Showing papers on "Ignition system published in 2019"

Chemistry of pyrotechnics : basic principles and theory

Abstract: Introduction Basic Chemical Principles Components of High-Energy Mixtures Pyrotechnic Principles Ignition and Propagation Sensitivity Heat Compositions: Ignition Mixes, Delays, Thermites, and Propellants Color and Light Production Smoke and Sound Appendix A Appendix B Index

Direct observation of imploded core heating via fast electrons with super-penetration scheme

Abstract: Fast ignition (FI) is a promising approach for high-energy-gain inertial confinement fusion in the laboratory. To achieve ignition, the energy of a short-pulse laser is required to be delivered efficiently to the pre-compressed fuel core via a high-energy electron beam. Therefore, understanding the transport and energy deposition of this electron beam inside the pre-compressed core is the key for FI. Here we report on the direct observation of the electron beam transport and deposition in a compressed core through the stimulated Cu Kα emission in the super-penetration scheme. Simulations reproducing the experimental measurements indicate that, at the time of peak compression, about 1% of the short-pulse energy is coupled to a relatively low-density core with a radius of 70 μm. Analysis with the support of 2D particle-in-cell simulations uncovers the key factors improving this coupling efficiency. Our findings are of critical importance for optimizing FI experiments in a super-penetration scheme. Fast ignition is an interesting scheme for nuclear fusion reaction. Here the authors show electron generation using intense short laser pulses and energy transport by coupling the laser energy to the imploded plasma core as in the ICF conditions.

A review on low temperature combustion engines: Performance, combustion and emission characteristics

Abstract: Low temperature combustion (LTC) is a recent engine technology that can reduce the oxides of nitrogen (NOx) and soot emissions simultaneously while maintaining higher thermal efficiency. The present review work investigates the performance, emission and combustion characteristics of LTC mode engines. Partially premixed LTC (PPLTC), homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI) and reactivity controlled compression ignition (RCCI) modes are researched under LTC mode. In recent decades, different engine strategies have been employed to reduce exhaust emissions and to enhance thermal efficiency. Exhaust gas recirculation, variable valve timing (VVT), advanced fuel injection technologies are adapted to achieve LTC mode in internal combustion (IC) engines to get improved outcomes. This review highlights the properties of fuels, fuel supply systems, valve actuation mechanisms, engine operating conditions and its effects on the engine characteristics. This review provides a perspective plan to the researchers for enhancing the performance, emission and combustion behavior of an engine by using LTC mode with lower NOx and soot emissions. Among LTC mode engines, RCCI mode engine operates well in 60% load, 60% premixed ratio, 35:1 air-fuel ratio and 56% brake thermal efficiency within the combustion phasing control.

Green Diesel: Biomass Feedstocks, Production Technologies, Catalytic Research, Fuel Properties and Performance in Compression Ignition Internal Combustion Engines

Abstract: The present investigation provides an overview of the current technology related to the green diesel, from the classification and chemistry of the available biomass feedstocks to the possible production technologies and up to the final fuel properties and their effect in modern compression ignition internal combustion engines. Various biomass feedstocks are reviewed paying attention to their specific impact on the production of green diesel. Then, the most prominent production technologies are presented such as the hydro-processing of triglycerides, the upgrading of sugars and starches into C15–C18 saturated hydrocarbons, the upgrading of bio-oil derived by the pyrolysis of lignocellulosic materials and the “Biomass-to-Liquid” (BTL) technology which combines the production of syngas (H2 and CO) from the gasification of biomass with the production of synthetic green diesel through the Fischer-Tropsch process. For each of these technologies the involved chemistry is discussed and the necessary operation conditions for the maximum production yield and the best possible fuel properties are reviewed. Also, the relevant research for appropriate catalysts and catalyst supports is briefly presented. The fuel properties of green diesel are then discussed in comparison to the European and US Standards, to petroleum diesel and Fatty Acid Methyl Esters (FAME) and, finally their effect on the compression ignition engines are analyzed. The analysis concludes that green diesel is an excellent fuel for combustion engines with remarkable properties and significantly lower emissions.

Tripled yield in direct-drive laser fusion through statistical modelling.

Abstract: Focusing laser light onto a very small target can produce the conditions for laboratory-scale nuclear fusion of hydrogen isotopes. The lack of accurate predictive models, which are essential for the design of high-performance laser-fusion experiments, is a major obstacle to achieving thermonuclear ignition. Here we report a statistical approach that was used to design and quantitatively predict the results of implosions of solid deuterium-tritium targets carried out with the 30-kilojoule OMEGA laser system, leading to tripling of the fusion yield to its highest value so far for direct-drive laser fusion. When scaled to the laser energies of the National Ignition Facility (1.9 megajoules), these targets are predicted to produce a fusion energy output of about 500 kilojoules-several times larger than the fusion yields currently achieved at that facility. This approach could guide the exploration of the vast parameter space of thermonuclear ignition conditions and enhance our understanding of laser-fusion physics.

