Nitrogen Oxide Emissions Research Articles

On the Influence of Engine Compression Ratio on Diesel Engine Performance and Emission Fueled with Biodiesel Extracted from Waste Cooking Oil

Despite the extensive research on biodiesels, further investigation is warranted on the impact of compression ratios on emissions and engine performance. This study addresses this gap by evaluating the effects of increasing the engine’s compression ratio on engine performance metrics—brake-specific fuel consumption (BSFC), power, torque, and exhaust gas temperature—and emissions—unburnt hydrocarbons (HCs), carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), and oxygen (O2)—when fueled with a 20% blend of waste cooking oil biodiesel (WCB20) and petroleum diesel (PD) under various operating conditions. The viscosity of the prepared fuels was measured at 25 °C and 40 °C. Experiments were conducted on a single-cylinder diesel engine under wide-open throttle conditions at three different speeds (1400 rpm, 2000 rpm, and 2600 rpm) and two compression ratios (16:1 and 18:1). The results revealed that at a lower compression ratio, both WCB20 and petroleum diesel exhibited reduced BSFC compared to higher compression ratios. However, increasing the compression ratio from 16:1 to 18:1 significantly decreased HC emissions but increased CO2 and NOx emissions. Engine power increased with engine speed for both fuels and compression ratios, with WCB20 initially producing less power than diesel but surpassing it at higher compression ratios. WCB20 demonstrated improved combustion quality with lower unburnt hydrocarbons and carbon monoxide emissions due to its higher oxygen content, promoting complete combustion. This study provides critical insights into optimizing engine performance and emission characteristics by manipulating compression ratios and utilizing biodiesel blends, paving the way for more efficient and environmentally friendly diesel engine operations.

Enhancing diesel engine performance and emission reduction through hydrogen enrichment in algal biodiesel blends.

The introduction of hydrogen into the engine could enhance its combustion efficiency and emission characteristics. The current study examines the attributes of compression ignition (CI) engines by introducing hydrogen into a biodiesel blend derived from algae. The improved thermal properties of hydrogen, when combined with algae biodiesel, significantly affect the performance, combustion, and emissions of dual-fuel engines. A study was conducted to evaluate the impact of hydrogen enrichment levels of 5%, 10%, 15%, and 20% of the nozzle volume on a biodiesel blend fuel. In comparison to diesel, algal biodiesel reduces emissions of unburned hydrocarbons (HC), carbon monoxide (CO), and oxygen (O2) by 5.19%, 3.61%, and 2.83%, respectively, while increasing nitrogen oxide (NO) emissions by 4.73%. In contrast to biodiesel, diesel demonstrated superior brake thermal efficiency (BTE) and lower specific energy consumption (SEC). Injecting hydrogen into A20 blend fuel at volumes of 5%, 10%, 15%, and 20% results in a respective increase in brake thermal efficiency of 2.65%, 2.97%, 3.50%, and 4.15%. The addition of hydrogen gas to biodiesel blends further enhances their combustion qualities, leading to elevated peak cylinder pressure, temperature, and heat release rate. The results indicate that A20H5, A20H10, A20H15, and A20H20 fuel reduced CO emissions by 3.75%, 8.75%, 12.5%, and 16.25%, respectively, compared to the A20 blend. In the same vein, HC emissions decreased by 5.76%, 10.29%, 15.52%, and 18.98%, respectively, as compared to A20 fuel. However, NO emissions rose by 5.36%, 10.20%, 15.28%, and 23.23%, respectively, for A20H5, A20H10, A20H15, and A20H20 test fuels. Ultimately, the utilization of algal biodiesel and hydrogen enrichment in diesel engines was proven to substantially reduce pollutants while increasing efficiency. This study contributes valuable insights into the intersection of renewable fuels, hydrogen enrichment, and engine technology, with the potential to drive significant advancements in sustainable transportation and environmental conservation.

