Solid-phase synthesis of ytterbium zirconate using mechanical activation

Nanocrystalline ytterbium zirconate Yb4Zr3O12 was prepared by the solid-phase method using mechanical activation of stoichiometric mixture of zirconium and ytterbium oxides. Mechanical activation was carried out in an AGO-2 centrifugal-planetary mill at a centrifugal factor of 40 g for 10 min. The processes occurring during the calcination of the mechanically activated mixture of ytterbium and zirconium oxides in the range from 600 to 1300 °C were investigated using X-ray phase analysis, IR spectroscopy, and complex thermal analysis.

Investigation of Thermal Radiation from Soot Particles and Gases in Oxy-Combustion Counter-Flow Flames

Oxy-combustion with high flame temperature, low heat loss, high combustion efficiency, and low NOx emissions is being extensively studied. The thermal radiation from soot particles and gases in oxy-combustion accounts for the vast majority of the total heat transfer. Based on a detailed chemical reaction mechanism coupled with the soot particle dynamics model and optically thin radiation model, the influence of the flame structure and temperature distribution on the thermal radiation in oxygen-enriched counterflow diffusion flames was studied in this paper. The results revealed that reasonable assignment of total recycled flue gas and the degree of dilution of fuel and oxidant were critical, which can be used to adjust the overall radiation situation of the flame. At the same adiabatic flame temperature, as the fuel concentration decreased and the oxidant concentration increased (the stoichiometric mixture ratio is from 0.3 to 0.6), the soot formation decreased, which led to the particle radiation disappearing while the main radiation zone of gases moved 0.04 cm toward the fuel side. At the same stoichiometric mixture fraction (0.4), the radiation area was broadened and the radiation of soot particles was gradually enhanced with the adiabatic flame increasing from 2300 K to 2700 K.

The effect of titanium-carbon mixture mechanical activation on SHS pressing parameters and consolidated titanium carbide microstructure

The paper studies the effect of mechanical activation (MA) modes when stirring a stoichiometric mixture of titanium and soot powders in a ball mill on the properties of mixtures, combustion parameters, relative density, and the microstructure of consolidated titanium carbide samples obtained by SHS. MA conditions for Ti + C reaction mixtures in a ball mill were determined. An increase in the mass of grinding bodies activates the MA mechanism. It was shown that the greatest effect from MA was obtained with a two-stage preparation of mixtures: firstly, the titanium powder was activated separately, then the components were mixed together, and this process included not only their mixing, but also soot powder activation. It was found that combustion behavior is affected by the activation of not only titanium, but also soot. After MA of both components, an anomalous increase in the burning rate (more than 100 cm/s) was found on pressed samples. At the bulk density, there was no effect of MA on the mixture combustion process, since in this case the burning rate of all mixtures was in the range of 1.5–2.5 cm/s. It was revealed that MA of reagents for pressed samples leads to an increase in the combustion temperature, an increase in the relative density of the consolidated refractory product to 93–95 %, and a decrease in the average size of TiC grains. A decrease in the residual porosity of consolidated TiC is due to an increase in the hot pressing temperature and plasticity of the product synthesized during the reaction mixture combustion after MA. The main reason is an increase in the exothermic interaction rate. It was shown that MA when mixing reagents makes it possible to control combustion parameters, the microstructure of consolidated products and opens up new opportunities for obtaining refractory materials featuring a unique structure and properties by SHS pressing.

