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The performance of diesel particulate filters (DPF) has historically been evaluated by gravimetric efficiency, which measures the mass of particulate matter (PM) trapped in the filters. This method does not measure the filtration efficiency at different PM size ranges and, therefore, cannot provide information on fractional performance of DPFs. This fact becomes significant because the adverse effects of diesel PM emissions on human health and the environment are size dependent. A previous study investigated the fractional performance of DPFs under steady state conditions using a scanning mobility particle sizer (SMPS). In the real world, however, nearly all engines operate under transient conditions. DPFs also have to perform under such conditions, so any measurement of performance must be able to react to quickly changing DPF conditions.

The characterization of engine particulate matter size distributions has become an important topic in the investigation of particulate matter formation, transport, and emission reduction technology. The majority of current size distribution analyses are conducted during steady state engine conditions. Although steady state analysis is valuable, most engines in mobile applications are operated under transient conditions, creating a demand for the transient state analysis of particulate emission patterns. In order to measure the instantaneous emissions of an engine under transient conditions, instrumentation must respond to the changing engine conditions as quickly as possible. In this study, a fast-scanning nanometer Aerosol Size Analyzer (n-ASA) was used to measure the emitted particles of a heavy duty diesel engine during transient simulations. The results showed patterns of PM emissions at key areas throughout the test.

Diesel oxidation catalyst (DOC) is one of the critical catalyst components in modern diesel aftertreatment systems. It mainly converts unburned hydrocarbon (HC) and CO to CO2 and H2O before they are released to the environment. In addition, it also oxidizes a portion of NO to NO2, which improves the NOx conversion efficiency via fast SCR over the downstream selective catalytic reduction (SCR) catalyst. HC light-off tests, with or without the presence of NOx, has been typically used for DOC evaluation in laboratory. In this work, we aim to understand the influences of DOC light-off experimental conditions, such as initial temperature, initial holding time, HC species, with or without the presence of NOx, on the DOC HC light-off behavior. The results indicate that light-off test with lower initial temperature and longer initial holding time (at its initial temperature) leads to higher DOC light-off temperature.

Introduction of modern diesel aftertreatment, primarily selective catalytic reduction (SCR) designed to reduced NOx, has increased the presence of urea decomposition byproducts, mainly ammonia, in the aftertreatment system. This increase in ammonia has been shown to lead to particle formation in the aftertreatment system. In this study, a state of the art diesel exhaust fluid (DEF)-SCR system was investigated in order to determine the influence of DEF dosing on solid particle count. Post diesel particulate filter (DPF) particle count (> 23 nm) is shown to increase by over 400% during the World Harmonized Transient Cycle (WHTC) due to DEF dosing. This increase in tailpipe particle count warranted a detailed parametric study of DEF dosing parameters effect on tailpipe particle count. Global ammonia to NOx ratio, DEF droplet residence time, and SCR catalyst inlet temperature were found to be significant factors in post-DPF DEF based particle formation.

Natural gas-powered engines are widely used due to their low fuel cost and in general their lower emissions than conventional diesel engines. In order to comply with emissions regulations, an aftertreatment system is utilized to treat exhaust from natural gas engines. Stoichiometric burn natural gas engines use three-way catalyst (TWC) technology to simultaneously remove NOx, CO, and hydrocarbon (HC). Removal of methane, one of the major HC emissions from natural gas engines, is difficult due to its high stability, posing a challenge for existing TWC technologies. In this work, degreened (DG), standard bench cycle (SBC)-aged TWC catalysts and a DG Pd-based oxidation catalyst (OC) were evaluated and compared under a variety of lean/rich gas cycling conditions, simulating stoichiometric natural gas engine emissions.

The effects of fuel sulfur content and dilution conditions on diesel engine PM number emissions have been researched extensively through steady state testing. Most results show that the concentration of nuclei-mode particles emitted increases with fuel sulfur content. A few studies further observed that fuel sulfur content has little effect on the emissions of heavily-used engines. It has also been found that primary dilution conditions can have a large impact on the size and number distribution of the nuclei-mode particles. These effects, however, have not yet been fully understood through transient testing, the method used by governments worldwide to certify engines and regulate emissions, and a means of experimentation which generates realistic conditions of on-road vehicles by varying the load and speed of the engine.

Selective catalytic reduction (SCR) is a promising technology for meeting the stringent requirements pertaining to NOx emissions. One of the most important requirements to achieve high DeNOx performance is to have a high uniformity of ammonia to NOx ratio (ANR) at the SCR catalyst inlet. Steady state 3D computational fluid dynamics (CFD) models are frequently used for predicting ANR spatial distribution but are not feasible for running a transient cycle like Federal Test Procedure (FTP). On the other hand, 1D kinetic models run in real time and can predict transient SCR performance but do not typically capture the effect of non-axial non-uniformities. In this work, two 3D to 1D coupling methods have been developed to predict transient SCR system performance, taking the effect of ANR non-uniformity into account. First is a probability density function (PDF) based approach and the second is a geometrical sector based approach.