Multiphase flow simulation and industrial application of an in-line gasifier for NOx emissions control from cement kiln

Following the power and steel industries, nitrogen oxides (NOx) in the cement industry have become an important part of the next stage of air pollutant control. Consequently, the multiphase flow simulation of an in-line coal gasification denitration system was carried out using the computational fluid dynamics (CFD) approach. Among them, the solid phase is simulated by the Multiphase Particle-In-Cell (MP-PIC) method, and the gas phase turbulence is accurately captured by the large eddy simulation (LES) method. The flow field characteristics distribution and the reaction kinetic of NO under different parameters (coal, raw meal, tertiary air) in the gasifier were investigated, and the operating condition values for guiding industrial applications are obtained. The simulation results show that the gasifier can completely remove NOx from the rotary kiln at 2.8 kg/s for coal, 30 kg/s for raw meal and 2.5 kg/s for tertiary air. The application results show that under 1.6 kg/t.cl of ammonia water combined with SNCR, NOx emission and ammonia slip can be controlled below 50 mg/Nm3 and 5 mg/Nm3, respectively. Compared to similar denitrification technologies, this technology shows the potential to achieve ultra-low NOx emission levels in the cement industry.

The influence of exhaust gas recirculation on combustion and emission characteristics of ammonia-diesel dual-fuel engines: Heat capacity, dilution and chemical effects

As the greenhouse effect intensifies, ammonia is garnering increasing attention as a carbon-free fuel. In the transport sector, ammonia-diesel dual-fuel (ADDF) engines are regarded as an effective means of reducing carbon emissions. The objective of this study is to investigate the combustion and emission optimization of an ADDF engine under high load conditions. To this end, an experimental optimization study of different start of diesel injection timing (SODI) and exhaust gas recirculation (EGR) rates was conducted at a load of 18 bar and an ammonia energy ratio of 80 %. The mechanism of heat capacity, dilution, and chemical effects of EGR was also revealed by numerical simulation based on the separated variables method. It was demonstrated that advancing SODI is effective in enhancing combustion efficiency. However, this approach is limited by the upper limit of in-cylinder pressure and results in higher nitrogen oxides (NOx) emissions, which can be mitigated by the EGR. The heat capacity effect of EGR increases the specific heat capacity and decreases the average temperature. The suppression of the combustion process leads to a reduction in thermal and fuel NOx, but an increase in nitrous oxide (N2O) emissions. The dilution effect of EGR results in insufficient oxygen, which decreases the heat release rate and combustion efficiency. Additionally, the NOx and N2O are significantly reduced. The chemical effect of EGR affects reactive groups and unburned components that accelerate heat release rate and increase accumulated heat release, resulting in significantly higher NOx. The comprehensive effect of EGR results in a decrease in N2O emissions and a significant reduction in thermal and fuel NOx. The EGR and further optimization of SODI enabled the ADDF engine to achieve a gross indicated thermal efficiency of 48.5 % with a load of 18 bar and an ammonia energy ratio of 80 %. In addition, NO emissions were reduced by 32.8 percent and greenhouse gas emissions by 63.3 percent.

Estimating global 0.1° scale gridded anthropogenic CO2 emissions using TROPOMI NO2 and a data-driven method

Satellite remote sensing is a promising approach for monitoring global CO2 emissions. However, existing satellite-based CO2 observations are too coarse to meet the requirements of fine-scale global mapping. We propose a novel data-driven method to estimate global anthropogenic CO2 emissions at a 0.1° scale, which integrates emissions inventories and satellite data while bypassing the inadequate accuracy of CO2 observations. Due to the co-emitted anthropogenic emissions of nitrogen oxides (NOx = NO + NO2) and CO2, high-resolution NO2 measurements from the TROPOspheric Monitoring Instrument (TROPOMI) are employed to map the global anthropogenic emissions at a global 0.1° scale. We construct the driving features from NO2 data and also incorporate gridded CO2/NOx emission ratios and NOx/NO2 conversion ratios as driving data to describe co-emissions. Both ratios are predicted using a long short-term memory (LSTM) neural network (with an R2 of 0.984 for the CO2/NOx emission ratio and an R2 of 0.980 for the NOx/NO2 conversion ratio). The data-driven model for estimating anthropogenic CO2 emissions is implemented by random forest regression (RFR) and trained using the Emissions Database for Global Atmospheric Research (EDGAR). The satellite-based anthropogenic CO2 emission dataset at a global 0.1° scale agrees well with the national CO2 emission inventories (an R2 of 0.998 with Global Carbon Budget (GCB) and an R2 of 0.996 with EDGAR) and consistent with city-level emission estimates from Carbon Monitor Cities (CMC) with the R2 of 0.824. This data-driven method based on satellite-observed NO2 provides a new perspective for fine-resolution anthropogenic CO2 emissions estimation.

