Nitrous Oxide Emission Characteristics Research Articles

Experimental and numerical analysis of unburned ammonia and nitrous oxide emission characteristics in ammonia/diesel dual-fuel engine

Ammonia (NH3) combustion has been investigated as a carbon-free fuel for internal combustion engines. The marine sector attempts to use NH3 as fuel for diesel engines. However, NH3 combustion in diesel engines can emit unburned NH3 and nitrous oxide (N2O) via the greenhouse effect, and the mechanisms of emission production remain unclear. In this study, the combustion of a premixed NH3–diesel dual-fuel initiated by a pilot fuel is investigated experimentally and numerically. The experiments reveal a change in combustion phasing and emission characteristics for up to 80% of the energy fraction of NH3. As the energy fraction of NH3 increases, the onset of combustion is delayed, the center of combustion is slightly advanced and then retracted, and the end of combustion is slightly advanced. NO and unburned NH3 emissions increased, whereas CO emission decreased as the energy fraction of NH3 increased; by contrast, N2O emissions increased. However, the increase in N2O diminished when the energy fraction of NH3 increased by 40% or more. Computation fluid dynamics simulations based on n-heptane and ammonia reaction kinetics qualitatively reproduced the experimental results. The numerical analysis facilitates the understanding of the underlying phenomena of emission via ammonia–diesel dual-fuel combustion. N2O formation can be categorized into two stages: a steep formation of N2O with main heat release and CO2 production, followed by a relatively low formation rate of N2O with a decreasing rate of NH3 decomposition and reduction in CO2 production. The early injection of pilot fuel allowed the pilot fuel to distribute to the wide area of the combustion chamber and NH3 to rapidly combust without remaining N2O. The rapid combustion eliminates the second stage of relatively slow combustion, which generated N2O. The low NH3 and N2O emissions observed experimentally with the early pilot fuel injection may be due to this mechanism

Effect of carbon source on nitrous oxide emission characteristics and sludge properties during anoxic/aerobic wastewater treatment process.

Carbon sources are an important parameter in wastewater treatment processes and are closely related to treatment efficiency and nitrous oxide (N2O) emissions. In this study, three parallel sequencing batch reactors (SBRs) were processed with acetic acid, propionic acid, and a 1:1 mixture of both acids (calculated in COD) to study the effect of carbon sources on N2O generation and sludge properties (including intracellular polymer content, extracellular polymeric substance (EPS) composition, particle size distribution, settleability, and microbial community structure). The results showed that the highest COD, NH4+-N, and TP removal efficiencies (92.2%, 100%, and 82.3%, respectively) were achieved by the reactor with mixed acid as the carbon source, whereas the reactor using acetic acid had the highest TN removal rate (82.6%) and the lowest N2O-N conversion rate (1.4%, based on TN removal). The reactor with the carbon source of mixed acid produced the highest polyhydroxyalkanoate (PHA) content, which led to an increase in N2O generation from the aerobic denitrification pathway. The SBR with mixed acid carbon source also had the highest concentration of EPS, which resulted in the largest particle size and the lowest settleability of sludge flocs among the SBRs. Microbial analysis results revealed that the difference in carbon sources resulted in a variation in the microbial community as well as in the relative abundances of functional microbes involved in biological nitrogen removal processes. The mixed acid promoted the development of ammonia-oxidizing bacteria (AOB), which conducted the primary N2O generation pathway of aerobic denitrification bioreactions. The carbon source of acetic acid promoted the growth of denitrifying bacteria (DNB), which led to the highest TN removal rate. This study provides a comprehensive understanding of the effects of carbon sources on N2O generation and sludge properties for WWTPs.

Methane and nitrous oxide emission characteristics of high-yielding rice field.

As representative varieties of the four phases of the super rice breeding project in China, Lianyoupei 9 (LYP9), Y Liangyou 1 (YLY1), Y Liangyou 2 (YLY2), and Y Liangyou 900 (YLY900) achieved higher yield under optimal cultivation techniques. However, the impact of these high-yield rice varieties on greenhouse gas (GHG) emissions under high-yield cultivation management practices remains poorly understood. In this study, we conducted field experiments to investigate CH4 and N2O emissions from paddies containing four elite rice varieties, managed with field drying at the ineffective tillering stage and alternate wet/dry irrigation at the grain-filling stage. The plants were fertilised with nitrogen (N) at three different rates. The results showed that CH4 emission was highest at the tillering stage. N2O emission flux was dramatically increased by field drying at the ineffective tillering stage, and with the rate of N application. Rice variety was among the most important factors affecting CH4 emission and global warming potential (GWP). N2O emission was mainly related to N application rate rather than rice variety. YLY2 achieved higher yield than LYP9, YLY1, and YLY900, and lower GHG emission than YLY900. Our results indicate that rice variety should be considered as a key factor to reduce GHG emissions from rice paddies under high-yield cultivation practices. Based on its high yield and low GHG emission at the study site, YLY2 may be an optimal rice variety.

