Showing papers on "NOx published in 2006"

Secondary organic aerosol formation from isoprene photooxidation.

Abstract: Recent work has shown that the atmospheric oxidation of isoprene (2-methyl-1,3-butadiene, C5H8) leads to the formation of secondary organic aerosol (SOA). In this study, the mechanism of SOA formation by isoprene photooxidation is comprehensively investigated, by measurements of SOA yields over a range of experimental conditions, namely isoprene and NOx concentrations. Hydrogen peroxide is used as the radical precursor, substantially constraining the observed gas-phase chemistry; all oxidation is dominated by the OH radical, and organic peroxy radicals (RO2) react only with HO2 (formed in the OH + H2O2 reaction) or NO concentrations, including NOx-free conditions. At high NOx, yields are found to decrease substantially with increasing [NOx], indicating the importance of RO2 chemistry in SOA formation. Under low-NOx conditions, SOA mass is observed to decay rapidly, a result of chemical reactions of semivolatile SOA components, most likely organic hydroperoxides.

Recent Advances in Catalytic DeNOX Science and Technology

Abstract: The catalytic removal of nitrogen oxide (NOx) under lean‐burn conditions is one of the most important targets in catalysis research. Some lean‐NOx control technologies such as the direct decomposition of NOx, NOx storage‐reduction (NSR), and selective catalytic reduction (SCR) using different reducing agents (diesel soot, NH3, or hydrocarbon) are described. The reaction mechanism of NSR, which is the most promising technology, together with some novel NSR catalysts is discussed. Some mechanisms of SCR of NOx by hydrocarbon (HC‐SCR) were classified into two categories: one is the adsorption/dissociation mechanism, and the other is the oxidation‐reduction mechanism. Based on the discussion of the reaction mechanism, the influence of some factors (catalyst support, metal loading, calcination temperature, catalyst preparation method, oxygen, reducing agents, water, and sulfur) on the activity of HC‐SCR catalyst is discussed. It seems that Ag/Al2O3 catalyst offers the most promising for SCR of NOx by hydrocarb...

Exhaust Emissions of Biodiesel, Petrodiesel, Neat Methyl Esters, and Alkanes in a New Technology Engine†

Abstract: Biodiesel is a renewable, alternative diesel fuel of domestic origin derived from a variety of fats and oils by a transesterification reaction; thus, it consists of the alkyl esters, usually methyl esters, of the fatty acids of the parent oil or fat. An advantage of biodiesel is its potential to significantly reduce most regulated exhaust emissions, including particulate matter (PM), with the exception of nitrogen oxides (NOx). In this work, three fatty acid methyl esters, neat methyl laurate, neat methyl palmitate, and technical grade methyl oleate, were selected for exhaust emissions testing in a heavy-duty 2003 six-cylinder 14 L diesel engine with exhaust gas recirculation. These fuels were compared with neat dodecane and hexadecane as well as commercial samples of biodiesel and low-sulfur petrodiesel as the base fuel, thus establishing for the first time a baseline of the exhaust emissions of neat hydrocarbon (alkane) fuels versus neat methyl esters. All fuels were tested over the heavy-duty diesel tr...

Advantages of Fuels with High Resistance to Auto-ignition in Late-injection, Low-temperature, Compression Ignition Combustion

Abstract: Oxides of nitrogen (NOx) and smoke can be simultaneously reduced in compression ignition engines by getting combustion to occur at low temperatures and by delaying the heat release till after the ...

NOx Reduction from Biodiesel Fuels

Abstract: The demand for energy around the world is increasing, specifically the demand for petroleum-based energy. Appeasing this growing energy demand without irreparably damaging the environment is of primary concern. With rising fuel prices and environmental concerns, alternative fuels could satisfy the need for renewable energy with low environmental impact. Some of the more popular alternative fuels for new vehicles are ethanol, hydrogen, and biodiesel. Although gasoline engines are expected to be replaced by hydrogen-powered fuel cells, compression-ignition engines, the diesel engines, are expected to remain in use for high-power applications because of limitations of hydrogen-storage densities. The viable environmental friendly alternative fuel for compression-ignition engines is methyl esters (commonly known as biodiesel), which is derived from vegetable oils or animal fats. Using biodiesel instead of conventional diesel fuel reduces emissions such as the overall life cycle of carbon dioxide (CO2), particu...