Impacts of the Chengdu 2021 world university games on NO2 pollution: Implications for urban vehicle electrification promotion

Emissions of nitrogen oxides (NOx) are a dominant contributor to ambient nitrogen dioxide (NO2) concentrations, but the quantitative relationship between them at an intracity scale remains elusive. The Chengdu 2021 FISU World University Games (July 22 to August 10, 2023) was the first world-class multisport event in China after the COVID-19 pandemic which led to a substantial decline in NOx emissions in Chengdu. This study evaluated the impact of variations in NOx emissions on NO2 concentrations at a fine spatiotemporal scale by leveraging this event-driven experiment. Based on ground-based and satellite observations, we developed a data-driven approach to estimate full-coverage hourly NO2 concentrations at 1 km resolution. Then, a random-forest-based meteorological normalization method was applied to decouple the impact of meteorological conditions on NO2 concentrations for every grid cell, the resulting data were then compared with the timely bottom-up NOx emissions. The SHapley-Additive-exPlanation (SHAP) method was employed to delineate the individual contributions of meteorological factors and various emission sources to the changes in NO2 concentrations. According to the full-coverage meteorologically normalized NO2 concentrations, a decrease in NOx emissions and favorable meteorological conditions accounted for 80 % and 20 % of the NO2 reduction, respectively, across Chengdu city during the control period. Within the strict control zone, a 30 % decrease in the meteorologically normalized NO2 concentrations was observed during the control period. The normalized NO2 concentrations demonstrated a strong correlation with NOx emissions (R = 0.96). Based on the SHAP analysis, traffic emissions accounted for 73 % of the reduction in NO2 concentrations, underscoring the significance of traffic control measures in improving air quality in urban areas. This study provides insights into the relationship between NO2 concentrations and NOx emissions using real-world data, which implies the substantial benefits of vehicle electrification for sustainable urban development.

STUDYING HOW DIESEL ENGINE ADDITIVES USING SILVER OXIDE (Ag2O) NANOPARTICLES AFFECT THE ENVIRONMENT

Abstract: Biodiesel has been defined as an alternative fuel that has the potential to be used instead of diesel fuel for years. In case of complete combustion reaction in engines, the products released do not directly threaten human health. Compared to diesel fuel, biodiesel has worse combustion performance due to some fuel properties. Therefore, incomplete combustion products such as hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOx), smoke emission and complete combustion products such as CO2 are thrown into the atmosphere. In this study, the changes in exhaust emissions of 50 ppm and 75 ppm Ag2O NPs were experimentally examined to improve the adverse combustion performance and emission characteristics of cottonseed oil methyl ester. In experiments, nano additive improved the thermal conductivity, mass dissipation and heat transfer of the test fuels, and resulted in reducing of CO emissions as it provided a higher oxidation rate of hydrocarbon molecules. Due to the improvement in the combustion reaction, CO2 emission increased with product of complete combustion. The increase in CO2 emissions was 3.17% and 3.97% for CAg-50 and CAg-75 fuels, respectively, when compared to C0 fuel at 40 Nm load. The NPs additive increased the lower calorific value of the fuel and cylinder temperature. This situation caused increase of NOx emissions by 3.69% and 7.47% CAg-50 and CAg-75 fuels 40 Nm load. Adding of NPs in base fuel reduced to viscosity and density provided better atomization. So a reduction in smoke emission was obtained with NPs addition by 35.09% and 47.32% in CAg-50 and CAg-75 fuels, respectively, compared to C0 fuel at 10 Nm load, while 7.45% and 19.43% at 40 Nm load.

