Showing papers on "Ignition system published in 2004"

The physics basis for ignition using indirect-drive targets on the National Ignition Facility

Abstract: The 1990 National Academy of Science final report of its review of the Inertial Confinement Fusion Program recommended completion of a series of target physics objectives on the 10-beam Nova laser at the Lawrence Livermore National Laboratory as the highest-priority prerequisite for proceeding with construction of an ignition-scale laser facility, now called the National Ignition Facility (NIF). These objectives were chosen to demonstrate that there was sufficient understanding of the physics of ignition targets that the laser requirements for laboratory ignition could be accurately specified. This research on Nova, as well as additional research on the Omega laser at the University of Rochester, is the subject of this review. The objectives of the U.S. indirect-drive target physics program have been to experimentally demonstrate and predictively model hohlraum characteristics, as well as capsule performance in targets that have been scaled in key physics variables from NIF targets. To address the hohlrau...

Nucleosynthesis in multi-dimensional SNIa explosions

Abstract: We present the results of nucleosynthesis calculations based on multidimensional (2D and 3D) hydrodynamical simulations of the thermonuclear burning phase in SNIa. The detailed nucleosynthetic yields of our explosion models are calculated by post-processing the ejecta, using passively advected tracer particles. The nuclear reaction network employed in computing the explosive nucleosynthesis contains 383 nuclear species. We analyzed two different choices of ignition conditions (centrally ignited, in which the spherical initial flame geometry is perturbated with toroidal rings, and bubbles, in which multi-point ignition conditions are simulated). We show that unburned C and O varies typically from ~40% to ~50% of the total ejected material.The main differences between all our models and standard 1D computations are, besides the higher mass fraction of unburned C and O, the C/O ratio (in our case is typically a factor of 2.5 higher than in 1D computations), and somewhat lower abundances of certain intermediate mass nuclei such as S, Cl, Ar, K, and Ca, and of 56Ni. Because explosive C and O burning may produce the iron-group elements and their isotopes in rather different proportions one can get different 56Ni-fractions (and thus supernova luminosities) without changing the kinetic energy of the explosion. Finally, we show that we need the high resolution multi-point ignition (bubbles) model to burn most of the material in the center (demonstrating that high resolution coupled with a large number of ignition spots is crucial to get rid of unburned material in a pure deflagration SNIa model).

Premixed Compression Ignition (PCI) Combustion for Simultaneous Reduction of NOx and Soot in Diesel Engine

Abstract: Investigations of Homogeneous Charge Compression Ignition (HCCI) combustion have been actively conducted as a new combustion technology to substantially and simultaneously reduce NOx and soot to comply with the future stringent exhaust emission regulations. In the past, a method of injecting fuel at the initial stage of the compression stroke has been proposed, but it is known that fuel adheres to the cylinder wall, causing a decline in combustion efficiency and oil dilution. The authors have developed Premixed Compression Ignition (PCI) combustion as a technology of solving the above problem as well as simultaneously reducing NOx and soot. In PCI combustion, fuel is injected into a combustion chamber in the vicinity of the top dead center for preventing fuel from adhering to the wall, and pre-mixture, which is formed shortly before ignition, is burnt. By pre-mixing, this combustion reduces the over-rich region of the mixture to reduce soot emissions, and at the same time lowers the combustion temperature by introducing a large amount of EGR to reduce NOx emissions. This paper reports the result of detailed examination of the basic characteristics of PCI combustion using a single-cylinder engine, and that PCI combustion which uses our investigated approaching can achieve substantial and simultaneous reduction of NOx and soot. This paper also studies the possibility of realizing Split-PCI combustion, which uses the two different combustion modes of PCI combustion and diffusion combustion during one cycle, in high-load operation where application of PCI combustion is restricted by diesel knock. As results of this study, this paper reports that it is available to reduce NOx and soot emissions to a large extent by Split-PCI combustion, even in high-load operation.

Internal combustion engine handbook - basics, components, systems and perspectives

Abstract: This is a translation of the German book Handbuch Verbrennungsmotor and considers all aspects of the internal combustion engine. The chapters include: historical review; definition and classification of reciprocating piston engines; characteristics; maps; thermodynamic fundamentals; crank gears; engine components; lubrication; friction; charge cycle; supercharging of internal combustion engines; mixture formation and related systems; ignition; combustion; combustion systems; electronics and mechanics for engine management and transmission shift control; the powertrain; sensors; actuators; cooling of internal combustion engines; exhaust emissions; operating fluids; filtration of operating fluids; calculation and simulation; combustion diagnostics; fuel consumption; noise emissions; alternative propulsion systems; and outlook.

