Low Global Warming Potential Research Articles

Risk assessment of particle and gaseous emissions from diesel and methanol–diesel advanced dual-fuel engines

The study investigates the influence of engine load and methanol energy share on the ultrafine particulate matter (PM) and unregulated emissions from advanced dual-fuel (reactivity-controlled compression ignition (RCCI)) and conventional diesel combustion (CDC) engines. An automotive diesel engine was modified to operate in RCCI mode by integrating a port fuel injection system with methanol. Real-time PM and gas-phase emissions were measured using a DMS 500 particle sizer and FTIR (Fourier-Transform Infra-Red) emission analyser. The study aims to evaluate the effect of combustion modes and operating conditions on exhaust emissions and their effect on human health and the environment. A comprehensive toxicity assessment was conducted which included quantifying the cytotoxicity on BEAS-2B epithelial lung cells exposed to PM, assessing lung retention of PM particles due to inhalation, and determining the cancer risk potential from carbonyl emissions. The risk assessment findings show that RCCI engine-emitted PM particles exhibit lower lung retention than those from the CDC engine. Furthermore, the environmental impact assessment reveals that RCCI engines emit unregulated emissions and exhibit lower global warming potential, acidification potential, and eutrophication potential than CDC engines. Notably, RCCI engines that emitted unsaturated HCs (Hydrocarbons) and carbonyl emissions show higher ozone-forming potential and cancer risk potential.

Thermodynamic Analysis of Two-stage Vapour Compression Refrigeration Systems Using Eco-friendly Refrigerants

As Nigeria continues to expand its industrial, commercial, and residential cooling needs, the demand for efficient and environmentally sustainable refrigeration systems is growing. However, the environmental impact of conventional refrigerants has raised concerns due to their high global warming potential and ozone depletion potential. This study presents a thermodynamic analysis of two-stage vapour compression refrigeration systems in Nigeria, utilizing eco-friendly refrigerants which offer low global warming potential and zero ozone depletion potential. The refrigeration system comprises a high-pressure stage compressor and a low-pressure stage compressor with the inter stage pressure taken to be the ideal inter stage pressure. Performance analysis of R-717, R-600, R-600a and R-290 two-stage vapour compression refrigeration systems were made using seven parameters. The effect of the variation of five operating/design parameters (evaporating temperature, condensing temperature, superheating temperature, sub cooling temperature and refrigerant mass flow rate) on Coefficient of Performance (COP) of two-stage vapour compression system was analysed using engineering equation solver software. The results showed that as evaporating temperature decreases from 0oC to -50oC, COP decreased for all the four refrigerants considered. R-717 gave the highest COP value of 7.636 at evaporating temperature of 0oC while R-600a gave the lowest value of 4.009 at the same temperature. The results also showed that the COP of all the four refrigerants increased with increase in sub cooling temperature and Superheating Temperature, whereas it decreased with increase in condensing temperature. The study revealed that, except for the mass flow rate, all other operating parameters significantly affect the COP of refrigeration systems considered.

Analysis of a simple vapor compression and ejector refrigeration systems working with eco-friendly refrigerants

Transitioning to alternative refrigerants with low Global Warming Potential (GWP) in both vapor compression and ejector refrigeration systems emerges as a viable strategy to address the environmental impact associated with refrigeration technologies. This shift necessitates a thorough examination of factors such as thermodynamic performance, safety considerations, and optimization of system design. The outcomes of this study contribute to the advancement of sustainable refrigeration systems, aligning with global initiatives to curb greenhouse gas emissions and preserve the environment. The study adopts a thermodynamic approach to numerically investigate several eco-friendly refrigerants with GWP below 150, including R1234yf, R1234ze, R1270, R152a, R290, and R600a, as potential alternatives for vapor compression and ejector refrigeration systems. Thermodynamic models, developed in MATLAB using refrigerant properties, reveal that R600a and R290 exhibit promising potential as replacements for R134a in vapor compression refrigeration systems. These alternatives demonstrate a noteworthy improvement in the thermodynamic coefficient of performance, with percentages of 2.47% and 2.12%, respectively, under similar working conditions. For ejector refrigeration systems, R152a, R717, and R1270 exhibit enhanced coefficients of performance, contributing to significant savings in generator heat load. The results highlight the ability of these refrigerants to improve both the efficiency and sustainability of refrigeration systems in diverse applications.

