Showing papers on "Autoignition temperature published in 1999"

Method and apparatus for emission control

Abstract: A converter for purifying exhaust gases from lean-burn engines, in particular for controlling the amount of NO x and soot from a diesel engine in transient operation such as a vehicle. The converter contains a catalyst bed with a catalyst effective for NO x reduction with a chemical reductant when the catalyst bed is with a certain temperature window and when the ratio between the molar amount of chemical reductant and NO x is above a certain minimum ratio. The catalyst bed is heated or cooled to a temperature within the temperature window and a switching valve is provided for reverse flowing the exhaust gases through the converter to maintain the catalyst bed at a temperature within the temperature window for a longer time than is possible with a conventional non-flow-reversing converter. A reductant delivery system adds chemical reductant to the exhaust gases in an appropriate amount so that the ratio between the molar amount of chemical reductant and NO x is above the certain minimum ratio when the exhaust gases pass over the catalyst bed. A soot trap may be provided in series with the catalyst bed in the converter, said reverse flowing of the exhaust gases through converter heating and continuously maintaining the soot trap at or above the ignition temperature of the soot.

Method for ignition of flameless combustor

Abstract: A combustor method and apparatus is provided. The method utilizes flameless combustion with one or more of three improvements to enhance ignition of the flameless combustor. A catalytic surface can be provided within a combustion chamber to provide flameless combustion at least in the vicinity of the catalytic surface at a temperature that is much lower than the autoignition temperature of fuel in air without the presence of the catalytic surface. Nitrous oxide or supplemental oxygen may also be used as an oxidant either instead of air or with air to reduce ignition temperatures. Further, electrical energy can be passed through the fuel conduit, raising the temperature of the conduit to a temperature above which the fuel will ignite when combined with the oxidant.

Development of catalysts based on pyrovanadates for diesel soot combustion

Abstract: Pyrovanadates of potassium and cesium were prepared and tested as catalysts for low-temperature combustion of carbon. Their catalytic activity was investigated by both temperature-programmed oxidation and thermogravimetric analysis and compared with that displayed by the metavanadates of the same elements, previously proposed as promising catalysts for soot combustion in diesel emissions. Pyrovanadates show an intrinsic catalytic activity noticeably higher than that of the corresponding metavanadates. In particular, cesium pyrovanadate is capable of lowering the ignition temperature of carbon down to 255°C and to provide a high combustion rate already at about 300°C. Such quite interesting results were confirmed in a pilot plant study on the performance of α-Al2O3 ceramic foam traps whose pore walls had been lined with catalysts based on either Cs meta- or pyro-vanadates, so as to enable trap self-regeneration by catalytic combustion of the filtered particulate.

3d Simulation of Di Diesel Combustion and Pollutant Formation Using a Two-Component Reference Fuel

Abstract: By separating the fluid dynamic calculation from that of the chemistry, the unsteady flamelet model allows the use of comprehensive chemical mechanisms, which include several hundred reactions. This is necessary to describe the different processes that occur in a DI Diesel engine such as autoignition, the burnout in the partially premixed phase, the transition to diffusive burning, and formation of pollutants like NOx and soot. The highly nonlinear reaction rates need not to be simplified, and the complete structure of the combustion process is preserved. Using the Representative Interactive Flamelet (RIF) model, the one-dimensional unsteady set of partial differential equations is solved online with the 3D CFD code. The flamelet solution is coupled to the flow and mixture field by several time dependent parameters (enthalpy, pressure, scalar dissipation rate). In return, the flamelet code yields the species concentrations, which are then used by the 3D CFD code to compute the temperature field and the density. The density is needed in the 3D CFD code for the solution of the turbulent flow and mixture field. Pollutant formation in a Volkswagen DI 1900 Diesel engine is investigated experimentally. The engine is fueled with Diesel and two reference fuels. One reference fuel is pure n-decane. The second is a two-component fuel consisting of 70% (liquid volume) n-decane and of 30% (liquid volume) alpha-methylnaphthalene (Idea-fuel). The experimental results show good agreement for the whole combustion cycle (ignition delay, maximum pressures, torque and pollutant formation) between the two-component reference fuel and Diesel. The simulations are performed for both reference fuels and are compared to the experimental data. Nine different flamelet calculations are performed for each simulation to account for the variability of the scalar dissipation rate, and its effect on ignition is discussed. Pollutant formation (NOx and soot) is predicted for both reference fuels. The contributions of the different reaction paths (thermal, prompt, nitrous, and reburn) to the NO formation are shown. Finally, the importance of the mixing process for the prediction of soot emissions is discussed.

