Optical and thermodynamic investigations of a methane and hydrogen blend fueled large bore engine

The following paper presents thermodynamic and optical investigations of the natural flame and OH radical chemiluminescence of a hydrogen enriched methane combustion compared to natural gas combustion. The engine under investigation is a port-fueled unscavenged prechamber 4.8 L single cylinder large bore engine. The blends under consideration are 2%V, 5%V,10%V, and 40%V of hydrogen expected to be blended within existing natural gas grids in a short and mid-term timeline in order to store green energy from solar and wind. These fuel blends could be used for stabilization of the energy supply by reconverting the renewable fuel CH4/H2 in combined heat and power plants. As expected, admixture of hydrogen extends the ignition limits of the fuel mixture toward lean ranges up to an air-fuel equivalence ratio of almost 2. No negative effect on combustion is observed up to an admixture of 40%V hydrogen. At 40%V hydrogen, abnormal combustion like backfire occurs at an air-fuel equivalence ratio of 1.5. The higher mixtures exhibit increased nitrogen oxide emissions due to higher combustion chamber temperatures, while methane slip and CO emissions are reduced due to more complete combustion. The optical investigation of the natural flame and OH radical chemiluminescence are in good agreement with the thermodynamic results verifying the more intense combustion of the fuel blends by means of the chemiluminescence intensity. Further, lube oil combustion and a continuing luminescence after the thermodynamic end of combustion are observed.

Biomass burning plume chemistry: OH-radical-initiated oxidation of 3-penten-2-one and its main oxidation product 2-hydroxypropanal

In order to enlarge our understanding of biomass burning plume chemistry, the OH-radical-initiated oxidation of 3-penten-2-one (3P2), identified in biomass burning emissions, and 2-hydroxypropanal (2HPr) was investigated at 298 ± 3 K and 990 ± 15 mbar in two atmospheric simulation chambers using long-path FTIR spectroscopy. The rate coefficient of 3P2 + OH was determined to be (6.2 ± 1.0) × 10−11 cm3 molec.−1 s−1 and the molar first-generation yields for acetaldehyde, methyl glyoxal, 2HPr, and the sum of peroxyacetyl nitrate (PAN) and CO2, used to determine the CH3C(O) radical yield, were 0.39 ± 0.07, 0.32 ± 0.08, 0.68 ± 0.27, and 0.56 ± 0.14, respectively, under conditions where the 3P2-derived peroxy radicals react solely with NO. The 2HPr + OH reaction was investigated using 3P2 + OH as a source of the α-hydroxyaldehyde adjusting the experimental conditions to shift the reaction system towards secondary oxidation processes. The rate coefficient was estimated to be (2.2 ± 0.6) × 10−11 cm3 molec.−1 s−1. Employing a simple chemical mechanism to analyse the temporal behaviour of the experiments, the further oxidation of 2HPr was shown to form methyl glyoxal, acetaldehyde, and CO2 with estimated yields of 0.27 ± 0.08, 0.73 ± 0.08, and 0.73 ± 0.08, respectively.

A new analytical method, using the dark Fenton reaction as an OH radical source to study oxidations of unsaturated (di)aldehydes in the aqueous phase

<p>Anthropogenic and biogenic sources produce numerous primary emitted gases, organic compounds, and aerosols in the atmosphere. An important group of such compounds are α, β-unsaturated carbonyl molecules, which can be formed in the atmosphere due to their secondary origin, including oxidation of their precursors such as hydrocarbons with common atmospheric oxidants such as hydroxyl radicals (‧OH). Since those compounds contain at least one double bond and one carbonyl group, they are characterized as water-soluble molecules, which can diffuse on the cloud droplets’ surface and undergo a phase transfer from the gas phase to the atmospheric aqueous phase. In the latter, the oxidized organic compounds can contribute to aerosol mass production through in-cloud processes, yielding aqueous phase secondary organic aerosols (aqSOA). Due to their strong photochemical behavior, the development of a new analytical approach for evaluating the OH radical kinetics in the aqueous phase under dark conditions was essential. One of the most studied non-photolytic reactions is Fenton chemistry (Fe(II)/H<sub>2</sub>O<sub>2</sub>), which serves as an OH radical source in the dark in the atmospheric aqueous phase after catalytic decomposition of H<sub>2</sub>O<sub>2</sub> in the presence of Fe(II) at acidic pH values. In a typical experiment, temperature-dependent second-order rate constants of OH radicals with unsaturated dialdehydes, such as (1) crotonaldehyde, and (2) 1,4-butenedial, were determined in a bulk reactor by using the competition kinetics method. In the newly developed method, the role of radical scavenger was performed by isotopically labeled 2-propanol (d8), while the OH-initiated oxidation produces deuterated acetone (d6), being analyzed with GC-MS after derivatization. The findings from our research will be incorporated in the CAPRAM model to explain discrepancies between experimentally observed and predicted aqSOA properties.</p>