Research on the performance of ultra-low temperature cascade refrigeration system based on low GWP refrigerants

The EU Security Council and Parliament have tentatively agreed to ban fluorinated gases with a global warming potential (GWP) higher than 150 in split air conditioners and heat pumps from 2027. This will further motivate the refrigeration industry to accelerate the search for refrigerants with low GWP and zero ozone depletion potential (ODP). At present, research into low GWP refrigerants for cascade systems is limited, focusing mainly on single refrigerant substitutes without comprehensive comparisons and lax GWP restrictions. In this study, the cascade refrigeration cycle (CRS) system is established to meet the demand of −100 to −50 °C. The GWP of the refrigerants is strictly controlled below 150, and a comprehensive screening of the four generations of refrigerants is carried out to identify refrigerant pairs that meet environmental and refrigeration requirements. The relationship between the high-temperature cycle (HTC) evaporation temperature and the optimal coefficient of performance (COP) is determined, and the effects of the low-temperature cycle (LTC) evaporation temperature Te concerning with mass flow rate, discharge temperature of compressor, compressor power consumption, exergy destruction, and exergy efficiency are analyzed in detail. The thermodynamically superior refrigerant pairs are identified by comparison with several conventional refrigerant pairs. The results show that when Te > −67 °C, R170/R600a is preferred, and when Te ≤ −67 °C, R170/R1270 is preferred. In the temperature range of −100 ∼ −50 °C, R170/R1270 is the better refrigerant pair, which can improve the performance by 6.39–13.11 % than traditional refrigerant pairs. Finally, the exergy destruction analysis of CRS components is carried out, which provides a reference for refrigerant selection and system optimization of CRS in the field of ULT.

4E analysis and multi-objective optimization of an ejector-expansion cascade refrigeration system for building cold storage using low GWP refrigerants

The need for efficient, eco-friendly refrigeration systems operating at ultra-low temperatures (-50°C to -100°C) has spurred interest in cascade designs. Traditional single-stage cycles are constrained by pressure ratios and temperature range, limiting their effectiveness. This study seeks to improve such systems with an ejector-expansion cascade refrigeration system (EECRS) incorporating low global warming potential (GWP) refrigerants and dual ejectors for both high- and low-temperature cycles. It uses a 4E (Energy, Exergy, Exergoeconomic, Exergoenvironmental) analysis and a three-objective optimization focused on cost rate, exergy efficiency, and Coefficient of performance (COP), utilizing TOPSIS methodology with refrigerants R744, R41, R1234yf, and R1234ze. The findings highlight that an R41-R1234yf refrigerant pair performs best at -55°C evaporator and 50°C condenser temperatures, achieving a COP of 1.44, exergy efficiency of 30.81%, and an operating cost of $0.791/h. It yields 13.07 kW cooling from the evaporator and 22.15 kW heat output from the condenser. Exergy destruction primarily occurs in the evaporator (43.75%), condenser (30.43%), and heat exchanger (19.77%), with lesser losses in other components. Environmental destruction factors are highest for the evaporator, condenser, and heat exchanger, with compressors 1 and 2 showing the highest environmental impact rates, at 7.539 and 3.775 mpts/h, respectively. This study introduces low-GWP refrigerants in an advanced EECRS, promoting high-efficiency, sustainable ultra-low temperature refrigeration ideal for industrial and commercial cold storage within building environments, balancing environmental and cost concerns.

Optimization and Thermodynamic Analysis of CO2 Refrigeration Cycle for Energy Efficiency and Environmental Control

Supermarket applications are significant contributors to greenhouse gas emissions, necessitating efforts to reduce carbon footprints in the food retail sector. Carbon dioxide (R744) is recognized as a viable long-term refrigerant choice due to its favorable properties, including low Global Warming Potential, non-toxicity, non-flammability, affordability, and widespread availability. However, enhancing the energy efficiency of pure CO2 systems in basic architecture units, particularly in warm regions like India, remains a challenge. To address this, modern refrigeration systems must prioritize low energy consumption and high coefficient of performance (COP) while meeting environmental standards. This study investigates different operating conditions to determine the optimal parameter range for maximizing COP and improving the efficiency of conventional CO2 refrigeration configurations. It examines both subcritical and transcritical refrigeration cycles under varying parameters, emphasizing the importance of understanding COP’s relationship with factors such as subcooling, superheating, ambient temperature, and evaporator temperature. The study advises against superheating in CO2 systems but highlights the substantial COP increase with higher degrees of subcooling, leading to enhanced system performance. Additionally, it provides a comprehensive theoretical comparison between advanced pure CO2 supermarket applications and commonly used hydrofluorocarbons-based systems, offering insights into energy efficiency and environmental impacts for informed decision-making in the industry.

