Self-ignition Temperature Research Articles

Operability Limits of Tubular Injectors With Vortex Generators for a Hydrogen-Fueled Recuperated 100 kW Class Gas Turbine

Abstract Vortex generators are known to be effective in augmenting the mixing of fuel jets with air. The configuration investigated in this study is a tubular air passage with fuel injection from one single orifice placed in the side wall. In the range of typical gas turbine combustor inlet temperatures, the performance vortex generator premixers (VGPs) have already been investigated for natural gas as well as for blends of natural gas and hydrogen. However, for highly reactive fuels, the application of VGPs in recuperated gas turbines is particularly challenging because the high combustor inlet temperature leads to potential risk with regard to premature self-ignition and flame flashback. As the current knowledge does not cover the temperature range far above the self-ignition temperature, an experimental investigation of the operational limits of VGPs is currently being conducted at the Thermodynamics Institute of the Technical University of Munich, Garching, Germany, which is particularly focused on reactive fuels and the thermodynamic conditions present in recuperated gas turbines with pressure ratios of 4–5. For the study presented in this paper, an atmospheric combustion VGP test rig has been designed, which facilitates investigations in a wide range of operating conditions in order to comply with the situation in recuperated microgas turbines (MGT), namely, global equivalence ratios between 0.2 and 0.7, air preheating temperatures between 288 K and 1100 K, and air bulk flow rates between 6 and 16 g/s. Both the entire mixing zone in the VGP and the primary combustion zone of the test rig are optically accessible. High-speed OH* chemiluminescence imaging is used for the detection of the flashback and blow-off limits of the investigated VGPs. Flashback and blow-off limits of hydrogen in a wide temperature range covering the autoignition regime are presented, addressing the influences of equivalence ratio, air preheating temperature, and momentum ratio between air and hydrogen on the operational limits in terms of bulk flow velocity. It is shown that flashback and blow-off limits are increasingly influenced by autoignition in the ultrahigh temperature regime.

Kinetics of plasma assisted pyrolysis and oxidation of ethylene. Part 1: Plasma flow reactor experiments

Pyrolysis and oxidation kinetics of ethylene were studied with and without a high-voltage plasma discharge at atmospheric pressure from 420K to 1250K. Experiments were performed in a nearly isothermal flow reactor using mixtures diluted in either argon, helium, or nitrogen to minimize the temperature changes from chemical reactions. At the end of the isothermal reaction zone, the gas temperature was rapidly lowered to quench the reaction. Gas composition was then determined using inline non-dispersive infrared analysis and sample extraction, where samples are stored in a multi-position valve for subsequent analysis with gas chromatography. Experiments were performed by fixing the flow rate or residence time in the reactor, and varying the temperature to achieve a reactivity map. The discharge region occupied approximately 11% of the total length of the isothermal reaction zone and could be placed anywhere along the length of the reactor. The discharge was found to enhance both the pyrolysis and oxidation reactions from 420K to the self-ignition temperature of the fuel. Ethylene pyrolysis was enhanced nearly as much as oxidation below 750K. For plasma-assisted pyrolysis, the results suggest that ethylene dissociation by electron-impact and collisional quenching with electronically excited states of argon, resulted in the direct formation of acetylene and the growth of larger hydrocarbons. During plasma-assisted oxidation, dissociation, and excitation of oxygen led to further fuel consumption, and enhanced the low temperature oxidative chemistry. Above 750K, thermal reactions began to couple to the plasma driven reactions providing further oxidation. At the highest temperatures, the radical production by thermal reactions became competitive and the effectiveness of the plasma discharge decreased.

Numerical investigation on the self-ignition behaviour of coal dust accumulations: The roles of oxygen, diluent gas and dust volume

Self-ignition of coal dust deposits poses a higher risk of fires in oxygen-enriched oxy-fuel combustion systems. In this work, we develop a numerical method, using the commercial software COMSOL Multiphysics, to investigate self-ignition behaviour of coal dust accumulations with a main emphasis on the roles of oxygen, diluent gas and dust volume. A one-step 2nd-order reaction kinetic model considering both coal density and oxygen density is used to estimate reaction rate using the kinetic parameters from previously conducted hot-oven tests. This model is validated to predict the transient temperature and concentration profiles of South African coal dusts until ignition. The computed self-ignition temperatures of dust volumes show a good agreement with experimental results. In addition, it is found that the inhibiting effect of carbon dioxide is comparatively small and oxygen consumption increases dramatically after ignition. Parameter analysis shows that the heating value and kinetic parameters have a comparatively pronounced effect on self-ignition temperature. The model provides a satisfactory explanation for the dependence of self-ignition behaviour on gas atmospheres, thus helping to further understand the fire risk of self-ignition in oxy-fuel combustion systems.