Dense high-temperature ceramics by thermal explosion under pressure

Abstract: Near fully dense in-situ particulate reinforced ceramic matrix composites (CMCs) were fabricated from fine Ti–B4C, Ti–BN, Ti–Al–BN, Ti–SiC, Ti–B6Si and Al–TiO2 powder blends with or without the addition of Ni. Two reactive synthesis techniques were employed: thermal explosion/TE (SHS) under pressure, where the compacted reagent blend was placed and rapidly heated in a pressure die preheated slightly above the ignition temperature, and reactive hot pressing/RHP. In both approaches, the processing or preheating temperature (≤1250°C) was considerably lower than those typical of the current methods used for the processing of ceramic matrix composites. Partial to full conversion of reagents into products was achieved during TE, and a moderate external pressure of ≤150 MPa was sufficient to ensure full density of the final products. Rapid cooling from the combustion temperature due to the ‘heat sink’ action of the pressure die resulted in the fine/micronsize microstructures of the in-situ composites synthesized. RHP processing yielded dense materials with even finer microstructures, however full conversion of reagents into products has not been achieved.

High-velocity thermal spray apparatus and method of forming materials

Abstract: The high-velocity oxygen-fuel or air-fuel apparatus and method to apply low-oxidized and high-density coatings and bulk materials by spraying of non-fused particles, said apparatus comprises a catalytic member in internal burner. Metallic or ceramic catalyst of the catalytic member allows stable combustion at gas temperatures below the melting point of spraying material. Lowering of combustion temperature occurs when increasing the pressure and flow rate of the oxidizer or fuel over stoichiometrical or when adding an inert gas into combustible mixture. The catalytic member contains a catalyst selected from the group of noble metals, or binary oxides of the noble metal and rare earth metal, or other high temperature resistant catalyst capable to lower an ignition temperature of the oxidizer and fuel mixture. The catalytic member is made in a form of a wire or wire-net insert, or a coating on walls and passages of the internal burner or a coating on at least one catalyst ceramic support placed in the internal burner.

Assessment of combustion modes for internal combustion wave rotors

Abstract: Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Three modes of combustion are assessed: premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selection are presented for two engine applications.

Assessment of Combustion Modes for Internal Combustion Wave Rotors

Abstract: Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Three modes of combustion are assessed, premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selectio are presented for two engine applications.

Solid-State Thermochemistry of Flaming Combustion

Abstract: : The thermal and chemical processes which occur in the solid state during flaming combustion are examined. A phenomenological model of fuel generation provides the relationships between macroscopic flammability parameters and polymer chemical structure and shows how the coupling of thermal diffusion and chemical kinetics occurs naturally in the pyrolysis zone. Fire behavior and flammability of solid polymers are predicted using the ignition temperature, heat of combustion, heat of gasification, and char yield calculated from the chemical structure; and the results are compared to experimental values. The objective of this work is to develop a consistent, solid-state physical chemistry of flaming combustion which bridges the gap between fire and material sciences to help guide the discovery of new, more fire-resistant polymers.

Natural gas engine with in situ generation of an autoignition product

Abstract: An apparatus and method for generating an autoignition substance such as DME for operating a diesel-type engine 12 with natural gas. A multi-stage reformer 18 is connected to a supply of natural gas 20 to receive a portion therefrom for production of an autoignition substance for supply to the microigniters 14 within a diesel-type engine 12 . An engine control unit 24 in communication with a microcontroller 22 receives signals from sensors within the engine 12 and multi-stage reformer 18 for optimizing engine performance and generation of autoignition substances thereto. The apparatus and method of the present invention allows the operation of a diesel-type engine with natural gas as the primary or even the sole fuel by providing an autoignition substance in situ.

Combustion control device for diesel engine

Abstract: In a diesel engine which conducts exhaust gas recirculation and low temperature pre-mixed combustion at a low compression ratio, an ambient temperature at initiation of combustion which is determined by a compression ratio and an intake gas temperature or engine load is determined to be in a low temperature region which is lower than a first target temperature T1 which supports pre-mixed combustion or not. When the ambient temperature at initiation of combustion is determined to be in a region that is lower than a first target temperature T1, a temperature increase control device is operated which increases the temperature of the operational gases in the cylinder so that the temperature at initiation of combustion exceeds a first target temperature. The main fuel injection timing is placed in the range of 5°-20° of the combustion top dead center so that the main combustion temperature is above a fixed value. In this way, low temperature pre-mixed combustion is stabilized at low load at which combustion becomes unstable when compression ratios are low.

Oxidation of automotive primary reference fuels at elevated pressures

Abstract: Automotive engine knock limits the maximum operating compression ratio and ultimate thermodynamic efficiency of spark-ignition (SI) engines. In compression-ignition (CI) or diesel cycle engines, the premixed burn phase, which occurs shortly after injection, determines the time it takes for autoignition to occur. In order to improve engine efficiency and to recommend more efficient, cleaner-burning alternative fuels, they must understand the chemical kinetic processes that lead to autoignition in both SI and CI engines. These engines burn large molecular-weight blended fuels, a class to which the primary reference fuels (PRF) n-heptane and iso-octane belong. In this study, experiments were performed under engine like conditions in a high-pressure flow reactor using both the pure PRF fuels and their mixtures in the temperature range 550-880 K and 12.5 atm pressure. These experiments not only provide information on the reactivity of each fuel but also identify the major intermediate products formed during the oxidation process. A detailed chemical kinetic mechanism is used to simulate these experiments, and comparisons of experimentally measured and model predicted profiles for O{sub 2}, CO, CO{sub 2}, H{sub 2}O and temperature rise are presented. Intermediates identified in the flow reactor are compared with those present in the computations, and the kinetic pathways leading to their formation are discussed. In addition, autoignition delay times measured in a shock tube over the temperature range 690-1220 K and at 40 atm pressure were simulated. Good agreement between experiment and simulation was obtained for both the pure fuels and their mixtures. Finally, quantitative values of major intermediates measured in the exhaust gas of a cooperative fuels research engine operating under motored engine conditions are presented together with those predicted by the detailed model.

