Showing papers on "NOx published in 1978"

Loss of fixed nitrogen from soils by nitric oxide exhalation

Abstract: LABORATORY studies1–8 have indicated that chemical de-nitrification processes in nitrogen rich soils and nitrite solutions can produce NO or NO2 and perhaps methyl nitrite9. It has been suggested1–6 that self decomposition of nitrite produces various gaseous nitrogen compounds including nitric oxide (NO) and it was thought that NO was unlikely to escape from the soil because in aerobic soils NO is readily oxidised by molecular oxygen to NO2 and this in turn is rapidly adsorbed by soil materials and by soil water1,2. However the half life of oxidation is dependent on the NO concentration because it is a termolecular reaction10,11. At concentrations of 100 p.p.m. or greater (as in some studies) the half life for oxidation of NO to NO2 by atmospheric oxygen is one hour or less respectively, whereas at low concentrations (∼0.01 p.p.m.) the half life for this oxidation is of the order of 104 h. This variation in the oxidation rate by molecular oxygen explains why NO at low concentrations in the field can pass unoxidised from the soil to the atmosphere and perhaps explains why in some of the laboratory studies (at high concentrations) NO2 and not NO is detected. This NO exhalation in the field could not be detected previously due to the lack of a sufficiently sensitive measurement technique. We report here the first measurements indicating that NO is continuously exhaled from soils including ungrazed, unfertilised grassland. The measured rates of exhalation from the soil to the atmosphere are 0.06 to 0.73 × 10−11 kg nitrogen m−2 s−1 (equivalent to 0.2 to 2.3 kg N ha−1 yr−1). We show that this exhalation of NO is a significant source of nitrogen oxides (NOx) in the lower atmosphere as has been previously suggested12,13. These nitrogen oxides exert a direct influence on the ambient ozone and hydroxyl radical concentrations14 which in turn predominantly determine the oxidation rate of almost all substances in the troposphere.

The impact of the chlorocarbon industry on the ozone layer

Abstract: By means of calculations with a one-dimensional photochemical-diffusive model of the atmosphere a theoretical estimate is given of the present and the possible future impact of large sections of the chlorocarbon industry on the ozone layer. Our estimates for 1976 are that past chlorocarbon emissions may be responsible for a 1.5% reduction in the global total ozone content (0.8% by CFCl3 and CF2Cl2, 0.5% by CCl4, and 0.2% by CH3CCl3). This estimate was obtained by comparison with the ozone content of a model atmosphere without industrial chlorocarbon emissions. The effect of the nonindustrial gas CH3Cl can best be described by stating that without CH3Cl, there would be almost 1% more ozone in the atmosphere. Considerable attention should also be given to the atmospheric effects of expanding uses of CH3CCl3. The potential impact on the ozone layer of CHFCl2 and CHF2Cl emissions is also discussed. However, there are too many uncertainties regarding the tropospheric concentrations of OH and its role as a scavenger to assess the effect of a number of chlorocarbon compounds reliably. The effect of other chlorocarbon compounds (C2Cl4, C2HCl3, C2H5Cl, C2H4Cl2, CHCl3) on the ozone layer is estimated as being comparatively negligible. Model-calculated vertical distributions of a large number of constituents are compared with observations. Substantial deviations between some theoretical and reported concentrations exist, especially for NOx, CO, and ClO. Uncertainties in our knowledge of stratospheric chemistry are discussed. It is concluded that these uncertainties are sufficiently numerous to take the given predictions of ozone reductions with some reservations.

Experimental Reduction of NOx, Smoke, and BSFC in a Diesel Engine Using Uniquely Produced Water (0 - 80%) to Fuel Emulsion

Abstract: With the aid of static mixer and non-ionic emulsifying agent, a comparatively stable water-fuel emulsion was obtained. Engine performance in a 4 cycle direct injection engine using these fuels were studied. A large reduction of NOx concentration was obtained over the wide range of engine operations, in spite of increased ignition lag and rapid combustion. Furthermore, improvements of economy and reduction of exhaust smoke were obtained. The reduction of NOx concentration, fuel consumption and smoke were even more remarkable when compared with operating same engine with water fumigation.

