Effects of fuel injection and intake parameters on low temperature combustion

The effects of fuel injection and intake parameters on low temperature combustion are investigated using CFD modeling in the present study. With the increase of injection pressure or decrease of nozzle hole diameter:the maximum in-cylinder pressure and temperature increase. Heat release from premixed combustion increases at the same oxygen concentration and oxygen concentration that obvious premixed combustion appears increases. As to emissions, soot emission decreases because of the improvement of mixing of fuel and air and NOx emission increases because the increase of local temperature in the cylinder. With the increase of intake pressure:the maximum cylinder pressure increases but the maximum cylinder temperature decreases. The ignition timing advances at the same oxygen concentration. The combustion efficiency increases. As to emissions, both soot and NOx emissions decrease.     

Chapter 12. A Wildfire and Emissions Policy Model for the Boise National Forest

Summary

We utilized the Boise National Forest's Hazard/Risk model, along with fire history records and fire behavior models, to estimate the current and anticipated levels of large wildfires and associated greenhouse gas and particulate emissions based on the forest condition and wildfire regime on the BNF. The model indicated that the forests at greatest risk of large, intense wildfires are the dense pondero-sa pine-Douglas-fir forests that make up over 1.1 million acres on the forest. We conclude that without an aggressive treatment program to reduce large areas of contiguous heavy fuel loadings the forest will be burned at an annual average rate of about 7.5% of the remaining at-risk forest. Using recent fire data to develop average patterns of intensity in wildfires within this forest type, we estimate that emissions will average around 1 million tons of carbon (C) per year over the next 20 years as the bulk of the ponderosa pine forests are burned. An aggressive treatment program featuring the removal of fuels where necessary, and prescribed fire as a means of re-introducing fire to these ecosystems, would result in a 30-50 percent reduction in the average annual wildfire experienced in the dense ponderosa pine forests, a 14-35% decrease in the average annual C emissions, and a 10-31% decrease in particulate emissions. We argue that the most effective way to curb emissions is with an aggressive treatment program linked to a landscape-based ecosystem management plan. This would have the effect of breaking up large contiguous landscape patterns so that fires become more patchy and diverse in their environmental impact, resulting in significantly reduced emissions as well as improved landscape diversity.     

Impacts of intensification of pastoral agriculture on soils: Current and emerging challenges and implications for future land uses

Abstract

AIM: To find evidence for localisation in the uterus, and fetal infection, of Leptospira spp. in farmed deer in the lower North Island of New Zealand during and shortly after the breeding season.

METHODS: Between February and July 2008, 116 blood samples, 120 kidneys, 120 uteri and 27 fetuses were collected from 120 mixed-age hinds from lines from nine farms, at a deer slaughter premises. Serum samples were tested for antibodies against Leptospira borgpetersenii serovar Hardjo-bovis and Leptospira interrogans serovar Pomona, using the microscopic agglutination test (MAT). For both serovars, a titre of >1:48 was considered positive. Samples from kidneys, uteri and fetal tissue were subjected to bacterial culture, using Ellinghausen-McCullough-Johnson-Harris (EMJH) medium, and real-time PCR, using DNA gyrase subunit B gene primers.

RESULTS: Thirty-four of 116 (29.3%) serum samples were positive for serovar Hardjo-bovis, and 13 (11.2%) for serovar Pomona. Seven of 120 kidneys were positive for serovar Hardjo-bovis by culture, and five of these, but no others, were positive by real-time PCR. Of 120 uteri, none was culture- or PCR-positive. None of 27 fetal samples was culture-positive but one was positive by real-time PCR. The dam of the PCR-positive fetus was culture-negative from the kidney, but had an MAT titre of 1:192 for Hardjo-bovis.

CONCLUSIONS: Attempts to isolate Leptospira spp. from the genital tracts and early fetuses of farmed deer were unsuccessful. However, molecular evidence suggested fetal infection in one case. This finding justifies further study of the role of leptospires in the genital tract and fetus and its association with reproductive loss in farmed deer.     

Effects of intensification of pastoral farming on greenhouse gas emissions in New Zealand

Abstract

AIMS: The aims of this cross-sectional study were to investigate the herd and cow-level prevalence of bovine digital dermatitis (BDD) in dairy farms in the northern Taranaki region of New Zealand, and to identify whether there was any spatial clustering of herds with the disease.

METHODS: A survey of 224 dairy farms in the northern Taranaki region of New Zealand was undertaken from September 2014 to February 2015. Following training in robust criteria to confirm BDD visually, a technician inspected the rear feet of every milking cow on the farms during milking. The identity of cows with lesions and the feet involved were recorded. The proportion of cows affected among the inspected population (cow-level prevalence), the proportion of a herd affected (farm-level prevalence), and proportion of farms with ≥1 cow with lesions, were calculated. A bivariate K function analysis was then used to assess whether farms with ≥1 cow with lesions were clustered, after accounting for the distribution of the farms involved in the study.