COMBUSTION OF GASOLINE AND ETANOL MIXTURE

Thanks to the pressure of the Environmental Society, the priority of engine manufacturers is to reduce emissions of harmful substances into the atmosphere and reduce fuel consumption while constantly increasing engine performance. One way to overcome the aforementioned technical and social problems is to use alcohols, natural or synthetic, such as ethanol to power engines. The objectives of manufacturers of alternative fuels is to provide consumers with the opportunity to use their product without changing the parameters of the main units in their vehicles, therefore the stoichiometry of the combustion of fuel mixtures is important, since this parameter can affect the amount of fuel burned, the quality of exhaust gases and the power of the internal combustion engine. Combustion in a car engine is exothermic, which means that a side effect of this chemical reaction is heat released into the environment. The condition for starting the combustion process is the thermal coefficient – for spark ignition engines – a spark, and for diesel engines – heat during compression of the fuel-air mixture. From the above it follows that after the oxidation reaction in the exhaust gases there should be no residual fuel particles, which in turn is an image of stoichiometric combustion. Since the stoichiometric mixture is very difficult to achieve outside laboratory conditions, a distinction is made between a non-greasy mixture (too much oxidizing agent) and a saturated mixture (too little oxidizing agent), but always strive to reach λ = 1, which corresponds to a stoichiometric mixture. The heavy weight when working with ethanol fuel is the one that affects the operation of the engine and its components. Therefore, it is important to compare the physicochemical data of gasoline and ethanol, as well as mixed fuel – E85. The article deals with the stoichiometry of combustion of an alternative fuel - a mixture of gasoline and ethanol. The economic and environmental conditions that initiated the production of this type of fuel were taken into account, the fuel mixtures were divided according to the content of fuel and oxidants in the combustion chamber. Attention is drawn to the determination of the stoichiometric mixture, as well as to the lambda coefficient (λ), which helps to determine the type of mixture. The properties of gasoline (in the form of iso-octane) and ethanol are described in separate sections and each is compared. One chapter is devoted to the description of the E85 mixture used in Flexi Fuel Vehicles engines, the requirements for this fuel are determined by the Minister of Economy on the requirements for the quality of biofuels, and attention is also paid to the effect of the mixture on the operation of the engine and the content of chemical compounds in the exhaust using E85 biofuel. It has been established that ethanol fuel (in particular E100) is undoubtedly a step forward in terms of ecology, transport economics and the development of alternative fuels. However, its physicochemical properties cause many problems in engine operation. Despite the improvement in the net power generated by the engine, it should be remembered that for the current mechanical parts and their materials, this is a “problem” mixture that requires frequent and accurate diagnostics and calibration. KEY WORDS: STOICHIOMETRIC MIXTURE, COMBUSTION, MIXTURE OF GASOLINE AND ETHANOL, ALTERNATIVE FUEL, IMPROVEMENT OF THE PHYSICAL AND CHEMICAL PROCESSES OF THE ENGINE.

Analysis of the Risks of Hydrogen Leakage from Hydrogen-Powered Cars and Their Possible Impact on Automotive Market Share Increase

For the safe operation of a hydrogen-powered car, one of the strategic requirements is to design the drive chain so that it is burdened with the least possible risk. At the same time, in order to be able to use it in normal operation, it is necessary to create a risk management system throughout the life of the car so that risks are minimized to the level of their acceptability not only by customers but also by a comprehensive infrastructure during its technical life. Experience has shown that one of the decisive risks in the operation of a hydrogen-powered car is the leakage of hydrogen from the car’s fuel system. The article analyzes the pressure effects on obstacles in the explosion of 1 m3 of a stoichiometric mixture of hydrogen and air. The analysis of the instantaneous pressures as a function of time describes the possible consequences for the human body and the surrounding objects with regard to the distance from the center of the explosion.

Effect of piston shape design on the scavenging performance and mixture preparation in a two-stroke boosted uniflow scavenged direct injection gasoline engine

Compared to a four-stroke engine, the two-stroke engine doubles firing frequency and has favourable power-to-weight or power-to-volume ratio as well as engine downsizing to improve the overall powertrain fuel economy. In order to overcome the shortcomings of the conventional cross-flow or loop scavenged two-stroke engines, a two-stroke boosted uniflow scavenged direct injection gasoline engine was designed and its performance was analysed. In this study, three-dimensional computational fluid dynamics simulations were performed to understand the impact of the piston shape design on the scavenging process, in-cylinder flow formation, turbulence level and subsequent fuel/air mixing process in the boosted uniflow scavenged direct injection gasoline engine. Both single injection and split injection strategies were investigated to study the interactions between piston designs and fuel injection strategies to achieve stoichiometric mixture around the spark plug. The results show that the optimised piston with the same opening timing for all scavenge ports could achieve much better scavenging performance than the baseline piston design. In particular, the shallow pistons, that is, Piston #1 and Piston #4, could produce stoichiometric mixture around the spark plug with relatively lower inhomogeneity and higher turbulence kinetic energy around top dead centre when implementing the split injection strategy with start of injection timing at 250/310 °CA.

Deflagration-to-detonation transition in air mixtures of polypropylene pyrolysis products

A new method for determining the detonability of fuel is proposed based on the measured values ​​of the detonation run-up distance and time in the standard pulsed detonation tube (PDT). Granulated polypropylene (GP) was used as a fuel. A test bench with the PDT and a gas generator was designed and manufactured for the preparation of the GP pyrolysis products at a decomposition temperature of up to 800 °C. Experiments on deflagration-to-detonation transition in air mixtures of pyrolysis products of the GP showed that such mixtures exhibit detonability close to that of liquefied hydrocarbon gas (LPG) of the propane-butane automobile brand in a stoichiometric mixture with air under normal conditions.