NOx Production Research Articles

Effect of advanced intake valve closing on the thermo-chemical characteristics of the homogeneous combustion in a DME fueled HCCI engine

This numerical study was performed to analyze the thermo-chemical characteristics of homogeneous combustion on the effect of advanced intake valve closing timing in a DME fueled HCCI engine. To achieve this, the engine simulation was performed using the detailed chemical kinetic mechanism, including 453 reactions for dimethyl ether (CH3OCH3), and the modified NOX mechanism was applied to analyze the NOX reaction pathway of the DME combustion. The experimental study was performed to validate the engine analysis using a single cylinder CI engine with the injection timing of BTDC 40 degree and IVC timing of BTDC 128 degree. The injection quantity and pressure were set to 8 mg and 50 MPa at 1500 RPM, respectively. The results of engine performance such as cylinder pressure, cylinder temperature, heat release rate, and IMEP were decreased and the ISFC and ignition delay were increased when the IVC timing was advanced since the overall rates of a chemical reaction and the reaction rate of OH radicals are reduced. Especially, the reduction of CH2OCH2O2H radicals was a very important factor it affects the ignition delay in the low temperature reaction. Consequently, it influences the LTC and HTC reactions and makes a difference in the fuel oxidation rate and combustion reaction. Furthermore, the OH radicals also had the greatest effect to the CO oxidation and NOX production. The CO and NOX emissions were primarily occurred by the forward reactions of HCO + O2 → CO + HO2 and HO2 + NO → NO2 + OH during the combustion period, respectively. The chemical reactivity and CO oxidation reaction were reduced as the fuel mass fraction increased in the low combustion temperature. In addition, the reaction path of NOX emission related to the thermal NOX reaction did not occur due to the low combustion temperature. Thus, the thermo-chemical characteristics of the DME homogeneous combustion of this work suggest that the chemical reaction of fuel oxidation and exhaust emissions are limited as the effect of chemical oxidation rate, reaction rate, and the OH radical depending on the IVC timing changes.

Liquid petroleum gas flame in a double-swirl gas turbine model combustor: Lean blow-out, pollutant, preheating

In this paper, lean blow-out limits in a double swirl GT model combustor were investigated experimentally for liquid petroleum gas fuel. The lean blow-out curve was extracted for different combustor configurations. While burner could operate reasonably under ultra-lean conditions, two different sets of operating conditions, one with a low flow rate and another one with high flow rate, are identified and studied in terms of lean blow-out and pollutant. Results showed that while the flame structure was similar in both cases, the chamber responses to geometrical changes and also preheating are minimal at the low flow rate. That means confinement and injector type have desirable effects on stability borders but not for the low flow rate. The channeled injector shifted down the lean blow-out limit around 28% at high flow rate. Measurements on the combustor exhaust gas composition and temperature indicate a region with relatively complete combustion and reasonable temperature and a very low level of exhaust NOx pollutants (i. e., below 10 ppm) at about 25-50% above the lean blow-out. In this operating envelope, a burner power increment led to a higher exhaust average temperature and combustion efficiency, while NOx formation decreased. Preheating the inlet air up to 100?C results in an improvement in burner stability in about 10%, but NOx production intensifies more than three times. Results indicate that the lean blow-out limit is con-figured more by the burner design and aerodynamic aspects rather than the fuel type.

Numerical Simulation of a Naturally Aspirated Natural Gas/Diesel RCCI Engine for Investigating the Effects of Injection Timing on the Combustion and Emissions

Abstract The start of injection (SOI) timing has a significant effect on increasing the homogeneity of the air–fuel mixture in an reactivity controlled compression ignition (RCCI) engine. In this paper, the impact of the SOI timing from 14 deg to 74 deg before top dead center (bTDC) and different inlet valve closing (IVC) temperatures on natural gas/diesel RCCI performance and emissions have been studied. Also, the simulations carried out by avl fire which is coupled with chemical kinetics. The results showed that in the SOIs of 14 deg, 24 deg, and 34 deg bTDC, the fuel is sprayed into the piston bowl; however, in the SOI of 44 deg bTDC, the fuel collides the bowl rim edge, because of the downward movement of the piston. With the advancement of diesel SOI timing from 14 deg to 74 deg bTDC, two different combustion trends can be observed. However, this advancement leads to a lower CO emission, but it raises the CO2 emission level. Although the pressure is a primary parameter for NOx emission, the difference between the trends of NOx and pressure plots indicates that different factors affect the NOx production and also increase the IVC temperature, and raises the in-cylinder pressure, heat release rate, NOx and CO2 emissions, while it reduces the CO emission.