Approach to Design Sustainable Alkali-Activated Slag Recycled Aggregate Concrete: Mechanical and Microstructural Characterization

There is a steep increase in demand for concrete as the need for infrastructure is increasing with a rapid increase in urbanization. Consequently, there has been a surging demand for cement across the globe. By using alkaline concrete activated with ground granulated blast furnace slag (GGBS), cement usage can be eliminated in concrete, which addresses the issue of CO2 emissions concerned with the cement manufacturing process and promotes the use of industrial by-products as sustainable building materials. The current study focuses on proposing a methodology to design sustainable GGBS-based alkali-activated concrete incorporated with 100% coarse recycled coarse aggregates (RCA) recovered from construction and demolition (C&D), for various strengths by optimizing the mix proportions and verifying the same through experiments. From the current study, it is evident that this mix design procedure can be adopted to design alkali-activated slag recycled aggregate concrete (AASRAC) mixes for strengths ranging from 44MPa to 85MPa. The optimum values of alkalinity factor (λ) and NaOH concentration (M) i.e., 1.5 and 12, have a significant role in the development of high strengths which is attributed to the formation of hydrotalcite. Micrographs captured using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) studies reveal that the alkaline binders promote the development of a denser and stronger interfacial transition zone (ITZ) that enhances the strength of lower AA/B concretes at the microstructural level as Ca/Si ratio is higher for lower AA/B concretes. Global warming potential (GWP) analysis reveals that the alkali-activated concretes have significantly lower GWP compared to conventional OPC-based concrete by approximately 2.5 times. The mix-design chart proposed in this study may pave the way to designing structural grade AASRAC with enhanced performance for the desired strength, which may find its application in fast-track construction and manufacturing of prefabricated elements.

Multi-Objective NSGA-II Optimization of Single- and Dual-Fluid ORC-VCC Systems Using Butane and Isobutane.

The urgent need for environmentally sustainable cooling technologies, driven by global regulatory constraints, has intensified the search for natural refrigerants with low global warming potential. This study evaluates the potential of natural refrigerants, specifically butane and isobutane, in advanced single- and dual-fluid Organic Rankine Cycle-Vapor Compression Cycle (ORC-VCC) systems to enhance energy efficiency and environmental sustainability. Using the Non-dominated Sorting Genetic Algorithm II (NSGA-II) within a multi-objective framework, the optimization maximizes key performance metrics such as coefficient of performance (COP) and cooling power, while the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method enables a refined ranking of optimal solutions. Findings reveal that the isobutane (ORC)-butane (VCC) dual-fluid configuration achieves the highest overall COP of 0.447 and a cooling capacity of 35.517 kW, surpassing the reference fluid R1233zd, which attains a COP of 0.374 and a cooling capacity of 30.361 kW. Isobutane-based configurations consistently deliver higher COP and cooling capacities than R1233zd, highlighting isobutane's suitability for applications demanding high energy efficiency. Pressure analysis revealed that R1233zd exhibits the highest pressure ratio of 4.10, necessitating more complex compressor designs. In contrast, isobutane configurations offer favorable pressure ratios and similar pressure parameters in both single and dual setups, simplifying compressor design requirements. This research provides valuable guidance for developing sustainable ORC-VCC systems by combining effective fluid selection and advanced multi-objective optimization techniques to meet both environmental and operational criteria.

