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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.

Lean-burn natural gas (NG) engines are used world-wide for both stationary power generation and mobile applications ranging from passenger cars to Class 8 line-haul trucks. With the recent introduction of hydraulic fracturing gas extraction technology and increasing availability of natural gas, these engines are receiving more attention. However, the reduction of unburned hydrocarbon emissions from lean-burn NG and dual-fuel (diesel and natural gas) engines is particularly challenging due to the stability of the predominant short-chain alkane species released (e.g., methane, ethane, and propane). Supported Pd-based oxidation catalysts are generally considered the most active materials for the complete oxidation of low molecular weight alkanes at temperatures typical of lean-burn NG exhaust. However, these catalysts rapidly degrade under realistic exhaust conditions with high water vapor concentrations and traces of sulfur.

Studies have shown that there are a significant number of chemical species present in engine exhaust particulate matter emissions. Additionally, the majority of current world-wide regulatory methods for measuring engine particulate emissions are gravimetrically based. As modern engines considerably reduce particulate mass emissions, these methods become less stable and begin to display higher levels of measurement uncertainty. In this study, a characterization of mass emissions from three heavy-duty diesel engines, with a range of particulate emission levels, was made in order to gain a better understanding of the variability and uncertainty associated with common mass measurement methods, as well as how well these methods compare with each other. Two gravimetric mass measurement methods and a reconstructed mass method were analyzed as part of the present study.

Diesel particulate filters are designed to reduce the mass emissions of diesel particulate matter and have been proven to be effective in this respect. Not much is known, however, about their effects on other unregulated chemical species. This study utilized source dilution sampling techniques to evaluate the effects of a catalyzed diesel particulate filter on a wide spectrum of chemical emissions from a heavy-duty diesel engine. The species analyzed included both criteria and unregulated compounds such as particulate matter (PM), carbon monoxide (CO), hydrocarbons (HC), inorganic ions, trace metallic compounds, elemental and organic carbon (EC and OC), polycyclic aromatic hydrocarbons (PAHs), and other organic compounds. Results showed a significant reduction for the emissions of PM mass, CO, HC, metals, EC, OC, and PAHs.

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.

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.

Light absorbing components of aerosols, often called black carbon (BC), are emitted from combustion sources and are believed to play a considerable role in direct atmospheric radiative forcing by a number of climate scientists. In addition, it has been shown that BC is associated with adverse health effects in a number of epidemiological studies. Although the optical properties (both absorbing and scattering) of combustion aerosols are needed in order to accurately assess the impact of emissions on radiative forcing, many models use radiative properties of diesel particulate matter that were determined over two decades ago. In response to concerns of the human health impacts of particulate matter (PM), regulatory bodies around the world have significantly tightened PM emission limits for diesel engines. These requirements have resulted in considerable changes in engine technology requiring updated BC measurements from modern engines equipped with aftertreatment systems.

With the on- and off-road diesel engine emission regulations getting more stringent across the world, diesel aftertreatment systems are expected to deliver outstanding performance and reliability. These objectives should be met by fulfilling tight packaging constraints and incurring only modest material and testing costs. A major strategy for meeting these often conflicting requirements is the effective use of simulation tools such as computational fluid dynamics (CFD) in system design and performance evaluation. Prerequisites for using this CFD analysis-led-design approach, however, are knowledge of the confidence level of the predictions and knowledge of the appropriate transfer functions that establish the relationships between the measured performance parameters and model predictions. The primary aim of the present work is to develop statistically and physically relevant measures that assess the uniformity of flow in aftertreatment systems.

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.

A comparative analysis was made on the emissions from a 2004 and a 2007 heavy-duty diesel engine to determine how new engine and emissions technologies have affected the chemical compounds found in the exhaust gases. Representative samples were collected from a source dilution sampling system and analyzed for both criteria and unregulated gaseous and particulate emissions. Results have shown that the 2007 regulations compliant engine and emissions technology not only reduced the specifically regulated exhaust pollutants, but also significantly reduced the majority of unregulated chemical species. It is believed that these reductions were achieved through the use of engine optimization, aftertreatment system integration, and ultra-low sulfur diesel fuel.

Selective catalytic reduction (SCR) of oxides of nitrogen with ammonia gas is a key technology that is being favored to meet stringent NOx emission standards across the world. Typically, in this technology, a liquid mixture of urea and water - known as Diesel Exhaust Fluid (DEF) - is injected into the hot exhaust gases leading to atomization and subsequent spray processes. The water content vaporizes, while the urea content undergoes thermolysis and forms ammonia and isocyanic acid, that can form additional ammonia through hydrolysis. Due to the increasing interest in SCR technology, it is desirable to have capabilities to model these processes with reasonable accuracy to both improve the understanding of processes important to the aftertreatment and to aid in system optimization. In the present study, a multi-dimensional model is developed to simulate DEF spray processes and the conversion of urea to ammonia. The model is then implemented into a commercial CFD code.

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.

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.

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.

Regulations on methane emissions from lean-burn natural gas (NG) and lean-burn dual fuel (natural gas and diesel) engines are becoming more stringent due to methane’s strong greenhouse effect. Palladium-based oxidation catalysts are typically used for methane reduction due to their relative high reactivity under lean conditions. However, the catalytic activity of these catalysts is inhibited by the water vapor in exhaust and decreases over time from exposure to trace amounts of sulfur. The reduction of deactivated catalysts in a net rich environment is known to be able to regenerate the catalyst. In this work, a multicycle methane light-off & extinction test protocol was first developed to probe the catalyst reactivity and stability under simulated exhaust conditions. Then, the effect of two different regeneration gas compositions, denoted as regen-A and regen-B, was evaluated on a degreened catalyst and a catalyst previously tested on a natural gas engine.

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.

Natural gas powered vehicles are attractive in certain applications due to their lower emissions in general than conventional diesel engines and the low cost of natural gas. For stoichiometric natural gas engines, the aftertreatment system typically consists only of a three-way catalyst (TWC). However, increasingly stringent NOx and methane regulations challenge current TWC technologies. In this work, a catalyst reactor system with variable lean/rich switching capability was developed for evaluating TWCs for stoichiometric natural gas engines. The effect of varying frequency and duty-cycle during lean/rich gas switching experiments was measured with a hot-wire anemometer (HWA) due to its high sensitivity to gas thermal properties. A theoretical reactor gas dispersion model was then developed and validated with the HWA measurements. The model is capable of predicting the actual lean/rich gas exposure to the TWC under different testing conditions.

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.

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.

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.