An integrated framework for plant data-driven process modeling using deep-learning with Monte-Carlo simulations

This study aims to develop a deep-learning-based and plant data-driven framework for process modeling to help understanding plant-wide processes. The systematic framework consists of the following steps: data processing based on domain-knowledge, deep-learning model development, model selection using information criteria, and global sensitivity analysis with Monte-Carlo simulations. The assessment of the quality of the optimal deep-learning model to support plant-wide process understanding is the key emphasis of this framework. The proposed framework was applied for analyzing long-term data from wastewater treatment plants to predict nitrous oxide emission characteristics. The results showed a promising potential of the framework to systematically and efficiently develop fit-for-purpose deep-learning models with highly favorable cross-validation statistics (R2). The framework is expected to facilitate the development of versatile deep-learning models based on plant data encompassing nonlinear and complex process phenomena, where especially mechanistic models are not available.

Effective biological nitrogen process and nitrous oxide emission characteristics for the treatment of landfill leachate with low carbon-to-nitrogen ratio

Biological nitrogen removal via nitrite has been applied extensively to treat low chemical oxygen demand to nitrogen (COD/N) ratio wastewater, e.g. landfill leachate. It is known that landfill leachate has a very complex organic and nutrients profile. During the treatment, the transformation behavior of organic pollutants and nitrogen, as well as the side-product of nitrous oxide (N2O) emission in this process has not been fully explored. In this study, a typical integrated anoxic-aerobic (low dissolved oxygen (0.1–1.0 mg O2 L−1)) process with sludge recirculation was employed for landfill leachate treatment. Results show that most of low molecular weight acids, building blocks and low molecular weight neutrals can be removed in the anoxic unit due to denitrification. A total nitrogen removal efficiency up to 84% was achieved with influent COD/N ratio of about 4.5, while the overall N2O emission was 2.8 ± 0.5% of the incoming nitrogen load. It was found that N2O emission was negligible from anoxic unit under COD/(NO2−-N + NO3−-N) ratio of 5.51 ± 0.83. However, reduced COD/(NO2−-N + NO3−-N) ratio in the anoxic unit caused enhanced N2O emission where nitrite accumulation was also observed. When COD/(NO2−-N + NO3−-N) ratio in the anoxic unit was decreased to 2.66 ± 0.76 and 1.39 ± 0.19, N2O emission in the process increased to 5.6 ± 1.8% and 9.5 ± 1.6% of incoming nitrogen load, respectively. Quantification of functional genes suggests that N2O emission was negatively correlated to the abundance of nirS, nosZ genes and nosZ/narG ratio, highlighting the role of effective denitrification potential and more N2O-consuming bacteria in lowering N2O emissions. This study shed light on conversion of different fractions of organic matter in the landfill leachate treatment, and provided strategies to minimize N2O emission.

Characteristics of Nitrous Oxide Emissions from Partial Nitrification Process Treating High Ammonium Wastewater

Nitrous oxide is a greenhouse gas, and biological nitrogen removal leads to nitrous oxide generation and emissions. In this study, the emission of nitrous oxide from partial nitrification process was investigated in two intermittently aerated SBRs (IASBRs). Activated sludge floc and aerobic granular sludge were feed into two IASBRs, respectively. In the steady state, partial nitrification was successfully achieved under intermittent aeration control strategy. Nitrous oxide emissions were 6.5% and 8.9% of the total influent nitrogen loading rate in IASBR1 and IASBR2, respectively. Nitrous oxide was mainly generated in non-aeration periods, but aeration period contributed to 91.8% and 90.6% of nitrous oxide emissions in two IASBRs, respectively. PHB can be used as the carbon source for heterotrophic denitrification, causing more nitrous oxide generated in IASBR2 which was seeded with aerobic granular sludge.