Carbon Ignition in Type Ia Supernovae: An Analytic Model

Abstract: The observable properties of a Type Ia supernova are sensitive to how the nuclear runaway ignites in a Chandrasekhar-mass white dwarf: at a single point at its center, off-center, or at multiple points and times. We present a simple analytic model for the runaway guided by a combination of stellar mixing-length theory and analogy to Rayleigh-Benard convection. The convective flow just prior to runaway is likely to have a strong dipolar component, although this dipole may be unstable at the very high Rayleigh number (1025) appropriate to the white dwarf core. A likely outcome is multipoint ignition with an exponentially increasing number of ignition points during the few tenths of a second that it takes the runaway to develop. The first sparks ignite approximately 150-200 km off-center, followed by ignition at smaller radii. Rotation may be important to break the dipole asymmetry of the ignition and give a healthy explosion.

An Investigation of the Relationship Between Measured Intake Temperature, BDC Temperature, and Combustion Phasing for Premixed and DI HCCI Engines

Abstract: Combustion phasing is one important issue that must be addressed for HCCI operation. The intake temperature can be adjusted to achieve ignition at the desired crank angle. However, heat-transfer during induction will make the effective intake temperature different from the temperature measured in the runner. Also, depending on the engine speed and port configuration, dynamic flow effects cause various degrees of charge heating. Additionally, residuals from the previous cycle can have significant influence on the charge temperature at the beginning of the compression stroke. Finally, direct injection of fuel will influence the charge temperature since heat is needed for vaporization. This study investigates these effects in a systematic manner with a combination of experiment and cycle simulation using WAVE from Ricardo. The results show that the amount of charge heating/cooling that occurs due to heat-transfer during the induction period can be computed from changes in the volumetric efficiency. The amount of charge cooling associated with vaporization of directly injected fuel changes with injection timing and can be related to the volumetric efficiency. A simple procedure for estimating the charge mixture temperature at the end of the intake stroke is presented. Several examples are given where this procedure can be used beneficially to explain experimental observations for fired HCCI operation where the charge temperature at the end of the intake stroke was related to the combustion phasing. Iso-octane was used as a gasoline surrogate since it facilitates comparison with chemical-kinetics models, in this case the detailed iso-octane mechanism from LLNL. Although this procedure is developed for HCCI operation, it can be applied to other types of engines as well. For example, the changes to the charge temperature that occur during the induction process are important for both tH'e occurrence of knock in Sl engines and NO x formation in Diesel engines.

Transient plasma ignition of quiescent and flowing air/fuel mixtures

Abstract: Transient plasmas that exist during the formative phase of a pulse-ignited atmospheric pressure discharge were studied for application to ignition of quiescent and flowing fuel-air mixtures. Quiescent methane-air mixture ignition was studied as a function of equivalence ratio, and flowing ethane-air mixture was studied in a pulse detonation engine (PDE). The transient plasma was primarily comprised of streamers, which exist during approximately 50 ns prior to the formation of an equilibrated electron energy distribution. Results of significant reduction in delay to ignition and ignition pressure rise time were obtained with energy costs roughly comparable to traditional spark ignition methods (100-800 mJ). Reduction in delay to ignition by factors of typically 3 in quiescent mixes to >4 in a flowing PDE (0.35 kg/s), and other enhancements in performance were obtained. These results, along with a discussion of a pseudospark-based pulse generator that was developed for these applications, will be presented.

Toroidal low-field reactive gas and plasma source having a dielectric vacuum vessel

Abstract: Plasma ignition and cooling apparatus and methods for plasma systems are described. An apparatus can include a vessel and at least one ignition electrode adjacent to the vessel. A total length of a dimension of the at least one ignition electrode is greater than 10% of a length of the vessel's channel. The apparatus can include a dielectric toroidal vessel, a heat sink having multiple segments urged toward the vessel by a spring-loaded mechanism, and a thermal interface between the vessel and the heat sink. A method can include providing a gas having a flow rate and a pressure and directing a portion of the flow rate of the gas into a vessel channel. The gas is ignited in the channel while the remaining portion of the flow rate is directed away from the channel.

Conversion of fuel moisture content values to ignition potential for integrated fire danger assessment

Abstract: Fuel moisture content (FMC) estimation is a critical part of any fire danger rating system, since fuel water status is determinant in fire ignition and fire propagation. However, FMC alone does not...

