Values Of Ignition Delay Times Research Articles

The effect of the distance between wood and coal particles on the characteristics of their joint ignition under conditions of high-temperature radiation-convective heating

The article presents the results of the experimental studies of the ignition processes of mixed fuels “wood + coal” under conditions corresponding to the furnace spaces of the boiler units of TPPs. It has been established that under conditions of relatively low ambient temperatures, the time characteristics of the ignition process of coal and wood particles in the composition of the mixture differ significantly from the analogous characteristics for the ignition of single particles. It is shown that woody biomass significantly accelerates the ignition of coal, compared to the ignition of homogeneous coal (the delay time is reduced by 20–30%). At the same time, it has been found that coal particles significantly slows down the process of wood ignition (on average by 30%).The analysis of the distance between particles (d) has shown that d has a significant effect on the ignition performance. It was found that there is a certain “optimal” value of d, at which the ignition delay times are minimal. It is also shown that with an increase in the ambient temperature, the effect of the distance between particles decreases significantly.Based on the results of the experimental studies, a mathematical model has been developed for the ignition of wood-coal fuel particles, which differs from the known ones by a detailed description of thermophysical and thermochemical processes occurring in the porous structure of fuels and in a small vicinity of these particles. A comparative analysis of theoretical and experimental values of ignition delay times has shown their good agreement. An asymptotic analysis of the ignition time has shown that the entire induction period can be conditionally divided into two stages: fuel heating and direct thermochemical reaction. The fuel heating time takes about 90% of the entire induction period.

Ignition of particles of finely dispersed fuel mixtures based on coal and fine wood

The purpose of this work is to experimentally determine conditions and characteristics of floating particles ignition of fuel mixtures based on coal dust with characteristic sizes of less than 80 μm and fine wood (typical sizes up to 200 μm) at various mass concentrations of fuel components. The experiments were conducted in a medium heated to high temperatures of still air (from 600 °C to 1200 °C). Record of the processes of heating of the researched fuel mixture that is quite promising for heat power engineering, their subsequent ignition and combustion was performed by a high-speed video camera (image format - 1024 × 1024 pixels, frame rate - up to 105 per second). It has been established that increase in the proportion of relatively large particles (compared to coal) of the wood component in the fuel mixture does not significantly affect the values of ignition delay times of all investigated wood-coal mixtures based on two typical grades of coal (long-flame and lean).

PENGARUH PERSENTASE BIODIESEL MINYAK JELANTAH - SOLAR TERHADAP KARAKTERISTIK PEMBAKARAN DROPLET

Fossil fuels need to be replaced with alternative energy sources such as household waste, used cooking oil. This research utilizes household waste such as used cooking oil as an alternative fuel. In this research biodiesel used waste cooking oil mixed with diesel with a percentage of 50%: 50%, 60%: 40%, 70%: 30%, 80%: 20%, and 90%: 10%. The mixture of waste cooking oil and diesel biodiesel was then made into a 1 mm droplet grain, then a droplet combustion test was carried out. The test results show that the value of ignition delay time increases with increasing percentage of biodiesel used waste cooking oil. The burning rate value increases with the increase in the percentage of used waste cooking oil biodiesel. The temperature value increases with the increasing percentage of biodiesel used waste cooking oil. The maximum fire height value that can be achieved decreases with increasing percentage of used waste cooking oil biodiesel.

Conditions and characteristics of mixed fuel granules ignition based on coal and finely dispersed wood

Analysis of the possibility of lumber waste disposal via combustion in a mixture with coal has been conducted. Conditions and characteristics of pellets ignition of fuel mixtures based on coal dust and grounded wood at various mass concentrations of the components have been experimentally determined. Fuel pellets were made by cold pressing on a hydraulic press. The experiments were performed in a medium of still air heated to high (from 600 °C to 800 °C) temperatures. Record of heating processes of the researched promising for thermal power engineering granules of mixed fuels, their subsequent ignition and combustion has been conducted using a high-speed video camera (image format - 1024 × 1024 pixels, frame rate - up to 100000 per second), which provides high discretization of registration results of processes characteristic times. It has been established that an increase in the proportion of wood components in the fuel granule significantly reduces values of ignition delay times of all researched mixtures based on 2B and 3B brown coal. The limit of stable ignition of such fuels has been determined. It is shown that ignition delay times of fuel pellets with characteristic sizes up to 8 mm (height) with diameter of 8 mm even at relatively low temperatures of the combustion medium do not exceed 16 s, which illustrates the promising application of such fuels even in small-scale power engineering.