Modeling of thermal explosion in constrained dies for B4C–Ti and BN–Ti powder blends

Abstract: The process of reactive in-situ synthesis of dense particulate reinforced TiB 2 /TiC and TiB 2 /TiN ceramic matrix composites from B 4 C–Ti and BN–Ti powder blends with and without the addition of Ni has been modeled. The objective of modeling was the determination of optimal thermal conditions preferable for production of fully dense ceramic matrix composites. Towards this goal heat transfer and combustion in dense and porous ceramic blends were investigated during heating at a constant rate. This process was modeled using a heat transfer–combustion model with kinetic parameters determined from the differential thermal analysis of the experimental data. The kinetic burning parameters and the model developed were further used to describe the process of combustion synthesis in a constrained die under pressure. It has been shown that heat removal from the reaction zone affects the ignition temperature of thermal explosion.

Analysis of OH Radical Emission Intensity During Autoignition in a 2-Stroke SI Engine

Abstract: This research focused on the light emission behavior of the OH radical (characteristic spectrum of 306.4 [nm]) that plays a key role in combustion reactions, in order to investigate the influence of the residual gas on autoignition. The test engine used was a 2 stroke, air cooled engine fitted with an exhaust pressure control valve in the exhaust manifold. Raising the exhaust pressure forcibly recirculated more exhaust gas internally. Emission measurements were made under three conditions : normal combustion without any forced application of internal EGR, forced application of light internal EGR and forced application of heavy EGR. When a certain level of internal EGR is forcibly applied, the temperature of the unburned end gas is raised on account of heat transfer from the hot residual gas and also due to compression by piston motion. As a result, the unburned end gas becomes active and autoignition tends to occur.

Chlorate-free autoignition compositions and methods

Abstract: Chlorate-free autoignition compositions are disclosed, and may be embodied in compositions comprised of (i) an azodiformamidine dinitrate (ADFD), a self-deflagrating, low ignition temperature fuel, (ii) an oxidizer (e.g., a perchlorate, nitrate or mixture thereof) and (iii) an ignition accelerator/augmentor (e.g., a metal or metal oxide powder). One especially preferred solid AIP composition in accordance with the present invention includes ADFD, a mixture of ammonium perchlorate and sodium nitrate, an iron oxide powder and a binder, such as a poly(alkylene carbonate).

Premixture compression autoignition engine and operating method for the same

Abstract: PROBLEM TO BE SOLVED: To protect an engine from damage and improve thermal efficiency by limiting an excessive combustion pressure and optimally selecting ignition timing. SOLUTION: In a premixture compression autoignition engine 1, which is run by autoigniting a premixture G of fuel gas and intake air using a piston 3 with a high compression ratio, a sub chamber 4 connected via a pressure regulating valve 5 to a combustion chamber V0 of the engine 1 is provided. An axially preloaded spring 8 is installed in a spring pedestal 5B formed perpendicularly to an axis on the end of the pressure regulating valve 5.

Experimental and Numerical Studies on the Autoignition Process of Fuel Droplets

Abstract: Spontaneous ignition of liquid fuels dispersed in hot air under elevated pressure plays a prodominant role in diesel engines and gas turbines. While in the first case autoignition is a prerequisit for proper engine operation in the latter case it has to be avoided to happen prior to entering the main combustion area. The common aim for a mostly perfect premixture of prevaporized fuel in air requests for a detailed knowledge of the primary physical and chemical processes in spray combustion. The study discussed hereafter focus on single droplets as the most fundamental element of spray ignition. Experiments on n-heptane droplets of different initial size under varied pressure and temperature applying interferometry and PLIF of formaldehyde are compared to results from direct numerical simulations incorporating liquid and gas phase simulation as well as low- and high temperature chemical reaction kinetics. For the preparation of simulations of technical fuels, a new binary model fuel for kerosene JET-A has been developed that realizes the same staged ignition behaviour and induction times as the technical fuel. Autoignition of heterogeneous systems Whenever alkane fuels have to reside partially or fully mixed in an oxidizing atmosphere at high temperatures, ignition can occur in a multistage mode, subsequently following completely different schemes of oxidation. This behaviour is experimentally well known for premixed gases [1] and for multiphase systems [2]. Fig. 1 exemplary shows the temperature history of an igniting n-dodecane droplet and indicates the definition of induction times referred to hereinafter. If the fuel is supplied in liquid phase, heating, vaporization, mixing