Effect of Methanol Addition on the Performance of Spark Ignition Engines

Abstract: This study is an experimental investigation into the effect of methanol addition to gasoline on the performance of spark ignition engines. The performance tests were carried out, at wide open throttle and variable speed conditions, over the range of 1000 to 2500 rpm, using various blends of methanol-gasoline fuel. It was found that methanol has a significant effect on the performance of the gasoline engine. The best engine performance (within the range studied) for maximum power output, and minimum brake specific fuel cosumption, occurs when a mixture of 15 volume percent methanol and 85% gasoline blend is used. The addition of methanol to gasoline increases the octane number, thus engines fueled with methanol-gasoline blend can operate at higher compression ratios.

Off-Center Carbon Ignition in Rapidly Rotating, Accreting Carbon-Oxygen White Dwarfs

Abstract: We study the effect of stellar rotation on the carbon ignition in a carbon-oxygen white dwarf accreting CO-rich matter. Including the effect of the centrifugal force of rotation, we have calculated evolutionary models up to the carbon ignition for various accretion rates. The rotational velocity at the stellar surface is set to the Keplerian velocity. The angular velocity in the stellar interior is determined by taking into account the transport of angular momentum due to turbulent viscosity. We have found that an off-center carbon ignition occurs even when the effect of stellar rotation is included if the accretion rate is sufficiently high; the critical accretion rate for the off-center ignition is hardly changed by the effect of rotation. Rotation, however, delays the ignition, i.e., the mass coordinate of the ignition layer and the mass of the white dwarf at the ignition are larger than those for the corresponding nonrotating model. The result supports our previous conclusion that a double-white dwarf merger would not be a progenitor of a Type Ia supernova (SN Ia).

Relating flame radiation to home ignition using modeling and experimental crown fires

Abstract: Wildland–urban fire destruction depends on homes igniting and thus requires an examination of the ignition requirements. A physical–theoretical model, based on severe case conditions and ideal heat...

Using Aluminum for Space Propulsion

Abstract: The combination of aluminum and water was theoretically analyzed to assess its performance potential for space propulsion, in particular for microrocket applications and whenever a compact package is desirable. Heat of reaction, impulse density, and handling safety are features making this combination interesting for chemical thrusters, especially because thrust is higher than typical of satellite electric thrusters. Ideal specific impulse I s p , thrust coefficient, adiabatic flame temperature, and combustion products were calculated for chamber pressures 1-10 atm, nozzle area ratios 25-100, and mixture ratios O/F 0.4-8.0. I s p reaches up to 3500 m/s. Also, the effect of hydrogen peroxide addition to aluminum and water on performance was explored. This combination improves performance slightly at the expense of simplicity, making it less attractive for microrocket engines. Ignition delay times were conservatively estimated assuming that aluminum was coated with its oxide and ignition occurred after the melting of the aluminum oxide. For this purpose heating and kinetics times were evaluated, the first by a one-dimensional physical model, the second by a reduced scheme. Results indicate that the heating time of a 0.1-μm-diameter aluminum particle may be of order 0.4 μs, whereas overall kinetics takes 10 μs: thus, the Al/water combination looks practical in principle for microrocket chambers characterized by short residence times.

Polar direct drive on the National Ignition Facility

Abstract: Three recent developments in direct-drive target design have enhanced the possibility of achieving high target gain on the National Ignition Facility (NIF): (1) Laser absorption was increased by almost 50% using wetted-foam targets. (2) Adiabat shaping significantly increased the hydrodynamic stability of the target during the acceleration phase of the implosion without sacrificing target gain. (3) Techniques to reduce laser imprint using pulse shaping and radiation preheat were developed. These design features can be employed for direct-drive-ignition experiments while the NIF is in the x-ray-drive configuration. This involves repointing some of the beams toward the equator of the target to improve uniformity of target drive. This approach, known as polar direct drive (PDD), will enhance the capability of the NIF to explore ignition conditions. PDD will couple more energy to the fuel than x-ray drive. The compressed fuel core can be more easily accessed for high-ρR diagnostic development and for fast-ign...

Compression ignition internal combustion engine

Abstract: It is an object of the present invention to provide a compression ignition internal combustion engine capable of making compatible an increase in compression self-ignition operating area with an optimum output torque control in the operating area and also smoothly switching between a self-ignition combustion and a spark ignition combustion. The compression ignition internal combustion engine operates by switching between the spark ignition combustion using an ignition device and the compression ignition combustion which self-ignites a mixture by piston compression. Variable valve mechanisms vary at least one of the valve timings and valve lifts of an intake valve and an exhaust valve. Intake air is regulated to vary the amount of air intake into a combustion chamber on the upstream side of a combustion chamber inlet of the compression ignition internal combustion engine. The variable valve mechanisms and the intake air regulation are controlled during the compression ignition combustion so as to perform the compression ignition combustion.