Observing U.S. Regional Variability in Lightning NO2 Production Rates

AbstractLightning is a large and variable source of nitrogen oxides (NOx ≡ NO + NO2) to the upper troposphere. Precise estimates of lightning NOx (LNOx) production rates are needed to constrain tropospheric oxidation chemistry; however, controls over LNOx variability are poorly understood. Here, we describe an observational analysis of variability in LNO2 with lightning type by exploiting U.S. regional differences in lightning characteristics in the Southeast, South Central, and North Central United States. We use satellite NO2 measurements from the Ozone Monitoring Instrument with Berkeley High Resolution vertical column densities, a combined lightning data set derived from the Earth Networks Total Lightning Network and National Lightning Detection NetworkTM measurements, and hourly winds from the European Centre for Medium‐Range Weather Forecasts climate reanalysis data set (ERA5) over May–August 2014–2015. We find evidence that cloud‐to‐ground (CG) strokes produce a factor of 9–11 more NO2 than intracloud (IC) strokes for storms with stroke rates of at least 2,800 strokes·cell−1·hr−1. We show that regional differences in LNO2 production rates are generally consistent with regional patterns CG and IC stroke frequency and stroke current density. A comparison of stroke‐based and flash‐based CG/IC LNO2 estimates suggests that CG LNO2 is potentially underestimated when derived with flash data due to the operational definition of CG lightning. We find that differences in peak current explain a large portion of CG/IC LNO2 variability, but that other factors must also be important, including minimum stroke rate. Because IC and CG strokes produce NOx in distinct areas of the atmosphere, we test the sensitivity of our results against the atmospheric NO2 vertical distribution assumed in the a priori profiles; we show that the relative CG to IC LNO2 was generally insensitive to the assumed NO2 vertical distribution.

Purification of Water and Air is Promoting Global Warming and Country Decline

Burning of fossil is increasing. Production of CO2 and NOx is increasing. Increased CO2 and NOx promoted the CO2 assimilation. Most produced CO2 is fixed by CO2 assimilation. But developed countries started purification of water and air by elimination of NOx and NP at around 1980. 6 billion tone NOx and 2 billion tone NP are eliminated. NOx is main nitrogen fertilizer and NP is main nitrogen and phosphorous fertilizer. Therefore plant growth is retarded. CO2 fix is retarded. CO2 is increasing. Food like grain, fish, and meat production is retarded. DGP increase rate decreased. Global warming and country decline are progressing. If developed countries stop NOx elimination by ammonia and close waste water purification station, global warming will stop and country decline will stop.

Synthesis and Characterization of Cobalt, Iron and Ruthenium Catalysts for the Production of Synthetic Diesel

Fossil fuels are currently the world's leading source of energy. Environmental legislations, the high price of fossil fuels, the concern about the supply of these fuels and technological development, makes it necessary to search for alternative sources of energy. The production of clean liquid fuels, such as synthetic diesel from synthesis gas, by Fischer-Tropsch (FT) method, is considered a very appropriate strategy for the solution of some of the inconveniences shown by fossil fuels. This method consists in the catalytic transformation of a gaseous mixture of CO and H2 into liquid fuels with variable chain lengths. The fuels produced by this process are clean, since they do not have aromatic compounds, sulphur or nitrogen-based compounds, preventing the production and release of NOx and SOx during combustion. FT processes involve the use of heterogeneous catalysts based on active metals (i.e., Co, Ru or Fe) highly dispersed on the surface of appropriate supports. In the present investigation, the synthesis of new catalysts has been carried out to produce synthetic diesel by means of FT processes. For this, spherical SiO2 particles have been used as support, on which nanoparticles of the different metals have been dispersed. The activity and selectivity of the synthesized catalysts was evaluated in FT processes under different experimental conditions.