Influence of NO2 on the selective catalytic reduction of NO with ammonia over Fe-ZSM5

Abstract: The influence of NO2 on the selective catalytic reduction (SCR) of NO with ammonia was studied over Fe-ZSM5 coated on cordierite monolith. NO2 in the feed drastically enhanced the NOx removal efficiency (DeNOx) up to 600 °C, whereas the promoting effect was most pronounced at the low temperature end. The maximum activity was found for NO2/NOx = 50%, which is explained by the stoichiometry of the actual SCR reaction over Fe-ZSM5, requiring a NH3:NO:NO2 ratio of 2:1:1. In this context, it is a special feature of Fe-ZSM5 to keep this activity level almost up to NO2/NOx = 100%. The addition of NO2 to the feed gas was always accompanied by the production of N2O at lower and intermediate temperatures. The absence of N2O at the high temperature end is explained by the N2O decomposition and N2O-SCR reaction. Water and oxygen influence the SCR reaction indirectly. Oxygen enhances the oxidation of NO to NO2 and water suppresses the oxidation of NO to NO2, which is an essential preceding step of the actual SCR reaction for NO2/NOx

Characterization of Partially Premixed Combustion

Abstract: Partially Premixed Combustion (PPC) provides the potential of simultaneous reduction of NOx and soot for diesel engines. This work attempts to characterize the operating range and conditions required for PPC. The characterization is based on the evaluation of emission and in-cylinder measurement data of engine experiments. It is shown that the combination of low compression ratio, high EGR rate and engine operation close to stoichiometric conditions enables simultaneous NOx and soot reduction at loads of 8bar, 12bar, and 15bar IMEP gross. The departure from the conventional NOx-soot trade-off curve has to be paid with a decline in combustion efficiency and a rise in HC and CO emissions. It is shown that the low soot levels of PPC come along with long ignition delay and low combustion temperature. A further result of this work is that higher inlet pressure broadens the operating range of Partially Premixed Combustion.

Selective catalytic reduction of NOx with NH3 over Cu-ZSM-5—The effect of changing the gas composition

Abstract: The selective catalytic reduction of nitrogen oxides (NOx) with ammonia over ZSM-5 catalysts was studied with and without water vapor. The activity of H-, Na- and Cu-ZSM-5 was compared and the result showed that the activity was greatly enhanced by the introduction of copper ions. A comparison between Cu-ZSM-5 of different silica to alumina ratios was also performed. The highest NO conversion was observed over the sample with the lowest silica to alumina ratio and the highest copper content. Further studies were performed with the Cu-ZSM-5-27 (silica/alumina = 27) sample to investigate the effect of changes in the feed gas. Oxygen improves the activity at temperatures below 250 °C, but at higher temperatures O2 decreases the activity. The presence of water enhances the NO reduction, especially at high temperature. It is important to use about equal amounts of nitrogen oxides and ammonia at 175 °C to avoid ammonia slip and a blocking effect, but also to have high enough concentration to reduce the NOx. At high temperature higher NH3 concentrations result in additional NOx reduction since more NH3 becomes available for the NO reduction. At these higher temperatures ammonia oxidation increases so that there is no ammonia slip. Exposing the catalyst to equimolecular amounts of NO and NO2 increases the conversion of NOx, but causes an increased formation of N2O.