Investigation of OH radical kinetics with glycine, alanine, serine and threonine in the aqueous phase

<p>Amino acids are key substances in biological activities and can be emitted into the atmosphere as constituents of primary aerosols. Understanding the radical kinetics of amino acids is necessary to evaluate their atmospheric effects. In the present study, the hydroxyl radical (OH) reaction kinetics of glycine, alanine, serine and threonine were investigated in the aqueous phase. The temperature and pH dependent rate constants were measured by a laser flash photolysis-long path absorption setup using the competition kinetics method. Based on the measurements and speciation calculations, the OH radical reaction rate constants of the fully protonated (H<sub>2</sub>A<sup>+</sup>) and neutral (HA<sup>±</sup>) form were determined. The following T-dependent Arrhenius expressions were derived for the OH radical reactions with glycine, <em>k</em>(<em>T</em>, H<sub>2</sub>A<sup>+</sup>) = (9.1 ± 0.3) × 10<sup>9</sup> × exp[(-2360 ± 230 K)/<em>T</em>], <em>k</em>(<em>T</em>, HA<sup>±</sup>) = (1.3 ± 0.1) × 10<sup>10</sup> × exp[(-2040 ± 240 K)/<em>T</em>]; alanine, <em>k</em>(<em>T</em>, H<sub>2</sub>A<sup>+</sup>) = (1.0 ± 0.1) × 10<sup>9</sup> × exp[(-1030 ± 340 K)/<em>T</em>], <em>k</em>(<em>T</em>, HA<sup>±</sup>) = (6.8 ± 0.4) × 10<sup>10</sup> × exp[(-2020 ± 370 K)/<em>T</em>]; serine, <em>k</em>(<em>T</em>, H<sub>2</sub>A<sup>+</sup>) = (1.1 ± 0.1) × 10<sup>9</sup> × exp[(-470 ± 150 K)/<em>T</em>], <em>k</em>(<em>T</em>, HA<sup>±</sup>) = (3.9 ± 0.1) × 10<sup>9</sup> × exp[(-720 ± 130 K)/<em>T</em>]; and threonine, <em>k</em>(<em>T</em>, H<sub>2</sub>A<sup>+</sup>) = (5.0 ± 0.1) × 10<sup>10</sup> × exp[(-1500 ± 100 K)/<em>T</em>], <em>k</em>(<em>T</em>, HA<sup>±</sup>) = (3.3 ± 0.1) × 10<sup>10</sup> × exp[(-1320 ± 90 K)/<em>T</em>] (in units of L mol<sup>-1</sup> s<sup>-1</sup>).</p> <p>The density functional theory calculation was performed using GAUSSIAN to simulate the energy barriers (<em>E<sub>Barrier</sub></em>) of OH radical induced H-atom abstraction. According to the simulated results, amino and carboxyl group increase the <em>E<sub>Barrier</sub></em> at the adjacent C‑atom and thus reduce the OH radical reactivity. Hydroxide and methyl group decrease the <em>E<sub>Barrier</sub></em> at the adjacent C-atom, leading to an increase in the OH radical rate constant.</p>

Influence of Controlling Plasma Gas Species and Temperature on Reactive Species and Bactericidal Effect of the Plasma

In this study, plasma gas species and temperature were varied to evaluate the reactive species produced and the bactericidal effect of plasma. Nitrogen, carbon dioxide, oxygen, and argon were used as the gas species, and the gas temperature of each plasma was varied from 30 to 90 °C. Singlet oxygen, OH radicals, hydrogen peroxide, and ozone generated by the plasma were trapped in a liquid, and then measured. Nitrogen plasma produced up to 172 µM of the OH radical, which was higher than that of the other plasmas. In carbon dioxide plasma, the concentration of singlet oxygen increased from 77 to 812 µM, as the plasma gas temperature increased from 30 to 90 °C. The bactericidal effect of carbon dioxide and nitrogen plasma was evaluated using bactericidal ability, which indicated the log reduction per minute. In carbon dioxide plasma, the bactericidal ability increased from 5.6 to 38.8, as the temperature of the plasma gas increased from 30 to 90 °C. Conversely, nitrogen plasma did not exhibit a high bactericidal effect. These results demonstrate that the plasma gas type and temperature have a significant influence on the reactive species produced and the bactericidal effect of plasma.

