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Urea-selective catalytic reduction (SCR) catalysts are the leading aftertreatment technology for diesel engines, but there are major challenges associated with meeting future NOx emission standards, especially under transient drive cycle conditions that include large swings in exhaust temperatures. Here we present a simplified, transient, one-dimensional integral model of NOx reduction by NH₃ on a commercial small-pore Cu-zeolite urea-SCR catalyst for which detailed kinetic parameters have not been published. The model was developed and validated using data acquired from bench reactor experiments on a monolith core, following a transient SCR reactor protocol. The protocol incorporates NH₃ storage, NH₃ oxidation, NO oxidation and three global SCR reactions under isothermal conditions, at three space velocities and at three NH₃/NOx ratios.

One scenario for reducing engine out NOx in a spark ignition engine is to introduce small amounts of supplemental hydrogen to the combustion process. The supplemental hydrogen enables a gasoline engine to run lean where NOx emissions are significantly reduced and engine efficiency is increased relative to stoichiometric operation. This paper reports on a mass and energy balance model that has been developed to evaluate the overall system efficiencies of a thermal reformer-heat exchanger system capable of delivering hydrogen to the air intake of a gasoline engine. The mass and energy balance model is utilized to evaluate the conditions where energy losses associated with fuel reformation may be offset by increases in engine efficiencies.

With new legislation and federal regulation for vehicle emission levels, automotive and truck manufacturers have been prompted to focus on emission control technologies that limit the level of exhaust pollutants. One of the primary pollutants, especially from diesel engines, is oxides of nitrogen (NOx). One possible solution to this pollution challenge is to design a more efficient internal combustion engine, which would require better engine operating parameter controls. However, there are limitations associated with such tight engine management. This need has led researchers and engineers to focus on the development of exhaust aftertreatment devices that will reduce NOx emissions with current diesel engines. An optimum aftertreatment device must be unaffected by exhaust-gas impurity poisoning such as sulfur products, and must have minimal impact on vehicle operations and fuel economy.

We present here a phenomenological analysis of a cascade of two-step discharge-catalyst reactors. That is, each step of the cascade consists of a discharge reactor in series with a catalyst bed. These reactors are intended for use in the reduction of tailpipe emission of NOx from diesel engines. The discharge oxidizes NO to NO2, and partially oxidizes HC. The NO2 then reacts on the catalyst bed with hydrocarbons and partially oxidized HCs and is reduced to N2. The cascade may be essential because the best catalysts for this purpose that we have also convert significant fractions of the NO2 back to NO. As we show, reprocessing the gas may not only be necessary, but may also result in energy savings and increased device reliability.

Brønsted acidity of solution ion-exchanged and solid-state exchanged zeolites was compared for NaY, BaY, CaY, NaX, and CaX zeolites. These materials were chosen because they all exhibit catalytic activity in SCR of NOx in combination with a non-thermal plasma. Brønsted acidity was characterized qualitatively with retinol as an indicator dye. Our results show that the solid-state exchange using a chloride salt creates zeolites with lower acidity than zeolites obtained by conventional solution ion-exchange. NO2 adsorption was also found to create a significant quantity of acid sites at room temperature and a slight increase in acidity at 200°C. We speculate that the acid sites created by NO2 adsorption, because of their vicinity to metal cation sites in the zeolite, may lead to preferential reactions that lead to NOx reduction. BaY made by solution ion-exchange and BaY made by solid-state exchange using a chloride salt were tested for NOx reduction in a plasma-catalyst reactor system.

Projected NOx and fuel costs are compared for a plasma-catalyst system and an active lean NOx catalyst system. Comparisons are based on modeling of FTP cycle performance. The model uses steady state laboratory device characteristics, combined with measured vehicle exhaust data to predict NOx conversion efficiency and fuel economy penalties. The plasma system uses a proprietary catalyst downstream of a plasma discharge. The active lean NOx catalyst uses a catalyst along with addition of hydrocarbons to the exhaust. For the plasma catalyst system, NOx conversion is available over a wide temperature range. Increased electrical power improves conversion but degrades vehicle fuel economy; 10 J/L energy deposition costs roughly 3% fuel economy. Improved efficiency is also available with larger catalyst size or increased exhaust hydrocarbon content. For the active lean NOx system, NOx conversion is available only in a narrow temperature range.

A double dielectric barrier discharge reactor driven by an alternating voltage is a relatively simple approach to promote oxidation of NO to NO2 for subsequent reduction in a catalyst bed. The chemical performance of such a non-thermal plasma reactor is determined by its current and electric field behavior in the gap, and by the fraction of the current carried by electrons, because the key reactants which initiate the NO oxidation and accompanying chemical changes are produced there, mostly by electron impact. We have tried to determine by models and experiments the bounds on performance of double dielectric barrier reactors and guidelines for optimization. Models reported here predict chemical results from time-resolved applied voltage and series sense capacitor data.

