Lower N2O Emissions Research Articles

Efficacy of three nitrification inhibitors to reduce nitrous oxide emissions from pig slurry and mineral fertilizers applied to spring barley and winter wheat in Denmark

Mineral fertilizers and livestock manure are major sources of nitrous oxide (N2O) emissions from agricultural soil. Meta-analyses consistently show that nitrification inhibitors reduce N2O emissions, and this study was established to evaluate the efficacy of three selected compounds, DMPP, nitrapyrin and Piadin, to reduce N2O emissions from spring-applied mineral fertilizers (NS 26–13 or UAN) and pig slurry. An N source either alone or combined with an inhibitor were established in 2020 and 2021. In 2020 these treatments were applied in late April before seeding of spring barley, and in 2021 the same treatments were applied in early April to winter wheat under conventional tillage (as in 2020) and no-till management, respectively. Nitrous oxide fluxes and soil mineral N dynamics were monitored during spring only. The range of N2O emissions in the spring barley experiment was typical for this site, bt much higher with pig slurry compared with mineral fertilizers. The winter wheat experiment the following year showed generally low N2O emissions. The effects of nitrification inhibitors, across all treatments, varied between 0 and 90% reduction of N2O emissions. The variable emission levels and treatment effects were explained with reference to climate (temperature, rainfall), distribution of fertilizers, and crop growth, and a need for comparative studies to resolve interacting effects was identified. Overall, the results were consistent with nitrification inhibitors being more effective at reducing N2O emissions from crops where mineral N uptake is delayed relative to the time of fertilization, from mineral N fertilizers in wet or compacted soil, and from organic fertilizers at moderate or even dry soil conditions.

Intrinsic kinetics mechanisms for the catalytic reduction of NO by Na-loaded char

An insight into the interaction between NO and Na-loaded char is essential to improve the catalytic ability of Na to NO reduction, which will be useful to lower NO emissions during thermal utilization of sodium-containing fuels. Here, the intrinsic kinetics mechanisms for the catalytic reduction of NO by Na-loaded char were discussed in details. Using density functional theory (DFT) calculations, possible reaction pathways were first obtained, followed by evaluation of the rate coefficients through transition state theory (TST) calculations. On this basis, the analyses of both sensitivity and rate of products (ROP) were performed to illustrate the intrinsic kinetic mechanism for the NO reduction by Na-loaded char in a certain combustion condition, with an emphasis on the effects of temperature and NO-to-CO stoichiometric ratio. Results indicated that the catalytic active center –ONa plays an important role in the catalytic reduction of NO by Na-loaded char. Specifically, in most cases, the interaction of NO with Na-loaded char largely depends on the elementary reaction of CNO-Na+NO+CO→21-IM3+CO2. As the stoichiometric ratio of NO to CO increases, the CO-Na+2NO→8-IM4+N2 becomes increasingly dominant. Moreover, higher temperature causes the CNO-Na+NO→20-P + N2O as the dominant reaction. Nonetheless, one thing that these reactions have in common is that they are all related to the catalytic active center –ONa. Therefore, the NO reduction Na-loaded char largely depends on the interaction of NO with the carbonaceous surface containing –ONa. Inspired by this, a conceptual approach was proposed to improve the catalytic performance of Na on NO reduction, and it has been shown to be theoretically feasible. To summarize, the combination of DFT, TST and kinetic calculations is useful to clarify the interaction between NO with Na-loaded char, and it gives a basis for the development of micro-kinetic model.

Experimental assessment of the performance of a commercial micro gas turbine fueled by ammonia-methane blends

