NOx Concentration Decrease Research Articles

Effects of Injection Strategies on Mixture Formation and Combustion in a Spark-Ignition Engine Fueled with Syngas-Biogas-Hydrogen

The paper presents the effects of blend injection and dual injection strategies on mixture formation and combustion of syngas-biogas-hydrogen fueling engine working in the solar-biomass hybrid renewable energy system. The research was performed by simulation method on a retrofitted Honda GX200 spark-ignition engine. The results show that at the end of the compression process, in the case of blend injection of 50% syngas-50% biogas, the fuel-rich zone was positioned on the top of the combustion chamber, whereas in the case of dual injection, this zone was found on the top of the piston. In the case of 50% syngas-50% hydrogen supplied, at the end of the compression process, the fuel-rich area observed on the top of the piston with slightly deflected towards the inlet port in both cases of blend and dual injection. When shifting from blend injection mode to dual injection mode, in the case of 50% syngas-50% biogas fueling engine, the mean temperature of the exhaust gas decreased from 1208 K to 1161 K and the NOx concentration decreased from 1919 ppm to 1288 ppm. In the case of a 50% syngas-50% hydrogen fueling engine, the mean exhaust gas temperature decreases from 1283 K to 1187 K leading to a decrease in NOx concentration from 3268 ppm to 2231 ppm. The dual injection has the advantage of lower NOx emission, whereas the blend injection has the advantage of higher efficiency

Experimental study on the effect of post-injection parameters on performance of extra-high pressure common-rail diesel engine

The diesel engine combustion process is mainly controlled by the fuel injection characteristics, which will have a direct impact on the performance of the diesel engine, more flexible injection strategy is the development direction of high pressure common-rail system. In order to obtain the change law of the performance of extra-high pressure common-rail diesel engine under variable injection strategy, and improve the overall performance of diesel engine, the effect of different post-injection parameters on the performance of diesel engine was studied on a self-designed extra-high pressure common-rail diesel engine experiment bench, and the relevant results were discussed and analyzed. The results show that: with the rise of post-injection fuel quantity, NOx concentration and soot concentration decrease gradually, and with the rise of post-injection interval angle, NOx concentration decreases gradually, while soot concentration first decreases and then increases. Therefore, choosing post-injection fuel quantity and post-injection interval angle rationally can achieve lower NOx and soot emission at the same time. Meanwhile, with the rise of post-injection fuel quantity or post-injection interval angle, the fuel consumption rate presents an increasing trend.

Chang impact analysis of level 3 COVID-19 alert on air pollution indicators using artificial neural network

In this study, mean monthly and diurnal variations in fine particulate matters (PM2.5), nitrate, sulfate, and gaseous precursors were investigated during the Level 3 COVID-19 alert from May 19 to July 27 in 2021. For comparison, the historical data during the identical period in 2019 and 2020 were also provided to determine the effect of the Level 3 COVID-19 alert on aerosols and gaseous pollutants concentrations in Taichung City. A machine learning model using the artificial neural network technique coupled with a kinetic model was applied to predict NOx, O3, nitrate (NO3−), and sulfate (SO42−) to investigate potential emission sources and chemical reaction mechanism. D during the Level 3 COVID-19 alert, a decrease in NOx concentration due to a decrease in traffic flow under the NOx-saturated regime was observed to enhance the secondary NO3− and O3 formation. The present models were shown to predict 80.1, 77.0, 72.6, and 67.2% concentrations of NOx, O3, NO3−, and SO42−, respectively, which could help decision-makers for pollutant emissions reduction policies development and air pollution control strategies. It is recommended that more long-term datasets, including water soluble inorganic salts (WIS), precursors including OH radicals, NH3, HNO3, and H2SO4, be provided by regulatory air quality monitoring stations to further improve the prediction model accuracy.

Hydrogen-Enriched Biogas Premixed Charge Combustion and Emissions in Direct Injection and Indirect Injection Diesel Dual Fueled Engines: A Comparative Study

Abstract This paper presents a comparative study on combustion and emissions of hydrogen-enriched biogas premixed charge direct injection dual-fuel (DIDF) engine and indirect injection dual-fuel (IDIDF) engine. The results show that the IDIDF engine outperforms the DIDF engine in terms of higher indicative engine cycle work (Wi) and lower emissions of CO, soot, and noise, but the disadvantage is higher NOx emission. Under the same fueling condition, the IDIDF engine’s Wi is on average 6% higher than that of the DIDF engine, but the NOx concentration in the combustion products of the IDIDF engine is 1.5 times higher than that of the DIDF engine. The IDIDF engine creates the stratified mixture distribution with higher O2 concentration in the auxiliary combustion chamber, which is favorable for auto-ignition and reduces the ignition delay. The biogas composition affects slightly CO and soot emissions, but significantly affects NOx emission. When the methane composition in biogas increases from 60% to 80%, the soot volume fraction is approximately 0.1 ppm in both types of combustion chambers, the CO concentration varies from 1.4% to 1.8%, and the NOx concentration varies from 3000 to 5000 ppm in the case of IDIDF engine and 2500–4500 ppm in the case of DIDF engine. For both types of dual-fuel engines, when engine speed increases, CO concentration and the soot volume fraction increase, while Wi and NOx concentration decrease.