Recent work has shown that energy efficiencies as well as yields and selectivities of the NOx reduction reaction can be enhanced by combining a plasma discharge with select catalysts. While analysis of gas phase species with a chemiluminescent NOx meter and mass spectrometer show that significant removal of NOx is achieved, high background concentrations of nitrogen preclude the measurement of nitrogen produced from NOx reduction. Results presented in this paper show that N2 from NOx reduction can be measured if background N2 is replaced with helium. Nitrogen production results are presented for a catalyst system where the catalyst is in the plasma region and where the catalyst is downstream from the plasma. The amount of N2 produced is compared with the amount of NOx removed as measured by the chemiluminescent NOx meter. The measured nitrogen from NOx reduction accounts for at least 40% of the total NOx removed for both reactor configurations.

NOx reduction under simulated lean burn conditions was studied using a non-thermal plasma in combination with zeolite and alumina catalysts. The influence of temperature and plasma treatment on the catalytic performance was investigated. Zeolite catalyst B showed high activity in the 150-300°C temperature region. Alumina Catalyst D was most active at temperatures higher than 250°C. In addition, the alumina catalyst was effective in oxidation of aldehydes formed during plasma treatment of the reaction mixture. When the reaction was carried out over a catalyst bed consisting of separate layers of the zeolite and alumina catalysts, the catalyst temperature range for significant NOx reduction was expanded to 150-500°C.

With ever more stringent CO2 emissions mandates, many automobile manufacturers are seeking the fuel economy benefits of diesel and lean-burn gasoline engines. At the same time the emissions standards that diesel and gasoline engines will have to meet in the next decade continue to reduce. Proposed solutions for meeting the stringent emissions standards all appear to have limitations, such as propensities to poisoning from sulfur, narrow operating temperature windows, and requirements for controls that give rapid rich excursions. Non-thermal plasma-catalyst systems have shown good performance in bench testing while being largely unaffected by these same issues. A two-stage system with a unique non-thermal plasma reactor combined with a zeolite-based catalyst has been constructed and shown to work over a wide temperature range.

The Office of Heavy Vehicle Technologies supports research to enable high-efficiency diesel engines to meet future emissions regulations, thus clearing the way for their use in light trucks as well as continuing as the most efficient powerplant for freight-haulers. Compliance with Tier 2 emission regulations for light-duty vehicles will require effective exhaust emission controls (aftertreatment) for diesels in these applications. Diesel-powered heavy trucks face a similar situation for the 2007 regulations announced by EPA in December 2000. DOE laboratories are working with industry to improve emission control technologies in projects ranging from application of new diagnostics for elucidating key mechanisms, to development and evaluation of prototype devices. This paper provides an overview of these R&D efforts, with examples of key findings and developments.

Conventional diesel engines will continue to hold a vital role in the heavy- and medium-duty markets for the transportation of goods along with many other uses. The ability to offset traditional diesel fuels with low-net-carbon biofuels could have a significant impact on reducing the carbon footprint of these vehicles. A prior study screened several hundred candidate biofuel blendstocks based on required diesel blendstock properties and identified 12 as the most promising. Eight representative biofuel blendstocks were blended at a 30% volumetric concentration with EPA certification ultra-low-sulfur diesel (ULSD) and were investigated for emissions and fuel efficiency performance. This study used a single cylinder engine (based on the Ford 6.7L engine) using Conventional Diesel Combustion (CDC), also known as Mixing Control Compression Ignition (MCCI). The density, cetane number, distillation curve and sooting tendency (using the yield sooting index method) of the fuels were measured.

The CRC Fuels for Advanced Combustion Engines working group has worked to identify a matrix of research diesel fuels for use in advanced combustion research applications. Nine fuels were specified and formulated to investigate the effects of cetane number aromatic content and 90% distillation fraction. Standard ASTM analyses were performed on the fuels as well as GC/MS and1H/13C NMR analyses and thermodynamic characterizations. Details of the actual results of the fuel formulations compared with the design values are presented, as well as results from standard analyses, such as heating value, viscosity and density. Cetane number characterizations were accomplished by using both the engine method and the Ignition Quality Tester (IQT™) apparatus.

Synergies between various catalytic converters such as SCR and DPF are vital to the success of an integrated aftertreatment system for simultaneous NO and particulate matter control in diesel engines. Several issues such as hydrocarbon poisoning, thermal aging and other coupled aftertreatment dynamics need to be addressed to develop an effective emission control system. This work is significant especially in an integrated DPF-SCR aftertreatment scenario where the SCR catalyst on the filter substrate is exposed to un-burnt diesel hydrocarbons during active regeneration of the particulate filter. This paper reports an experimental and modeling study to understand the effect of hydrocarbons on a Fe-zeolite urea-SCR catalyst. Several bench-reactor tests to understand the inhibition of NO oxidation, to characterize hydrocarbon storage and to investigate the impact of hydrocarbons on SCR reactions were conducted.