This study reports on the performance of the Ansaldo AE-T100 commercial micro gas turbine (mGT) when fueled by ammonia-methane blends instead of its design fuel, natural gas. This micro gas turbine was used as the experimental platform to understand effects of ammonia addition, and its hardware was only marginally updated. Ammonia was added to the main fuel line in varying proportions, but the pilot flame fuel line was only fed with methane. Experiments were performed for constant electrical output power and turbine outlet temperature of 60 kWe and 645°C, respectively. Important operational parameters and exhaust emissions were continually monitored during the turbine's operation. Results show that stable operation on the mGT was possible until the volume fraction of ammonia in the fuel blend reached XNH3 = 0.63. To reach this ammonia fraction, it was necessary to increase the power of the pilot flame that provides a continuous ignition source at the base of the main flame. Concentrations of carbon monoxide and unburned hydrocarbon measured in the exhaust did not increase significantly until XNH3 = 0.22. However, above this value, concentrations increased rapidly, which is indicative of a drop in the combustion efficiency and, in turn, in the thermal efficiency. For XNH3 = 0.63, the measured thermal efficiency was ∼0.23, which is significantly lower than that found for operation with pure methane, ∼0.27. Although the CO2 concentration was found to decrease linearly when the ammonia fraction was increased, measurements reveal that NOx emissions increased rapidly, with a maximum NOx concentration of 2161 ppmvd. The concentration of N2O also increased rapidly when the ammonia fraction was increased. Due to N2O's very large global warming potential, this more than canceled the benefits associated with the reduction of CO2 emissions. Consequently, results showed that, even though stable operation of the Ansaldo AE-T100’s mGT in its original configuration is possible with ammonia-methane blends at least up to 60 kWe, hardware modifications will be required to comply with current NOx regulations and ensure sufficiently low N2O emissions.

Effects of hydrogen mixture ratio and scavenging air temperature on combustion and emission characteristics of a 2-stroke marine engine

A numerical study was conducted to investigate the effects of hydrogen and scavenging air temperature (SAT) on the combustion and emission characteristics of a 2-stroke heavy-duty dual-fuel (DF) marine engine at full load. The engine had a 700 mm bore fuelled with hydrogen–methane (H2-CH4) mixtures. Three-dimensional simulations of the combustion and emission formation inside the engine cylinder with various H2 contents in the H2-CH4 mixture were performed. ANSYS FLUENT simulation software was used to analyse the engine performance, in-cylinder pressure, temperature, and emission characteristics. The CFD models were validated against the measured data recorded from the engine experiments. The results showed that an increase in the in-cylinder peak pressure increased the engine power when the H2 content in the H2-CH4 mixture increased. Notably, CO2 and soot emissions decreased (up to more than 65%) when the H2 content in the gaseous mixture increased to 50%. Specific NO emissions in the DF modes were lower than that of the diesel mode, when the H2 content in the gaseous mixture was lower than 40%. However, they increased compared to the diesel mode when the H2 content continued to increase. This limits the H2 amount that should be used in a gaseous mixture creating NO emissions. The results also showed that the SAT cooling method can further reduce emission problems while enhancing engine power. In particular, reducing the SAT to 28 °C in the gaseous mixture with 10% H2 ensured that the DF mode emitted the lowest NO emissions compared to the diesel mode. This reduced NO emissions by 37.92% compared to the measured NO emissions of the research engine (a Tier II marine engine). This study successfully analysed the benefits of using an H2-CH4 mixture as the primary fuel and the SAT cooling method in a 2-stroke ME-GI heavy-duty marine engine.

Nitrous oxide emissions and productivity of irrigated potato: Effects of nitrogen fertilization options

AbstractImproved N management is needed in intensive agriculture to mitigate nitrous oxide (N2O) emissions while sustaining high yields. We assessed the effectiveness of polymer‐coated urea (PCU); nitrification inhibitor 2,4‐dimethylpyrazol succinic acid (DMPSA), a biostimulant; and their combinations with granular urea and ammonium sulfate nitrate (ASN) fertilizers to reduce N2O emissions and to improve potato (Solanum tuberosum L.) productivity under irrigation. Sites were located in Lethbridge and Brooks, Alberta, Canada over two growing seasons. Tuber yield, grade, specific gravity, and N uptake were quantified. We used the chamber method to measure N2O fluxes from potato hills and furrows. The N2O emissions from furrow positions were at least two‐fold greater than those from hills at the Lethbridge site. Peak N2O emissions and increased N concentrations in potato petiole and soils occurred shortly after fertilizer applications. The overall average emission factor (EF) of N2O was 0.056% kg N2O–N kg−1 N fertilizer (accounting for emissions from unfertilized controls). Urea alone commonly exhibited the highest N2O fluxes. Admixing DMPSA with either urea or ASN lowered N2O emissions in only certain cases. For instance, in one growing season at the Brooks site, adding DMPSA to urea reduced the N2O emissions by 57%. Likewise, in one of the four site‐years in the study, 36% higher potato marketable yields were obtained when applying either ASN treated with DMPSA or PCU compared with the unfertilized controls (45 vs. 33 Mg ha−1). Results showed that under specific conditions, N application strategies using DMPSA admixed with either urea or ASN can maintain high potato yields while reducing N2O emissions relative to soils receiving these fertilizers without this additive.