Effects of changing power plant NOx emissions on ozone in the eastern United States: Proof of concept

Abstract: [1] Recent decreases in nitrogen oxide (NOx = NO + NO2) emissions from eastern U.S. power plants and their effects on regional ozone are studied. Using the EPA 1999 National Emission Inventory as a reference emission data set, NOx and sulfur dioxide (SO2) emission rates at selected power plants are updated to their summer 2003 levels using Continuous Emission Monitoring System (CEMS) measurements. The validity of the CEMS data is established by comparison to observations made on the NOAA WP-3 aircraft as part of the 2004 New England Air Quality Study. The impacts of power plant NOx emission decreases on O3 are investigated using the WRF-Chem regional chemical forecast model. Summertime NOx emission rates decreased by approximately 50% between 1999 and 2003 at the subset of power plants studied. The impact of NOx emission reductions on ozone was moderate during summer 2004 because of relatively cool temperatures and frequent synoptic disturbances. Effects in individual plant plumes vary depending on the plant's NOx emission strength, the proximity of other NOx sources, and the availability of volatile organic compounds (VOCs) and sunlight. This study provides insight into the ozone changes that can be anticipated as power plant NOx emission reductions continue to be implemented throughout the United States.

Investigation of the impact of biodiesel fuelling on NOx emissions using an optical direct injection diesel engine

Abstract: The impact of biodiesel fuelling on NOx emissions was investigated using an optically accessible diesel engine. A soy-based biodiesel (B100) and three separate primary reference fuel (PRF) blends were evaluated over a range of loads at an engine speed of 800 r/min. Experimental operating conditions were carefully controlled to maintain a constant start of combustion (SOC), and a PRF blend was identified that would eliminate differences in premixed-burn fraction. A load-averaged NOx increase of ∼10 per cent was observed for B100 relative to the PRF blend with matched premixed-burn fraction. The results indicate that factors other than SOC and premixed-burn fraction affect the tendency for biodiesel to increase NOx. Equilibrium calculations reveal no significant differences in stoichiometric adiabatic flame temperature between the test fuels; however, experimental data suggest that actual flame temperatures may be influenced by differences in soot radiative heat transfer. The effect of biodiesel on ...

Selective catalytic reduction of nitrogen oxides by ammonia on iron oxide catalysts

Abstract: In this study, new Fe 2 O 3 based materials are developed for the selective catalytic reduction (SCR) of NO x by NH 3 in diesel exhaust. As a result of the catalyst screening, performed in a synthetic model exhaust, ZrO 2 is considered to be the most effective carrier for Fe 2 O 3 . The modification of the Fe 2 O 3 /ZrO 2 system with tungsten leads to drastic increase of SCR performance as well as pronounced thermal stability. These results show that tungsten acts as bifunctional component. The highest catalytic activity is observed for ZrO 2 that is coated with 1.4 mol% Fe 2 O 3 and 7.0 mol% WO 3 (1.4Fe/7.0W/Zr). By the use of this catalyst quantitative conversion of NO x is obtained between 285 and 430 °C with selective formation of N 2 . Here, the turnover frequency of NO x per Fe atom is found to be 35 × 10 −5 s −1 that indicates a high catalytic performance. The SCR activity of the 1.4Fe/7.0W/Zr material is decreased in the presence of H 2 O and CO 2 , whereas it is increased by NO 2 . Temperature programmed reduction by H 2 (HTPR) analyses show that the Fe sites of the 1.4Fe/7.0W/Zr catalyst are mainly in the form of crystalline Fe 2 O 3 , whereby relatively small oxide entities are also present. The strongly aggregated Fe 2 O 3 species are associated with the presence of the promoter tungsten. Based upon stationary catalytic examinations as well as diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) studies we postulate an Eley Rideal type mechanism for SCR on 1.4Fe/7.0W/Zr catalyst. The mechanistic model includes a redox cycle of the active Fe sites. As first reaction step, we assume dissociative adsorption of NH 3 that leads to partial reduction of the iron as well as to production of very reactive amide surface species. These amide intermediates are supposed to react with gaseous NO to form N 2 and H 2 O. In the final step, the reduced Fe sites be regenerated by oxidation with O 2 . As a side reaction of SCR, imide species, originated from decomposition of amide, are oxidized by NO 2 or O 2 into NO.