CH Kinetics Measurements and Their Importance for Modeling Prompt NOx Formation in Gas Turbines

Abstract Recent work by the authors and others has uncovered the need for further chemical kinetic-related modeling and experiments, specifically for NOx kinetics at engine conditions. In particular, data on CH formation at realistic combustion conditions are needed for further refinement of the prompt-NOx kinetics. To this end, a series of shock-tube experiments to obtain CH concentration time histories at elevated temperatures was performed behind reflected shock waves at the Aerospace Corporation using a tunable laser. This Ti-Sapphire laser was operated in the near infrared at about 854 nm; blue light at 426.9 nm was obtained using an external, frequency-doubling crystal. The resulting light was used in a differential absorption setup with common-mode rejection to measure CH time histories. New measurements in CH4–C2H6–O2 mixtures highly diluted in argon were performed at temperatures between 1890 K and 2719 K. These new data are compared to several modern, detailed chemical kinetics mechanisms with updated NOx submechanisms. Sensitivity and rate of production analyses at the shock-tube conditions along with a gas turbine model are used to elucidate the current state of affairs in CH prediction by the literature models and its effect on NOx production, particularly through the prompt mechanism. A brief discussion of the chemical kinetics for an important reaction in the production of CH is also presented to emphasize the need for further study and refinement of reactions leading to CH production.

Design of new clean and efficient combustion mode and thermodynamics research using NSGA-II algorithm

In order to study a new clean and efficient combustion mode, which can relieve the pressure of traditional energy and ensure low emissions, in this study, a diesel/natural gas dual fuel engine is designed by non-dominant sorting genetic algorithm (NSGA-?), and its thermodynamic characteristics are studied. The WP10.290 Diesel engine is modified into a diesel/natural gas dual fuel engine. The emissions of harmful substances and thermal efficiency of the modified engine under different working conditions are compared. The combustion chamber structure and adaptability between combustion chamber and injection parameters are optimized by using NSGA-II algorithm and CFD software. The results show that the emission of NOx and CH4 and the fuel consumption rate can be reduced simultaneously by using the composite combustion model compared with the original engine. When the CH4 emission is close to zero, the fuel consumption rate decreases obviously, and NOx slightly increases. When the angle between the injection holes is 141.57? the amount of NOx in the cylinder is large. When the injection advance angle is 21.91?CA, the pressure in the cylinder is the highest, the CH4 production is the lowest, the NOx production is higher, and the oxygen content in the combustion mixture is less. The NOx production is the lowest. diesel/natural gas dual fuel engine can ensure efficient combustion while reducing emissions. In this study, the performance of the dual fuel engine at various speeds can be further studied, which can provide theoretical support for the design of diesel/natural gas dual fuel engine.

Baicalin improves the survival in endotoxic mice and inhibits the inflammatory responses in LPS-treated RAW 264.7 macrophages

Introduction: Sepsis is a severe disease with a high morbidity and mortality. Baicalin, an active compound of Chinese medicine, Scutellaria baicalensis Georgi (Huang Qui), exhibits several beneficial effects. In this study, we examined whether administration of baicalin increases the survival in mice with endotoxemia and investigated its anti-inflammatory mechanisms in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. Methods: The production of NOx, PGE2, and pro-inflammatory cytokines, the mRNA and protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), and the nuclear translocation of NF-κB in LPS-stimulated macrophages or endotoxic mice were determined. The model of severe endotoxic mice was established by injection of LPS (60 mg/kg, i.p.). Results: Baicalin significantly inhibited the production of NO, PGE2, and pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6 in LPS-stimulated macrophages. Baicalin treatment also markedly suppressed LPS-induced iNOS and COX-2 expression at the transcriptional and translational levels, and the nuclear translocation of NF-κB in macrophages. Similarly, the serum concentrations of NOx, PGE2, and pro-inflammatory cytokines, and the lung myeloperoxidase activity were greatly reduced in baicalin-treated endotoxic mice. Notably, after LPS injection, the 3-day survival rate of mice treated with pre- or post-administration of baicalin (50 mg/kg, i.p.) remarkably increased to 100% and 90%, respectively compared with LPS-injected alone mice with a survival rate of 0%. Conclusion: Baicalin has a potent anti-inflammatory activity in LPS-stimulated macrophages and endotoxic mice. Moreover, treatment with baicalin dramatically increased the survival in the severe septic mice, suggesting that baicalin may be a potential agent for sepsis therapy.

