Search Results

To meet increasingly stringent diesel engine emission regulations, diesel engines are required to use ultra-low sulfur diesel (ULSD) and are equipped with advanced aftertreatment systems. Cu-SSZ-13 zeolite catalysts are widely used as selective catalytic reduction (SCR) catalysts due to their high NOx reduction and excellent hydrothermal stability. However, active Cu sites of Cu-SSZ-13 catalysts can be poisoned by exposure to engine exhaust sulfur species. This poison effect can be mitigated with the use of ULSD and high temperature exposure from engine operation. On the other hand, ULSD is still not universally available where regulations require it, and vehicles may inadvertently operate with high sulfur diesel fuel (HSD) in some locations. The high concentration of exhaust sulfur species resulting from HSD combustion may rapidly poison the Cu-SSZ-13 SCR catalyst. In this study, the catalytic performance of a sulfur poisoned Cu-SSZ-13 SCR catalyst is analyzed.

Diesel engines have been identified as contributing to more than half of the transport sectors black carbon (BC) emissions in the US. This large contribution to atmospheric BC concentrations has raised concern about source specific emission rates, including off-highway engines. The European Union has recently implemented more stringent particulate regulations in the form of particle number via the Particle Measurement Programme (PMP) methodology. The PMP method counts the non-volatile fraction of particulate matter (PM) above 23 nm and below 2.5 μm via a condensation particle counter. This study evaluates a surrogate black carbon method which uses the PMP particle count method with a correlation factor to the BC fraction. The transient capable Magee Scientific Aethalometer (AE-33) 880 nm wavelength channel was used to determine the BC fraction.

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.

In this study, the formation and decomposition of ammonium nitrate (AN) on a state-of-the-art extruded vanadium-based SCR catalyst (V-SCR) under simulated exhaust conditions has been evaluated. Results show that AN readily forms and accumulates at temperatures below 200°C when exposed to NH3 and NO2. The rate of AN accumulation increases with decreasing temperature. A new low temperature NH3 release peak (not present following NH3 storage conditions with NH3 only) becomes apparent after AN accumulation at 100 and 125°C. This new NH3 release, with a peak release temperature of approximately 180°C, is evaluated in detail to better determine its origin. BET surface area, and thermal gravimetric analysis/differential scanning calorimetry (TGA/DSC), and reactor-based experiments are all used to characterize AN formed on the V-SCR catalyst in comparison to pure AN.

Diesel emission aftertreatment system is usually designed to meet stringent packaging constraints, rendering a difficult situation to achieve perfect flow distribution inside the catalytic unit. The non-uniform flow pattern leads to a mal-distribution of flow velocity, temperature, and gas species in catalyst unit. Some catalysts are exposed to harsh working environment, while the rest catalysts are underutilized. This lowers the efficiency of overall catalyst unit and thus requires an oversized system to meet emission requirements. The flow mal-distribution also accelerates the uneven catalyst degradation, lowering the system durability. Hence, a quantitative description of packaging impact on catalyst performance is critical to assess the system efficiency and durability. In the present work, a mapping method is developed to combine catalyst performance with computational fluid dynamics (CFD) simulation.

Advanced emission control systems for diesel engines usually include a combination of Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), and Ammonia Slip Catalyst (ASC). The performance of these catalysts individually, and of the aftertreatment system overall, is negatively affected by the presence of oxides of sulfur, originating from fuel and lubricant. In this paper, we illustrated some key aspects of sulfur interactions with the most commonly used types of catalysts in advanced aftertreatment systems. In particular, DOC can oxidize SO2 to SO3, collectively referred to as SOx, and store these sulfur containing species. The key functions of a DOC, such as the ability to oxidize NO and HC, are degraded upon SOx poisoning. The impact of sulfur poisoning on the catalytic functions of a DPF is qualitatively similar to DOC.