Spatial-temporal variations of nitrous oxide emissions in coffee agroforestry systems in Costa Rica

This study investigates spatial-temporal trends in N2O emissions from coffee production systems in Costa Rica with a focus on the effects of nitrogen fertilisation, topography and soil type. This is done by combining (i) multi-year continuous dynamic chamber measurements from sites with different fertilisation levels, (ii) static chamber measurements taken along a typical sloping coffee field and (iii) measurements from a laboratory incubation experiment with nutrient addition to different soil types. In the field and in the laboratory, additions included standard NPK fertiliser, ammonium nitrate (NH4NO3) as well as potassium nitrate (KNO3). Soils in a laboratory experiment were incubated under both drained and flooded conditions. Continuous measurements from automatic chambers show that annual N2O fluxes were dominated by bursts over few weeks following N-fertilisation with peak emissions up to 60 g N-N2O ha−1 day−1. A two-month slope experiment with static chambers after KNO3-fertilisation with 90 kg N ha−1 showed N2O significant differences between the highest daily emission rates from the top and the bottom of the slope (134 ± 20 g N-N2O ha−1 and 336 ± 104 g N-N2O ha−1, respectively) which can be explained by NO3- transport downhill and flooded conditions favouring denitrification at the bottom of the slope. Incubation experiments indicate that denitrification is the main process controlling N2O emissions but also that nitrification can result in low N2O emission rates under drained conditions. It can be concluded that the reported N2O emissions from the coffee agroforestry systems are generally low, but may be underestimated, as both poorly drained depressions functioning as N2O hotspots as well as temporal N2O bursts need to be taken into account.

Partial substitution of manure reduces nitrous oxide emission with maintained yield in a winter wheat crop

Conventional fertilization of agricultural soils results in increased N2O emissions. As an alternative, the partial substitution of organic fertilizer may help to regulate N2O emissions. However, studies assessing the effects of partial substitution of organic fertilizer on both N2O emissions and yield stability are currently limited. We conducted a field experiment from 2017 to 2021 with six fertilizer regimes to examine the effects of partial substitution of manure on N2O emissions and yield stability. The tested fertilizer regimes, were CK (no fertilizer), CF (chemical fertilizer alone, N 300 kg ha−1, P2O5 150 kg ha−1, K2O 90 kg ha−1), CF + M (chemical fertilizer + organic manure), CFR (chemical fertilizer reduction, N 225 kg ha−1, P2O5 135 kg ha−1, K2O 75 kg ha−1), CFR + M (chemical fertilizer reduction + organic manure), and organic manure alone (M). Our results indicate that soil N2O emissions are primarily regulated by soil mineral N content in arid and semi-arid regions. Compared with CF, N2O emissions in the CF + M, CFR, CFR + M, and M treatments decreased by 16.8%, 23.9%, 42.0%, and 39.4%, respectively. The highest winter wheat yields were observed in CF, followed by CF + M, CFR, and CFR + M. However, the CFR + M treatment exhibited lower N2O emissions while maintaining high yield, compared with CF. Four consecutive years of yield data from 2017 to 2021 illustrated that a single application of organic fertilizer resulted in poor yield stability and that partial substitution of organic fertilizer resulted in the greatest yield stability. Overall, partial substitution of manure reduced N2O emissions while maintaining yield stability compared with the synthetic fertilizer treatment during the wheat growing season. Therefore, partial substitution of manure can be recommended as an optimal N fertilization regime for alleviating N2O emissions and contributing to food security in arid and semi-arid regions.

Native Rhizobia Improve Plant Growth, Fix N2, and Reduce Greenhouse Emissions of Sunnhemp More than Commercial Rhizobia Inoculants in Florida Citrus Orchards.

Sunnhemp (Crotalaria juncea L.) is an important legume cover crop used in tree cropping systems, where there is increased interest by growers to identify rhizobia to maximize soil nitrogen (N) inputs. We aimed to isolate and identify native rhizobia and compare their capabilities with non-native rhizobia from commercial inoculants to fix atmospheric dinitrogen (N2), produce and reduce nitrous oxide (N2O), and improve plant growth. Phylogenetic analyses of sequences of the 16S rRNA and recA, atpD, and glnII genes showed native rhizobial strains belonged to Rhizobium tropici and the non-native strain to Bradyrhizobium japonicum. Plant nodulation tests, sequencing of nodC and nifH genes, and the acetylene-dependent ethylene production assay confirmed the capacity of all strains to nodulate sunnhemp and fix N2. Inoculation with native rhizobial strains resulted in significant increases in root and shoot weight and total C and N contents in the shoots, and showed greater N2-fixation rates and lower emissions of N2O compared to the non-native rhizobium. Our results suggest that native rhizobia improve plant growth, fix N2, and reduce greenhouse emissions of sunnhemp more than commercial rhizobia inoculants in Florida citrus orchards.