Seasonal ground level ozone prediction using multiple linear regression (MLR) model

To assess the surface ozone concentration (O3), there is a need to establish relationship between air pollutants and meteorological parameters. The study was conducted on variation of air pollutants, viz. O3, nitrogen oxides (NOX = NO2 + NO) and carbon monoxide (CO) along with meteorological parameters like temperature (Temp), relative humidity (RH), solar radiation (SR) and wind speed (WS). The precursor gases were recorded in Hyderabad at Tata Institute of Fundamental Research-National Balloon Facility (TIFR-NBF; 17.47° N, 78.58° E). Correlation analysis is done on hourly averaged trace gases concentration and metrological data for the entire year 2016. O3 is in negative correlation with NOX, CO and RH. NOX which is one of the precursor gases plays a major role in formation of O3 by photo-chemical reaction (PCR). The increase in O3 concentration is in proportion with the decrease in NOX concentration. O3 correlated positively with Temp, SR and WS. Two sets of four models were constructed with multiple linear regression (MLR) representing the data for the three seasons (summer, winter and monsoon) and for the total year as well. The adjusted R2 was determined and found to be in the range of 0.6 to 0.9 for the models using precursor gases and 0.9 by meteorological parameters. The models were validated by various performance indicators, viz. root mean square error (RMSE), mean absolute error (MAE) and mean biased error (MBE).

Effect of Operational Parameters on Combustion and Emissions in an Industrial Gas Turbine Combustor

Enhancing a combustion system requires increased combustion efficiency, fuel savings, and reduction of combustion emissions. In this paper, the combustion of CH4 in the combustor of an industrial gas turbine is studied and NO and CO formation/emission is simulated numerically. The objective of the current work is to investigate the influence of combustive parameters and varying the percentage of distributed air flow rate via burning, recirculation, and dilution zone on the reactive flow characteristics, NOx and CO emissions. The governing equations of mass, momentum, energy, turbulence quantities Renormalized group (RNG) (k–ε), mixture fraction and its variance are solved by the finite volume method. The formation and emission of NOx is numerically simulated in a postprocessing fashion, due to the low concentration of the pollutants as compared to the main combustion species. The present work focuses on different physical mechanisms of NOx formation. The thermal-NOx and prompt-NOx mechanism are considered for modeling the NOx source term in the transport equation. Results show that in a gaseous-fueled combustor, the thermal NOx is the dominant mechanism for NOx formation. Particularly, the simulation provides more insight into the correlation between the maximum combustor temperature, exhaust average temperatures, and the thermal NO concentration. Results indicate that the exhaust temperature and NOx concentration decrease while the excess air factor increases. Moreover, results demonstrate that as the combustion air temperature increases, the combustor temperature increases and the thermal NOx concentration increases dramatically. Furthermore, results demonstrate that the NO concentration at the combustor exit is at maximum value in a swirl angle of 55 deg and a gradual rise in the NOx concentration is detected as the combustion fuel temperature increases. In addition, results demonstrate that the air distribution of the first case at laboratory conditions is optimal where the mass fractions of NO and CO are minimum.

Characteristics of syngas reburning in a natural gas firing furnace - Effects of combustible gas species in the syngas

Co-firing of synthesis gas (syngas) produced from biomass/waste gasification is a promising option for increasing renewable energy production from existing boilers burning fossil fuels. This study presents an experimental approach to utilizing syngas as reburn fuel for NOx emissions reduction. In a 65 kWth furnace firing natural gas, the reburning characteristics for simulated syngas representing main syngas components, such as CH4, CO and H2, were evaluated for co-firing ratios up to 20%. The heating value and gas residence time of the syngas were maintained in the reburn zone by adjusting the N2 concentration. Detailed distribution of temperature, O2 and NOx concentrations within the furnace were measured for the test conditions. The lower stoichiometric ratios of the primary combustion zone by reburning were favorable in reducing NOx formation from the main fuel. Among the syngas components, CH4 was most efficient, exhibiting an immediate decrease in NOx concentration after injection through the formation of HCN. CO and H2 also contributed to the reduction of NOx emissions by suppressing further formation of NOx in the reburn zone. The NOx removal efficiency was diminished by an increase in NOx concentrations in the burnout zone.

