Fuel Communications最新文献

Ammonia (NH₃) reactivity in a micro flow reactor with a controlled temperature profile (MFR) is reexamined through species measurements utilizing two heating sources in the MFR: an H₂/air flat flame and an electric heater. The maximum wall temperatures (T_w,$$_max) formed in the reactor vary in a range of T_w,$$_max = 1100–1400 K. A stoichiometric NH₃/air mixture is tested, and exhaust NH₃ is detected by a quadrupole mass spectrometer (QMS). Unexpectedly, NH₃ is completely consumed at temperatures at least 100 K lower in the H₂/air flat flame case compared to the electric furnace case, despite nearly identical conditions of a MFR characteristic residence time estimated by the wall temperature profiles and the convective flow velocity. Considering the non-thermal characteristics of the two heating sources that the H₂/air flat flame emits ultraviolet light, whereas infrared light as thermal radiation is emitted within the electric furnace, the possibility of NH₃ photolysis in the H₂/air flat flame case is discussed based on literature regarding emissions from the H₂/air flames, the transmittance of the quartz tube, and the photodissociation of NH₃ in the ultraviolet region. When ultraviolet light emitted from the H₂/air flat flame passes through the quartz tube and decomposes NH₃ into NH₂ and H radicals, these produced radicals enhance the growth of OH radicals, resulting in increased NH₃ reactivity. These findings suggest the possibility of photolysis-assisted ammonia combustion, which could be an additional method to overcome the low reactivity of NH₃.

Hydrogen's ability to enhance carbon neutrality in combustion processes puts forward the use of hydrogenated fuels, both in the form of fuel and an energy carrier as a potential decarbonization solution. However, because of the nature of hydrogen, blending it with hydrocarbons causes crucial structural changes in the flame structure, including higher flame propagation velocities and higher flame temperatures, decreased instantaneous flame thickness, and increased risks of flame flashback and an increasing potential of NO_x emissions due to higher flame temperatures. These attributes encourage a thorough examination of hydrogenated blends of hydrocarbon fuels. Using lean premixed fuels is another technique to achieve efficient and cleaner combustion. However, due to the problem of flame instability in lean premixed combustion, forecasting the design points in terms of flame attributes is critical for better combustor designs.

In this study, conical (Bunsen type) lean premixed turbulent flames of hydrogenated natural gas-air mixtures are experimentally studied. Through chemiluminescence measurements of the OH* and CH* radicals and laser-induced Mie scattering, lean natural gas-air premixed flames are examined with subsequently increasing hydrogen addition rates up to 20% by volume and keeping the premixture velocity constant. The obtained data is utilized for exploring the dynamics of the turbulent flame front. The main turbulent premixed flame parameters we identified relate to the instantaneous and average topology of the flame such as the turbulent flame brush thickness and flame height. We also inferred global combustion parameters like the turbulent flame propagation speed from the experimental findings.

The aviation sector’s significant contribution to greenhouse gas emissions has spurred interest in sustainable aviation fuels (SAF) as a means to mitigate environmental impact. This study examines user diversity in the public acceptance of power-to-liquid aviation fuels (eSAF), exploring varying attitudes towards the environment, flying, and eSAF adoption. Through a quantitative survey of a representative German sample, three distinct segments emerged: the Environment-Centered Approvers, the Flying-Centered Approvers, and the Skeptical. The Environment-Centered Approvers prioritize environmental concerns and perceive moral obligations to use eSAF for climate protection. In contrast, the Flying-Centered Approvers prioritize the continuation of flying with reduced environmental impact, while the Skeptical exhibit a more cautious and uncertain stance towards eSAF adoption. The study highlights the importance of tailoring communication strategies based on the unique motivations and concerns of each subgroup to effectively promote eSAF adoption.

