Numerical Simulation of the Influence of CO2 on the Combustion Characteristics and NOX of Biogas

The existence of inert gases such as N2 and CO2 in biogas will reduce the proportion of combustible components in syngas and affect the combustion and NOX formation characteristics. In this study, ANSYS CHEMKIN-PRO software combined with GRI-MECH 3.0 mechanism was used to numerically simulate the effects of different CO2 concentrations (CO2 volume ratio in biogas is 0–41.6%) on flame combustion temperature, flame propagation speed and nitrogen oxide formation of complex biogas with low calorific value. The results showed that when the combustion reaches the chemical equilibrium, the flame combustion temperature and flame propagation speed decrease with the increase of CO2 concentration, and the flame propagation speed decreases even more slowly. Meanwhile, the molar fraction of NO at chemical equilibrium decreases with the increase of CO2 concentration and the decrease is decreasing, which indicates that the effect of CO2 concentration in biogas on NO is simpler. While the molar fraction of NO2 does not change regularly with the change of CO2 concentration, the effect of CO2 concentration in biogas on NO2 is complicated. The highest molar fraction of NO2 was found at chemical equilibrium when the CO2 concentration was 33.6%, when the target was a typical low calorific value biogas.

The Effect of Inert Fuel Compounds on Flame Characteristics

To describe the effects of inert compounds in gaseous fuel, experiments on three different process burners (staged fuel burner, staged air burner, and low-calorific burner) were carried out. The tested burners are commercially available, but they were specially designed for experimental usage. Tests were carried out in the semi-industrial burner testing facility to investigate the influence of inert gases on the flame characteristics, emissions, and heat flux to the combustion chamber wall. Natural gas was used as a reference fuel, and, during all tests, thermal power of 500 kW was maintained. To simulate the combustion of alternative fuels with lower LHV, N2 and CO2 were used as diluents. The inert gas in the hydrocarbon fuel at certain conditions can lower NOx emissions (up to 80%) and increase heat flux (up to 5%). Once incombustible compounds are present in the fuel, the higher amount of fuel flowing through nozzles affects the flow in the combustion chamber by increasing the Reynolds number. This can change the flame pattern and temperature field, and it can be both positive and negative, depending on actual conditions.

Medium-Energy Synthesis Gases from Waste as an Energy Source for an Internal Combustion Engine

The aim of the presented article is to analyse the influence of synthesis gas composition on the power, economic, and internal parameters of an atmospheric two-cylinder spark-ignition internal combustion engine (displacement of 686 cm3) designed for a micro-cogeneration unit. Synthesis gases produced mainly from waste contain combustible components as their basic material (methane, hydrogen, and carbon monoxide), as well as inert gases (carbon dioxide and nitrogen). A total of twelve synthesis gases were analysed that fall into the category of medium-energy gases with lower heating value in the range from 8 to 12 MJ/kg. All of the resulting parameters from the operation of the combustion engine powered by synthesis gases were compared with the reference fuel methane. The results show a decrease in the performance parameters for all operating loads and an increase in hourly fuel consumption. Specifically, for the operating speed of the micro-cogeneration unit (1500 L/min), the decrease in power parameters was in the range of 7.1–23.5%; however, the increase in hourly fuel consumption was higher by 270% to 420%. The decrease in effective efficiency ranged from 0.4 to 4.6%, which in percentage terms represented a decrease from 1.3% to 14.5%. The process of fuel combustion was most strongly influenced by the proportion of hydrogen and inert gases in the mixture. It can be concluded that setting up the synthesis gas production in the waste gasification process in order to achieve optimum performance and economic parameters of the combustion engine for a micro cogeneration unit has an influential role and is of crucial importance.

STUDY OF METHODS FOR MEASURING THE OPTICAL CHARACTERISTICS OF LOW-PRESSURE MERCURY LAMPS

Obtaining experimental data on the electrical and photometric parameters of low-pressure tubular amalgam lamps with a discharge in a mixture of mercury vapor and inert gases at high current densities of 0.5-1.2 A/cm2 with frequencies of tens of kilohertz is one of the key problems of modern metrology. Since a full-fledged study of the properties of experimental samples of mercury lamps is impossible without a reliable method of photometric measurements, and for ozone lamps such a technique, taking into account the features of the object of study, has not yet been proposed, its development and testing is the main task of this work. Based on the analysis of existing techniques, a technique for measuring the fluxes of the 185 and 254 nm lines of a low-pressure mercury lamp is proposed, taking into account the change in the nature of the spatial distribution of radiation during operation, without directly measuring the RIC. The method proposed by the author for measuring the fluxes of ozonizing and bactericidal radiation can be used as the basis for the development of an automated system for measuring parameters and monitoring the quality of gas-discharge UV radiation sources.