디젤엔진에 있어서 연료의 성분이 아산화질소 배출에 미치는 영향

디젤엔진에 있어서 연료의 성분이 아산화질소 배출에 미치는 영향

Characteristics of nitrous oxide emissions and the affecting factors from vegetable fields on the North China Plain

Nitrous oxide (N2O) is one of the most important greenhouse gases emitted from fertilized agricultural soils. Vegetable fields, mostly managed under intensive mode with higher rate nitrogen application, frequent irrigation, and multiple planting-harvest cycles, does contribute to national GHG inventory greatly due to the increasing planting area in China. N2O emissions from four different fields – a maize field (maize), a newly established open-ground vegetable field converted from a maize field four years earlier (OV4), an established open-ground vegetable field converted from a maize field more than 20 years ago (OV20), and an established sunlight heated greenhouse vegetable field converted from a maize field more than 20 years ago (GV20) with four different fertilization treatments for the OV4 field were measured using the closed chamber method between March 15th, 2012 and March 14th, 2013 in suburban area of Beijing, North China Plain. Results showed that the annual N2O emissions from vegetable fields were 3.1–4.6 times higher than the typical maize field. All the N2O emission peaks were occurred after fertilization and the fertilization associated emissions accounted for 81.1% (ranging from 77.0% to 87.2%) of the annual N2O emission with 22.2% time duration in the whole year for vegetable fields. Both the occurrence data and duration of N2O emission peaks were associated with N input type (chemical or manure) and the application rate. The N2O emission peaks appeared earlier (on the 3rd day after application) and lasted shorter when only chemical N was applied; while they appeared later (on the 7th to 10th day after application) and lasted longer when the combination of manure and chemical N were applied. The magnitudes of N2O emission peaks increased when the N application rate was higher. Dicyandiamide (DCD) decreased N2O emissions by 30.1% and 21.1% in the spring cucumber and autumn cabbage seasons respectively (averaged of 24.7% over the whole year). Calculations showed that it is critical to estimate the emission factor (EF) by N type in order to decrease the uncertainty of regional N2O emissions when using EF as calculation method. EFs were 0.20% and 0.42% for manure N in the cucumber and cabbage seasons respectively; and were 0.55–1.30% and 0.8–1.59% for chemical N in the cucumber and cabbage seasons respectively.

船舶運航条件が亜酸化窒素排出に及ぼす影響

船舶運航条件が亜酸化窒素排出に及ぼす影響

EINOx scaling in a non-premixed turbulent hydrogen jet with swirled coaxial air

The effect of swirl flow on pollutant emission (nitrous oxide) was studied in a non-premixed turbulent hydrogen jet with coaxial air. A swirl vane was equipped in a coaxial air feeding line and the angle of the swirl vane was varied from 30 to 90 degrees. Under a fixed global equivalence ratio of φ G = 0.5, fuel jet air velocity and coaxial air velocity were varied in an attached flame region as u F = 85.7–160.2 m/s and u A = 7.4–14.4 m/s. In the present study, two mixing variables of coaxial air and swirl flow were considered: the flame residence time and global strain rate. The objective of the current study was to analyze the flame length behavior, and the characteristics of nitrous oxide emissions under a swirl flow conditions, and to suggest a new parameter for EINOx (the emission index of nitrous oxide) scaling. From the experimental results, EINOx decreased with the swirl vane angle and increased with the flame length ( L). We found the scaling variables for the flame length and EINOx using the effective diameter ( d F ,eff) in a far-field concept. Normalized flame length ( L divided by d F ,eff) fitted well with the theoretical expectations. EINOx increased in proportion to the flame residence time (∼ τ R 1/2.8) and the global strain rate (∼ S G 1/2.8).

수소 난류 확산화염에서의 선회류에 의한 배기배출물 특성

동축공기 수소 난류 확산화염에서 선회류가 NOx에 미치는 영향을 연구하였다. 공기와의 혼합을 증가시키기 위해 동축공기관에 스월러의 각도를 30, 45, 60, 90°로 바꾸어가며 화염길이와 질소산화물 배출수준을 측정하였다. 연료 속도를 85.7~160.2 ㎧, 동축공기 속도는 7.4~14.4 ㎧로 조절하였다. 실험을 통해 동축 공기 속도 증가에 따라 화염길이와 질소산화물 배출수준은 증가하였고, 회전류 증가에 따라 감소함을 관찰하였다. EINOx에 미치는 동축공기와 회전류 영향을 상사하기 위하여 far-field 개념의 유효직경 (d<SUB>F,eff</SUB>)을 도입하여 동축공기와 선회류에 의한 혼합효과를 표현하였다. 질소산화물 배기배출지표는 화염체류시간(~τ<SUB>R</SUB><SUP>1/2.8</SUP>)과 전체 신장률(~S<SUB>G</SUB><SUP>1/2.8</SUP>)영향을 받았다.