Closed‐loop combustion control of homogeneous charge compression ignition (HCCI) engine dynamics

Abstract: Homogeneous charge compression ignition (HCCI) is a hybrid of the sparkignition and compression ignition engine concepts. As in a sparkignition engine, a homogeneous fuel-air mixture is created in theinlet system. During the compression stroke the temperature of themixture increases and reaches the point of auto ignition, just as in acompression ignition engine (or Diesel). One challenge with HCCI engines isthe need for good timing control of the combustion. Auto ignition of ahomogeneous mixture is very sensitive to operating condition. Evensmall variations of the load can change the timing from too early totoo late combustion. Thus a fast combustion timing control isnecessary since it sets the performance limitation of the loadcontrol. As measurement for combustion timing feedback, the crank angleof 50% burnt has been used. This paper performs a comparative studyof different cylinder-pressure based methods for estimating the crankangle of 50% burnt. The estimates are compared in terms of accuracy,robustness and feasibility for cycle-to-cycle real-time control.Dynamic models of CA50 are estimated using system identification asa means to find models relevant to engine control. (Less)

Laser driven inertial fusion energy: present and prospective

Abstract: Recent progress in laser driven implosion is reviewed. Improvements in the uniformity of irradiation by laser beams on fuel pellets have achieved quantitative progress in implosion performance. The recent results of the direct drive–central ignition experiments give us confidence in achieving fusion ignition, burning and energy gain using a multi-beam megajoule laser with full implementation of beam smoothing techniques. Fast ignition research is also reviewed, which could give us a higher energy gain with lower laser energy. The science and technology of laser fusion power plants are beginning to attract wider attention, as forming the road map to achieve commercial power plants for cleaner, safer and abundant fusion energy.Corrections were made to this article on 28 April 2004

Analysis of the Effect of Charge Inhomogeneity on HCCI Combustion by Chemiluminescence Measurement

Abstract: In the HCCI Engine, inhomogeneity in fuel distribution and temperature in the pre-mixture exists microscopically, and has the possibility of affecting the ignition and combustion process. In this study, the effect of charge inhomogeneity in fuel distribution on the HCCI combustion process was investigated. Two-dimensional images of the chemiluminescence were captured by using a framing camera with an optically accessible engine in order to understand the spatial distribution of the combustion. DME was used as a test fuel. By changing a device for mixing air and fuel in the intake manifold, inhomogeneity in fuel distribution in the pre-mixture was varied. The result shows that luminescence is observed in a very short time in a large part of the combustion chamber under the homogeneous condition, while luminescence appears locally with considerable time differences under the inhomogeneous condition. It is also shown that the local luminescence durations are almost the same in both conditions.

A study of gasoline-fuelled HCCI engine equipped with an electromagnetic valve train

Abstract: Schemes to extend the operational region of gasoline compression ignition were explored using single (optial) and 4-cylinder 4-stroke engines equipped with an electromagnetic valve train. This report focuses mainly on the use of direct fuel injection devices (multi-hole and pintle types),exhaust gas recirculation (EGR) through valve timing, and their effects on the compression ignition operating ranges, and emissions. Also considered is charge boost HCCI using a mechanical supercharger. The results indicated that use of either direct fuel injection or charge boost increased (relative to homogeneous charge operation using port injection) the upper load range from an IMEP peak of about 400 kPa to 650 kPa, but the use of direct fuel injection deteriorated both the co-variation in IMEP (up to about 6%) and the NO x emission levels (up to about 8 g/kWh). In contrast, charge boost retained the very low NOx emission levels of port injection HCCI. At the lower load range, a small amount of fuel injection during negative valve overlap expanded the operational range at the lower load range. It is presumed that the EGR with negative valve overlap has a similar effect as injection during negative overlap namely the oxidation of residual unburned hydrocarbons from the prior cycle during this period. This facilitates compression ignition.

A TG/DTA study on the effect of coal blending on ignition behaviour

Abstract: Understanding the ignition behaviour of coal is of utmost importance for the design of boilers and control of the combustion process. In recent years there has been an increasing utilisation of coal blends for combustion, but information on the possible interactive effects during ignition of the individual components is scarce. In this work the ignition behaviour of a series of coal blends, made up from three coals of different rank, sub-bituminous, high volatile and low volatile bituminous, was studied. To this end a thermogravimetric analyser linked to a mass spectrometer for evolved gas analysis was used. Different ignition behaviour was observed for the coals studied; the sub-bituminous and low volatile bituminous coals ignited heterogeneously, while homogeneous ignition occurred for the high volatile bituminous coal. In the case of blends of the low and high volatile bituminous coals, different mechanisms of ignition were observed depending on the blends composition.