We present data in this paper showing that non-thermal plasma in combination with heterogeneous catalysis is a promising technique for the treatment of NOx in diesel exhaust. Using a commonly available zeolite catalyst, sodium Y, to treat synthetic diesel exhaust we report approximately 50% chemical reduction of NOx over a broad, representative temperature range. We have measured the overall efficiency as a function of the temperature and hydrocarbon concentration. The direct detection of N2 and N2O when the background gas is replaced by helium confirms that true chemical reduction is occurring.

Almost one-third of the fuel energy is wasted through the exhaust of a vehicle. An efficient waste heat recovery (WHR) process will undoubtedly lead to improved fuel efficiency and reduced greenhouse gases (GHG) emission. Currently, there are multiple WHR technologies that are being investigated by various entities in the auto industry. One relatively simple device to extract heat energy from the exhaust is a heat exchanger. Heat exchangers are used in some automotive applications to transfer heat from the hot exhaust gas to the colder coolant fluid to raise the coolant temperature. The warmer coolant fluid can be used for several purposes such as; faster heating of the engine’s lubrication oil and transmission fluids during cold starts, and faster cabin heating, which in turn, can potentially improve the overall engine efficiency and reduce exhaust emissions.

Although the urea-SCR technology exhibits high NO reduction efficiency over a wide range of temperatures among the lean NO reduction technologies, further improvement in low-temperature performance is required to meet the future emission standards and to lower the system cost. In order to improve the catalyst technologies and optimize the system performance, it is critical to understand the reaction mechanisms and catalyst behaviors with respect to operating conditions. Urea-SCR catalysts exhibit poor NO reduction performance at low-temperature operating conditions (T ≺ 150°C). We postulate that the poor performance is either due to NH₃ storage inhibition by species like hydrocarbons or due to competitive adsorption between NH₃ and other adsorbates such as H₂O and hydrocarbons in the exhaust stream. In this paper we attempt to develop one-dimensional models to characterize inhibition and competitive adsorption in Fe-zeolite-based urea-SCR catalysts based on bench reactor experiments.

In the discharge-catalyst treatment of diesel exhaust the discharge chemistry is known to oxidize NO to NO2 as well as to produce partially oxidized hydrocarbons for the heterogeneous reduction step. We find NO2 to be much more easily reduced to N2 on our catalysts, as long as there is a sufficient supply of reductant present. Unfortunately we typically find that a fraction of the NO2 is only partially reduced back to NO. Since much of the original hydrocarbon survives both the plasma and our catalyst, a subsequent stage of plasma will oxidize NO back to NO2 while at the same time replenishing the supply of partially oxidized hydrocarbon for another stage of heterogeneous catalysis. We present experimental evidence illustrating the advantages of multi-step discharge-catalyst treatment of NOx in simulated diesel exhaust.

NOx reduction efficiency under simulated lean burn conditions is examined for a non-thermal plasma in combination with borosilicate glass, alumina, titania, Cu-ZSM-5 and Na-ZSM-5. The non-thermal plasma alone or with a packed bed of borosilicate glass beads converts NO to NO2 and partially oxidizes hydrocarbons. Alumina and Na-ZSM-5 reduce a maximum of 40% and 50% of NOx respectively; however, the energy cost is high for Na- ZSM-5. Cu-ZSM-5 converts less than 20% with a very high energy consumption. The anatase form of titania reduces up to 35% of NOx at a relatively high energy consumption (150J/L) when the catalyst is contained in the plasma region, but does not show any appreciable conversion when placed downstream from the reactor. This phenomenon is explained by photo-activation of anatase in the plasma.

The objective of this research is a detailed investigation of particulate sizing and number count from a spark-ignited, direct-injection (SIDI) engine at different operating conditions. The engine is a 549 [cc] single-cylinder, four-valve engine with a flat-top piston, fueled by Tier II EEE. A baseline engine operating condition, with a low number of particulates, was established and repeatability at this condition was ascertained. This baseline condition is specified as 2000 rpm, 320 kPa IMEP, 280 [°bTDC] end of injection (EOI), and 25 [°bTDC] ignition timing. The particle size distributions were recorded for particle sizes between 7 and 289 [nm]. The baseline particle size distribution was relatively flat, around 1E6 [dN/dlogDp], for particle diameters between 7 and 100 [nm], before dropping off to decreasing numbers at larger diameters. Distributions resulting from a matrix of different engine conditions were recorded.