Computational analysis of ammonia-hydrogen blends in homogeneous charge compression ignition engine operation

Ammonia (NH3) is considered a promising alternative fuel due to its renewable and carbon-free nature. The addition of hydrogen (H2) significantly improves its flammability, making it suitable for use in internal combustion engines. The homogeneous charge compression ignition (HCCI) technique offers a practical solution for high-efficiency NH3-H2 operation, but it is not extensively discussed in existing literature. To enhance the understanding of NH3-H2 HCCI engines, this study employs a zero-dimensional model validated against experimental results to investigate engine efficiency and nitrogen oxides (NOx) emissions. The results indicate that an ammonia-dedicated HCCI mode would misfire at a 22:1 compression ratio and an engine speed of 1500 rpm if the intake pressure and temperature are insufficient. Hydrogen addition can help overcome the misfire issue and reduce the intake pressure and temperature required for combustion initiation. However, higher hydrogen addition ratios decrease thermal efficiency and increase NOx emission levels. In lean NH3-H2 HCCI operation, NOx emissions are primarily driven by fuel-borne mechanisms and peak at an equivalence ratio of around 0.5. A higher hydrogen addition ratio should be avoided as it increases the risk of ringing, thereby reducing the maximum allowable equivalence ratio and engine load. As a result, a moderate hydrogen addition ratio, such as 20 %, is preferable for NH3-H2 HCCI engines. Additionally, an equivalence ratio of approximately 0.3 is optimal, balancing multiple performance indicators such as thermal efficiency, NOx emission levels, and engine operating stability. These findings suggest that the operating range of NH3-H2 HCCI engines is limited, making them more suitable for off-road applications, such as power generation.

An investigation on the H2O, unburned H2 and NO emission characteristics from a direct injection hydrogen engine

Hydrogen engines show great potential as a power source with good combustion performance, zero carbon emissions, and diverse sources. However, the exhaust emission characteristics with high water vapor (H2O) content have not yet been clarified. This study presents the exhaust emissions of a heavy-duty direct-injection hydrogen engine under various operational parameters, with a focus on the H2O content. The results reveal important exhaust emissions characteristics of the hydrogen engine, including lower exhaust temperature (200 °C–400 °C), higher unburned H2 emissions (up to 17100 ppm), less nitrogen oxide (NO) generation (<1000 ppm), and higher H2O content (6%–40%). Additionally, unburned H2 rises, and NO and H2O decrease as the excess air ratio (λ) increases. When λ is greater than 3, NO levels fall sharply to below 100 ppm. Optimal emissions performance is achieved with a 5 °CA BTDC ignition timing where low levels of H2, H2O, and NO are maintained. Increasing hydrogen injection pressure decreases H2 but raises exhaust temperature, H2O, and NO emissions. Excessively delaying hydrogen injection timing adversely affects the concentration gradient in the cylinder, increasing unburned H2 emissions. The best emissions performance is observed at a hydrogen injection timing of 110 °CA BTDC.

Optimization of CRDI engine operating parameters using response surface methodology utilizing lemon peel oil biofuel enriched with hydroxy gas

The current study aims to optimize the operational variables of a CRDI engine in Dual-Fuel Mode (DFM). Hydroxy gas (HHO) was generated through water electrolysis using a concentric four-cylinder dry cell electrolyzer with NaOH catalyst, and it was introduced into the inlet manifold as the primary fuel. The pilot fuel consisted of Lemon Peel Oil (LPO) and pure diesel directly injected into the cylinder. An experimental matrix comprising 17 distinct runs was designed using Design of Experiments (DoE), utilizing Box-Behnken Design (BBD) based on Response Surface Methodology (RSM). The RSM model was created depending on the experimental data, and then operating parameters were optimized utilizing the desirability technique. The optimal engine operational variables were identified for the B25 LPO mixture with a constant HHO gas flow rate of 0.5 LPM, a Compression Ratio (CR) of 21.5, an Injection Pressure (IT) of 450 bars, and an inlet air temperature of 87℃. The optimized results were 30.18 % for Brake Thermal Efficiency (BTE), 9.532 g/kW-hr for Carbon Monoxide (CO) emission, 0.253 g/kW-hr for Unburned Hydrocarbon (UHC) emission, and 23.510 g/kW-hr and Nitrogen Oxides (NOx) emission, yielding a total desirability of 0.7641. Empirical validation of the optimized responses at these input conditions demonstrated their conformity to acceptable error ranges.