Pollutant-free low temperature slurry combustion process utilizing the super-critical state

Abstract: A continuous process for the combustion of solid fuels in the presence of an aqueous liquid phase under conditions such that oxides of nitrogen are not formed and oxides of sulfur and particles of ash are effectively prevented from contaminating the gaseous products released to the atmosphere Fuel is charged as a slurry in alkaline aqueous solution and contacted with combustion air so that the catalytic properties of both water and alkali operate to permit rapid and complete combustion at comparatively low temperatures Temperatures in the adiabatic reactor are, however, permitted to exceed the critical temperature of the liquid phase Under the conditions of the process, formation of nitrogen oxides is negligible, sulfur in the fuel goes to sulfur trioxide which dissolves completely in the alkaline liquid phase which also retains particles of ash and unburned fuel The resulting flue gas is essentially free from objectionable pollutants Heat is made available at a temperature high enough to generate and superheat steam

Method for reducing NO{HD x {b emission to the atmosphere

Abstract: An improved method and apparatus for reducing NOx emissions to the atmosphere from stationary combustion sources. The improvement is accomplished by providing a plurality of zones and/or stages for injecting a suitable reducing gas and then injecting the reducing gas through one or more of said zones. The particular zone or zones actually used will be determined by temperature of the combustion effluent gas in the immediate vicinity thereof. Similarly, the exact composition of the reducing gas employed will be determined by the same temperature.

The effect of the HO 2 +NO reaction rate constant on one-dimensional model calculations of stratospheric ozone perturbations

Abstract: With the aid of a one-dimensional steady-state, stratospheric model we have calculated ozone changes coused by atmosphric injections of NOx, N2O and chlorofluoromethanes. Adopting the fast rate constant, for the reaction HO2+NO»OH+NO2 measured by Howard and Evenson, we calculate much smaller perturbations of the ozone layer by NOx and N2O additions than previously estimated, but about two times larger ozone reductions as a result of continued emissions of chlorofluoromethanes, CF2Cl2 and CFCl3. The model results are sensitive to adopted values for the rate coefficients for the reactions HO2+O3»OH+2O2 and OH+HO2»H2O+O2 and the eddy diffusion profile near the tropopause. More accurate assessments of ozone perturbations require the development of photochemical models that incorporate meteorological processes in more than one dimension.

Two-stage catalysis of engine exhaust

Abstract: The invention relates to reduction of nitric oxide in exhausts from hydrocarbon burning engines. The nitric oxide is reacted with ammonia over a first catalyst and then the excess ammonia is reacted with oxygen present in the exhaust gas over a second catalyst. The resulting effluent stream has greatly reduced nitric oxide content without having an objectionable content.

Conversion of nitrogen oxides

Abstract: Zeolite catalyzed reduction of nitrogen oxides in exhaust gases is conducted with catalytic elements in the form of multi-channel structures in which parallel channels are defined by thin walls constituted by refractory oxides having zeolite dispersed therein and accessable to diffusion from surfaces of the channel walls. Such structures, preferably monolithic honeycomb forms, are prepared by calcining extruded or cast forms or kaolin at elevated temperatures and treating the calcined kaolin honeycomb with a caustic solution to develop a desired zeolite within the wall members and etch the wall surfaces to provide diffusion paths to and from the embedded zeolite. Such structures are peculiarly suited to high space velocity processes such as reduction of nitrogen oxides in providing for protection of the zeolite catalyst against erosion by high velocity gas streams while also providing adequate diffusivity for reactants at the high space velocities typical of the known reaction between oxides of nitrogen and a reducing agent such as ammonia.