Satellite-observed U.S. power plant NOx emission reductions and their impact on air quality

Abstract: [1] Nitrogen oxide (NOx) emissions resulting from fossil fuel combustion lead to unhealthy levels of near-surface ozone (O3). One of the largest U.S. sources, electric power generation, represented about 25% of the U.S. anthropogenic NOx emissions in 1999. Here we show that space-based instruments observed declining regional NOx levels between 1999 and 2005 in response to the recent implementation of pollution controls by utility companies in the eastern U.S. Satellite-retrieved summertime nitrogen dioxide (NO2) columns and bottom-up emission estimates show larger decreases in the Ohio River Valley, where power plants dominate NOx emissions, than in the northeast U.S. urban corridor. Model simulations predict lower O3 across much of the eastern U.S. in response to these emission reductions.

Effects on Particle Size Distribution from the Diesel Engine Operating on RME-Biodiesel with EGR

Abstract: In the present study, the effects of the neat biodiesel (rapeseed methyl ester, RME) fueled diesel engine with the use of EGR on the particle size distribution were examined The combustion of REM significantly improves the engine smoke and total particle mass but increases both NOx and particle concentration with low aerodynamic diameters (<0091 μm) when compared to the diesel (ultralow sulfur diesel, ULSD) fueled engine Although the particle size and mass distribution were not affected significantly by the different EGR additions, the particle total number and mass were increased considerably for both fuels For the RME fueled engine, the EGR addition reduces the particles in the lowest aerodynamic diameter measured (0046 μm) The use of EGR better suits the RME combustion, as apart from resulting in the higher NOx reduction, it maintained the smoke (soot, particulate matter) at relatively low levels The results are also confirming that it is challenging to reduce simultaneously total particle mass

Significant enhancements of nitrogen oxides, black carbon, and ozone in the North Atlantic lower free troposphere resulting from North American boreal wildfires

Abstract: enhancements of CO, BC, NOy and NOx, with levels up to 250 ppbv, 665 ng m 3 , 1100 pptv and 135 pptv, respectively. Enhancement ratios relative to CO were variable in the plumes sampled, most likely because of variations in wildfire emissions and removalprocessesduringtransport.AnalysesofDBC/DCO,DNOy/DCOandDNOx/DCO ratios indicate that NOy and BC were on average efficiently exported in these plumes and suggest that decomposition of PAN to NOx was a significant source of NOx. High levels of NOx suggest continuing formation of O3 in these well-aged plumes. O3 levels were also significantly enhanced in the plumes, reaching up to 75 ppbv. Analysis of DO3/DCO ratios showed distinct behaviors of O3 in the plumes, which varied from significant to lower O3 production. We identify several potential reasons for the complex effects of boreal wildfire emissions on O3 and conclude that this behavior needs to be explored further in the future. These observations demonstrate that boreal wildfire emissions significantly contributed to the NOx and O3 budgets in the central North Atlantic lower free troposphere during summer 2004 and imply large-scale impacts on direct radiative forcing of the atmosphere and on tropospheric NOx and O3.

Analysis of the Injection of Urea-Water-Solution for Automotive SCR DeNOx-Systems: Modeling of Two-Phase Flow and Spray/Wall-Interaction

Abstract: The selective catalytic reduction (SCR) based on ureawater-solution is an effective technique to reduce nitrogen oxides (NOx) emitted from diesel engines. A 3D numerical computer model of the injection of urea-water-solution and their interaction with the exhaust gas flow and exhaust tubing is developed to evaluate different configurations during the development process of such a DeNOxsystem. The model accounts for all relevant processes appearing from the injection point to the entrance of the SCR-catalyst:

Investigation of the selective catalytic reduction of NO by NH3 on Fe-ZSM5 monolith catalysts