Biodiesel is a promising alternative to traditional diesel fuel due to its similar combustion properties to diesel and lower carbon emissions on a well-to-wheel basis. However, combusting biodiesel still generates hydrocarbon (HC), CO, NOx and particulate matter (PM) emissions, similar to those from traditional diesel fuel usage. Therefore, aftertreatment systems will be required to reduce these emissions to meet increasingly stringent emission regulations to minimize the impact to the environment. Diesel oxidation catalysts (DOC) are widely used in modern aftertreatment systems to convert unburned HC and CO, to partially convert NO to NO2 to enhance downstream selective catalytic reaction (SCR) catalyst efficiency via fast SCR and to periodically clean-up DPF via controlled soot oxidation. In this work, we focus on the performance difference between biodiesel and diesel over a commercial DOC catalyst to identify the knowledge gap during the transition from diesel fuel to biodiesel.

Titanium dioxide supported vanadium oxide catalysts have been successfully utilized for the selective catalytic reduction (SCR) of nitrogen oxides emitted from both stationary and mobile sources. Because of their cost and performance advantages in certain applications, vanadium-based SCR catalysts are now also being considered for integration into some U.S. Tier IV off-highway aftertreatment systems. However, concern exists that toxic vanadium compounds, such as vanadium pentoxide, could be released from these catalysts as a result of mechanical attrition or high temperature volatility. An experimental study has been conducted to compare various techniques for measuring the release of particle and vapor-phase vanadium from SCR catalysts. Previous research has utilized a powder reactor-based method to measure the vapor-phase release of vanadium, but there are inherent limitations to this technique.

To meet stringent emission regulations, particulate filters will be required for diesel engines. Effective filters should reduce both the mass and number concentrations of particulate matter. For this reason, the performance of diesel particulate filters (DPFs) should be evaluated by measuring both gravimetric and fractional efficiency. This paper reports on a method developed for measuring particulate emissions on a mass and number basis. A two-stage dilution process was used in which the entire engine exhaust gas is directed into a primary dilution tunnel with a critical flow venturi. This constant volume system maintains proportional sampling throughout temperature excursions. A portion of the diluted exhaust gas is directed to a secondary dilution tunnel, for further dilution and determination of particle size distribution using a scanning mobility particle sizer. The engine was run at ISO 8178 modes.

Upcoming, stricter diesel exhaust emissions standards will likely require aftertreatment architectures with multiple diesel exhaust fluid (DEF) introduction locations. Managing NH3 slip with technologies such as an ammonia slip catalyst (ASC) will continue to be critical in these future aftertreatment systems. In this study, we evaluate the impact of SO2 exposure on a state-of-the-art commercially available ASC. SO2 is co-fed at 0.5 or 3 ppmv to either approximate or accelerate a real-world exhaust SO2 impact. ASC performance during sulfur co-feeding is measured under a wide variety of simulated real-world conditions. Results indicate that the loss of NO conversion during SCR is dependent on the cumulative SO2 exposure, regardless of the inlet SO2 concentration. Meanwhile, N2O formation under SCR conditions is nonlinearly affected by SO2 exposure, with formation increasing during 0.5 ppmv SO2 exposure but decreasing in the presence of 3 ppmv SO2.

Diesel exhaust fluid, DEF, (32.5 wt.% urea aqueous solution) is widely used as the NH3 source for selective catalytic reduction (SCR) of NOx in diesel aftertreatment systems. The transformation of sprayed liquid phase DEF droplets to gas phase NH3 is a complex physical and chemical process. Briefly, it experiences water vaporization, urea thermolysis/decomposition and hydrolysis. Depending on the DEF doser, decomposition reaction tube (DRT) design and operating conditions, incomplete decomposition of injected urea could lead to solid urea deposit formation in the diesel aftertreatment system. The formed deposits could lead to engine back pressure increase and DeNOx performance deterioration etc. The formed urea deposits could be further transformed to chemically more stable substances upon exposure to hot exhaust gas, therefore it is critical to understand this transformation process.

Cu-SSZ-13 selective catalytic reduction (SCR) catalysts are broadly applied in diesel aftertreatment systems for the catalytic conversion of oxides of nitrogen (NO + NO2). Diesel exhaust contains a wide range of water vapor concentrations depending on the operating condition. In this study, we evaluate the impact of water vapor on the relevant SCR catalytic functions including NOx conversion, NO oxidation, NH3 oxidation, and N2O formation under both standard and fast SCR conditions. Reactor-based experiments are conducted in the presence and absence of water vapor. Results indicate that water vapor can have both a positive and negative impact on low temperature NOx conversion for standard SCR reaction. At low inlet NOx concentrations, the presence of water vapor has a negative effect on NOx conversion, whereas, at high inlet NO concentrations, water vapor improves NOx conversion.