Conversion of coastal wetland to aquaculture ponds decreased N2O emission: Evidence from a multi-year field study

Land reclamation is a major threat to the world's coastal wetlands, and it may influence the biogeochemical cycling of nitrogen in coastal regions. Conversion of coastal marshes into aquaculture ponds is common in the Asian Pacific region, but its impacts on the production and emission of nitrogen greenhouse gases remain poorly understood. In this study, we compared N2O emission from a brackish marsh and converted shrimp aquaculture ponds in the Shanyutan wetland, the Min River Estuary in Southeast China over a three-year period. We also measured sediment and porewater properties, relevant functional gene abundance, sediment N2O production potential and denitrification potential in the two habitats. Results indicated that the pond sediment had lower N-substrate availability, lower ammonia oxidation (AOA and comammox Nitrospira amoA), nitrite reduction (nirK and nirS) and nitrous oxide reduction (nosZ Ⅰ and nosZ Ⅱ) gene abundance and lower N2O production and denitrification potentials than in marsh sediments. Consequently, N2O emission fluxes from the aquaculture ponds (range 5.4–251.8 μg m–2 h–1) were significantly lower than those from the marsh (12.6–570.7 μg m–2 h–1). Overall, our results show that conversion from marsh to shrimp aquaculture ponds in the Shanyutan wetland may have diminished nutrient input from the catchment, impacted the N-cycling microbial community and lowered N2O production capacity of the sediment, leading to lower N2O emissions. Better post-harvesting management of pond water and sediment may further mitigate N2O emissions caused by the aquaculture operation.

Impacts of monoculture cropland to alley cropping agroforestry conversion on soil N2O emissions

AbstractMonoculture croplands are a major source of global anthropogenic emissions of nitrous oxide (N2O), a potent greenhouse gas that contributes to ozone depletion. Agroforestry has the potential to reduce N2O emissions. Presently, there is no systematic comparison of soil N2O emissions between cropland agroforestry and monoculture systems in Central Europe. We investigated the effects of converting the monoculture cropland system into the alley cropping agroforestry system on soil N2O fluxes at three sites (each site has paired agroforestry and monoculture) in Germany, where agroforestry combined crop rows and poplar short‐rotation coppice (SRC). We measured soil N2O fluxes monthly over 2 years (March 2018–January 2020) using static vented chambers. Annual soil N2O emissions from agroforestry ranged from 0.21 to 2.73 kg N ha−1 year−1, whereas monoculture N2O emissions ranged from 0.34 to 3.00 kg N ha−1 year−1. During the rotation of corn crop, with high fertilization rates, agroforestry reduced soil N2O emissions by 9% to 56% compared to monocultures. This was mainly caused by low soil N2O emissions from the unfertilized agroforestry tree rows. Soil N2O fluxes were predominantly controlled by soil mineral N in both agroforestry and monoculture systems. Our findings suggest that optimized fertilizer input will further enhance the potential of agroforestry for mitigating N2O emissions.

Study on using graphene and graphite nanoparticles as fuel additives in waste cooking oil biodiesel