Mathematical model simulation of the reaction process between 2,4,6-trinitrotoluen and hydroxyl radio in water environment

In this study, the author formulated the equation that describes the reaction rate (mathematical modelling) of 2,4,6-trinitrotoluen and hydroxyl radical (OH*) of v = 4.3×108×[CTNT]1.1×[COH*]3.2 and mathematical simulation for the reaction process of 2,4,6-trinitrotoluen and OH* radical. The simulation results showed a decrease in concentration [CTNT] and a reaction rate proportional to each other; during the first 0-30 minutes of the reaction, the reaction speed is very fast. From the experimental results, the authors also determined that the 2,4,6-trinitrotoluen treatment performance in wastewater of the nonthermal plasma model reached >99% when increasing the treatment time to 120 minutes.

Evaluation of Portable Rhodamine B Analyzer for Monitoring OH Radical Scavenging Demand in Ultraviolet Advanced Oxidation Processes

A portable OH radical scavenging demand analyzer that can be installed and operated on site was developed to measure water quality indicators that influence the generation of OH radicals from UV/hydrogen peroxide reactions to determine the UV dose and the hydrogen peroxide injection concentration. Rhodamine B (RhB) was used as an indicator for the continuous measurement of the OH radical scavenging demand of four samples with different water quality parameters using the rapid, easy, and real-time UV-Vis spectrophotometer method. The results demonstrated that the estimated rate constant for the RhB color decay rate resulting from direct UV photolysis was low enough to verify its suitability as a probe compound. The mean values of the OH radical scavenging demand for target water samples at different organic concentrations were 20,659 s−1 for plant N, 42,346 s−1 for plant C, 32,232 s−1 for plant Y, and 81,669 s−1 for plant B. Variations in the monitoring results for the target water treatment plants suggest that on-site OH radical scavenging demands should be considered to determine the UV dose and the hydrogen peroxide injection concentration for the UV advanced oxidation process.

The impacts of marine-emitted halogens on OH radical in East Asia during summer

Relationships between oceanic emissions and air chemistry are intricate and still not fully understood. For regional air chemistry, a better understanding of marine halogen emission on hydroxyl (OH) radical is crucial. OH radical is a key species in atmospheric chemistry because it can oxidize almost all trace species in the atmosphere. In the marine atmosphere, OH level could be significantly affected by the halogen species emitted from the ocean. However, due to the complicated interactions of halogens with OH through different pathways, it is not well understood how halogens influence OH and even great uncertain in the signs of net effect. Therefore, in this study, we aim to quantify the impact of marine-emitted halogens (including Cl, Br, and I) through different pathways on OH in the high OH season by using WRF-CMAQ model with process analysis and state-of-the-art halogen chemistry in the East Asia Seas. Results show a very complicated response of OH production rate (POH) to marine halogen emissions. The monthly POH is generally decreased over the ocean with maxima of about 10–15 % in the Philippine Sea, but is increased in many nearshore areas with maxima of about 7–9 % in the Bohai Sea. In the coastal areas of southern China, the monthly POH could also decrease 3–5 % in the Greater Bay Area, but with a daytime hourly maximum decrease over 30 %. Analysis to the individual reactions using integrated reaction rate (IRR) show that the net change of POH is controlled by the competitions of three main pathways through different halogen species. Sea spray aerosols (SSA) and inorganic iodine gases are the main species to influence the strengths of these three pathways and therefore have the most significant impacts on POH. Both of these two types of species decrease POH through physical processes, while generally increase POH through chemical processes. In the ocean atmosphere, the controlling species are inorganic iodine gases and the complicated iodine chemistry determines the basic pattern of ΔPOH, while over the continent, SSA is the controlling species and the SSA extinction effect leads to the negative ΔPOH in the southern China. Our results indicate that marine-emitted halogen species have notable impacts over the ocean and have potential impact on the coastal atmospheric oxidation. The identified main (previously known or unknown) pathways and their controlling factors from different halogen species to OH radical explains the halogen-induced change of POH East Asia and also can be applied in other circumstances (e.g., different domains, regions, and emission rates).