K. Ya. Troshin

Gas-phase spontaneous ignition of hydrocarbons

The ignition of hydrocarbons at low temperatures is experimentally studied in a rapid-mixture-injection static reactor. The ignition process was monitored using a high-speed color video camera. It was found that, at low temperatures, ignition starts in kernels, a feature also characteristic of methods for measuring the ignition delay time at high and medium temperatures (shock tube, rapid compression machine). Kernel-mode ignition is associated with gas-dynamic phenomena inherent in different techniques of heating the gas to the desired temperature. Ignition in the kernel is of chain-thermal nature. The emergence of a visible kernel can be considered the beginning of hot flame propagation. It is shown that, in the self-ignition mode, the propagation of the flame front from the initial kernel occurs by the induction mechanism, proposed by Ya.B. Zel’dovich, rather than by the diffusion-heat-conduction mechanism. Introduction of a platinum wire into the reactor produces a catalytic effect in the negative temperature coefficient region, while virtually unaffecting the ignition delay at lower temperatures.

Burning velocity of methane-hydrogen mixtures at elevated pressures and temperatures

The effect of the initial pressure, temperature, and equivalence ratio on a number of combustion characteristics of methane-air mixtures with hydrogen additives in a closed vessel is experimentally studied. Experiments are conducted at 1, 5, and 10 atm and temperatures from 22 to 300°C. The hydrogen content in the fuel is 0, 10, and 20 vol %. The fuel equivalence ratio varies from 0.6 to 1.0. The limitations imposed by buoyancy on measurements of the laminar burning velocity by the constant-volume bomb method with recording of pressure-time histories are analyzed. It is shown that the laminar burning velocity can be appreciably increased by adding no less than 20 vol % of hydrogen to the fuel.

Influence of inert and active additives on the initiation and propagation of laminar spherical flames in stoichiometric mixtures of methane, pentane, and hydrogen with air

The propagation of a laminar spherical flame in stoichiometric mixtures of methane, and pentane with air in the presence of argon and carbon dioxide and in hydrogen-air-propylene mixtures at atmospheric pressure in a constant-volume bomb is investigated using high-speed color cinematography. It is shown that, under the experimental conditions employed (at T0 = 298 K and a spark energy of E0 = 0.91 J), dilution of the combustible mixtures with these additives can cause a more than 10-fold increase in the time of formation of a steady flame front, with the inhibiting effect of carbon dioxide being stronger than that of argon. Small additives of propylene, a chemically active inhibitor, are demonstrated to substantially increase the time it takes to form a steady flame front and reduce the flame propagation velocity.

Experimental study of the ignition of n -hexane- and n -decane-based surrogate fuels

Surrogate fuels on the basis of mixtures of n-hexane, n-decane, and benzene are fuels alternative to petroleum motor fuels, similar to the former in thermodynamic and kinetic properties. The fact the surrogate fuels are composed of a limited number of components makes it possible to develop both detailed and global kinetic mechanisms of their ignition in mixtures with oxidizers. In turn, the possibility of the kinetic modeling of the ignition of such fuels over wide temperature and pressure ranges is of critical importance for the numerical modeling of combustion-to-detonation transition phenomena. An experimental method for measuring ignition delay times of mixtures of air with liquid fuels with low vapor pressure under normal conditions is developed and tested. In the present work, the ignition of stoichiometric mixtures of air with n-hexane, n-decane, and surrogate fuels composed of 20% n-hexane and 80% n-decane, 20% benzene and 80% n-decane, and 9.1% n-hexane, 18.2% benzene, and 72.7% n-decane is experimentally investigated in a static reactor. The ignition delay time is determined by recording pressure oscillograms at temperatures of 530–1030 K and pressures of 1–9 atm.

Low-temperature autoignition of binary mixtures of methane with C3–C5 alkanes

The influence of C3–C5 alkanes on the ignition of their binary mixtures with methane in air at a temperature of 523–1000 K and a pressure of 1 atm is studied. It is shown that the presence of only 1% C3–C5 alkanes considerably reduces the ignition delay of methane. At a concentration of 10–20%, the ignition delay practically corresponds to the autoignition delay of the added alkane. The effect of additives of heavy alkanes becomes less noticeable with increasing initial temperature. These results can be used to estimate the permissible content of C5+ heavy species in gas turbine engine fuel at which their influence on the fuel knock resistance is sufficiently low. It is only 0.5%.