Discovery of argon in air-hydrate crystals in a deep ice core using scanning electron microscopy and energy-dispersive X-ray spectroscopy

Tiny samples of ancient atmosphere in air bubbles within ice cores contain argon (Ar), which can be used to reconstruct past temperature changes. At a sufficient depth, the air bubbles are compressed by the overburden pressure under low temperature and transform into air-hydrate crystals. While the oxygen (O2) and nitrogen (N2) molecules have indeed been identified in the air-hydrate crystals with Raman spectroscopy, direct observational knowledge of the distribution of Ar at depth within ice sheet and its enclathration has been lacking. In this study, we applied scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to five air-hydrate crystals in the Greenland NEEM ice core, finding them to contain Ar and N. Given that Ar cannot be detected by Raman spectroscopy, the method commonly used for O2 and N2, the SEM-EDS measurement method may become increasingly useful for measuring inert gases in deep ice cores.

Vaporization, Diffusion and Combustion of Laser-Induced Individual Magnesium Microparticles in Inert and Oxidizing Atmospheres

Although the gas phase combustion of metallic magnesium (Mg) has been extensively studied, the vaporization and diffusive combustion behaviors of Mg have not been well characterized. This paper proposes an investigation of the vaporization, diffusion, and combustion characteristics of individual Mg microparticles in inert and oxidizing gases by a self-built experimental setup based on laser-induced heating and microscopic high-speed cinematography. Characteristic parameters like vaporization and diffusion coefficients, diffusion ratios, flame propagation rates, etc., were obtained at high spatiotemporal resolutions (μm and tens of μs), and their differences in inert gases (argon, nitrogen) and in oxidizing gases (air, pure oxygen) were comparatively analyzed. More importantly, for the core–shell structure, during vaporization, a shock wave effect on the cracking of the porous magnesium oxide thin film shell-covered Mg core was first experimentally revealed in inert gases. In air, the combustion flame stood over the Mg microparticles, and the heterogeneous combustion reaction was controlled by the diffusion rate of oxygen in air. While in pure O2, the vapor-phase stand-off flame surrounded the Mg microparticles, and the reaction was dominated by the diffusion rate of Mg vapor. The diffusion coefficients of the Mg vapor in oxidizing gases are 1~2 orders of magnitude higher than those in inert gases. However, the diffusive ratios of condensed combustion residues in oxidizing gases are ~1/2 of those in inert gases. The morphology and the constituent contents analysis showed that argon would not dissolve into liquid Mg, while nitrogen would significantly dissolve into liquid Mg. In oxidizing gases of air or pure O2, Mg microparticles in normal pressure completely burned due to laser-induced heating.

Revisiting decompression sickness risk and mobility in the context of the SmartSuit, a hybrid planetary spacesuit

Gas pressurized spacesuits are cumbersome, cause injuries, and are metabolically expensive. Decreasing the gas pressure of the spacesuit is an effective method for improving mobility, but reduction in the total spacesuit pressure also results in a higher risk for decompression sickness (DCS). The risk of DCS is currently mitigated by breathing pure oxygen before the extravehicular activity (EVA) for up to 4 h to remove inert gases from body tissues, but this has a negative operational impact due to the time needed to perform the prebreathe. In this paper, we review and quantify these important trade-offs between spacesuit pressure, mobility, prebreathe time (or risk of DCS), and space habitat/station atmospheric conditions in the context of future planetary EVAs. In addition, we explore these trade-offs in the context of the SmartSuit architecture, a hybrid spacesuit with a soft-robotic layer that, not only increases mobility with assistive actuators in the lower body, but it also applies some level of mechanical counterpressure (MCP). The additional MCP in hybrid spacesuits can be used to supplement the gas pressure (i.e., increasing the total spacesuit pressure), therefore reducing the risk of DCS (or reduce prebreathe time). Alternatively, the MCP can be used to reduce the gas pressure (i.e., maintaining the same total spacesuit pressure), therefore increasing mobility. Finally, we propose a variable pressure concept of operations for the SmartSuit spacesuit. Our framework quantifies critical spacesuit and habitat trade-offs for future planetary exploration and contributes to the assessment of human health and performance during future planetary EVAs.