Modeling the impact of plastic oil obtained from xlpe cable wastes on diesel engine performance and combustion parameters with the response surface method

The world's expanding population requires alternative energy sources to meet its energy needs. One such alternative is the efficient recovery of plastic waste through pyrolysis. The liquid produced from waste plastics via pyrolysis is a valuable commodity that may serve as fuel substituted for internal combustion engines. In this study, waste plastic oil (WPO) and diesel fuel (D100) blends (10%, 20%, 30%, 40% and 50% by volume) obtained by pyrolysis of waste XLPE cables were experimentally investigated and analyzed using response surface methodology (RSM) to determine their effects on the combustion parameters of a four-stroke, single cylinder diesel engine at different engine loads (750, 1500, 2250, 3000, 3750 and 4500 W). A response surface model was constructed using a two-factor central composite complete design and analysis of variance based on the experimental results obtained. The model determined the optimum values of WPO ratio and engine load that correspond to one of the finest brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NOx), and smoke emission levels. The study's optimization findings indicated that the optimal WPO ratio is 19.6%, and the optimal engine load is 2600 W. The BTE, BSFC, CO, HC, NOx, and smoke were found to be 22.3%, 332.3 g/kWh, 0.033%, 31.5 ppm, 397.9 ppm, and 1.63%, respectively, at the optimal WPO ratio and engine load. The R2 (correlation coefficient) values for BTE, BSFC, CO, HC, NOx, and smoke emissions were determined to be 99.95%, 97.76%, 98.10%, 99.74%, 99.74%, 99.79%, and 95.67%, respectively. The mean error rates, ranging from 0.64% to 4.27%, were deemed satisfactory when comparing the replies to the experimental data. The findings of this study demonstrated that the response surface method is a very efficient approach for forecasting and enhancing a diesel engine's performance and emission characteristics by using waste plastic oil.

Evaluating CHASER V4.0 global formaldehyde (HCHO) simulations using satellite, aircraft, and ground-based remote-sensing observations

Abstract. Formaldehyde (HCHO), a precursor to tropospheric ozone, is an important tracer of volatile organic compounds (VOCs) in the atmosphere. Two years (2019–2020) of HCHO simulations obtained from the global chemistry transport model CHASER at a horizontal resolution of 2.8° × 2.8° have been evaluated using the Tropospheric Monitoring Instrument (TROPOMI) and multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations. In situ measurements from the Atmospheric Tomography Mission (ATom) in 2018 were used to evaluate the HCHO simulations for 2018. CHASER reproduced the TROPOMI-observed global HCHO spatial distribution with a spatial correlation (r) of 0.93 and a negative bias of 7 %. The model showed a good capability to reproduce the observed magnitude of the HCHO seasonality in different regions, including the background conditions. The discrepancies between the model and satellite in the Asian regions were related mainly to the underestimated and missing anthropogenic emission inventories. The maximum difference between two HCHO simulations based on two different nitrogen oxide (NOx) emission inventories was 20 %. TROPOMI's finer spatial resolution than that of the Ozone Monitoring Instrument (OMI) sensor reduced the global model–satellite root-mean-square error (RMSE) by 20 %. The OMI- and TROPOMI-observed seasonal variations in HCHO abundances were consistent. The simulated seasonality showed better agreement with TROPOMI in most regions. The simulated HCHO and isoprene profiles correlated strongly (R=0.81) with the ATom observations. However, CHASER overestimated HCHO mixing ratios over dense vegetation areas in South America and the remote Pacific region (background condition), mainly within the planetary boundary layer (&lt; 2 km). The simulated seasonal variations in the HCHO columns showed good agreement (R&gt;0.70) with the MAX-DOAS observations and agreed within the 1σ standard deviation of the observed values. However, the temporal correlation (R∼0.40) was moderate on a daily scale. CHASER underestimated the HCHO levels at all sites, and the peak occurrences in the observed and simulated HCHO seasonality differed. The coarseness of the model's resolution could potentially lead to such discrepancies. Sensitivity studies showed that anthropogenic emissions were the highest contributor (up to ∼ 35 %) to the wintertime regional HCHO levels.