Ammonia oxidation (AMOX) catalysts are critical parts of most diesel aftertreatment systems around the world. These catalysts are positioned downstream of selective catalytic reduction (SCR) catalysts and remove unreacted NH3 that passes through the SCR catalyst. In many configurations, the AMOX catalyst is situated after a diesel oxidation catalyst and catalyzed diesel particulate filter that oxidize CO and hydrocarbons. However, in Euro V and proposed Tier 4 final aftertreatment architectures there is no upstream oxidation catalyst. In this study, the impact of hydrocarbons is evaluated on two different types of AMOX catalysts. One has dual washcoat layers-SCR washcoat on top of PGM washcoat-and the other has only a PGM washcoat layer. Results are presented for NH3 and hydrocarbon oxidation, NOx and N2O selectivity, and hydrocarbon storage. The AMOX findings are rationalized in terms of their impact on the individual oxidation and SCR functions.

Achieving high NOx conversion at low-temperature (T ≤ 200 °C) is a topic of active research due to potential reductions in regulated NOx emissions from diesel engines. At these temperatures, ammonium nitrate may form as a result of interactions between NH3 and NO2. Ammonium nitrate formation can reduce the availability of NH3 for NOx conversion and block active catalyst sites. The thermal decomposition of ammonium nitrate may result in the formation of N2O, a regulated Greenhouse Gas (GHG). In this study, we investigate the formation and thermal and chemical decomposition of ammonium nitrate on a state-of-the-art dual-layer ammonia oxidation (AMOX) catalyst. Reactor-based constant-temperature ammonium nitrate formation, temperature programmed desorption (TPD), and NO titration experiments are used to characterize formation and decomposition.

Selective catalytic reduction (SCR) of oxides of nitrogen (NOx) with gaseous ammonia is the leading technology used to meet on- and off-highway NOx emission standards across the world. In typical SCR systems, a low-pressure injector introduces a solution of urea and water (UWS) into hot exhaust gases leading to atomization and subsequent spray processes that finally lead to production of gaseous ammonia. Through their synergetic effect, the UWS injector and mixing enhancement devices (such as static mixers or baffles) help deliver a uniform mixture of ammonia and NOx to the SCR catalyst with minimal urea-derived solid deposits. To develop an efficient and robust aftertreatment system, it is essential to have experimental and simulation capabilities to assess the behavior of sprays under flow conditions representative of engine exhaust.

While most reductions in diesel particulate matter (PM) have been implemented through internal engine improvements and aftertreatment systems, additional reductions may be found by controlling intake contaminants. Under the ideal conditions of operating with ultra low sulfur diesel fuel and filtered and conditioned intake air, a diesel engine produces a certain amount of PM. The PM emission levels may increase when intake air is polluted during harsh on- or off-road conditions. In this study, contaminants were allowed to enter the intake tract of the engine to determine whether or not increased particle ingestion leads to increased particulate matter expulsion. Diesel and test dust contaminants dispersed in intake air were filtered using both a conventional filtering medium and a nano-medium to determine their effects on diesel engine-out PM emissions. The paper characterizes the two media by microstructure, permeability, porosity, and fractional efficiency.

Titania supported vanadia catalysts have been widely used for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) in diesel exhaust aftertreatment systems. Vanadia SCR (V-SCR) catalysts are preferred for many applications because they have demonstrated advantages of catalytic activity for NOx removal and tolerance to sulfur poisoning. The primary shortcoming of V-SCR catalysts is their thermal durability. Degradation in NOx conversion is also related to aging conditions such as at high temperatures. In this study, the impact that short duration hydrothermal aging has on a state-of-the-art V-SCR catalyst was investigated by aging for 2 hr intervals with progressively increased temperatures from 525 to 700°C. The catalytic performance of this V-SCR catalyst upon aging was evaluated by three different reactions of NH₃ SCR, NH₃ oxidation, and NO oxidation under simulated diesel exhaust conditions from 170 to 500°C.

In order to comply with tightening environmental standards, diesel particulate filters will be used for engine particle emission control. A well-defined testing method is needed to characterize and evaluate the diesel particulate filters. A previously developed testing method yielded unexpected results which were believed to be caused by dilution air contamination and particle formation downstream of the filters. In this study, the testing method has been modified in order to address these issues. Various wall-flow diesel particulate filters of fibrous and porous materials were tested using the modified method in this study. The results were compared with the previous data to evaluate the level of improvement. The results were also analyzed using particle size distributions and filtration mechanisms described by various theories. Particle size distributions demonstrated significant improvement of the modified testing method.

The gravimetric method is commonly used in engine air filtration technology for air cleaner, filter element and filter media testing. An “absolute” filter is employed in-line to collect any dust particles passing through the test filter. Air filter efficiency is calculated by comparing the mass of dust collected by the test filter with that fed to the filter. This method measures only the mass of dust penetrating the filter. It does not provide information on contaminant particle size. Moreover, this method, in many cases, has inadequate precision to distinguish between filters. Both the dust mass and its particle size are needed to estimate engine wear. Therefore, the SAE J726 Air Cleaner Committee initiated work on a test method to measure engine air cleaner fractional efficiency. This paper discusses problems associated with development of the fractional efficiency method for engine air cleaners.