Characteristics and mechanism of toluene removal by double dielectric barrier discharge combined with an Fe2O3/TiO2/γ-Al2O3 catalyst

Removal of volatile organic compounds (VOCs) by non-thermal plasma technology produced by dielectric barrier discharge has become a hotspot due to its rapid reaction at room temperature, convenience without preheating and high removal efficiency of VOCs. Ways to improve the removal efficiency of mixed VOCs and the control of by-products in the discharge process are urgently needed. In view of the above shortcomings, the research progress of catalysts to improve the removal efficiency of VOCs by dielectric barrier discharge in recent years was reviewed; in this research, we conducted experiments on the removal efficiency of toluene under high flow rate experimental conditions (input voltage 10–70 V, mixed gas flow rate 1 m3 h−1, inlet concentration 1000 mg m−3). The research used γ-Al2O3, TiO2/γ-Al2O3 and Fe2O3/TiO2/γ-Al2O3 as catalysts in a reactor with a discharge gap of 6 mm, and a 99.7% removal efficiency of toluene was achieved when the SIE was 183.4 J L−1. The added catalyst significantly reduced the concentration of by-products. At the same time, experiments with multiple catalysts to improve the removal efficiency and the performance of the discharge effect under different humidity levels were analyzed. The removal efficiency of toluene was optimized and recyclable, the formation of by-products was effectively suppressed when the catalysts in the reactor were Fe2O3/TiO2/γ-Al2O3, TiO2/γ-Al2O3 and γ-Al2O3, and the discharge length was 1 : 2 : 2.

Lightning NOx Production in the Tropics as Determined Using OMI NO2 Retrievals and WWLLN Stroke Data

AbstractNitrogen oxide (NOx) production by lightning in the tropics is estimated using tropospheric NOx amounts (LNOx*) over deep convective grid boxes derived from Ozone Monitoring Instrument (OMI) nitrogen dioxide (NO2) slant columns and detection‐efficiency–adjusted World Wide Lightning Location Network (WWLLN) flashes. The lightning NOx production efficiency (LNOx PE) in the tropics is determined for the austral and boreal summers of 2007 to 2011 by regressing regional mean daily values of LNOx* for individual seasons against daily flash totals during flash windows prior to the OMI overpass. LNOx PE is determined to be approximately two times larger over marine locations than over continental locations possibly because marine flashes are more energetic. Overall, the mean LNOx PE for the tropics is calculated to be 170 ± 100 mol per flash with values over the tropical Pacific (low flash rate region) being largest. The main contributors to uncertainties in PE are uncertainties in WWLLN flash detection efficiency, upper tropospheric NOx lifetime in the near field of convection, and air mass factor biases.

Prediction of homogeneous combustion by modification of the fuel combustion mechanism in a DME fueled CI engine