Explosive characteristics of tetrafluoroethylene

The minimum energies required to initiate the combustion of gaseous tetrafluoroerthy1ene (TFE) and mixtures thereof with nitrogen, argon, and helium at various initial pressures and temperatures are determined. Flame transition from the gas to the liquid phase of TFE is investigated. Liquid TFE is demonstrated to be virtually nondetonable. The fuel-lean flammability and detonability limits of TFE-air mixtures under normal conditions are demonstrated to be identical, 12.2 vol %.

Single-stage conversion of associated petroleum gas and natural gas to syngas in combustion and auto-ignition processes

Single-stage conversion of alkane mixtures simulating associated petroleum gas (APG) to syngas is studied in a static installation and in a flow reactor based on the rocket combustion chamber. Yields of the desired reaction products close to their thermodynamically equilibrium values are obtained. A range of experimental parameters, in which ignition delays of APG-oxygen mixtures exhibit negative or zero temperature coefficients, is determined for the first time. Such a behavior of ignition delays is proved to be a fundamental property of fuel-rich APG mixtures. The range of abnormal temperature dependence of ignition delays is shown to be extended as the initial pressure rises, which makes it possible to significantly increase the reaction rate by increasing the initial working pressure.

Manufacture of Synthesis Gas by the Methane Combustion Process: The Formation of Soot and Its Physicochemical Characteristics

The formation of a solid carbon phase (soot) during the production of synthesis gas in the combustion process of superrich methane mixtures was experimentally studied in a static apparatus, rapid compression machine and in a rocket-engine based flow reactor. It was shown experimentally that admixtures of steam (5–15 wt % of methane mass) suppress the formation of soot during the burning of methane-oxygen mixtures with an excess oxidant factor of α ≥ 0.35. The influence of the combustion regimes on the yield of soot was examined, and its properties were studied.

Structure and reactivity of mechanoactivated Mg (Al)/MoO3 nanocomposites

X-ray diffraction and thermal analyses, microscopy, and specific surface area measurements are used to study the formation, structure, and reactivity of mechanoactivated Mg/MoO3 and Al/MoO3 nanocomposites during slow heating (10°C/min). The optimal mechanoactivation dose is determined. The mechanoactivated Mg/MoO3 composite is a dense mixture of two nanosized components with a contact surface of ~8 m2/g (upper estimate). The area of the contact surface between the components of the Al/MoO3 composite is less than 2 m2/g, with the sample consisting of micron-sized aluminum flakes coated with nanoparticles oxide nanoparticles. When heated, the Mg/MoO3 system explodes, with the temperature of explosion being determined by the heating conditions. The minimum temperature of conversion is ~250°C, close to the temperature of autoignition of fuel–air mixtures promoted by these additives. The Al/MoO3 system is characterized by a phased progress of the reaction in the temperature range of 200 to 1000°C. The reasons for the differences in the reactivity of the mixtures are discussed.

Promotion of the self-ignition of fuel–air mixtures with mechanoactivated Al (Mg)–MoO3 particles

The ignition delay times of heptane–air and diesel oil–air mixtures with and without additives of mechanoactivated Mg–MoO3, Al–MoO3, and Mg–fluoroplastic nanopowders are measured using a rapid-mixture-injection setup. At temperatures below a certain threshold value, the metal–MoO3 additives produce practically no effect on the ignition delay time, whereas at higher temperatures, these additives sharply reduce the ignition delay time, down to the resolution time of the experimental method. The promoting efficiency of the small heterogeneous additives tested is many times superior to that of the known homogeneous promoters. Magnesium–fluoroplastic additives are demonstrated to produce no promoting effect on the ignition of the fuel–air mixtures studied. The mechanism of the action of the heterogeneous additives on the gasphase self-ignition of fuels is discussed.