Environmental Exhaust Emissions reduction and Performance Improvement Analysis of biodiesel operated Diesel Engine Performance Using Operating Parameters

&lt;p style="margin-top:3px; margin-bottom:3px; text-align:justify; text-indent:31.5pt"&gt;The present investigation aims to study the performance and emission characteristics of a CI DI diesel engine using biodiesel blends derived from Jatropha seed feedstock. Four blends, namely B25, B50, B75, and B100, are employed as fuels to run the diesel engine at a rated speed of 1500 rpm, and their performance and emission characteristics are determined under different operating conditions in the first phase. The blend B25 of JME is found to be the optimum blend, and the optimum compression ratio is found to be 18.5.The optimum blend exhibits better performance in terms of brake specific fuel consumption (BSFC) and brake thermal efficiency (BTHE), along with a decline in the emissions of carbon monoxide (CO) and hydrocarbons (HC), except for the emission of nitrogen oxides (NOX) at the optimum compression ratio of 18.5. At maximum load, with a compression ratio of 18.5, the optimum blend results in better BSFC and BTHE, which are 0.255 kg/kW-hr and 31.87%, respectively.&lt;/p&gt;

Exploring composite particles in ammonia decomposition for algae biodiesel integrated fuel and assessing energy and ecology metrics

The present study aims to investigate the catalytic effect of a zinc sulfide-induced copper composite particles in ammonia decomposition and to analyze the energy and environmental metrics when combined with algae biodiesel blending. This study is the first attempt to employ composite particles as catalysts in order to expedite ammonia decomposition and reduce the energy required for activation in engine applications. Chlorella vulgaris algae were cultivated from treated effluent and converted into biodiesel, which was then blended with diesel at a 30 % volume and with aqueous ammonia at a 10 % volume. The test fuel's combustion performance and emission characteristics were assessed and revealed that Chlorella vulgaris biodiesel (CVB) blended diesel fuel reduces engine performance by 4.2–8.7 %. However, incorporating composite particles leads to improvements in performance parameters ranging from 6.5 % to 8.1 %. The utilisation of CVB blended fuel results in a 10.3 % rise in nitrogen oxides (NOx) emissions, accompanied by a decrease of 17.3 % in hydrocarbon (HC) emissions and a decrease of 11.2 % in carbon monoxide (CO) emissions. Introducing aqueous ammonia emulsion decreases NOx, HC, and CO emissions by 3.8 %, 16.9 %, and 14.1 %, respectively. When the composite material is combined with emulsion fuel, HC, CO, and NOx emissions are further reduced by 6.2 %, 14.5 %, and 13.1 %, respectively.

Deflector device optimization for controlling nitrogen oxide emissions and pressure drop in selective catalytic reduction denitrification system

ABSTRACT Selective catalytic reduction technology effectively controls nitrogen oxide emissions from coal-fired power plants. In denitrification systems, exceeding nitrogen oxide emissions and excessive local pressure drop are common issues. Numerical simulation methods are used in this study to optimize the flow field to enhance denitrification efficiency and reduce pollutant emissions. Specifically, four deflector plate schemes for the variable-section flue duct segment are proposed. In actual retrofitting, the optimization scheme led to a reduction in nitrogen oxide emissions from 97.3 mg/Nm3 to 48.6 mg/Nm3 and an increase in the outlet pressure of the denitrification system from −3000 Pa to −2959 Pa, resulting in a 41 Pa decrease in local pressure drop. This optimization will further reduce pollutant emissions from power plants and the power consumption of induced draft fans.