Plasma Atomic Layer Etching of Dielectric Materials with Low Global Warming Fluoro-Ether Isomers

In this work, the comparative study of the plasmas of C5F10O and C4H3F7O isomers with low global warming potential (GWP) was conducted in plasma atomic layer etching (ALE) processes of dielectric materials. Plasma atomic layer etching processes for silicon oxide and silicon nitride were developed with perfluoropropyl vinyl ether (PPVE) and perfluoroisopropyl vinyl ether (PIPVE) as C5F10O isomers, and heptafluoropropyl methyl ether (HFE-347mcc3) and heptafluoroisopropyl methyl ether (HFE-347mmy) as C4H3F7O isomers. In the surface fluorination step, the dielectric surfaces were fluorinated with C5F10O and C4H3F7O isomer plasmas and the fluorinated layer was removed by ion bombardment with Ar plasma. The F1s/C1s ratio of the fluorocarbon layer in PPVE plasma analyzed by X-ray photoelectron spectroscopy (XPS) was higher when it is compared to those in PIPVE, HFE-347mcc3, and HFE-347mmy plasmas. In the removal step, ALE window was identified in 50.0 ~ 57.5 V for C5F10O isomers and 50 ~ 60 V for C4H3F7O isomers and the etch per cycle (EPC) of SiO2 was determined to be 5.4, 3.3, 2.1, and 1.8 Å/cycle for PPVE, PIPVE, HFE-347mcc3, and HFE-347mmy, respectively in the ALE window region. The EPC of SiO2 was the highest in the PPVE with a high F1s/C1s ratio of 1.57, and the lowest in the HFE-347mmy with a low F1s/C1s ratio of 1.05. The global warming effect of the exhaust gases was evaluated by carbon dioxide equivalent values determined from the concentration of the exhaust gases. The carbon dioxide equivalent was reduced up to 90%, compared to that of C4F8 plasma. The carbon dioxide equivalent of C4H3F7O isomer plasmas was the lower than that of C5F10O isomer plasmas due to the generation of HF and CO, having much lower GWPs as major reaction products.

Enhancing waste management in batang regency: Integrating circular economy principles with life cycle assessment and material flow analysis

Batang Regency encountered persistent waste management challenges, requiring effective mitigation strategies. This study evaluated residential waste management utilizing life cycle assessment (LCA) and material flow analysis (MFA) to propose sustainable plans. Three scenarios were compared: the current conditions (Scenario 1) had the highest environmental impact. In contrast, Scenarios 2 and 3, which included sorting and recycling processes, demonstrated improved energy and product recovery, making them more sustainable. The results indicated that Scenario 1 had a global warming potential (GWP) of up to 1.65E+04 CO2 eq/t MSW, Scenario 2 had up to 2.88E+03 CO2 eq/t MSW, and Scenario 3 had up to 3.08E+03 03 CO2 eq/t MSW. Scenario 2 exhibited a lower GWP than Scenario 1, while Scenario 3, although higher in GWP, was recommended for excluding landfills. These findings highlighted the potential for waste sorting improvements and adjustments to classified waste treatment with environmental regulations, supporting sustainability in Batang Regency's waste management.

Seasonal performance comparison of R-410A and R-454B in a variable-speed air-cooled scroll chiller

In recent years, there has been increasing concern about the impact of air conditioning and refrigeration on global warming. This is particularly related to the emissions of refrigerants with high global warming potentials (GWP), such as R-410A, which is used in air conditioning and chiller systems. There has been a concerted effort within the HVAC industry to find lower GWP refrigerants to replace R-410A in HVAC systems. In this paper, a 10.5 kW (3 TR) air-cooled variable-speed scroll chiller has been utilized to conduct an experimental comparison of R-410A (GWP of 2088) and its low GWP A2L alternative R-454B (GWP of 466) according to AHRI 551/591 testing condition at rating and part load condition with optimized charge. The compressor speed and suction superheat were matched for both refrigerants at all the test conditions. R-454B shows 98 % capacity and 102 % efficiency compared to R-410A at rating conditions of 35 °C outdoors and water return temperature of 12 °C. The IPLV of the R-454B chiller was just 1 % higher than R-410A. The discharge temperature of R-454B and compressor isentropic efficiency is 8 % higher and almost like R-410A, respectively. The optimized charge of R-454B was 5 % lower refrigerant charge compared to R-410A. The LCCP analysis for major Indian cities over a 15-year operational span demonstrates a notable reduction, ranging from 6.6 % to 7.3 %, in overall R-454B emissions compared to R-410A. The study demonstrates that R-454B is a drop-in replacement to R-410A designs and reduces the direct GHG emission from the chiller by 76 %.