• Graphene and graphite nanoparticle additives showed lower NO emissions and higher thermal efficiency. • Graphene and graphite nanoparticle additives showed lower BSFC than neat biodiesel fuel. • At full load, both nanoparticles showed similar heat release as compared to neat diesel operation. • The combustion characteristics of fuel blends with graphite additives outperformed that of those with graphene additives. Utilising waste cooking oil biodiesel in internal combustion engines for power generation and transport is of increasing importance, as it is the least pollutant disposal method for waste cooking oil. Besides, researchers have recently shown an increasing interest in utilising graphene and its derivatives in different applications due to its unique thermal and physical characteristics, including enhancing the combustion characteristics of biofuels. Therefore, this article studies the characteristics of waste cooking oil biodiesel blended with few-layered graphene and graphite nanoparticles additives and their influence on combustion and engine emissions and benchmark them against neat biodiesel and diesel fuels. The biodiesel was synthesised through a transesterification method from waste cooking oil and blended with diesel or butanol after adding few-layered graphene and graphite nanoparticles. Few-layered graphene and graphite nanoparticle additives led to greater peak in-cylinder pressure by 0.5–2.5% increment and 1–4% lower heat released rate at full load. As such, employing few-layered graphene and graphite in a fuel mix reduced NOx emission by 0.7–5 % compared to 100% diesel counterpart. Besides, at full engine load, waste cooking biodiesel blended with 100 ppm few-layered graphene and graphite nanoparticles showed an increment in brake thermal efficiency by 8–10% compared to pure fossil diesel and waste cooking biodiesel. The results show the feasibility of using graphene-based nanoparticle additives in biodiesel to enhance biodiesel fuel combustion characteristics, hence lowering NOx emissions.

The use of double-cropping in combination with no-tillage and optimized nitrogen fertilization reduces soil N2O emissions under irrigation

The irrigation systems of the Ebro valley can lead to high N2O emissions. The effects that crop diversification, such as double-cropping in combination with conservation tillage and different N fertilizer ratios, has on soil N2O emissions have not been extensively studied in this region. The goal of this research was to measure N2O soil emissions and determine the tillage practices and N fertilization rates that provide the lowest emissions when combined with double-cropping systems. The work compared monocropping maize (MC) versus legume-maize double-cropping (DC) with two tillage systems (conventional tillage, CT; and no-tillage, NT), and three mineral N fertilization rates (zero, medium and high). Pea for grain (2019), vetch for green manure (2020), and vetch for forage (2021) were the legumes employed. The N2O emissions ranged from 0 to 15.5 mg N2O-N m−2 d−1 and were concentrated in the fertilization periods. Soil temperature and water filled pore space (WFPS) content significantly influenced soil N2O emissions. For both cropping systems, the conditions with the highest N2O emissions were soil temperatures above 20 °C and a WFPS of 50–60 %. The use of legumes facilitated reduced N fertilization in DC without affecting crop yield and led to reduced N2O emissions in this cropping system. DC reduced the emission factor (EF), which in all cases was lower than the default IPCC EF (1 %). With DC, a medium N fertilization rate produced similar yields to the high rate commonly applied by farmers, and also entailed lower N2O emissions. The no-tillage system, although producing higher levels of N2O, achieved lower yield-scaled N2O emissions due to greater crop yields. This work underlines the advantages of using double-cropping no-tillage systems combined with medium rates of N fertilization to reduce soil N2O emissions.

Balancing high yields and low N2O emissions from greenhouse vegetable fields with large water and fertilizer input: a case study of multiple-year irrigation and nitrogen fertilizer regimes

Balancing high yields and low N2O emissions from greenhouse vegetable fields with large water and fertilizer input: a case study of multiple-year irrigation and nitrogen fertilizer regimes

Effects of sewage sludge hydrochar on emissions of the climate-relevant trace gases N2O and CO2 from loamy sand soil

This work explores the effects of amending a loamy sand soil with hydrochars having different physicochemcial characteristics. The effects of different hydrochars on emissions of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) were investigated together with the relationship between the hydrochar's mineral nitrogen content and the soil microbial biomass. Soil samples were amended with eleven different hydrochars and feedstocks having different carbon and nitrogen contents at application rates of 5 t ha−1 and 25 t ha−1. Microbial immobilization was the main mineral nitrogen sink in soil following hydrochar application. Moreover, the processing conditions applied during hydrochar production (i.e., the pyrolysis temperature and residence time) had significant effects on N2O and CO2 emissions: treatment with incubated hydrochars yielded significantly lower N2O emissions than treatment with non-carbonized feedstocks, particularly at the highest level of hydrochar application (25 t ha−1). Further analysis revealed that increasing the process temperature and residence time during hdyrochar production significantly increased the final product's total organic carbon content but reduced its content of hot water extractable carbon. Hydrochars produced with higher process temperatures and longer residence times therefore yielded lower CO2 emissions during a 44-day incubation experiment than raw feedstocks or hydrochars produced under less severe conditions. Hydrochars formed from sewage sludge at high process temperatures and with long residence times are thus promising soil additives for reducing GHG emissions.