Effects of combustion-chamber surface temperature on the exhaust emissions of a single-cylinder spark-ignition engine

Abstract: The effect of combustion-chamber surface temperature on exhaust emissions was investigated for wide ranges of air/fuel ratio, speed and volumetric efficiency A single-cylinder research engine was operated on propane over a range of speed (1000 to 2500 r/min), volumetric efficiency (20% to 80%) and air/fuel ratio (13 to 225), while combustion-chamber surface temperature was varied independently It was found that oxides of nitrogen (NOx) emissions significantly increase with increasing surface temperature This effect is strongest at lean air/fuel ratios In rich mixtures, the demonstrated weak influence of surface temperature on NOx emissions is attributed to NO decomposition reactions occurring during the expansion stroke With the exception of the extremely lean condition (225 air/fuel ratio), the sensitivity of hydrocarbon emissions to surface temperature was found to be essentially independent of air/fuel ratio No significant effect of surface temperature on carbon monoxide emissions was found

Long-range transport of tropospheric ozone

Abstract: Models of ozone and other oxidants are suggested for episodes where air masses of continental origin reach the British Isles during fair weather in summer. It is shown that ozone stays at high levels for several days, allowing for transport over long distances (∼ 1,000 km). Ozone exhibits pronounced diurnal variation in air masses continuously mixed with precursor emissions, while the ozone level is almost constant in ageing air masses due to the rapid drop in NOX.

Method of decomposing nitrogen oxide (NO{HD x{b )

Abstract: A method of decomposing NOx which includes exciting effluent gas containing nitrogen and NOx, or nitrogen, NOx and oxygen and/or carbon dioxide, and so on, with microwave irradiation.

NOx Control in cracking catalyst regeneration

Abstract: The amount of NOx formed during regeneration of a cracking catalyst in the presence of a metallic carbon monoxide combustion catalyst is decreased without substantially adversely affecting the carbon monoxide combustion activity of the promoter by subjecting the combustion-promoting catalyst to steam treatment prior to employing it in the cracking catalyst regeneration operation.

Method and thin film semiconductor sensor for detecting NOx

Abstract: The concentration of NOx in a gaseous mixture is measured using a solid state sensor comprising a surface thin film of semiconductive material. In a preferred embodiment, the thin film semiconductor comprises tin oxide having an oxygen to tin atomic ratio of between 1.5 and 1.95, preferably between 1.8 and 1.9, and is formed by reactive sputtering from a tin or tin oxide target in an argon-oxygen atmosphere. The electrical resistance of the tin oxide thin film is highly sensitive to NOx species, but is essentially unaffected by the presence of other common gases such as CO, H2, O2, SO2, NH3 and hydrocarbons. Water vapor present in the mixture has a small effect upon the resistance of the film. The thin film tin oxide sensor may be used to measure NOx in air and, in one particularly advantageous aspect of this invention, is employed to measure NOx emissions in automotive exhaust gas.

Reaction and transport of nitrogen oxides in nitrous acid solutions

Abstract: Depletion of nitrous acid from its aqueous solution is studied over a wide range of experimental conditions. The rate and stoichiometry of this process are determined as a function of mass transfer characteristics of gas-liquid contacting devices. It is found that the depletion of nitrous acid is brought about by three different mechanisms: 1) simultaneous hydration of N2O4 and evolution of NO, both existing in equilibrium with HNO2, 2) desorption of nitrous acid molecules and 3) decomposition of HNO2 into NO and NO2 occurring in the vicinity of the liquid surface. A quantitative analysis is made using the various rate and equilibrium constants with the oxides of nitrogen. The relative importance of the three mechanisms and, hence, the rate and stoichiometry of the whole process vary with the mass transfer characteristics of the gas-liquid contactors. The rate constants of the hydration of N2O4 and of the decomposition of nitrous acid (2HNO2→NO+NO2+H2O) as well as the solubility of N2O4 were established.