RESULTS: Bovine digital dermatitis lesions were observed on 143/224 (63.8 (95% CI=57.5–70.1)%) farms. Within-farm prevalence was 0% on 81 (36.2%) farms, between >0 and <3% on 120 (53.5%) farms, with a maximum prevalence of 12.7% on one farm. Overall, cow-level prevalence was 707/60,455 (1.2 (95% CI=0.9–3.0)%), and on affected farms was 707/41,116 (1.7 (95% CI=1.4–2.1)%). In affected cows, 268/707 (37.9%) had a lesion on left foot only, 262/707 (37.1%) on the right foot only and 177/707 (25.0%) on both feet. The K function analysis showed no evidence of clustering of farms with BDD.

CONCLUSIONS: Bovine digital dermatitis was widespread among the survey farms, but there was no evidence that there was any clustering of herds with BDD. The cow-level prevalence on affected farms was much lower than reported elsewhere.

CLINICAL RELEVANCE: Although the prevalence at the cow level was low, if these data are representative of other regions of New Zealand, BDD could easily become a major problem on dairy farms in New Zealand, as has been observed in other countries.     

河北省二氧化碳排放驱动因素研究——基于STIRPAT模型

首次以河北省为研究对象,基于扩展的STIRPAT模型,应用岭回归分析,对1980~2011年二氧化碳排放驱动因素进行研究,然后结合河北省产业布局和特点,提出碳减排政策建议。结果表明,经济增长是二氧化碳排放量增多的决定性因素;城市化水平、能源强度和人口规模是重要因素;第三产业比重、第二产业比重和能源消费结构对碳排放影响不显著。     

城乡融合对农业碳排放强度的影响研究北大核心CSCD

发挥城乡融合对农业碳排放强度的抑制作用,对促进农村绿色低碳转型以及助力农业农村现代化具有重要的现实意义。本文基于城乡融合发展理论,利用2005—2020年30个省(市、区)面板数据,采用经典面板模型分析城乡融合对农业碳排放强度的影响,并探讨了其作用机制和异质性。结果表明,全国和三大区域(东、中、西部地区)的城乡融合发展水平呈持续上升趋势,而农业碳排放强度则呈显著下降趋势,两者之间的波动趋势呈相反态势。城乡融合对农业碳排放强度具有显著的负向影响。基于地理区位和粮食生产地区分析,城乡融合对东部地区和粮食主产区的农业碳排放强度抑制作用更为明显;城乡融合通过提高农业技术进步和农业规模化经营来抑制农业碳排放强度。为此,积极推动精准的城乡融合政策,加强农业技术进步和农业规模化经营,重视城乡融合减排效应的差异性,是实现降低农业碳排放强度的关键方向。     

碳排放约束下中国大豆全要素生产率增长与分解

本文将碳排放纳入大豆全要素生产率分析框架,为实现大豆低碳生产提供参考依据。首先测算并分析2006-2016年中国大豆主产区碳排放量和密度的时空特征,然后利用基于方向性距离函数的Malmquist-Luenberger指数测度碳排放约束下2006-2016年中国大豆主产区11个省市全要素生产率。结果表明:2016年中国大豆碳排放量较2006年降低11.70%,年均负增长1.24%,而碳排放密度较2006年增长14.02%,年均增长1.32%,皆呈先升后降的趋势。按省份比较,黑龙江和内蒙古碳排放量最多,吉林和山西碳排放密度最大。2006-2016年碳排放约束下中国大豆全要素生产率年均增长2.32%,其中技术效率年均提升0.6%,前沿技术进步年均增长1.66%,中国大豆全要素生产率增长主要依靠前沿技术进步拉动,技术效率提升作用不明显。从地区分布看,碳排放约束下中国大豆全要素生产率存在地区不平衡现象,西部地区增长最快,东部地区增长最慢,各省市全要素生产率增长模式存在差异。中国大豆主产区缺少"环境技术创新者"。根据结果本研究提出提高中国大豆全要素生产率的政策建议。     

Relationship between greenhouse gas emissions and changes in soil gas diffusivity in a field experiment with biochar and lime

Reducing greenhouse gas emissions from arable soil while maintaining productivity is a major challenge for agriculture. Biochar is known to reduce N₂O emissions from soil, but the underlying mechanisms are unclear. This study examined the impact of green waste biochar (20 Mg ha^?1) and lime (CaCO₃; 2 Mg ha^?1) application on soil gas transport properties and related changes in these to soil N₂O and CO₂ emissions measured using automated chambers in a field experiment cropped with maize. In situ soil water content monitoring was combined with laboratory measurements of relative soil gas diffusion coefficient (D_p/D₀) at different matric potentials, to determine changes in D_p/D₀ over time. Cumulative N₂O emissions were similar in the control and lime treatment, but much lower in the biochar treatment. Cumulative CO₂ emissions decreased in the order: lime treatment > biochar treatment > control soil. When N₂O emissions were not driven by excess N supply shortly after fertilisation, they were associated with D_p/D₀ changes, whereby decreases in D_p/D₀ corresponded to N₂O emissions peaks. No distinct pattern was observed between CO₂ emissions and D_p/D₀. Cumulative N₂O emissions were positively related to number of days with D_p/D₀ < 0.02, a critical limit for soil aeration. These results indicate that improved soil gas diffusivity, and hence improved soil aeration, may explain the effect of biochar in reducing N₂O emissions. They also suggest that knowledge of D_p/D₀ changes may be key to explaining N₂O emissions.     