Ignition of granulated mixed fuel based on lignite and wood waste

Analysis of utilization possibility of sawmill waste when burning pellets in a mixture with coal. Conditions and characteristics of pellets ignition of fuel mixtures based on coal dust and fine wood at various mass concentrations of the components have been experimentally determined. Fuel pellets were made by cold pressing on a hydraulic press. The experiments were carried out in a medium heated to high (from 600 ° C to 800 ° C) temperatures of still air. It was established that increase of wood component proportion in the fuel granule significantly reduces the values of ignition delay times of all studied mixtures based on brown coal of 3B grade. The limit of stable ignition of such fuels is 600 ° C. The obtained results reflect the possibility of using granules of mixed fuels based on crushed coal and wood in the case of fuel-bed combustion in coal-fired boilers, as well as hot water boilers.

Co-combustion of coal processing waste, oil refining waste and municipal solid waste: Mechanism, characteristics, emissions

This experimental research studies co-combustion of wet coal processing waste (filter cakes) with typical municipal solid waste (wood, rubber, plastic, cardboard) and used turbine oil, as combustible components of composite liquid fuel. Ignition mechanisms and characteristics of single droplets of three fuel composition groups have been investigated in a motionless heated air with using a high-speed video recording system. Analyzing video frames, a physical model of the process under study was developed. The values of the guaranteed ignition delay times have been determined for three fuel groups with different compositions at the ambient temperature 600–1,000 °C. The minimum values of ignition delay times are about 3 s, the maximum ones are about 25 s. In addition to the established difference in the ignition delay times, the various fuel compositions also differ in combustion temperatures. Maximum values reaching 1,300 °C for compositions with 10% of used oil. It has also been determined that fuels with municipal solid waste are notable for lower nitrogen and sulfur oxide concentrations in flue gases as compared to filter cakes in initial state. Adding used oil to such fuel compositions increases the anthropogenic emissions but these worsening environmental characteristics do not exceed the regulated allowable limits of pollutants for solid fossil fuel combustion by thermal power plants. The obtained results are the backbone for the development of an environmentally friendly, cost- and energy-efficient co-combustion technology for municipal solid waste recovery by burning it as part of composite fuels, e.g., in boiler furnaces instead of coal.

Conditions of the Water–Coal Fuel Drop Dispersion at Their Ignition in the Conditions of High-Temperature Heating

ABSTRACTThe results of a numerical analysis of the conditions and characteristics of the dispersion of the water–coal particles during ignition under the conditions of an intense radiation-convective heating have been presented in the article. A comparative analysis of the theoretical and experimental values of ignition delay times of the fuel particles has showed their good correlation. Also, a comparative analysis of the characteristic dispersion times, obtained theoretically and established in the experiments, has showed a good correlation between them. According to the results of the numerical simulation, it has been established that dispersion of the water–coal particles during their heating before their ignition can occur as a result of the occurrence of the filtration stresses in the porous structure of the fuel. It has been found that the dispersion of the particles occurs before a complete evaporation within the pore moisture.The theoretical analysis has shown that the permeability of a dry coal structure has a significant effect on the characteristics and dispersion conditions. The influence of the values of the dimensionless Darcy criterion (Da) on the dispersion conditions has also been analyzed. It has been established that as the value of Da increases, the dispersion time decreases substantially. This is due to a decrease in the permeability of the porous structure of the fuel.

Municipal solid waste recycling by burning it as part of composite fuel with energy generation

In this work, it has been shown that the involvement of composite fuels in thermal power engineering will enable to recycle both industrial and municipal combustible wastes while saving fossil fuels. The ignition and combustion stability of composite fuel droplets up to their complete burnout was experimentally substantiated under the conditions typical of boiler furnaces, using the example of several fuel compositions with wood, food waste, plastic, and cardboard, each added separately. The values of the guaranteed delay times for the ignition of droplets with a size of about 1 mm were established for the considered fuel compositions in a wide range of the ambient temperature variation (600–1000 °C). The minimum values of ignition delay times were about 3 s, the maximum values were about 25 s. It was established experimentally that the concentration of nitrogen and sulfur oxides in flue gases was lower for the fuel compositions containing municipal solid waste (MSW) in comparison with those without it. The maximum difference between NOx and SOx concentrations for such fuel compositions was about 60% and 35% (in absolute units about 110 ppm and 45 ppm). As a result of the theoretical analysis, it was found that partial replacement of coal (50% of energy generation) by composite fuel in the amount equivalent in terms of energy generation will save about 1 billion tons/year of high-quality solid fossil fuel in the course of 20 years (the regulated period of safe operation of a boiler in thermal power engineering).