Low nox coal burner

Abstract: An improved burner for reducing formation of nitric oxide in pulverized fuel furnaces, particularly coal furnaces. Aerodynamic spoilers extend into the wake of the primary air and fuel line to produce fuel-rich and air-rich zones near the burner. Less near-burner adiabatic combustion occurs and that which does occur, occurs fuel-rich. This reduces both the thermal formation of NO x and the chemically bound fuel nitrogen conversion to NO x . The improved apparatus may be readily added to existing burners with a minimum of modification, or incorporated into new burner designs.

Performance and NOx Emissions of Spark Ignited Combustion Engines Using Alternative Fuels—Quasi One-Dimensional Modeling I. Hydrogen Fueled Engines

Abstract: Hydrogen and methanol have been suggested as potential non-petroleum derived substitutes for current reciprocating engine fuels. The present paper reports the results of a computer simulation of the performance and NOx emissions of hydrogen fueled spark ignition engines. The engine combustion process is modeled by employing a semi-empirical turbulent flame speed expression. The NOx emissions are determined by integrating the chemical rate equations resulting from the extended Zeldovich mechanism over the boundary conditions determined by the cycle analysis. Hydrogen exhibits very rapid burning rates and the resulting high pressures and temperatures lead to fast NO formation and destruction rates. Maximum NO emissions are predicted for lean mixtures near φ = 0.8 in agreement with experimental observations. For richer mixtures rapid decomposition of NO during the expansion stroke lowers exhaust emissions. NOx control by exhaust gas recirculation is much more effective in lean mixtures than in stoic...

Pollutant-free low temperature combustion process having carbonaceous fuel suspended in alkaline aqueous solution

Abstract: A continuous process for the combustion of carbonaceous fuels under conditions such that oxides of nitrogen are not formed and oxides of sulfur and particles of ash are effectively prevented from contaminating the gaseous products released to the atmosphere. Fuel is charged as a slurry in alkaline aqueous solution and contacted with combustion air so that the catalytic properties of both water and alkali operate to permit rapid and complete combustion at unusually low temperatures. Useful heat is extracted from the heated mixture. At the low combustion temperatures, sulfur in the fuel oxidizes to the trioxide which dissolves completely in the alkaline liquid phase which also retains particles of ash and unburned fuel.

Method of producing plate-shaped catalyst unit for NOx reduction of exhaust gas

Abstract: The present invention relates to a method of producing a plate-shaped catalyst unit for NOx reduction of exhaust gas, wherein molten metal is sprayed upon surfaces of a metal plate allowing the molten metal to accumulate thereon to form rough surfaces, and the rough surfaces thus obtained are deposited with a catalytic substance for NOx reduction of exhaust gas. The catalyst units thus obtained are each disposed in parallel with the gas flow, and generally arranged across the gas flow and at intervals in the catalytic reactor which is placed in an exhaust gas duct and used as an apparatus for nitrogen oxides (NOx) reduction of exhaust gas.

Simultaneous treating method for desulfurization and denitration of flue gas

Abstract: PURPOSE:To prevent the lowering of the desulfurizing and denitrating capacity of the absorbing liquid, by generating a soluble sulfite by carrying out the thermal decomposition treatment, etc. to the deposited (crystallized) substance which is obtained by contacting the exhaust gas containing SOx and NOx with the absorbing liquid containing, for example, Na2SO3 and EDTA iron chelate compound and then by circulating this soluble sulfite to the absorbing liquid.

Conversion of fuels containing nitrogen to oxides of nitrogen in hydrogen and methane flames

Abstract: Nitrogen-containing compounds such as hydrogen cyanide, acetonitrile, acrylonitrile, pyridine, benzonitrile, ammonia and methylamine, which are typical of the products likely to be encountered during the decomposition of nitrogen-containing polymers in fires, have been introduced into hydrogen and methane flames burning in oxygen-argon atmospheres. There is a complete conversion of fuel nitrogen in all cases to oxides of nitrogen and molecular nitrogen. The relative conversion to oxides of nitrogen (as NOx/N2) increases as the injection rate of nitrogen-containing fuels is decreased. The relative yields of oxides of nitrogen tend to be similar with methane and hydrogen premixed flames and markedly greater than observed with hydrogen diffusion flame. In all cases the yield of oxides of nitrogen-containing products such as hydrogen cyanide can also present a toxic risk during the burning of nitrogen-containing polymers, particularly when high temperature are involved. The combustion of these products in flame zones cannot be assumed to alleviate the additional toxic risk because of their conversion to oxides of nitrogen.