Organic geochemical parameters for estimation of petrogenic inputs in the coastal area of Kavala City,Greece

Background, aims, and scope  Sediments and soils in coastal areas are frequently polluted by anthropogenic contaminants as the result of both riverine or terrestrial discharge and autochthonic marine emissions. In order to determine petrogenic contamination in the coastal industrial area of Kavala City in northern Greece, a combination of polycyclic aromatic hydrocarbon (PAH) and organic geochemical petroleum biomarker analyses has been performed on marine and freshwater sediments as well as soils. Materials and methods  Soils, freshwater, and marine sediments have been treated by standard extraction methods. The dried and desulphurized sample extracts have been fractionated by column chromatography, followed by addition of surrogate standards. Qualitative and quantitative data were obtained by gas chromatograph connected with a flame ionization and electron capture detector (GC-FID/ECD) and by GC linked to a mass spectrometer (GC/MS), whereas identification of compounds was based on EI⁺-mass spectra and gas chromatographic retention times. Quantitative data were obtained by integration of specific ion chromatograms. Results  The total PAH concentrations measured in the area varied highly, showing different levels from 18 up to 318,000 ng g⁻¹ dry weight (dw). Several PAH ratios, as well as the ratio of pristane (Pr) to phytane (Phyt), have been considered. Out of 39 samples, 22 revealed a specific distribution of hopane fingerprints indicating petrogenic input. Finally, in numerous samples, the ratio of 17α(H)-22,29,30-trisnorhopane (Tm) and 18α(H)-22,29,30-trisnorhopane (Ts) was calculated, as well as the ratio of 22S-17α(H),21β(H)-30 homohopane (αβC₃₁-hopane 22S) and 22R-17α(H),21β(H)-30 homohopane (αβC₃₁-hopane 22R). Discussion  Based on the specific PAH ratios, a group of samples was clearly characterized to be contaminated dominantly by combustion-derived emissions, whereas a second group of samples exhibited mixed influence from petrogenic and pyrogenic PAHs. On the other hand, the exhibition of specific hopane fingerprints in many samples indicates a direct petrogenic input. Finally, the values of the ratio of Tm/(Ts + Tm) and of αβC₃₁-hopanes 22S/(22S+22R)-isomer demonstrated an input of highly mature organic matter that has to be clearly attributed to petroleum-derived contamination, while the ratio of Pr/Phyt showed that most samples exhibited an input of organic matter. Conclusions  The coastal area of Kavala is strongly affected by anthropogenic contaminants. Petrogenic emissions were pointed out firstly by PAH analyses that separated dominantly pyrogenic contaminated sites from areas affected by both pyrogenic and petrogenic emissions. However, analyses of organic geochemical biomarkers revealed a much higher sensitivity in identifying petroleum-derived contaminations and were successfully used to differentiate several petrogenic contaminations in the marine and terrestrial samples. Recommendations and perspectives  Based on this study, it was recommended to use a complementary approach of source-specific substances to successfully characterize petrogenic emissions. Generally, a PAH-based source identification of petrogenic versus pyrogenic contaminations should be combined with petroleum biomarker analysis. PAH and biomarker ratios as well as individual biomarker fingerprints revealed a more comprehensive view on the quality and quantity of petrogenic emissions in sediments and soils.     

基于文献计量分析作物水肥一体化研究特征、热点和趋势

为了解作物水肥一体化领域研究特征、热点问题和发展趋势,基于Web of Science数据库,利用CiteSpace和VOSviewer等可视化软件对作物水肥一体化领域相关文献(2003—2022年)进行文献计量分析。结果表明:1)该领域文章发表数量呈波动上升趋势,研究涉及农艺学、水资源学和植物科学等学科,最具影响力和权威性的期刊是Agricultural Water Management。2)国际合作方面,中国学者与美国、加拿大等国合作密切,其中与美国相关机构的学者合作最为密切;作物水肥一体化研究机构和学者较为分散,中国农业大学、佛罗里达大学、中国科学院和西北农林科技大学等机构和张富仓、康跃虎、林杉和Morgan Kelly T.等人开展了大量水肥一体化研究工作。3)作物水肥一体化研究主要采用田间试验和模型模拟方法,研究内容由早期的果树和甜椒等栽培作物产量和果实品质研究,过渡到作物水分、养分运移和硝酸盐淋溶再到注重提高作物的养分吸收和水肥利用效率并兼顾环境效益。综上,作物水肥一体化的研究热点主要集中在土壤水分、养分运移和硝酸盐淋溶动态的模拟研究、水肥耦合对作物产量影响研究、水肥利用效率提升与水肥精准调控、水肥一体化过程中温室气体排放与减排农艺管理措施等方面。随着物联网和人工智能等新兴技术的发展,未来作物水肥一体化研究将朝着数字化、智能化和精准化的方向发展。