Determination of the Self-ignition Behaviour of Bulk Materials from Heat Storage Tests below Atmospheric Pressure

Is a displacement of the self-ignition temperature up to higher temperatures possible by a pressure reduction? Therefore, the influence of an air pressure reduction on the self-ignition temperature of dust bulks is investigated. First, major effects which might influence the self-ignition temperature and the combustion behaviour of dust bulks under reduced pressure are described. Based on these theoretical considerations, basic experiments are carried out to determine the self-ignition temperature under reduced pressure. Thereby, the determination of the self-ignition temperature is carried out by isoperibolic heat storage tests according to DIN EN 15188:2007. The results of the investigations show that self-ignition temperatures of different bulk materials shift to higher temperatures within a pressure reduction.

SHS of Oxide Systems Based on the “Mechano-Chemical” Quartz Modified by Organometallic Compounds

<p>The differences of the effects of mechanical substance pre-activation in the mills with divers force effect schemes on the self-propagating high temperature synthesis (SHS) of the SiO<sub>2</sub> + 37.5 % Al system are shown. The power saturation of activated material is determined by particle defect intensity and effects on the thermal and physical characteristics of the material. The variations of activated material state are estimated referring on the variations of dilatometry curve paths. The effects of activation time on the temperature of sample self-ignition in the furnace, combustion temperature and completeness of the quartz reaction with aluminum are determined. The enhancing effects of organic modificators of quartz particle surfaces on the further SH synthesis development are shown.</p>

Low-weight TiAl3 composites by thermal explosion

Dispersion-strengthened TiAl3-based material with uniform structure and high compression strength (σc ≈ 850 MPa) was SHS-produced from Ti–Al–B4C blends in a mode of thermal explosion by using the B4C particles coated with a TiB2/TiC layer as a strengthening agent and preliminary mechanical activation of Ti–Al powder mixtures. The Ti + 3Al mixtures were mechanically activated in a planetary mill for 3 or 6 min and then 10 or 20 wt % of coated B4C particles were added. Pelleted samples were placed into a reaction chamber and heated in an electric furnace under Ar to a self-ignition temperature. The process was optimized and recommended for practical implementation.

Self-ignition in structured packed columns, fundamentals of methodology development

A combination of a residual film of flammable organic substance, air and structured packing may result in a fire during maintenance, at start up or after shut down. The self-ignition temperature depends on the substance (reactivity, volatility), construction and geometry of packing, heat loss conditions and accident scenario.In this article a dynamic model to determine heat transfer data and a over-adiabatic model to determine formal reaction kinetic data for the system studied are presented. These data are used as a basis for SIT simulation. The simulation basis is described as well. Next, experimental heat transfer and formal reaction kinetic data and experimental SIT study results are documented for the system (LEX/LDX packing/fatty acid Ti05, a mixture of oleic acid (67%) and linoleic acid (13%)).Comparison of simulated with experimental SIT data show acceptable agreement. As a conclusion of the studies a new and efficient procedure for SIT prediction in packing systems is proposed.

A Sensitive and Self-Regenerable Particulate Matter Sensor with a H3PO4-Modified BaZr0.8Y0.2O3-δ Electrolyte and an IrO2-Catalyzed Sensing Electrode

There have been many attempts to develop solid-state sensor devices for detecting particulate matter (PM) in diesel exhaust; however, in most of these, the accumulated PM must be burned intermittently to allow subsequent sensing cycles. Here, we report a self-regenerable PM sensor using a proton conductive solid electrolyte and an active working electrode for PM oxidation. The withstanding voltage capability of BaZr0.8Y0.2O3-δ was greatly improved by the growth of a dense Zr1-xYxP2O7 film on the electrolyte surface. The reaction of PM with active oxygen under anodic polarization was further enhanced by the addition of IrO2 to the working electrode. As a result of these combined modifications, when the working electrode was anodically polarized, PM was oxidized to CO2 according to a four-electron reaction (C + 2H2O → CO2 + 4H+ + 4e−) while remaining below the self-ignition temperature. This amperometric sensor successfully produced a current signal corresponding to the quantity of PM in a gas stream at an operating temperature of 300°C. These results demonstrate that the sensor can carry out continuous monitoring of PM concentrations while self-regenerating.