Thermodynamic and technoeconomic limitations of Brayton refrigeration for air conditioning

With global cooling demand increasing, there is a need for refrigeration cycles that use low global warming potential (GWP) refrigerants. Researchers have flirted with the idea of using the Brayton cycle for refrigeration over the years, but it has yet to prove competitive in performance or cost when compared to the widely used vapor compression cycle. The recent development of an electrochemical Brayton refrigeration cycle has renewed interest in the thermodynamics of Brayton refrigeration. This work provides a parametric study of the COP of a Brayton cycle air conditioner (either mechanical or electrochemical in nature) as a function of the characteristics of the cycle components (thermal conductances and isentropic efficiencies). When the isentropic efficiencies of the adiabatic components (i.e., the compressor and turbine in the mechanical Brayton cycle) are 90 %, the cycle COP is limited to a value of ∼1. Furthermore, a thermodynamic comparison to the vapor compression cycle reveals that the Brayton refrigeration cycle generates ∼8 × more entropy, and that the thermodynamic favorability of the vapor compression cycle is due to the presence of phase change.

Life cycle assessment of ethanol production from broken wheat and rice grains

Ethanol from broken grains will contribute to India’s fuel mix, therefore, the environmental impacts must be systematically quantified. This work performs a detailed life cycle assessment (LCA) of ethanol production from broken wheat and rice in the Indian context. Cradle-to-gate system boundary is considered, and the functional unit is 1 L ethanol. Process inventory is based on literature studies and basic process engineering calculations. Ecoinvent® v3.3 database is also used to get required inventory data. OpenLCA 1.11.0 software and the ReCiPe midpoint (H) model are used for the calculations. A key conclusion is that ethanol from broken grains has substantially lower global warming potential (GWP) (0.536–0.983 kg CO2 eq.) as compared to other fuels. Ethanol from rice has higher GWP and water depletion than that from wheat. The results also show the impacts are dominated by the farming stage. About 98% of water depletion was due to the agricultural stage for both grains. The other import impact factors are fossil depletion, human toxicity, metal depletion, marine eutrophication, and terrestrial acidification. The main driving factors for these are the depletion of coal, natural gas, and crude oil and by the emissions in the form of methane, mercury, manganese, and other metals.

Accurately measuring slowly propagating flame speeds: Application to ammonia/air flames

Environmental concerns have driven the development of alternative fuels and refrigerant working fluids with low global warming potential. Ammonia (NH3) is a potential zero-carbon fuel, while hydrofluorocarbons (HFCs) like R-32 and R-1234yf are being adopted as refrigerants. When mixed with air, these compounds can sustain slowly propagating flames with laminar flame speeds less than 10 cm/s. Unlike typical hydrocarbon-fueled flames, these slow flames are influenced by buoyancy-induced flow and radiation heat loss. In this study, we experimentally investigate the flame speeds of NH3/air mixtures using the constant-pressure spherically expanding flame method, while circumventing gravity-induced natural convection, and account for radiation-induced inward flow. To mitigate buoyant convection, a low-cost drop tower was built and used to study slow spherically expanding flames in free fall. A computational model (SRADIF) is utilized that combines thermodynamic equilibrium and finite rate optically thin limit radiation heat loss calculations to estimate the inward flow. The developed methodology is utilized to investigate slowly propagating NH3/air flames over a range of equivalence ratios. A systematic approach was undertaken to understand and quantify the errors that could arise when deriving the laminar flame speed. It was found that attempting to study slowly propagating flames in a static configuration, as opposed to in free fall, results in large differences in flame dynamics and subsequently all derived quantities. It is necessary to study slowly propagating flames in free-fall. Additionally, using experimental data that has not been corrected for radiation-induced flow leads to large errors in all derived quantities. Furthermore, direct comparisons of experimental measurements and detailed flame simulations are found to be necessary to determine if existing extrapolation approaches are applicable to these slowly propagating flames, which are challenging to study.