A comprehensive analysis of energy, exergy, performance, and emissions of a spark-ignition engine running on blends of gasoline, ethanol, and isoamyl alcohol

This present study showed a comprehensive analysis of energy, exergy, performance, and emission characteristics of a spark-ignition engine powered by blends of gasoline-isoamyl alcohol-ethanol at volume proportions (100_0_0)% (P0E0), (90_5_5)% (P5E5), (80_5_15)% (P5E15), and (70_5_25)% (P5E25) at various engine speeds and compression ratios (CR). The outcomes of thermodynamic analyses revealed that the highest exergy and energy efficiency were 28.92 % (P0E0, 2600 rpm, CR of 9:1) and 31.01 % (P0E0, 2600 rpm, CR of 9:1), respectively. In addition, the average brake power and brake thermal efficiency for P0E0, P5E5, P5E15, and P5E25 increased by (30.36 %, 27 %, 26.74 %, 27.84 %) and (0.34 %, 0.07 %, 0.35 %, 0.33 %) respectively, while brake specific fuel consumption decreased by (2.5 %, 0.64 %, 3.62 %, 6.33 %) in the engine speed range of 2600–3200 rpm. Compared to gasoline, the maximum reduction of carbon monoxide emissions was 6.13 %, 8.81 %, and 9.96 %, while unburnt hydrocarbon emissions exhibited the maximum decrement by 5.8 %, 10.75 %, 12.58 % for P5E5, P5E15, and P5E25, respectively. However, nitrogen oxide (NOx) emissions for P5E25 tended to increase significantly compared to P0E0, while the difference in NOx emissions for P5E15 and P0E0 was marginal. Overall, P5E15 could be considered as the potential alternative fuel for spark-ignition engines towards the goal of sustainable energy conversion.

Unraveling the hydropower vulnerability to drought in the United States

Abstract Drought, a potent natural climatic phenomenon, significantly challenges hydropower systems, bearing adverse consequences for economies, societies, and the environment. This study delves into the profound impact of drought on hydropower generation (HG) in the United States, revealing a robust correlation between hydrologic drought and hydroelectricity generation. Our analysis of the period from 2003 to 2020 for the Contiguous United States (CONUS) indicates that drought events led to a considerable decline in hydroelectricity generation, amounting to approximately 300 million MWh, and resulting in an estimated loss of $28 billion to the sector. Moreover, our findings highlight the adverse environmental effect of drought-induced HG reductions, which are often compensated by increased reliance on natural gas usage, which led to substantial emissions of carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen oxide (NO X ), totaling 161 700 kilotons, 1199 tons, and 181 977 tons, respectively. In addition to these findings, we assess the state-level vulnerability of hydropower to drought, identifying Washington and California as the most vulnerable states, while Nevada exhibits the least vulnerability. Overall, this study enhances understanding of the multifaceted effects of drought on hydropower, which can assist in informing policies and practices related to drought management and energy production.

NOx precipitation and valorization driven by photocatalysis and adsorption over red soil

Nitrogen oxides (NOx) emissions can cause air pollution that is harmful to human health, even producing serious ecological problems. Whether it is diluted in the air or not, the management and valorization of NOx from industrial emissions have been constrained by technology and finance. This study shows that red soil can be used as a photocatalyst to convert NOx into soil nitrate nitrogen (NO3−-N) in the soil. The addition of zinc oxide (ZnO) and titanium dioxide (TiO2) onto the soil surface improves the photocatalytic precipitation efficiency of 1 ppm NO, approaching a removal efficiency of 77 % under ultraviolet (UV) light. The efficiency of red soil in precipitating NOx through adsorption exceeded that of photocatalysis at 100 ppm NOx (e.g. 16.02 % versus 7.70 % in 0.1-mm soil). Pot experiment reveals that the precipitated NO3−-N promoted biomass of water spinach (Ipomoea aquatica Forsk). Additionally, adding ZnO or TiO2 also affects mineral nutrition. This demonstration of converting air pollutants into available nitrogen (N) for plant growth not only provides a new perspective on treatment and valorization for NOx but also sheds light on the transport of N in the air-soil-plant path.