Optimizing Spark Timing of Spark Ignited Ethanol Engine

Alcohol is a good alternate fuel by comparing its performance, availability and renewability against fossil fuels. Ethanol is widely used in IC engines by blending small amount with petroleum fuels, but it is not solely used because its high boiling point and self-ignition temperature makes it difficult to burn in engines because, auto ignition also is not possible because of its high octane number and engine needs spark ignition. In order to overcome this problem we need a spark ignited engine with high compression ratio. So a high compression ratio engine is modified into spark ignited engine. A carburetor with 2mm main jet to supply excess fuel into engine is used in order to compensate its low calorific value. The engine used in this experiment was a single-cylinder direct injection diesel engine with a cylinder bore of 95mm, a stroke of 110 mm and a compression ratio of 13:1. The rated power was 5.3 kW at 1500 rpm. The engine has been tested at different loads for Ethanol against spark timings when piston is at TDC, 5 degree before TDC, 10 degree before TDC, 15 degree before TDC respectively. The optimum spark timing is found among the experimental basis for Ethanol.

Phase formation dynamics upon thermal explosion synthesis of magnesium diboride

Time-resolved X-ray diffraction was used to study the dynamics of phase formation in magnesium diboride produced by self-propagating high-temperature synthesis in the thermal explosion mode. The MgB2 phase was demonstrated to emerge without the formation of intermediate compounds. The effect of the mixture heating rate on the formation mechanism of the MgB2 phase was established. The presence of oxygen impurities has a significant impact on the kinetics and formation mechanism of MgB2. If the heating rate exceeds 150°/min, the oxide coating is not formed around the magnesium particles, which results in the solid-phase reaction of Mg+2B=MgB2 through a reaction diffusion mechanism. Moreover, the self-ignition temperature of the mixture is lower than the melting point for magnesium. Mechanical activation of the mixture leads to variations in the kinetics of MgB2 formation, significantly increases the period of simultaneous existence of Mg and MgB2, and reduces the temperature at which the reaction occurs.

Utilization of biogas released from palm oil mill effluent for power generation using self-preheated reactor

In palm oil mills, for one ton crude palm oil (CPO) production, 70m3 biogas is released from palm oil mill effluent (POME) which can endanger the environment. Palm oil mills without appropriate strategies for biogas collection can participate in greenhouse gases (GHGs) generation actively. In this paper, a typical palm oil mill with annual capacity of 300,000ton oil palm production and 3MW electricity demand is considered as a pilot plant and feasibility of power generation by POME biogas is modeled by Aspen Plus considering flameless mode in combustion system. A new design of lab-scale flameless reactor called self-preheated flameless combustion (SPFC) system is presented and employed in power generation modeling. In SPFC system, the flameless chamber is employed as a heater to preheat an oxidizer over the self-ignition temperature of the fuel. A helical stainless steel pipe (called self-preheating pipe) is installed inside the chamber to conduct the oxidizer from exhaust zone to the combustion zone inside the chamber and preheat oxidizer. In the flameless mode, the diluted oxidizer is injected to the helical pipe from the exhaust zone and the preheated oxidizer at the burner is conducted to the flameless furnace through a distributor. In SPFC system external heater for preheating oxidizer is removed and the rate of power generation increases. The results show that 10.8MW power could be generated in ultra-lean POME biogas SPFC. However, the rate of pollutant especially CO2 and NOx is high in this circumstances. In stoichiometric condition, 4MW power could be available in stable conditions with lower pollutant formation. Since, hydrogen is one of the ingredients of POME biogas, calculations confirm that the rate of power generation increases around 0.7MW when just 2% hydrogen is added to biogas.

Preparation and reactivity of gasless nanostructured energetic materials.

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the balls. Among other applications, it is a versatile technique that allows for effective preparation of gasless reactive nanostructured materials with high energy density per volume (Ni+Al, Ta+C, Ti+C). The structural transformations of reactive media, which take place during HEBM, define the reaction mechanism in the produced energeticcomposites. Varying the processing conditions permits fine tuning of the milling-induced microstructures of the fabricated composite particles. In turn, the reactivity, i.e., self-ignition temperature, ignition delay time, as well as reaction kinetics, of high energy density materials depends on its microstructure. Analysis of the milling-induced microstructures suggests that the formation of fresh oxygen-free intimate high surface area contacts between the reagents is responsible for the enhancement of their reactivity. This manifests itself in a reduction of ignition temperature and delay time, an increased rate of chemical reaction, and an overall decrease of the effective activation energy of the reaction. The protocol provides a detailed description for the preparation of reactive nanocomposites with tailored microstructure using short-term HEBM method. It also describes a high-speed thermal imaging technique to determine the ignition/combustion characteristics of the energetic materials. The protocol can be adapted to preparation and characterization of a variety of nanostructured energetic composites.

