with empirical results acquired from similar exhaust temperature and particulate matter conditions that were confirmed as the assumptions were established. Further, the research is based on an empirical investigation of particulate matter evolution and the impact of the external cooling of an exhaust tailpipe. The cooling was produced using copper coil tube windings with a decreasing pitch along the length of the pipe and supplied with an ice water and antifreeze mixture solution. The external cooling of the exhaust tailpipe was an important parameter to study the effects of external cooling on the particulate matter flowing through the internal space of the tailpipe. The evolution of the particulates and the impact of the reduction in temperature gradient provided agreeable results. The objective was achieved in understanding and contributing to the knowledge of particulate behaviour inside the tailpipe under various engine operating conditions. In consideration of the previous studies mentioned above, it is critical to research the control of particulate matter and gas emissions at this stage. Hence, a diesel particulate filter is equipped as an exhaust after-treatment system for the abatement and oxidation of toxic gases and particulate matter. A catalyst is developed to be coated on the filter substrate with a novel nano-fibrous morphology using a rare-earth metal catalyst. The conceptualisation of the research was to investigate the morphological effects on particle trapping and the oxygenated catalytic effect on soot burn at low exhaust temperatures. Tests were performed at laboratory scale and test bench scale, where the filter substrate was coated with the catalyst; and the results acquired depicted an increased filtration efficiency consistent at 95–99%, and a high oxidation and continuous regeneration rate at reduced local exhaust temperatures, contributing to overall lower back pressure on the particulate filter and engine. Finally, the thesis provides details of the research findings and conclusions to provide a valuable contribution to the knowledge of exhaust emissions’ characteristics and their control

Doped ceria nanostructures for the oxidation of pollutants: investigations into the role of defect sites

L'abstract è presente nell'allegato / the abstract is in the attachmen

Technological approaches to improve the engine efficiency and to reduce pollutant emissions of automotive diesel engines.

The research work was mainly focused on the technological approach to improve engine efficiency and reduce pollutant emissions applicable to diesel engines which are very often incompatible were assessed through a set of full- scale tests on a real diesel engine in order to satisfy the new emissions limits. (1) The first strategy evaluated in this work to improve the engine efficiency was the reduction of the mechanical losses: through the incorporation of nanomaterials in the lubricant formulation. The effect of the lubricant oil additivated with MoS2 nanopowders was assessed through a set of full - scale tests on a real diesel engine – several engine points and cooling water temperatures were investigated for both a reference oil and a MoS2-additivated one. (2) Other strategy to reduce pollutant emissions included in this PhD thesis was the effects of using a 30% by volume blend of a renewable fuel, called Farnesane, and fossil diesel in a small Euro 5 displacement passenger car diesel engine. (3) And finally, the CeO2/BaO/Pt system was selected in order to perform an NO2-assisted soot oxidation, as a aftertreatment strategy to reduce pollutant emissions. The aim of such catalytic system is to couple the catalytic functionality for soot abatement during DPF regeneration, namely CeO2, and an embedded lean NOx trap (LNT) functionality given by BaO, for NOx storage, whose oxidation over Pt to form adsorbed nitrates is facilitated by the presence of CeO2 itself

Light off temperature based approach to determine diesel oxidation catalyst effectiveness level and the corresponding outlet NO and NO2 characteristics

According to the latest EPA emission regulations, the NOx (Nitrogen oxide compounds) emissions from heavy duty compression ignition engines need to see a dramatic reduction. The current technology used for this purpose is the selective catalytic reduction (SCR) system, which achieves NOx reduction of around 90% [9]. This involves urea injection which is influenced by the NO: NO2 ratio at the inlet to the SCR. Thus, the role of the DOC (Diesel Oxidation Catalyst) where most of the oxidation of the NOx compounds takes place, comes to fore. The focus is also on the effectiveness of the catalyst as it thermally ages. Therefore, the aim of this research project is to correlate the aging in the DOC with the light off temperature of the catalyst and subsequent variation in the NO and NO2 concentration at the outlet of the DOC. This shall be achieved through means of a model developed after extensive experimental procedures. Also, further exhaustive experiments to validate the model over multiple aging cycles of the catalyst shall be undertaken. ^ The DOC was subjected to 2 rigorous kinds of experiments aimed at determining the light off temperature shift as the catalyst aged and to determine the NO and NO2 concentrations at the DOC outlet as it aged. Exhaust stream compounds were measured using exhaust analyzers and DOC temperatures were determined using thermocouples installed inside the DOC and at its inlet and outlet. ^ The data thus obtained was then analyzed and 2 separate models were developed, one for the light off experiments, and the other for the NOx experiments. Aging procedures were carried out at an oven according to prescribed techniques and the DOC was subjected to similar experiments again. Analysis was carried out on the data. From the light off experiments and the model analysis, a clear positive shift in light off temperatures was observed from one aging level to another across the range of set points. It was also observed that even after subjecting the DOC to three thermal aging exercises, its conversion efficiency went up to 90%. Also, as the DOC aged, the NO concentration at the DOC outlet showed a downward trend which was observed across the spectrum of engine set points and aging levels. These experiments were repeated for consistency so that the models could be rendered more useful

MRI Studies of Gas Hydrodynamics in Automotive Particulate Filters

Particulate filters are used to remove harmful particulate matter (PM) from the exhaust gas of automobiles. They are required in most modern vehicles to achieve compliance with legal limits set on vehicle emissions and are often combined with a catalyst to increase their functionality as an emission control technology. Knowledge of the exhaust gas hydrodynamics in filter systems is crucial for the optimisation of their structure and operation. The nature of most filters, i.e. opaque and brittle, means most anemometry methods are inapplicable. In this work, magnetic resonance imaging (MRI) is applied to measure gas hydrodynamics in such filters. This methodology is used as it provides a non-invasive means of measuring gas flows in complex geometries. The first part of this thesis focuses on the fundamental hydrodynamics of gas at the ends and in the channels of filters. The first measurements of laminar and turbulent flows at the filter entrance and exit are made. These show the features expected from literature simulations but also additional turbulent effects not previously predicted. Possible challenges facing future CFD comparisons with this work are also explored. The gas flow fields in the channels are measured, allowing calculation of the through-wall or filtration velocity. This provides data for comparison with 1D and 3D CFD models at a range of flow rates. The 3D CFD model is validated for modest Reynolds numbers and allowed parameters such as flow profile shape and wall friction to be explored. The 1D model shows agreement with the measured data when these parameters were allowed to vary with the through-wall velocity. The MRI data is also combined with an analytical filtration model to predict the filtration behaviour and total filtration efficiency of PM. The second part of this thesis explores the preparation and operation of filters. Catalysts are applied to filters using a washcoat slurry, a process which can cause non-uniform distributions of washcoat in the filter and perturb the gas flow. Washcoat distributions are difficult to measure non-destructively due to the filter opacity. MRI allows perturbations to the gas flow fields to be measured and changes to the wall permeability estimated using the aforementioned 1D model. This is performed for three model washcoated GPF samples. The permeability estimations agree with porosimetry measurements and reveal a variety of non-uniform washcoat distributions in the filters, which is predicted to impact the pressure drop and filtration behaviour. This method is applied to commercial filters which are loaded with PM from a real-world engine to three different levels. The PM-free filters show a non-uniform washcoat distribution and the PM deposits mostly in the regions of low washcoat loading and high through-wall velocity