The influence of operating variables and prechamber size on combustion in a prechamber stratified-charge engine

Abstract: Experimental and computer simulation studies were conducted to analyze the combustion process in the prechamber, three-valve, stratified-charge engine. Prechamber and main-chamber pressure data and matched computer simulation calculations were used to determine effects of variations in overall air/fuel ratio, engine speed and load, and prechamber volume and orifice diameter on parameters defining the combustion process (spark advance for optimum torque, ignition delay, and combustion duration); on cylinder pressure diagrams (mean main-chamber pressure, mean pressure difference across the orifice, and cycle-by-cycle pressure fluctuations); and on exhaust emissions. Observed trends in combustion parameters and exhaust emissions showed that ignition delay, main combustion duration, and spark advance for maximum brake torque (MBT) timing increased with increasing overall air/fuel ratio, with increasing engine speed, and with decreasing engine load. Nitrogen oxide (NOx) emissions decreased with increasing overall air/fuel ratio (in lean operation) and increased somewhat with increasing engine speed and load. The overall air/fuel ratio had a much stronger influence on combustion parameters and exhaust emissions than did engine speed or load. Combustion duration exhibited only a modest change, even with varying the overall air/fuel ratio. Spark advance for MBT timing, ignition delay, and main combustion duration increased with increasing prechamber orifice size. These trends were attributed to a decrease in mixing rates in the prechamber and main chamber resulting from decreasing jet kinetic energy as orifice size increased. Cycle-to-cycle variation NOx emissions increased slightly with orifice size. The principal effect of increasing prechamber volume was leaning out of the air/fuel ratio in the main chamber. The only part of the normalized, mass fraction burned curve substantially altered by studied parametric variations was the ignition delay period (time of spark to 10% mass fraction burned). Data comparing combustion time to the mixing time calculated from the orifice flow kinetic energy are insufficient to demonstrate a proportional relationship.

Effect of changes in stratospheric water vapor on ozone reduction estimates

Abstract: Previous studies of the effect of water vapor on the destruction of ozone in the stratosphere perturbed by NOx or ClX pollutants did not include temperature feedback effects (i.e., they assumed a fixed temperature profile). These studies indicated that if an increase in stratospheric water vapor concentration were induced (perhaps as a result of an increase in the temperature of the tropical tropopause caused by a change in stratospheric ozone), there would be a significant further reduction in total ozone. Our results from using a one-dimensional transport kinetics model with a fixed temperature profile confirm these earlier findings. However, when the temperature profile is allowed to change as the species concentrations change, the sensitivity of total ozone to changes in water vapor abundance is greatly reduced. In the case of an NOx injection at 20 km there is even a reversal of sign such that an increase in stratospheric water vapor leads to an ozone increase relative to the case with no change in water vapor.

Nitric Oxide Formation in Gas Turbine Engines: A Theoretical and Experimental Study

Abstract: A modified Zeldovich kinetic scheme was used to predict nitric oxide formation in the burned gases. Nonuniformities in fuel-air ratio in the primary zone were accounted for by a distribution of fuel-air ratios. This was followed by one or more dilution zones in which a Monte Carlo calculation was employed to follow the mixing and dilution processes. Predictions of NOX emissions were compared with various available experimental data, and satisfactory agreement was achieved. In particular, the model is applied to the NASA swirl-can modular combustor. The operating characteristics of this combustor which can be inferred from the modeling predictions are described. Parametric studies are presented which examine the influence of the modeling parameters on the NOX emission level. A series of flow visualization experiments demonstrates the fuel droplet breakup and turbulent recirculation processes. A tracer experiment quantitatively follows the jets from the swirler as they move downstream and entrain surrounding gases. Techniques were developed for calculating both fuel-air ratio and degree of nonuniformity from measurements of CO2, CO, O2, and hydrocarbons. A burning experiment made use of these techniques to map out the flow field in terms of local equivalence ratio and mixture nonuniformity.