This study was performed to predict numerically the homogeneous combustion characteristics where the fuel combustion mechanism was modified in a DME fueled CI engine. To achieve this, detailed chemical kinetic reaction mechanisms were used for the prediction of homogeneous combustion of hydrocarbon fuels (diesel and DME). The results were compared in terms of cylinder pressure, heat release rate, and CO and NOX emissions. Calculations were performed using the detailed chemical kinetic mechanism, including 671 species and 2933 reactions for n-heptane (n-C7H16) and 96 species and 453 reactions for dimethyl ether (CH3OCH3). In addition, a modified NOX mechanism was added to investigate the accumulated results of NOX production. The engine experiments were conducted using a single cylinder CI engine with a common-rail injection system. The fuel injection quantity was set to 8 mg, and the injection pressure was maintained at 50 MPa at 1500 RPM. In this study, DME and diesel fuels were injected for inducing the homogeneous combustion at BTDC 60 and BTDC 40 degree. The modified mechanism hardly affected the overall chemical reactions, which was almost identical in comparison to the results of the conventional mechanism. In addition, the ignition delay was slightly faster in the calculation of the n-heptane mechanism because it showed that a high reaction rate was involved in the fuel oxidation and reaction of the NTC region. The combustion and exhaust emission characteristics of the homogeneous combustion simulation were in good agreement with the engine experimental results at BTDC 60 degree of injection timing, but the CO emission was over predicted when the n-heptane mechanism was employed in the DME combustion simulation. The chemical reactions of the DME combustion process were dominated by the forward reaction, which were CH3OCH3+O→CH3OCH2+OH and CH3OCH3+OH→CH3OCH2+H2O reactions. Furthermore, this study confirmed that an increase of OH radicals promotes the fuel oxidation reaction, and it can influence the combustion temperature, which also affected the processes of NOX production and CO oxidation reactions.

Experimental and numerical evaluation of low-temperature combustion of bio-syngas

Environmental regulations have strongly incentivized the development of alternative technologies and renewable sources for the energy supply, including bio-syngas and low-temperature combustion. However, accurate estimation methods for low-temperature chemistry of these mixtures are still missing. Hence, experimental data with the limited impact of fluid dynamics aspects are strongly required. To this aim, the heat flux burner has been adopted in this work for the measurements of the laminar burning velocity. Data were compared to evaluate the accuracy of the kinetic mechanism developed at the University of Bologna (KIBO) and exiting mixing rules. Hirasawa's correlation has been found as the most reliable empirical correlation. Furthermore, the KIBO model has been validated and compared with existing models for the investigated conditions. These results have allowed for the evaluation of the effects of fuel composition on the preferable reaction paths and on the NOx production rate.

An updated short chemical‐kinetic nitrogen mechanism for carbon‐free combustion applications

Chemical-kinetic combustion mechanisms for hydrogen-oxygen-nitrogen systems, motivated originally by concerns about NOx emissions during hydrogen burning, have recently acquired renewed interest as a result of the possibility of employing ammonia-hydrogen mixtures in gas turbines and reciprocating engines as drop-in fuel to replace the use of natural gas. Specifically, this is of relevance to the implementation of engineering approaches for economical power generation with carbon sequestration or to large-scale energy-storage schemes, based on hydrogen or efficient hydrogen carriers such as ammonia. Because computational investigations are facilitated by short mechanisms (since the use of large mechanisms is often prohibitively expensive in reactive flow simulations), in response to the original concerns, a short nitrogen mechanism was developed in San Diego in the 1990s (not updated since 2004), without consideration of ammonia combustion. In view of the renewed interest in this topic, that mechanism has now been expanded to encompass 60 elementary steps among 19 reactive chemical species, including ammonia burning and NOx production, as reported herein, greatly improving predictions. With particular attention to high reactant temperatures and high-pressure conditions, relevant to industrial applications, it is shown that the present short mechanism retains satisfactory accuracy, exhibiting deviations that in most cases are within acceptable bounds (±20%). The revisions maintain the shortness of the original mechanism, adding only one more reactive species and six more elementary steps (while updating values of rate parameters of nine other steps, on the basis of newly available information). In addition, the short mechanism is applied herein to the analysis of fundamental combustion properties of ammonia/hydrogen/nitrogen-air laminar premixed flames, at unstrained and strained conditions, for comparison with methane-air flames as a reference gas-turbine fuel. It is found by comparing carbon-free and hydrocarbon laminar flames that these reactive mixtures, even if characterized by nearly identical adiabatic flame temperature and laminar flame speeds, nevertheless exhibit substantially different resistance to strain, with the ammonia/hydrogen flames exceeding the strain limit of methane flames by a factor of 5.