The Main Elements of a Strategy for Combined Utilization of Industrial and Municipal Waste from Neighboring Regions by Burning it as Part of Composite Fuels

An experimental study has been conducted into the ignition and combustion processes of composite fuel droplets fed into a heated muffle furnace on a holder. Consistent patterns and characteristics of physical and chemical processes have been established for a group of fuel compositions: wet coal processing waste (a mixture of fine coals and water) 85% + municipal solid waste (wood, or plastic, or rubber) 10% + used oil 5%. Burning a coal-water slurry instead of dry coal dust is characterized by a positive environmental effect. Adding used oil to a coal-water slurry results in better energy performance characteristics of the composite fuel during combustion. Adding fine municipal solid waste (MSW) to the fuel composition makes it possible to effectively recover it by burning in boiler furnaces with energy performance characteristics of combustion and environmental characteristics of flue gases that are as good as those of composite fuel compositions without MSW. Sustainability of the composite fuel ignition process and complete burnout of liquid and solid combustible components have been determined. The values of the guaranteed ignition delay times for droplets with a size (diameter) of about 2 mm have been established for the composite fuel compositions under study in the ambient temperature range 600–1000 °C. The minimum values of ignition delay times are about 3 s, the maximum values are about 15 s under the near-threshold ignition conditions. The obtained findings enabled to elaborate the main elements of the strategy for combined recovery of industrial and municipal waste by burning it as part of composite fuels.

Experimental and kinetic studies of ignition processes of the methane–n-heptane mixtures

Ignition delay times of methane–n-heptane mixtures at different methane contents were determined at various initial temperatures through a shock tube setup. Based on comparisons between the experimental and modeled values of ignition delay times of methane–n-heptane mixtures, the applicability of two reaction schemes to the simulation of the zero-dimensional constant-volume adiabatic ignition processes of the mixtures at the present conditions was validated. Then mole fractions of the species and main radicals involved and rates of the main elementary reactions for the formation and consumption of methane and n-heptane in the ignition processes were analyzed. The results show that a nonlinear relationship exists between the ignition delay time of methane–n-heptane mixtures and the methane content. The ignition delay time of methane will change significantly when even a little amount of n-heptane is mixed with methane. It is proved that the two reaction mechanisms studied can predict accurately the ignition delay times of the mixtures under the present initial conditions. Due to the existence of n-heptane, all methane will be reacted early, and the more n-heptane there exists, the earlier all methane is consumed. Different from HO2, CH3 and H2O2, concentrations of OH, H and O remain low during the ignition period, and only when approaching the ignition time points, their concentrations begin to rise. The formation and consumption reactions for methane occur mainly near the ignition time points. For n-heptane, it is consumed in a short time, and the decomposition reactions prevail at the start of the ignition period. Then the reactions between n-heptane and the radicals take the dominant positions. Compared to methane, n-heptane has a stronger competitiveness for the radicals.

Ignition of a Droplet of Composite Liquid Fuel in a Vortex Combustion Chamber

Experimental study results of a droplet ignition and combustion were obtained for coal-water slurry containing petrochemicals (CWSP) prepared from coal processing waste, low-grade coal and waste petroleum products. A comparative analysis of process characteristics were carried out in different conditions of fuel droplet interaction with heated air flow: droplet soars in air flow in a vortex combustion chamber, droplet soars in ascending air flow in a cone-shaped combustion chamber, and droplet is placed in a thermocouple junction and motionless in air flow. The size (initial radii) of CWSP droplet was varied in the range of 0.5–1.5 mm. The ignition delay time of fuel was determined by the intensity of the visible glow in the vicinity of the droplet during CWSP combustion. It was established (under similar conditions) that ignition delay time of CWSP droplets in the combustion chamber is lower in 2–3.5 times than similar characteristic in conditions of motionless droplet placed in a thermocouple junction. The average value of ignition delay time of CWSP droplet is 3–12 s in conditions of oxidizer temperature is 600–850 K. Obtained experimental results were explained by the influence of heat and mass transfer processes in the droplet vicinity on ignition characteristics in different conditions of CWSP droplet interaction with heated air flow. Experimental results are of interest for the development of combustion technology of promising fuel for thermal power engineering.

Experimental Study of the Influence of the Structure of Local Energy Sources on the Conditions and Characteristics of the Ignition of Liquid Fuels

Experimental studies have been made of the laws of ignition of a group of typical liquid fuels (kerosene, diesel fuel, mazut) by single particles of metals and porous particles of metal oxides heated to high temperatures. We have established the dependences of numerical values of ignition delay times of liquid fuels on the temperature of porous particles formed by welding and of monolithic steel particles in the form of disks. The experimental results show that the delay times of ignition of the typical distillate fuels — kerosene and diesel fuel — by "hot" particles formed by welding metals are shorter than for the ignition of the same fuels by monolithic steel particles of adequate sizes. The ignition delay times of the highly viscous fuel — mazut — are independent of the particle porosity.