Novel integrated system for power, hydrogen, and ammonia production using direct oxy-combustion sCO2 power cycle with automatic CO2 capture, water electrolyzer, and Haber-Bosch process

Renewable energy-based multigeneration systems for power, hydrogen, and ammonia production suffer from intermittency issues and high production costs. On the other hand, conventional fossil-fuel-based systems yield high levels of CO2 emissions. Thus, to eliminate the intermittency issue with low production costs and near zero CO2 emissions, a novel integrated, efficient, compact, and interactive system for power, hydrogen (H2), and ammonia (NH3) production is developed and investigated in this study. A direct oxy-combustion supercritical carbon dioxide (DOC-sCO2) power plant is integrated with a water electrolyzer (WE) and Haber-Bosch process (HBP) system for the cogeneration of power, H2, and NH3, respectively. The power consumption of the air separation unit (ASU) of the DOC-sCO2 cycle is significantly reduced by the utilization of the oxygen produced from the WE system. Moreover, the cost of ammonia production is minimized by the internal utilization of the nitrogen gas produced by the ASU. Furthermore, the feedwater of the WE system is supplied internally from the DOC-sCO2 power block. In addition, the CO2 emissions of the system are captured to realize near-zero emissions to the ambiance. Based on these features, thorough energy, exergy, economic, and environmental (4E) analyses were performed to evaluate the performance of the proposed system. The obtained results showed an impressive levelized cost of electricity of 3.72¢/kWh, levelized cost of hydrogen of 1.162$/kgH2, and ammonia of 0.197$/kgNH3 at an overall energy and exergy efficiencies of 44.09 %, and 63.6 %, respectively. The system has no emissions of nitrogen oxides (NOx) and reduces the CO2 emissions of the H2 production by 49.6 % and of the NH3 production by 48.8 % compared to the conventional gasification, SMR, and HBP systems, respectively. This research work also provides insights into wet versus dry cooling, part load operation, and the advantages over renewable-based systems in terms of stability, reliability, and economic feasibility.

Numerical investigation of the hydrogen-enriched ammonia-diesel RCCI combustion engine

Incorporating hydrogen into the fuel blend of ammonia/diesel in reactivity controlled compression combustion (RCCI) engines, while maintaining high indicated mean effective pressure (IMEP) and combustion efficiency (CE), presents a promising approach for mitigating nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), unburnt ammonia emissions and nitrous oxide (N2O) greenhouse gas (GHG)-a pressing challenge in the field. By supplementing ammonia/diesel combustion with hydrogen, potential issues related to incomplete combustion can be mitigated, along with a reduction in intake valve close temperature (TIVC). This study aims to assess the impact of hydrogen enrichment on combustion characteristics in RCCI engines utilizing ammonia and diesel as fuels, employing the kinetic mechanism of combustion reactions within Converge software. The effect of TIVC on key engine parameters, including in-cylinder pressure, heat release rate (HRR), CE, IMEP, and exhaust emissions, are analyzed by considering chemical reaction pathways. The findings reveal that introducing hydrogen into the ammonia /diesel RCCI combustion blend, leads to significant enhancements in CE and IMEP while simultaneously lowering emissions of CO, HC, unburnt ammonia, and N2O greenhouse gas (GHG). Specifically, when utilizing 80 % ammonia energy fraction (AEF) without hydrogen, minimum TIVC of 440 K is necessary to prevent incomplete combustion, increasing NOx emissions by approximately 20 g/kWh. However, by addition of 20 % hydrogen energy fraction (HEF) into the fuel mixture, the TIVC requirement drops to 380 K, thereby reducing NOx emissions to around 13 g/kWh, while maintaining consistent level of N2O GHG (2.7 g/kWh).