More stringent emission requirements for nonroad diesel engines both in the U.S. and Europe have spurred the development of engines and exhaust aftertreatment technologies. In this study, one such system consisting of a diesel oxidation catalyst, zeolite-based selective catalytic reduction catalyst, and an ammonia oxidation catalyst was evaluated using both nonroad transient and steady-state cycles in order to understand the emission characteristics of this configuration. Criteria pollutants were analyzed and particular attention was given to organic compound and NO2 emissions since both of these could be significantly affected by the absence of a diesel particulate filter that typically helps reduce semi-volatile and particle-phase organics and consumes NO2 via passive soot oxidation. Results are then presented on a detailed speciation of organic emissions including alkanes, cycloalkanes, aromatics, polycyclic aromatic hydrocarbons and their derivatives, and hopanes and steranes.

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.

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.

The oxidation of short-chain alkanes, such as methane, ethane, and propane, from the exhaust of lean-burn natural gas and lean-burn dual-fuel (natural gas and diesel) engines poses a unique challenge to the exhaust aftertreatment community. Emissions of these species are currently regulated by the US Environmental Protection Agency (EPA) as either methane (Greenhouse Gas Emissions Standards) or non-methane hydrocarbon (NMHC). However, the complete catalytic oxidation of short-chain alkanes is challenging due to their thermodynamic stability. The present study focuses on the oxidation of short-chain alkanes by vanadium-based and Cu/zeolite selective catalytic reduction (SCR) catalysts, generally utilized to control NOx emissions from lean-burn engines. Results reveal that these catalysts are active for short-chain alkane oxidation, albeit, at conversions lower than those generally reported in the literature for Pd-based catalysts, typically used for short-chain alkane conversion.

An advanced exhaust aftertreatment system (ATS) for Tier 4 compliant locomotive applications was successfully designed and developed for use on Cummins QSK95 engines. The engine and ATS were introduced in late 2016. This system provided nitrogen oxides (NOx) reduction capability in excess of 95%. Vanadia-based selective catalytic reduction (V-SCR) extruded catalyst technology was chosen over other readily available component technologies such as diesel oxidation catalyst (DOC) or a combination of DOC and SCR systems to address the stringent Tier 4 standards. In addition to NOx reduction, substantial oxidation of gaseous hydrocarbons (HCs) from unburnt fuel and lubricating oil soluble organic fraction (SOF) was also achieved. This dual functionality (oxidation and reduction capability) was one of the key factors in adopting this technology as the prime path and rendering it suitable for the harsh locomotive application environment.

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.

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.

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.

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.

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.

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.

After treatment (AT) system has evolved over the period of time with ever changing stringent emission norms. Systems are still developing to meet new evolving challenges of diesel engine to meet fuel economy & necessary power to drive the end application. Times have changed when the purpose of AT system was to take care of not only treating engine exhaust but also responsible for attenuation of engine propagated noise. The systems today have become sophisticated and smart enough to work wide range of test conditions & duty cycle to meet the emission norms. Current trend is to meet the performance targets by making these designs compact & less restrictive in terms of backpressure. This creates tradeoff within acoustics attenuation, performance parameters & backpressure offered by these devices. One of the major constraint in development of AT, is available customer packaging space & time to develop these designs in shortest period.

Tailpipe particle number (PN) emission limits for heavy-duty diesel engines have been introduced as part of the off-highway Stage V standards. To meet the required limits a diesel particulate filter (DPF) with high filtration efficiency is required. The DPF relies on formation of a soot cake layer on the channel walls to achieve this high filtration efficiency. Off highway Stage V certification cycles are significantly higher in temperature than their on-highway counterparts, leading to difficulty in creating and maintaining a soot cake in the DPF. Hence for these applications meeting particle number requirements is challenging. To meet the high filtration efficiency requirements the DPF will have to reduce mean pore size, pore standard deviation, and increase wall thickness, in turn increasing backpressure, which results in a fuel consumption penalty. Another option is to evaluate the impact of temperature stable ash accumulation on DPF filtration efficiency.