Abstract: Fe-ZSM5 coated on cordierite monolith was investigated in the selective catalytic reduction (SCR) of NO with ammonia over a broad temperature range, applying simulated diesel exhaust gas conditions. The catalyst exhibited over 80% NOx reduction (DeNOx) from 400 to 650 °C at very good selectivity. The dosage of variable amounts of ammonia in the catalytic tests revealed that the SCR reaction is inhibited by ammonia. At very high temperatures DeNOx is reduced due to the selective catalytic oxidation (SCO) of ammonia to nitrogen and the oxidation to NO. Water-free experiments resulted in generally higher DeNOx values, which are explained by the inhibiting effect of water on the NO oxidation capability of Fe-ZSM5. The catalyst was stable upon thermal ageing and only 5–15% loss in DeNOx activity was observed after hydrothermal treatment. This loss in DeNOx is in parallel with a loss of ammonia storage capacity of the aged catalyst. Characterization by NH3 TPD and MAS 27Al NMR spectroscopy revealed dealumination of the zeolite by hydrothermal ageing, which reduces the Bronsted acidity of the catalyst.

Enhanced NOx in 2006 linked to strong upper stratospheric Arctic vortex

Abstract: [1] Measurements from the Atmospheric Chemistry Experiment show pronounced downward transport of NOx (NO+NO2) to the Arctic stratosphere in Feb–Mar 2006. NOx mixing ratios in the upper stratosphere were 3–6 times larger than observed previously in either the Arctic or Antarctic, aside from the extraordinary winter of 2003–2004. There was only minimal geomagnetic activity in late 2005 and early 2006, however, suggesting that NOx produced via energetic particle precipitation was not significantly elevated. On the other hand, the Arctic polar vortex at stratopause altitudes in Feb 2006 was exceptionally strong, implying greater confinement of air in the polar night. Carbon monoxide data also indicate enhanced confined descent of air from the mesosphere. These results confirm that impacts of EPP on the atmosphere are modulated by meteorological conditions; this has implications for understanding interannual variability and trends in stratospheric NOx and ozone.

Secondary Organic Carbon and Aerosol Yields from the Irradiations of Isoprene and α-Pinene in the Presence of NOx and SO2

Abstract: A laboratory study was carried out to investigate the secondary organic carbon (SOC) yields of α-pinene and isoprene in the presence of SO2, which produces acidic aerosol in the system. Experiments were based on irradiating each hydrocarbon (HC) with NOx in a 14.5 m3 smog chamber operated in the dynamic mode. The experimental design consisted of several multi-part experiments for each HC. In the first part of each experiment, an HC/NOx irradiation was conducted in the absence of SO2 and was followed by irradiations with the addition of SO2 in subsequent parts. Filter-based analyses for organic carbon were made using a thermal-optical approach either with an off-line instrument or in situ with an automated instrument. For isoprene in the absence of SO2, the SOC yield was approximately 0.001, a value consistent with earlier work from this laboratory. With the addition of up to 200 ppb SO2, the yield increased by a factor of 7. For α-pinene in the absence of SO2, the SOC yield of the irradiated mixture was f...

Low Temperature Combustion in a Heavy Duty Diesel Engine Using High Levels of EGR

Abstract: The possibilities for extending the range of engine loads in which soot and NOx emissions can be minimised by using low temperature combustion in conjunction with high levels of EGR was investigated in a series of experiments with a single cylinder research engine. The results show that very low levels of both soot and NOx emissions can be achieved at engine loads up to 50 % by reducing the compression ratio to 14 and applying high levels of EGR (up to approximately 60 %). Unfortunately, the low temperature combustion is accompanied by increases in fuel consumption and emissions of both HC and CO. However, these drawbacks can be reduced by advancing the injection timing. The research engine was a 2 litre direct injected (DI), supercharged, heavy duty, single cylinder diesel engine with a geometry based on Volvo's 12 litre engine, and the amount of EGR was increased by adjusting the exhaust back pressure while keeping the charge air pressure constant.