Fuel-NO formation mechanism in MILD-oxy combustion of CH4/NH3 fuel blend

MILD-oxy combustion operates conventional oxy-combustion processes under moderate or intense low-oxygen dilution (MILD) condition, which offers a practical approach towards the synergetic control of CO2 and NOx emissions. This numerical work investigates the MILD combustion characteristics and NO emission of CH4/NH3 fuel blend under N2, CO2 and H2O dilutions, aiming at revealing the fuel-NO formation mechanism under MILD-oxy condition. It is found that relative to MILD-N2 combustion, the flame temperature is reduced under MILD-CO2 and MILD-H2O combustion, while the reaction zone is expanded and reduced, respectively, due to the altered co-flow properties. CO2 dilution lowers the radical pool level, while the formation of OH radical is boosted under H2O dilution. Overall NO emission (EINO) under MILD-N2 combustion is the largest while that under MILD-H2O generates the lowest value, showing its low-NOx emissions superiority. NH3 is converted into NO via routes NH3 → NH2 → HNO → NO and NH3 → NH2 → NH → HNO → NO under MILD-CO2 combustion. By contrast, the importance of route NH3 → NH2 → NH → N → NO in producing NO is largely strengthened under MILD-H2O combustion, wherein the direct formation of NO via HNO is inhibited with the enhanced availability of reactive N-containing species, contributing to lower NO emission under MILD-H2O combustion over MILD-CO2 combustion.

UTILIZATION OF BLACK STICKY RICE FOR BIOETHANOL PRODUCTION AS GASOLINE FUEL BLENDS FOR MOTORCYCLES

Despite possessing non-renewable properties, fossil fuel is still widely used as a major energy source. Subsequently, the fossil fuel demand has been increasing while the supply is depleting over time leading to an energy crisis. Fossil fuel also causes associated environmental problems such as emissions as the primary driver of global warming and climate change. Thereby, the development of alternative fuels, such as bioethanol, is beneficial to combat the fossil fuel challenges. Bioethanol is a promising fuel owing to its renewable and environmentally friendly characteristics. In this study, bioethanol was synthesized by a fermentation process over yeast (Saccharomyces Cerevisiae). The feedstock for this process is an abundant resource namely black sticky rice. Bioethanol resulting from this process was mixed with gasoline and applied to a motorcycle machine. The performance of bioethanol was defined by power, torque, and emission. The proportion of the mixture was varied with bioethanol content of 0%, 10 %, 20 %, 30 %, and 40%. The mixture of bioethanol-gasoline produced higher power and torque value compared to gasoline. The E40 mixture had the highest power and torque value with 8.5 hp and 9.2 Nm respectively. However, the combustion of bioethanol-gasoline resulted in more CO2 emission, while the emissions of O2, NO, and NOx were lower. The lowest NOx emissions content was obtained at E30 and E40 blends, about 7 ppm. Meanwhile, the lowest NO emission content was obtained at E30 and E40 blends, about 6 ppm.

Managing fertilizers and water treatments on rice production and N2O emission

Addressing issues about climate change and higher food demand requires improve management practices. Fertilizer and water input are the critical resources to ensure high yield and low impact to environment in paddy field. The aim of this study was to determine whether higher grain yield and lower nitrous oxide (N2O) emission can be achieved by managing fertilizer and water input. A field experiment was conducted during rice paddy season under conventional practice (CP) that comprised of farmer practice and continuous flooded. In contrast to CP, balanced fertilizer application and intermittent irrigation was applied for another treatment that namely technology introduction (TI). Results showed that the average of seasonal N2O in the TI treatment decreased by 54% compared with the CP treatment. Aerobic–anaerobic increased in N2O emissions. Lower N2O emission at higher rate of N fertilization. Those findings indicated that enhancing rice production and mitigating GHG emission under application of balanced fertilizer and proper water management from paddy field can contribute to sustainable agriculture.