Particulate matter and gaseous emission rate from combustion of Thai lignite and agricultural residues in a fixed-bed combustor

ABSTRACTThis research has been conducted in order to obtain a database of emission rate of particulate matter and gases (CO, NO, and SO2) from combustion of lignite and agricultural residues, such as rice husk. The experimental investigation was performed in a fixed-bed combustor. Thirteen stages–electrical low-pressure impactor was used to collect particles ranging in sizes from 40 nm to 10 μm. The results show that emission rate of total mass of particulate matter from combustion of rice husk is lower than that of lignite combustion but the total number of particles emitted is higher. This implies lower particle density from agricultural residue combustion. For co-firing lignite and rice husk, particulate matter emission is found to be higher than combustion of either lignite or rice husk and an increase in rice husk mass fraction in fuel mixture leads to an increase in particulate matter emission. From these quantitative data, it could be mentioned that the fuel characteristics influenced directly on particulate emission. For gaseous emission factors, CO and NOx concentration decrease as SA/TA ratio increases. Meanwhile, SO2 emission tends to increase. Both NOx and SO2 emissions are reduced as increased rice husk mass fraction in fuel mixture.

Emission characteristic of hydrogen and gasoline blend in spark-ignited engine

Hydrogen is an energy carrier that can transform our fossil fuel-dependent economy into a hydrogen economy, which can provide an emission-free transportation fuel. Hydrogen-fuelled engines are known for several advantages, among which is the very low concentration of pollutants in the exhaust gases compared with internal combustion engines using traditional or other alternative fuels. Hydrogen-driven vehicles thus reduce both local and global emissions. It is an energy carrier that can be used in internal combustion engines or fuel cells producing virtually no greenhouse gas emissions when combusted with oxygen. The only significant emission is water vapour. The effect of blending of hydrogen with gasoline is analysed in this current paper. Both HC and NOx concentration decrease with the increase in hydrogen fractions. The results were analysed by collecting data on different crank angles and at 5%, 10%, 15% and 20% of hydrogen introduction into combustion chamber along with gasoline as base fuel.

Effects of anthropogenic heat on ozone air quality in a megacity

Anthropogenic heat released into the atmosphere in urban areas affects the characteristics/structures of boundary layer and local circulation and thus can affect local air quality. In this study, the effects of anthropogenic heat on ozone (O3) air quality in the Seoul metropolitan area, Republic of Korea, are examined using the Community Multiscale Air Quality (CMAQ) model coupled with the Weather Research and Forecasting (WRF) model. The release of anthropogenic heat is found to increase O3 concentration by 3.8 ppb in the urban area, and this effect is larger in the nighttime (5.3 ppb) than in the daytime (2.4 ppb). As stronger anthropogenic heat is released, the urban boundary layer becomes deeper and NOx concentration becomes lower due to the dilution. The decrease in NOx concentration causes the chemical loss of O3 by the reaction with NO to be reduced. In addition to the enhanced net chemical production of O3 in the deepened urban boundary layer, the strengthened urban-breeze circulation by anthropogenic heat contributes to an increase in O3 concentration in the urban area. The O3-rich air in the surroundings of Seoul, where biogenic volatile organic compound (BVOC) emissions are high and NOx emissions are low, is brought into the urban area by the urban breeze. Moreover, in the daytime, the advection of oxidant products of BVOCs by the urban breeze contributes to an enhanced chemical production of O3 in the urban area. Anthropogenic heat also modifies the sea/land-breeze circulations, which, in turn, is found to influence O3 concentration in the urban area.

Performance and emission characteristics of biogas used in diesel engine operation

The objective of this study it to evaluate the impact of the carbon dioxide concentration in biogas on the operating characteristics and exhaust gas emissions of a diesel engine running on a mixture of biogas and mineral diesel fuel. The tests were carried out in two stages. In the first stage, the impact of different biogas compositions and the exhaust gas recirculation system (EGR) on the engine parameters was determined.Lower pollutant levels were measured in the studies without the EGR system, except for the nitrogen oxides NOx levels. The NOx concentration decrease was directly proportional to the concentration of methane in the common fuel mixture.In the second stage, the gas with the highest methane content was used to determine the impact of the start of injection timing on the engine operating parameters. As the methane content in the common fuel mixture increased, the start of injection timing had to be progressively advanced to increase the thermal efficiency and to lower the fuel consumption, the CO and HC concentrations and the smokiness of the exhaust; however, advancing the start of injection timing increased NOx pollution.