Preparation and Reactivity of Gasless Nanostructured Energetic Materials

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the balls. Among other applications, it is a versatile technique that allows for effective preparation of gasless reactive nanostructured materials with high energy density per volume (Ni+Al, Ta+C, Ti+C). The structural transformations of reactive media, which take place during HEBM, define the reaction mechanism in the produced energetic composites. Varying the processing conditions permits fine tuning of the milling-induced microstructures of the fabricated composite particles. In turn, the reactivity, i.e., self-ignition temperature, ignition delay time, as well as reaction kinetics, of high energy density materials depends on its microstructure. Analysis of the milling-induced microstructures suggests that the formation of fresh oxygen-free intimate high surface area contacts between the reagents is responsible for the enhancement of their reactivity. This manifests itself in a reduction of ignition temperature and delay time, an increased rate of chemical reaction, and an overall decrease of the effective activation energy of the reaction. The protocol provides a detailed description for the preparation of reactive nanocomposites with tailored microstructure using short-term HEBM method. It also describes a high-speed thermal imaging technique to determine the ignition/combustion characteristics of the energetic materials. The protocol can be adapted to preparation and characterization of a variety of nanostructured energetic composites.

Determination of spontaneous combustion of thermally dried sewage sludge

The general purpose of this research was the determination of self-ignition tendency of thermally dried sewage sludge. Eight Spanish plants located in Madrid, Barcelona and Málaga were selected to develop this study and ten samples were collected. Three different testing methodologies for studying the self-ignition of dusts have been undertaken. Thermogravimetric techniques, self-ignition temperature analyses and UN Division 4.2 tests were developed. The results of these analyses showed the risk of self-ignition during storage and transportation of these substances.

Self-ignition in stone wool insulation contaminated with fatty acid (fundamentals, case study, analysis methodology)

A combination of a residual film of flammable organic substance, air and porous structures like insulation material (e.g. stone wool) may result in a fire. The initiating self-heating process depends on the substance (reactivity, volatility), amount of accumulated liquid, volume and temperature. Specific information is given for application and extension of the Thomas criterion with a 2nd order reaction. The experimental part includes new experimental techniques to determine heat transfer and formal reaction kinetic data. The applied self-ignition temperature (SIT) simulation model relies on liquid film volume and not on liquid film surface reaction. As a further result of the studies detailed working procedure of three simplified methodologies for estimation of SITs in technical scale are presented. New techniques to determine parameters necessary for SIT prediction, especially in combination with Methodology III, have the power to reduce the costs for estimating the SIT up to 80%.

Application of HCCI Engine in Motorcycle for Emission Reduction and Energy Saving

The exhaust emission of motorcycle engine is a big problem in Asia countries due to the large number of motorcycles. This study developed a homogeneous charge compression ignition (HCCI) engine for motorcycle application with high-operating efficiency and low exhaust emissions. The development was carried out on a 150 cc spark-ignition (SI) engine with an increased compression ratio to enhance compression temperature. Dimethyl ether (DME) was selected as the main fuel for HCCI operation due to the low self-ignition temperature. Gasoline was used as an additional fuel to adjust the ignitibility of the dual fuel mixture. The dual fuel and exhaust gas recirculation (EGR) were incorporated to expand the engine operating range. Experiments of varying DME flow rates, EGR ratios, and gasoline flow rates were performed to observe HCCI operating characteristics and to identify methods for controlling HCCI combustion. And then, the engine could be operated at speeds ranging from 2000 to 4000 rpm and BMEP (Brake Mean Effective Pressure) ranging from 1.56 to 4.86 bar. These operating points were found to have lower brake specific fuel consumption and lower CO and NO emissions as compared with the original SI engine. A range-extended electric motorcycle (REEM) was built from a conventional motorcycle by using the proposed HCCI engine as a range extender. The HCCI engine was operated at 3500 rpm with very stable and high efficiency to match the REEM. The fuel economy of the proposed motorcycle is 75.62 km L–1, a 132% improvement compared with the original motorcycle. The control of switch from SI to HCCI will be the future work.