Environmental assessment of cenosphere and GGBFS-based geopolymers: A path to greener construction materials

This study investigates the viability of utilizing cenospheres as an alternative precursor material for geopolymer formulation, comparing their performance against ground-granulated blast furnace slag (GGBFS) across various parameters such as strength, durability, cost, and environmental impacts. A cradle-to-gate life cycle assessment was performed to evaluate the environmental impact of geopolymer mixtures containing varying proportions of cenosphere and GGBFS, relative to conventional cement mortar (CM). Additionally, a multi-criteria decision-making (MCDM) analysis was employed by assigning varied importance levels to identify the optimal formulation derived from performance (strength and durability), cost, and environmental impact. The findings demonstrate that GGBFS/cenosphere-based geopolymers lower global warming potential (GWP) by 24–33 % compared to CM. Moreover, incorporating 25–75 % cenospheres in geopolymers reduces GWP by 4–7 % and energy consumption by 5 % compared to purely GGBFS-based geopolymers. The eutrophication potential (EP) and acidification potential (AP) were also reduced by 3–10 % and 5–15 %, respectively, by adding 25–75 % cenospheres in geopolymers. However, the cost is also increased by 6–18 %. Based on the MCDM analysis, geopolymers containing cenosphere possess higher overall sustainability than conventional cement-based mortars.

Techno-economic studies of low GWP-organic Rankine cycle for low-level geothermal waste heat utilization in Remote Island of Indonesia

With global decarbonization trends, the energy supply challenge persists, especially in archipelagic nations like Indonesia. The Ulumbu Geothermal Power Plant at Flores Island of Indonesia currently uses a type of back pressure where the expanded steam is discharged directly to the atmosphere at a pressure of 0.98 bar and a temperature of 98.7 °C. This steam could be harnessed to generate electrical energy using Organic Rankine Cycle system. This study thermodynamically and economically assessed two ORC systems: Binary Cycle-Organic Rankine Cycle (BC-ORC) and Recuperator (BC-ORCR), both using low global warming potential (GWP) working fluids of R1233zd (E), R1224yd (Z), R1234ze (Z), R1234ze (E), R1243zf, and R1234yf, paired with air- and water-cooled condensers. The results indicate that the BC-ORCR system with a water-cooled condenser using R1233zd (E) as the working fluid achieved the highest net output power value and system efficiency of 2213 kW and 10.14 %, respectively. This could support up to 65 % of the electricity load of the GI Ulumbu and GI Ruteng substations. Economically, this system also emerged as the most favorable option, offering the highest production capacity, with a TL Sales Target of 16,476,847 USD, a net present value (NPV) of 3,982,761 USD and a Payback Period of 9.39 years, outperforming other systems in the analysis.

Greenhouse gas emissions and net energy production of dark fermentation from food waste followed by anaerobic digestion

There are diverse estimations regarding the carbon reduction effects of alternative hydrogen production technologies. This study assessed the greenhouse gas (GHG) emissions and energy balance of a two-stage process combining dark fermentative hydrogen production and anaerobic digestion from food waste using the cradle-to-gate life cycle assessment (LCA). The system boundary included collection and transportation, pretreatment and feedstock storage, dark fermentation, H2 purification, anaerobic digestion and heat and power generation and the estimated GHG emission was compared with a single anaerobic digestion of food waste. GHG emission of the biohydrogen production was estimated as 2.48 kg CO₂-eq per kg H₂ without considering avoided emissions from heat and power generation. The environmental impacts were majorly influenced by electricity use. The net energy ratio of the two-stage process was calculated to be 8.18, confirming a net energy gain and the potential GHG emission avoidance for electricity and heat use. Given that the single-stage anaerobic digestion of 16 tons of food waste is replaced by the two-stage dark fermentation process, 76.6 kg CO₂-eq would be avoided. Sensitivity analysis revealed that energy-saving strategies are the most sensitive factors for achieving positive net energy production and low global warming potential.

The Effect of the Use of a Novel Urease Inhibitor Coated Urea on the Greenhouse Gas Emissions and Ammonia Volatilization Losses from a Maize Field

Nitrogen fertilizers are essential for enhancing agricultural productivity but are also major contributors to greenhouse gas (GHG) emissions and ammonia volatilization, which affect environmental sustainability. This study evaluated the effect of cashew nut shell liquid (CNSL)-coated urea on GHG emissions and ammonia losses from maize fields in the Indo-Gangetic Plains, known for excessive nitrogen fertilizer usage. A randomized block design was employed with four treatments: control (no nitrogen), prilled urea, neem-coated urea (NCU), and CNSL-coated urea (CCU). Gas samples were collected using the closed chamber method, and emissions of CO₂ and N₂O were analyzed via gas chromatography. Ammonia volatilization was measured using the forced air draft method. Results showed that the CCU treatment significantly reduced ammonia volatilization compared to prilled urea (15.84% reduction), with reductions of 9% to those observed with NCU. Moreover, CCU-treated plots exhibited reduced cumulative GHG and lower global warming potential (GWP) without compromising maize yields. Cumulative GHG emissions varied among the treatments in the order urea> CCU> NCU> Control. CCU treated plots exhibited a net GWP decrease of 8.59% compared to urea and an increase of 4.13% compared to NCU. These findings suggest that CNSL-coated urea can serve as an eco-friendly alternative to conventional urea, potentially mitigating environmental impacts associated with nitrogen fertilization. Further studies are recommended to assess the long-term efficacy of CNSL in various soil types and climatic conditions.

