{"title":"高压下绵延的氨/氢弱火焰的存在和化学性质","authors":"Shumeng Xie , Huangwei Zhang","doi":"10.1016/j.combustflame.2024.113528","DOIUrl":null,"url":null,"abstract":"<div><p>Recently, a two-stage ignition phenomenon of NH<sub>3</sub>/H<sub>2</sub> mixtures was experimentally observed in a rapid compression machine, which is closely linked to the concept of flame bifurcations and cool flames. One interesting question may arise: do similar flame bifurcations exist in NH<sub>3</sub>/H<sub>2</sub> mixtures? To answer this, this study employs the premixed counterflow configuration and examines the potential bifurcations of the NH<sub>3</sub>/H<sub>2</sub>/air flame with one-dimensional simulations. For the first time, a novel weak combustion mode of NH<sub>3</sub>/H<sub>2</sub> mixtures is observed and termed as the weak flame in the following. Unlike the conventional hot flame, the weak flame exhibits significantly lower flame temperatures (1300–1500 K) and a mere 1 % of the heat release rate (∼10<sup>9</sup> J/m<sup>3</sup>/s) associated with hot flames. Within the weak flame, H<sub>2</sub> is entirely oxidized to H<sub>2</sub>O, whereas only a portion of NH<sub>3</sub> is partially oxidized, resulting in the formation of H<sub>2</sub>O, N<sub>2</sub>, N<sub>2</sub>O, and NO. Further reaction path analyses reveal that the NH<sub>3</sub> (+OH) → NH<sub>2</sub> (+NO<sub>2</sub>) → H<sub>2</sub>NO (+NH<sub>2</sub>, +HO<sub>2</sub>, +O<sub>2</sub>, +NO<sub>2</sub>) → HNO (+O<sub>2</sub>) → NO (+HO<sub>2</sub>) → NO<sub>2</sub> → N<sub>2</sub>O pathway is the primary oxidation route of ammonia in the weak flame. Furthermore, the effects of pressure, hydrogen content, and equivalence ratio are systematically assessed to explore the operation conditions of the ammonia/hydrogen weak flame. The study reveals that the weak flame is promoted at elevated pressures, and exists with a moderate hydrogen addition, i.e., <span><math><msub><mi>x</mi><mrow><mi>H</mi><mn>2</mn></mrow></msub></math></span> = 0.02–0.4. A regime diagram is further proposed to summarize the combined influences of hydrogen molar fraction and equivalence ratio. In the end, the impacts of chemical mechanisms are tested and the dominant ammonia oxidization path in the weak flame persists for models capable of predicting weak flames.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":5.8000,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Existence and chemistry of stretched ammonia/hydrogen weak flames at elevated pressures\",\"authors\":\"Shumeng Xie , Huangwei Zhang\",\"doi\":\"10.1016/j.combustflame.2024.113528\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>Recently, a two-stage ignition phenomenon of NH<sub>3</sub>/H<sub>2</sub> mixtures was experimentally observed in a rapid compression machine, which is closely linked to the concept of flame bifurcations and cool flames. One interesting question may arise: do similar flame bifurcations exist in NH<sub>3</sub>/H<sub>2</sub> mixtures? To answer this, this study employs the premixed counterflow configuration and examines the potential bifurcations of the NH<sub>3</sub>/H<sub>2</sub>/air flame with one-dimensional simulations. For the first time, a novel weak combustion mode of NH<sub>3</sub>/H<sub>2</sub> mixtures is observed and termed as the weak flame in the following. Unlike the conventional hot flame, the weak flame exhibits significantly lower flame temperatures (1300–1500 K) and a mere 1 % of the heat release rate (∼10<sup>9</sup> J/m<sup>3</sup>/s) associated with hot flames. Within the weak flame, H<sub>2</sub> is entirely oxidized to H<sub>2</sub>O, whereas only a portion of NH<sub>3</sub> is partially oxidized, resulting in the formation of H<sub>2</sub>O, N<sub>2</sub>, N<sub>2</sub>O, and NO. Further reaction path analyses reveal that the NH<sub>3</sub> (+OH) → NH<sub>2</sub> (+NO<sub>2</sub>) → H<sub>2</sub>NO (+NH<sub>2</sub>, +HO<sub>2</sub>, +O<sub>2</sub>, +NO<sub>2</sub>) → HNO (+O<sub>2</sub>) → NO (+HO<sub>2</sub>) → NO<sub>2</sub> → N<sub>2</sub>O pathway is the primary oxidation route of ammonia in the weak flame. Furthermore, the effects of pressure, hydrogen content, and equivalence ratio are systematically assessed to explore the operation conditions of the ammonia/hydrogen weak flame. The study reveals that the weak flame is promoted at elevated pressures, and exists with a moderate hydrogen addition, i.e., <span><math><msub><mi>x</mi><mrow><mi>H</mi><mn>2</mn></mrow></msub></math></span> = 0.02–0.4. A regime diagram is further proposed to summarize the combined influences of hydrogen molar fraction and equivalence ratio. In the end, the impacts of chemical mechanisms are tested and the dominant ammonia oxidization path in the weak flame persists for models capable of predicting weak flames.</p></div>\",\"PeriodicalId\":280,\"journal\":{\"name\":\"Combustion and Flame\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":5.8000,\"publicationDate\":\"2024-06-08\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Combustion and Flame\",\"FirstCategoryId\":\"5\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0010218024002372\",\"RegionNum\":2,\"RegionCategory\":\"工程技术\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"ENERGY & FUELS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Combustion and Flame","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0010218024002372","RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ENERGY & FUELS","Score":null,"Total":0}
Existence and chemistry of stretched ammonia/hydrogen weak flames at elevated pressures
Recently, a two-stage ignition phenomenon of NH3/H2 mixtures was experimentally observed in a rapid compression machine, which is closely linked to the concept of flame bifurcations and cool flames. One interesting question may arise: do similar flame bifurcations exist in NH3/H2 mixtures? To answer this, this study employs the premixed counterflow configuration and examines the potential bifurcations of the NH3/H2/air flame with one-dimensional simulations. For the first time, a novel weak combustion mode of NH3/H2 mixtures is observed and termed as the weak flame in the following. Unlike the conventional hot flame, the weak flame exhibits significantly lower flame temperatures (1300–1500 K) and a mere 1 % of the heat release rate (∼109 J/m3/s) associated with hot flames. Within the weak flame, H2 is entirely oxidized to H2O, whereas only a portion of NH3 is partially oxidized, resulting in the formation of H2O, N2, N2O, and NO. Further reaction path analyses reveal that the NH3 (+OH) → NH2 (+NO2) → H2NO (+NH2, +HO2, +O2, +NO2) → HNO (+O2) → NO (+HO2) → NO2 → N2O pathway is the primary oxidation route of ammonia in the weak flame. Furthermore, the effects of pressure, hydrogen content, and equivalence ratio are systematically assessed to explore the operation conditions of the ammonia/hydrogen weak flame. The study reveals that the weak flame is promoted at elevated pressures, and exists with a moderate hydrogen addition, i.e., = 0.02–0.4. A regime diagram is further proposed to summarize the combined influences of hydrogen molar fraction and equivalence ratio. In the end, the impacts of chemical mechanisms are tested and the dominant ammonia oxidization path in the weak flame persists for models capable of predicting weak flames.
期刊介绍:
The mission of the journal is to publish high quality work from experimental, theoretical, and computational investigations on the fundamentals of combustion phenomena and closely allied matters. While submissions in all pertinent areas are welcomed, past and recent focus of the journal has been on:
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