Influence of inert materials on the self-ignition of flammable dusts

Flammable solid bulk materials, including dusts, often undergo spontaneous combustion and the spread of reaction fronts. By addition of inert substances, the ignition and combustion behavior can be influenced. In a series of experiments different types of coal were mixed with inert powders to study the effect of the composition on the self-ignition temperature and on the formal kinetic parameters.Hot storage tests as well as simultaneous-thermal analysis were used as experimental techniques with the latter being coupled to FTIR measurements to analyze the composition of gaseous reaction products.All conducted hot storage experiments led to the conclusion that the self-ignition temperature was increased by admixing inert material if the decomposition temperature of the inert matter was higher than the self-ignition temperature of the combustible component at the sample characteristic length. If (exothermic) decomposition of the inert material occurred before a noticeable growth of reaction rate of the combustible material, even a reduction in the self-ignition temperature could be observed. In addition, significantly higher maximum reaction temperatures were observed for the mixtures than for the combustible material alone.

Operation of neat pine oil biofuel in a diesel engine by providing ignition assistance

The notion to provide ignition support for the effective operation of lower cetane fuels in a diesel engine has been ably adopted in the present study for the sole fuel operation of pine oil biofuel. Having noted that the lower cetane number and higher self-ignition temperature of pine oil biofuel would inhibit its direct use in a diesel engine, combined ignition support in the form of preheating the inlet air and installing a glow plug in the cylinder head has been provided to improve the auto-ignition of pine oil. While, an air preheater, installed in the inlet manifold of the engine, preheated the inlet air so as to provide ignition assistance partially, the incorporation of glow plug in the cylinder head imparted the further required ignition support appropriately. Subsequently, the operational feasibility of neat pine oil biofuel has been examined in a single cylinder diesel engine and the engine test results were analyzed. From the experimental investigation, though the engine performance and emissions such as CO (carbon monoxide) and smoke were noted to be better for pine oil with an inlet air temperature of 40°C, the engine suffered the setback of knocking due to delayed SOC (start of combustion). However, with the ignition support through glow plug and preheating of inlet air, the engine knocking was prevented and the normal operation of the engine was ensured. Categorically, at an inlet air temperature of 60°C, BTE (brake thermal efficiency) was found to be in par with diesel, while emissions such as CO and smoke were reduced by 13.2% and 16.8%, respectively, for neat pine oil biofuel at full load condition.

Effect of Fuel Concentration on the Properties of Combustion Synthesized MgAl2O4 Spinel Powders

Stoichiometric solution of aluminium nitrate and magnesium nitrate along with 4.66 to 7.66 moles of urea (fuel) concentrations were prepared and heated slowly to evaporate the water till a homogeneous gel was formed. Critical temperatures for the formation of MgAl2O4 spinel were identified using TG/DSC analysis of the gel and the reaction mixture was introduced into the resistive heating furnace preheated at 350oC. Powder mass thus obtained was characterized and was calcined at 1000oC for removal of retained carbon and crystallization. The powder was further characterized for phase purity, powder morphology, particle size and BET surface area. A fuel concentration beyond 6.66 moles generated excess gases resulting from the decomposition of unreacted urea which got occluded in the foamy combustible mixture. On reaching the self-ignition temperature, combustion occured and the sudden escape of these gases led to highly porous, fragile fluffy mass. Surface area and sinterability of the powder showed a clear correlation with the fuel concentration in the reaction mixture. Spark plasma sintered samples in comparison to the conventional sintered samples exhibited enhanced density values with finer grain sizes.

Characterisation of the Key Fuel Properties of Oxygenated Diethyl Ether-Diesel Blends

Diethyl Ether (DEE) is a promising oxygenated renewable bio-base resource fuel for CI engines owing to its high ignition quality. DEE has several favourable properties, including exceptional cetane number, very low self-ignition temperature, high oxygen content, broad flammability limits and reasonable energy density for on-board storage. It is a liquid at ambient conditions, which makes it attractive for fuel handling and fuel infrastructure requirements and hence, it is a compatible fuel for use in CI engine. Diethyl ether is the simplest ether expressed by its chemical formula CH3CH2-O-CH2CH3, consisting of two ethyl groups bonded to a central oxygen atom. It can be mixed in any proportion in diesel fuel as it is completely miscible with diesel fuel. It was observed that density, kinematic viscosity and calorific value of the blends decreases while the oxygen content and cetane number of the blends increases with the concentration of DEE addition. The presence of DEE increases the front end volatility of the blends and decreases boiling point in comparison to baseline diesel fuel. No significant difference was observed in the tail-end volatility of the blends. The blended fuel retains the desirable physical properties of diesel fuel but includes the cleaner burning capability of DEE.