Uranium oxide prodn. by thermal decomposition of uranyl nitrate - with catalytic reduction of the nitrogen oxide(s) produced to provide heat for the process

Abstract: In the termal decomposition of uranyl nitrate into uranium oxide and oxides of nitrogen, the oxides of nitrogen produced are catalytically reduced to N2 and the resulting heat is utilised for the thermal decomposition of further uranyl nitrate. The process is autothermic and gives UO3 with sufficiently high reactivity for subsequent processing into UF6 in known manner. The process proceeds without the prodn. of contaminated effluents or of nitric acid which cannot be used in the process.

The Effect of Fuel Injection on NOx Emissions and Undesirable Combustion for Hydrogen-Fueled Piston Engines

Abstract: Direct cylinder injection for hydrogen-fueled piston engines was studied experimentally with an ASTM-CFR (Cooperative Fuel Research) engine. An injection scheme was devised for which the combustion occurs during the period of hydrogen injection so that little unburned hydrogen accumulates in the cylinder. This scheme should preclude flashback and preignition, and lowers the rate of cylinder pressure rise to acceptable levels. The potential of hydrogen as a low pollution fuel was investigated by comparing the NOx emissions from the same engine operated on hydrogen and hydrocarbon fuel. NOx emissions for hydrogen are very low provided the equivalence ratio is less than 0.5, and provided the hydrogen and air are well mixed. For equivalence ratios greater than 0.5, NOx emissions for hydrogen fuel were higher than for hydrocarbon fuel. With hydrogen injection, indicated mean effective pressure was varied between 0.07 MPa and 0.78 MPa without intake air throttling. Indicated efficiencies higher than 40% were achieved for part-load equivalence ratios, near 0.3. The timing of hydrogen injection has a significant effect on NOx emissions.

Development of a Hybrid Catalytic Combustor

Abstract: The pollution problems associated with unburned hydrocarbons and carbon monoxide in the idle mode, and NOx and smoke production in the power mode of aircraft gas turbine operation can be minimized using hybrid catalytic combustion. A hybrid catalytic combustor (HCC) consists of a fuel-rich precombustor, secondary air quenching zone, and monolithic catalyst stage which rapidly oxidizes CO and UHC produced in the precombustor. The concentration of thermally produced NOx in the precombustor is very low because of the lack of oxygen. However, the formation of NOx precursors such as HCN and NH3 produced under fuel rich conditions must be considered. Data showed that nitrogenous species produced in the rich precombustion zone were efficiently converted to NOx by catalysts under very lean mixture conditions. The equivalence ratio in the precombustor was varied from 0.5 to 1.5, while the overall mixture, after secondary air injection, was in the range of 01–0.3. The noble metal catalysts on various monolithic support geometries and compositions were found to be the most active materials for CO and UHC oxidation in the temperature range of 700–1200 K. The HCC combustion efficiency of JP-4 which contained 535-ppm sulfur was determined to be 99.8 percent under realistic conditions. The combustor pressure drop was less than 6 percent. The average emission indices of CO, UHC, and NOx leaving the HCC were on the order of 0.95, 0.43, and 1.8 g/kg of fuel, respectively, for metal supported Pt catalyst. This catalyst was effective in reducing CO by 86 percent and UHC by 94 percent, and increasing NOx by 68 percent. Using approximate methods for calculating EPA emission parameters, it was estimated that the HCC can meet the 1979 new aircraft emission standards but fails to meet the 1981 new aircraft emission standards because UHC are slightly too high.