Assessing the life cycle and economic impact of cement-modified biochar compared to conventional adsorbents for heavy metal removal in stormwater

Modified biochar is used for heavy metal removal from stormwater, but current modifications rely on high-cost chemicals and result in highly toxic effluents. Additionally, there is limited research on these modifications' environmental impact and cost. This study aims to investigate the life cycle analysis (LCA) and economics of the process of absorption of Cu, Pb and Zn from synthetic stormwater utilizing cement-modified biochar adsorbent and compared it with commonly available adsorbents, activated carbon and zeolite. The cradle-to-gate LCA used experimental data and the Ecoinvent 3.0 database. Adding 1.5 % cement to biochar reduced its negative environmental impact by two to three times compared to plain biochar. Cement addition enhances heavy metal removal by raising pH, promoting precipitation, and reducing metal mobility. Combined with biochar, it increases the available surface area for adsorption, further boosting the system's efficiency in contaminant removal. The cement-modified biochar had the lowest global warming potential (kg CO2 eq), about half of Paddy Husk Biochar (PHBC). Approximately 50–90 % of the environmental impact of cement-modified biochar, zeolite, and PHBC was attributed to raw material collection. The Saw Dust Biochar (SDBC) had the highest sensitivity towards transportation distances among the adsorbents considered. Due to its heightened adsorption capacity, the 98.5 % PHBC composite demonstrated the lowest environmental impacts for Cu and Zn removal in multi-metal systems. Transportation of raw materials and labor costs were the primary cost drivers for biochar-based adsorbents. Among the adsorbents, 98.5 % PHBC was the best, being cost-effective and efficient for heavy metal removal. It is suitable for at-source pollutant removal in low-rainfall and high-pollution areas. Overall, this study helped identify performance weaknesses and modification opportunities for cement modification of biochar in heavy metal pollution control.

Experimental comparison of cycle modifications and ejector control methods using variable geometry and CO2 pump in a multi-evaporator transcritical CO2 refrigeration system

To reduce the direct global warming impact of refrigerants in HVAC&R applications, low-global warming potential (GWP) refrigerants, including natural refrigerants, have been extensively investigated as alternatives to hydrofluorocarbon (HFC) refrigerants. Among the natural refrigerants, Carbon Dioxide (CO2) offers several advantages, such as excellent transport and thermo-physical properties, being neither toxic nor flammable, and having a low price and high availability around the world. However, the high critical pressure and low critical temperature of CO2 often lead to transcritical operation, resulting in lower efficiency due to the additional compressor power necessary to achieve transcritical operation relative to subcritical HFC cycles. Therefore, a number of cycle modifications are used to enhance the coefficient of performance (COP) of transcritical CO2 cycles to meet or surpass those of HFC cycles. This paper provides a systematic experimental investigation of four such cycle architectures by employing the same multi-stage, two-evaporator CO2 refrigeration cycle test stand, 3 of these configurations in transcritical and 1 in subcritical conditions. The four cycles architectures included intercooling, open economization, an internal heat exchanger and two different ejector control approaches. Specifically, a variable-diameter motive nozzle and a variable-speed liquid CO2 pump located directly upstream of the ejector motive nozzle inlet were analyzed. Based on the experimental data, the maximum COP improvements are 4.64 % and 9.47 % when the ejector and the internal heat exchanger are used, respectively. The CO2 pump, once successfully stabilized, can control the ejector, increase its efficiency by up to 15 % and increase the cooling capacity to a maximum of 6.2 %. Nevertheless, a reduction in COP is measured when the pump is in use; however, unlike the other three different configurations, it was only analyzed under subcritical conditions.