Full scale demonstration of air-purifying pavement

Experiments concerning a full-scale demonstration of air purifying pavement in Hengelo, The Netherlands, are reported. The full width of the street was provided with concrete pavement containing TiO2 over a length of 150m (“DeNOx street”). Another part of the street, about 100m, was paved with normal paving blocks (“Control street”). The outdoor monitoring was done during 26 days for a period exceeding one year, and measured parameters included traffic intensity, NO, NO2 and ozone concentrations, temperature, relative humidity, wind speed and direction, and the visible and UV light irradiance. Prior and parallel to these field measurements, the used blocks were also measured in the lab to assess their performance. The NOx concentration was, on average, 19% (considering the whole day) and 28% (considering only afternoons) lower than the obtained values in the Control street. Under ideal weather conditions (high radiation and low relative humidity) a NOx concentration decrease of 45% could be observed.

Nitrogen dynamics in land cleared of alien vegetation (<i>Acacia saligna</i>) and impacts on groundwater at Riverlands Nature Reserve (Western Cape, South Africa)

Woody invading alien plants, many of which are nitrogen-fixing legumes (Fabaceae family), are currently cleared in South African catchments to reduce water loss and preserve streamflow, and for the restoration of the ecosystem. This study tested the hypothesis that clearing invasive alien vegetation may disturb the vegetation-micro-organism-soil N cycling system by producing a large once-off input of fresh tree litterfall rich in N and by eliminating a large N sink. Three experimental plots were established at the Riverlands Nature Reserve (Western Cape, South Africa): a site invaded by Acacia saligna to be used as control; a site cleared of Acacia saligna; and a site with natural vegetation to be used as background. Nitrogen concentrations in soil and groundwater, volumetric soil water contents, root density and weather conditions were measured during 2007. Oxidised forms of nitrogen, in particular NO3-, were dominant in the system. Recharge and leachate were simulated with the HYDRUS-2D model and used as inputs into Visual MODFLOW to predict the spatial distribution of nitrate plus nitrite (NOx) in groundwater. NOx levels in soil and groundwater were higher in alien-invaded areas compared to fynbos-covered land. A quick release of NOx into groundwater was observed due to high residual N reserves in the rooting zone, decreased  evapotranspiration and increased recharge in the treatment cleared of alien vegetation. In the long run, high NOx concentrations in groundwater underlying cleared land will last only until all the excess nitrogen has been leached from the soil. A decrease in NOx concentration in groundwater can be expected thereafter. Clearing land of alien invasive legumes may therefore have a beneficial effect by reducing groundwater contamination from NOx and reducing water losses in catchments.

C141 アルコール水溶液/重油エマルジョン燃料の燃焼特性に及ぼすアルコール種類および濃度の影響(OS-5: これからの燃焼研究(4))

The present study performed spray combustion experiments of alcohol aqueous solution/heavy oil emulsified fuel to investigate the effects of alcohol concentration on the flame temperature and exhaust gas concentration. In the experiment, the emulsified fuel is produced by mixing heavy oil A and an ethanol aqueous solution by varying the ethanol concentration of the solution. The emulsified fuel flame shows the maximum temperature closer to the burner than the heavy oil flame, indicating that the combustion characteristics are improved in the emulsified fuel owing to the micro-explosion. In addition, a decrease in NOx concentration is observed in the emulsified fuel with increasing the ethanol concentration in the solution.

Measurement of Gas Species, Temperatures, Coal Burnout, and Wall Heat Fluxes in a 200 MWeLignite-Fired Boiler with Different Overfire Air Damper Openings

Measurements were performed on a 200 MWe, wall-fired, lignite utility boiler. For different overfire air (OFA) damper openings, the gas temperature, gas species concentration, coal burnout, release rates of components (C, H, and N), furnace temperature, and heat flux and boiler efficiency were measured. Cold air experiments for a single burner were conducted in the laboratory. The double-swirl flow pulverized-coal burner has two ring recirculation zones starting in the secondary air region in the burner. As the secondary air flow increases, the axial velocity of air flow increases, the maxima of radial velocity, tangential velocity and turbulence intensity all increase, and the swirl intensity of air flow and the size of recirculation zones increase slightly. In the central region of the burner, as the OFA damper opening widens, the gas temperature and CO concentration increase, while the O2 concentration, NOx concentration, coal burnout, and release rates of components (C, H, and N) decrease, and coal particles ignite earlier. In the secondary air region of the burner, the O2 concentration, NOx concentration, coal burnout, and release rates of components (C, H, and N) decrease, and the gas temperature and CO concentration vary slightly. In the sidewall region, the gas temperature, O2 concentration, and NOx concentration decrease, while the CO concentration increases and the gas temperature varies slightly. The furnace temperature and heat flux in the main burning region decrease appreciably, but increase slightly in the burnout region. The NOx emission decreases from 1203.6 mg/m3 (6% O2) for a damper opening of 0% to 511.7 mg/m3 (6% O2) for a damper opening of 80% and the boiler efficiency decreases from 92.59 to 91.9%.