Citric acid modified biochar application at a low dosage can synchronically mitigate the nitrogenous gas pollutants emission from rice paddy soils

Raw biochar with high pH possibly stimulated ammonia (NH3) volatilization in the agricultural soil. We hypothesized that the modified biochar (MBC) with low pH can synchronically decrease the NH3 and nitrous oxide (N2O) losses. We performed a two-year experiment to clarify how citric acid MBC influence the NH3 volatilization and N2O emission as well as the underlying mechanisms. Two typical paddy soils, i.e., Hydragric Anthrosol and Haplic Acrisol, receiving equal urea N with 240 kg ha−1 but varied rates of MBC with 0, 5, 10, and 20 t ha−1 (named Urea, Urea + MBC5, Urea + MBC10, and Urea + MBC20, respectively) were studied. The results showed that MBC-amended treatments effectively mitigated the NH3 volatilization from Hydragric Anthrosol and Haplic Acrisol by 29.6%–57.9% and 30.5%–62.4% in 2017, and by 16.5%–21.0% and 24.5%–35.0% in 2018, respectively, compared to Urea treatment. In addition, significantly lower N2O emissions with averaged 38.3% and 43.1% in 2017, and 51.7% and 26.7% were recorded under Hydragric Anthrosol and Haplic Acrisol, respectively, following the MBC application (P < 0.05). Increased MBC addition performed higher efficacy on mitigating NH3 volatilization, particularly in the first rice season, while this “dosage effect” was not found for N2O reduction. Lowered pH in overlying water, enhanced adsorption of NH4+-N and its nitrification rate likely contributed to the lower NH3 volatilization as result of MBC addition. The nirS and nosZ gene copies were not changed by MBC, while the nirK gene copies were decreased as result of MBC amendment by 8.3%–25.2% under Hydragric Anthrosol and by 21.8%–24.9% under Haplic Acrisol. Consequent lower ratio of nirK/(nirS + nosZ) explained the mitigation effect of MBC on N2O emission. In conclusion, the present two-year study recommends that MBC applied at a low dosage can perform positive effect on controlling the nitrogenous gas pollutants from paddy soil.

Comparative study on combustion and emission of SI engine blended with HHO by different injection modes of gasoline

As a hydrogen fuel for real-time production without storage, HHO has great research prospect and significance. In this paper, we conducted experiments on a spark ignition (SI) engine which has two independent fuel supply systems to compare two combination modes of gasoline port injection plus HHO (GPI + HHO) and gasoline direct injection plus HHO (GDI + HHO) at different HHO flow rate, λ, engine speed and load. The results show that, in both modes, HHO addition increases the maximum cylinder pressure and torque. With the increase of HHO flow rate, the flame development period and flame propagation period shorten, the crank angle corresponding to the maximum cylinder pressure is closer to top dead center. In addition, GDI + HHO mode has better engine performance. HHO has a significant effect on improving combustion stability. Especially at λ = 1.4, as HHO flow rate increases from 0 to 16 L/min, the coefficient of indicated mean effective pressure variation of GPI + HHO and GDI + HHO mode decreases by 69.17% and 58.29%, respectively. Moreover, HHO addition improves HC and CO emissions but increases NOx emissions. CO and HC emissions of GDI + HHO mode are the lowest under all conditions, and reaching the lowest value when HHO flow rate = 16 L/min. Besides, GDI + HHO mode not only has lower NO emissions under normal working conditions (λ = 1) but also can maintain a better combustion environment under lean-burn conditions (λ = 1.2, 1.4). In general, the application of HHO as fuel in engine can improve combustion and emission characteristics and GDI + HHO mode is the best combination of gasoline and HHO.

The effect of ammonia gas and UWS injection on the N2O formation in diesel engine after-treatment systems under steady and transient conditions

In this study, the N2O emission formation from heavy-duty diesel engine was studied by injecting ammonia gas and urea water solution (UWS) in Cu-zeolite SCR. Furthermore, the effect of exhaust gas temperature and NH3/NOx (α) ratio on the N2O formation were investigated. The ammonia was supplied using an ammonium carbamate (AC) based ammonia generating system. Experiments were performed under the European stationary cycle (ESC), world harmonized transient cycle (WHTC), and non-road transient cycle (NRTC). Ammonia gas injection produced a higher amount of tailpipe N2O than UWS injection for all test conditions. Compared with UWS an increment of 27% in N2O formation for ammonia gas was observed during the ESC test. The N2O emissions of ammonia gas injection in the WHTC and NRTC were increased compared with that of UWS during the cold phase by 63% and 55%, respectively, and during the hot phase by 57% and 74%, respectively. Meanwhile, NO and NO2 emissions were decreased by injecting ammonia gas compared with UWS. The higher NH3/NOx (α) ratio led to higher tailpipe N2O and lower NO and NO2 emissions. For each reductant test, the concentration of N2O formation was high at the exhaust gas temperature of 200–250 °C. These presented results provide useful information about the N2O formation from after-treatment systems of diesel engines when ammonia gas is used.