NOX reduction in an axially staged gas turbine model combustor through increase in the combustor exit Mach number

Advanced combustion technologies to limit NOX production are needed to meet rigorous emissions standards, which are required due to the harmful effect of NOX on the environment. One such advanced concept involves axially staging the fuel to create a staged combustion system. This paper reports on emissions measurements obtained for premixed natural gas and air reacting jets into vitiated crossflow with negligible swirl at conditions corresponding to elevated inlet temperatures of 500–600 K and an elevated combustor pressure of 500 kPa. A significant NOX reduction was achieved when the staged combustor exit Mach number was increased and the axial residence time was reduced. Based on this preliminary investigation, a test matrix was developed to independently vary the exit Mach number for a constant axial residence time by utilizing modular rig hardware to change the length of the axial combustor. Up to 70% reduction in NOX produced by the axial stage was observed when the combustor exit Mach number was increased from about 0.26 to 0.66 at a constant residence time of 1.4 ms. NOX reduction based on variation in the Mach number and at a constant residence time has not been previously reported in the literature to the best of our knowledge. This decrease in NOX is hypothesized to be due to the lower static temperature of a compressible flow and potentially better mixing of the jet with the crossflow due to the interaction occurring at high speeds. The effects of axial residence times on NOX emissions were also investigated at a constant Mach number of 0.44 for axial residence times between 0.8 and 2.3 ms. Varying the axial residence time was observed to have a strong effect on NOX emissions for exit total temperatures greater than 1900 K, which agrees well with existing trends.

Specific energy cost for nitrogen fixation as NOx using DC glow discharge in air

We report on factors influencing the specific energy costs of producing NOx from pin-to-pin DC glow discharges in air at atmospheric pressure. Discharge current, gap distance, gas flowrate, exterior tube wall temperature and the presence and position of activated Al2O3 catalyst powder were examined. The presence of heated catalyst adjacent to the plasma zone improved energy efficiency by as much as 20% at low flows, but the most energy efficient conditions were found at the highest flowrates that allowed a stable discharge (about 10–15 l min−1). Under these conditions, the catalyst had no effect on efficiency in the present study. The lowest specific energy cost was observed to be between about 200–250 GJ/tN. The transport of active chemical species and energy are likely key factors controlling the specific energy costs of NOx production in the presence of a catalyst. Air plasma device design and operating conditions must ensure that plasma-generated active intermediate chemical species transport is optimally coupled with catalytically active surfaces.

ROS directly activates transforming growth factor β type 1 receptor signalling in human vascular smooth muscle cells

BackgroundWidely used NAPDH oxidase (Nox) inhibitor, apocynin is a prodrug that needs to be converted to its pharmacologically active form by myeloperoxidase. In myeloperoxidase deficient non phagocytic cells such as vascular smooth muscle cells (VSMCs) apocynin stimulates the production of ROS. ROS is generated by the activation of many signalling pathways, thus we have used apocynin as a pharmacological tool to characterise the role of endogenous ROS in activating the transforming growth factor beta receptor (TGFBR1) without the activation of other pathways. MethodsThe in vitro study utilized human VSMCs. Western blotting and quantitative real time PCR were performed to assess signalling pathways and gene expression, respectively. Intracellular ROS levels was measured using fluorescence detection assay. ResultsTreatment with apocynin of human VSMCs stimulated ROS production and the phosphorylation of TGFBR1 and subsequent activation of TGFBR1 signalling leading to the formation of phosphorylated Smad2 which consequently upregulates the mRNA expression of glycosaminoglycan synthesizing enzyme. ConclusionsThese findings outline a specific involvement of ROS production in TGFBR1 activation. Furthermore, because apocynin stimulates Nox and ROS production, apocynin must be used with considerable care in vitro as its actions clearly extend beyond the stimulation of Nox enzymes and it has consequences for cellular signalling. General significanceApocynin can stimulate Nox leading to the production of ROS and the outcome is completely dependent upon the redox properties of the cell.