Compared to traditional hydrocarbon fuels, ammonia presents significant challenges as a fuel, including high ignition energy, low reactivity, slow flame propagation, and high NO${}_x$ emissions, which hinder its use as a renewable fuel. Blending ammonia with fossil fuels like natural gas improves its combustion reactivity and helps mitigate CO${}_2$ emissions. However, there is still much to understand about the complex dynamics of ammonia and its blends with hydrocarbons. Key areas such as reaction kinetics mechanisms, ignition properties, flame propagation behaviors, and methods for controlling combustion performance under various conditions require further elucidation. This paper reviews recent advancements in experiments and numerical simulations aimed at developing stable, and low-emission combustors for ammonia-fired power generation. Recent burner and flame configurations, including non-swirling jets, single-stage swirl burners, two-stage burners, and newly developed double-swirl burners are analyzed for their flame stability and pollutant emission potential when firing ammonia and ammonia blends. Chemical kinetic modeling of ammonia and its blends plays a crucial role in understanding combustion behavior and pollutant emissions, particularly for NO${}_x$. However, there are challenges in predicting NO${}_x$ emissions accurately, with significant disparities among different models. High-fidelity numerical simulations using detailed and skeletal mechanisms, direct numerical simulation, and large eddy simulation, have helped uncover crucial operational conditions affecting combustion and pollutant emissions, such as combustor pressure, air dilution, wall cooling, fuel/air mixing, and fuel blending. Nonetheless, the accuracy of chemical kinetic models and their integration into turbulent flow simulations remain critical limitations for numerical simulations of ammonia combustion.

The combustion of ammonia requires, for most energy conversion systems, a combustion promoter such as hydrogen to guarantee the start-up, stability and combustion efficiency. Partially cracked ammonia (PCA) can provide sufficient hydrogen concentrations to enhance the burning velocity in comparison with pure ammonia. However, little work exists on the use of PCA blends operating under relevant turbulent conditions. To that end the outwardly propagating spherical flame configuration was employed to determine the laminar and turbulent flame propagation characteristics of PCA (NH₃/(H₂+N₂)) and corresponding binary (NH₃/H₂) mixtures across various turbulent combustion regimes. First, PCA and ammonia-hydrogen blends exhibit similar flame propagation rates under various turbulent intensities, even for the laminar case. The highest turbulent burning velocity was observed at leanest conditions, as opposed to laminar flames which exhibited highest flame speed at conditions above stoichiometry. Under rich conditions, no substantial flame enhancement due to turbulence was measured irrespective of the hydrogen content. This lack of flame enhancement under turbulent conditions is attributed to the effect of preferential diffusion with good agreement observed with trends in measured Markstein numbers. The normalized turbulent flame speed is dominated by the enhanced molecular diffusivity afforded by the presence of hydrogen up to 15 % enrichment, prior to decreasing upon further hydrogen addition under lean and stoichiometric conditions. This ‘bending’ phenomenon may be the contribution of several factors including; the transitioning between combustion regimes associated with low Damköhler numbers (Da) and flame thickening; merging of flamelets due to the presence of ammonia enhancing wrinkling; and combined changes in laminar burning velocity and preferential diffusional behavior. Furthermore, good agreement for turbulent flame speed is observed with a correlation that includes the influence of turbulent stretch (Ka) and non-equidiffusion (Le), with the agreement reducing with decreasing chemical to turbulent time scale ratios (Da << 1).

Cities continue to expand along with the growth of population, while our mobility systems often fail to meet the demands for social, environmental and economic sustainability. The second industrial revolution enabled the extensive use of private vehicles, posing various challenges to the sustainability of such systems. Luckily, several best practices aiming at tackling this issue have been identified in the past, facilitating progress towards sustainability. Nowadays, this progress is strongly supported by the call for cities to develop Sustainable Mobility Plans (SUMPS), which stands as an opportunity for best practices to be implemented in coordination with relevant policies. This research identifies the best practices that promote a modal shift, while it investigates their alignment with the strategy that enhances public transport services, encourages active mobility and disincentivizes private vehicle usage. Therefore, the presentation of these practices, introduces a set of initiatives that under aforementioned strategy promotes a modal shift. Furthermore, through the identification of best practices in various locations, several insights and inferences are drawn, providing useful guidance.