Chemical kinetic simulation of kerosene combustion in an individual flame tube

The use of detailed chemical reaction mechanisms of kerosene is still very limited in analyzing the combustion process in the combustion chamber of the aircraft engine. In this work, a new reduced chemical kinetic mechanism for fuel n-decane, which selected as a surrogate fuel for kerosene, containing 210 elemental reactions (including 92 reversible reactions and 26 irreversible reactions) and 50 species was developed, and the ignition and combustion characteristics of this fuel in both shock tube and flat-flame burner were kinetic simulated using this reduced reaction mechanism. Moreover, the computed results were validated by experimental data. The calculated values of ignition delay times at pressures of 12, 50bar and equivalence ratio is 1.0, 2.0, respectively, and the main reactants and main products mole fractions using this reduced reaction mechanism agree well with experimental data. The combustion processes in the individual flame tube of a heavy duty gas turbine combustor were simulated by coupling this reduced reaction mechanism of surrogate fuel n-decane and one step reaction mechanism of surrogate fuel C12H23 into the computational fluid dynamics software. It was found that this reduced reaction mechanism is shown clear advantages in simulating the ignition and combustion processes in the individual flame tube over the one step reaction mechanism.

A new reduced reaction mechanism of a surrogate fuel for kerosene

AbstractThe introduction of detailed chemical reaction mechanisms for aviation fuels into complex multidimensional fluid dynamics problems is not practical at the present time. Simplified reaction mechanisms that have been thoroughly evaluated must be developed to address specific issues arising in realistic combustor configurations. A reduced chemical kinetic mechanism features 210 elemental reactions (including 92 reversible reactions and 26 irreversible reactions) and 50 species for the ignition and combustion of n‐decane was compiled and validated for a wide range of combustion regimes. Validations were performed using experimental measurements on a premixed flame of Jet‐A1, O2 and N2, stabilised at 1 atm on a flat‐flame burner, as well as from n‐decane shock‐tube ignition experiments. Numerical calculations were performed using this reduced mechanism and the detailed mechanism respectively for n‐decane surrogate fuel. The calculated values of ignition delay times at pressures of 12, 50 bar and equivalence ratio is 1.0, 2.0, respectively and the main reactants and main products mole fractions agree well with experimental data. The present study shows that this reduced mechanism for the n‐decane surrogate can be employed to predict premixed combustion of kerosene. © 2012 Canadian Society for Chemical Engineering

Ignition of methane and propane in high-temperature oxidizers with various oxygen concentrations

In this investigation, ignition processes of methane (CH 4 > 98%) and propane (C 3H 8 > 95%) using a high-temperature oxidizer ( T oxi > T ai) with a varying oxygen concentration ( z O 2 = 0.05 ÷ 0.21 ), applying two types of experimental installations, viz. a constant–volume bomb (CVB) and a co-flow reactor (CFR) were investigated. The influence of the initial temperature of the oxidizer (for methane T oxi = 960 ÷ 1234 K and for propane T oxi = 803 ÷ 1055 K), the equivalence ratio and oxygen concentration in the oxidizer on ignition of gaseous fuels is analyzed and discussed. It is shown that in order to achieve an effective reaction of ignition (taking into account the minimum value of ignition delay time τ ig and maximal value of the increment of temperature Δ T) the oxidizer temperature need not be maximized. There are optimal values of temperature of the oxidizer (for methane T oxi ≈ 1100 K and for propane T oxi ≈ 950 K) in which the parameters mentioned above reach their extreme values.

The reaction zone structure of cylindrical detonations in monodisperse sprays

Schlieren framing and streak photographs, and pressure transducer traces describing thedetailed structure of detonations propagating through low and high vapor pressure sprays are presented. The experiments were performed using a pie shaped test chamber with an included angle of 20°, a length of 140 cm and a width of 5.2 cm. Detonations were initiated with a small explosive charge at the vertex of the tube and propagated through a monodisperse spray of 400 μm decane and heptane droplets generated by 322 hypodermic needles fed by an oscillating pressure supply. The structure of low vapor pressure decane sprays in oxygen is driven by droplet shatteringand by the sudden explosion of fuel entrapped in the droplet wake after a certain ignition delay period t ig . The blast waves generated by these wake explosions are clearly shown in both the framing and streak photographs. Superposition of a pressure trace and streak photograph indicates the source of the pressure oscillations usually observed in the reaction zone of spray detonations. Values of ignition delay time and wake blast wave parameters derived from the streak photographs are presented. Different results are obtained for high vapor pressure heptane sprays in oxygen. A gaseous detonation propagates through the already vaporized fuel with properties determined by the vapor. Droplet breakup, shattering, and explosion follows at a considerable distance behind this front and does not appear to affect the detonation velocity. The structure of such “Hybrid” detonations is clearly illustrated by schlieren framing photographs.