Control of NOx and other emissions in micro gas turbine combustors fuelled with mixtures of methane and ammonia

Methane–ammonia mixtures have potentials as low-carbon fuels for gas turbines, however significantly high fuel NOx production in their flames present challenges to their application. This study aims to provide deep insight into the physical and chemical processes involved in the formation and control of emissions from the combustion of CH4NH3–air with up to 30% ammonia by heat fraction in gas turbine combustors. Hence, laser diagnostics techniques such as Particle Image Velocimetry (PIV), and Planar Laser Induced Fluorescence (PLIF) imaging, in addition to Fourier Transform Infrared (FTIR) gas analysis were employed to study the flow field, flame structure and emissions characteristics of a micro gas turbine swirl combustor fuelled with CH4NH3–air mixtures. The control of emissions from the flames was further studied using Large Eddy Simulation (LES) of a model swirl combustor. The results show that NOx emissions from premixed CH4NH3–air in single-stage combustion were more than 5000 ppmv at equivalence ratios, Φ = 0.8–1.1, which is about twice more than the values already reported for NH3–air. Trends in NOx emissions correspond with the trends in OH radicals concentration in the combustor owing to the relevance of OH radicals in fuel NOx production. Emissions control leading to significantly low emissions such as 49 ppmv of NOx, 2 ppmv of CO and approximately zero N2O, HCN and NH3 emissions with a 99.8% combustion efficiency was achieved using rich-lean combustion. An optimum Φ of the primary combustion zone for low NOx emission was identified, which varied from 1.30 to 1.35 depending on the ammonia fraction. For Φ richer (leaner) than the optimum Φ, NOx emission increased due to an increase in NOx production in the secondary (primary) combustion zone. Rich-lean combustion of CH4NH3–air emitted less NOx than that of NH3-air because the higher flame speed of CH4NH3–air mixtures ensured lower NOx production in the secondary combustion zone.

Lightning NO<sub>2</sub> simulation over the contiguous US and its effects on satellite NO<sub>2</sub> retrievals

Abstract. Lightning is an important NOx source representing ∼10 % of the global source of odd N and a much larger percentage in the upper troposphere. The poor understanding of spatial and temporal patterns of lightning contributes to a large uncertainty in understanding upper tropospheric chemistry. We implement a lightning parameterization using the product of convective available potential energy (CAPE) and convective precipitation rate (PR) coupled with the Kain–Fritsch convective scheme (KF/CAPE-PR) into the Weather Research and Forecasting-Chemistry (WRF-Chem) model. Compared to the cloud-top height (CTH) lightning parameterization combined with the Grell 3-D convective scheme (G3/CTH), we show that the switch of convective scheme improves the correlation of lightning flash density in the southeastern US from 0.30 to 0.67 when comparing against the Earth Networks Total Lightning Network; the switch of lightning parameterization contributes to the improvement of the correlation from 0.48 to 0.62 elsewhere in the US. The simulated NO2 profiles using the KF/CAPE-PR parameterization exhibit better agreement with aircraft observations in the middle and upper troposphere. Using a lightning NOx production rate of 500 mol NO flash−1, the a priori NO2 profile generated by the simulation with the KF/CAPE-PR parameterization reduces the air mass factor for NO2 retrievals by 16 % on average in the southeastern US in the late spring and early summer compared to simulations using the G3/CTH parameterization. This causes an average change in NO2 vertical column density 4 times higher than the average uncertainty.

Plasma-Assisted Combustor Dynamics Control at Realistic Gas Turbine Conditions

ABSTRACT This study investigated the effectiveness of implementing a plasma discharge to improve combustor dynamics and flame stability. Specifically, a nano-second pulsed plasma discharge (NSPD) was applied to a premixed gaseous fuel/air dump combustor for mitigation of dynamic combustion instabilities with a minimal NOX penalty. As a result, a significant reduction of pressure fluctuation level (2X to 4X) was observed at realistic low-power conditions of aero-engine combustors. The plasma power required for the reduction increased with increasing combustor inlet velocity and pressure. The change of fuel from methane to propane required significantly (2X) higher plasma power to achieve a similar noise reduction. The lean blowout limit was significantly extended due to the plasma; however, substantial incomplete combustion occurred in the extended regime. The incremental NOX production in the presence of the plasma was low (~ < 1EINOX); however, it increased with decreasing velocity and pressure, and increasing temperature.