Experimental and numerical study, under LTC conditions, of ammonia ignition delay with and without hydrogen addition

Abstract: For long-term storage, part of the excess renewable energy can be stored into various fuels, among which ammonia and hydrogen show a high potential. To improve the power-to-fuel-to-power overall efficiency and reduce NOx emissions, the intrinsic properties of Low Temperature Combustion (LTC) engines could be used to convert these carbon-free fuels back into electricity and heat. Yet, ignition delay times for ammonia are not available at relevant LTC conditions. This lack of fundamental kinetic knowledge leads to uncertain ignition delay predictions by the existing ammonia kinetic mechanisms and prevents from determining optimal LTC running conditions. Using a Rapid Compression Machine (RCM), we have studied the ignition delay of ammonia with hydrogen addition (0%, 10%, and 25%vol.) under LTC conditions: low equivalence ratios (0.2, 0.35, 0.5), high pressures (43 and 65 bar) and low temperatures (1000–1100 K). This paper presents the comparison of the experimental data with simulation results obtained with five kinetic mechanisms found in the literature. It then provides a sensitivity analysis to highlight the most influencing reactions on the ignition of the ammonia-hydrogen blends. The obtained range of ignition delays for pure ammonia and for the ammonia-hydrogen blends prove their suitability for LTC engines. Still the hydrogen addition must be greater than 10%vol. to produce a significant promotion of the ignition delay. The two best performing mechanisms still predict too long ignition delays for pure ammonia, while the delays become too short for ammonia-hydrogen blends. A third mechanism captures correctly the relative influence of hydrogen addition, but is globally over-reactive. Through a sensitivity analysis, H2NO has been identified as the main cause for the under-reactive pure ammonia kinetics and N2Hx has been identified as the main cause for globally over-reactive ammonia-hydrogen mechanisms.

A comparative study on partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI) in an optical engine

Abstract: Partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI) are two new combustion modes in compression-ignition (CI) engines. However, the detailed in-cylinder ignition and flame development process in these two CI modes were not clearly understood. In the present study, firstly, the fuel stratification, ignition and flame development in PPC and RCCI were comparatively studied on a light-duty optical engine using multiple optical diagnostic techniques. The overall fuel reactivity (PRF number) and concentration (fuel-air equivalence ratio) were kept at 70 and 0.77 for both modes, respectively. Iso-octane and n-heptane were separately used in the port-injection (PI) and direct-injection (DI) for RCCI, while PRF70 fuel was introduced through direct-injection (DI) for PPC. The DI timing for both modes was fixed at –25°CA ATDC. Secondly, the combustion characteristics of PPC and RCCI with more premixed charge were explored by increasing the PI mass fraction for RCCI and using the split DI strategy for PPC. In the first part, results show that RCCI has shorter ignition delay than PPC due to the fuel reactivity stratification. The natural flame luminosity, formaldehyde and OH PLIF images prove that the flame front propagation in the early stage of PPC can be seen, while there is no distinct flame front propagation in RCCI. In the second part, the higher premixed ratio results in more auto-ignition sites and faster combustion rate for PPC. However, the higher premixed ratio reduces the combustion rate in RCCI mode and the flame front propagation can be clearly seen, the flame speed of which is similar to that in spark ignition engines but lower than that in PPC. It can be concluded that the ratio of flame front propagation and auto-ignition in RCCI and PPC can be modulated by the control over the fuel stratification degree through different fuel-injection strategies.

Three-dimensional modeling and hydrodynamic scaling of National Ignition Facility implosions

Abstract: The goal of an inertially confined, igniting plasma on the National Ignition Facility (NIF) [M. L. Spaeth, Fusion Sci. Technol. 69, 25 (2016)] remains elusive. However, there is a growing understanding of the factors that appear to be limiting current implosion performance. And with this understanding, the question naturally arises: What conditions will ultimately be required to achieve ignition, either by continuing to improve the quality of current implosions, or by hydrodynamically scaling those implosions to larger driver energies on some future facility? Given the complexity of NIF implosions, answering this question must rely heavily on sophisticated numerical simulations. In particular, those simulations must respect the three-dimensionality of real NIF implosions and also resolve the wide range of scales for the many perturbation sources that degrade them. This prospectus article reviews the current state of detailed modeling of NIF implosions, the scaling to ignition from recent experiments that that modeling implies, and areas for future improvements in modeling technique that could increase understanding and further enhance predictive capabilities. Given the uncertainties inherent in any extrapolation, particularly for a process as nonlinear as ignition, there will be no definitive answer on the requirements for ignition until it is actually demonstrated experimentally. However, with continuing improvements in modeling technique and a growing experience base from NIF, the requirements for ignition are becoming clearer.

Experimental study on the ignition characteristics of cellulose, hemicellulose, lignin and their mixtures

Abstract: Ignition behaviour of biomass is an essential knowledge for plant design and process control of biomass combustion. Understanding of ignition characteristics of its main chemical components, i.e. cellulose, hemicellulose, lignin and their mixtures will allow the further investigation of ignition behaviour of a wider range of biomass feedstock. This paper experimentally investigates the influences of interactions among cellulose, hemicellulose and lignin on the ignition behaviour of biomass by thermogravimetric analysis. Thermal properties of an artificial biomass, consisting of a mixture of the three components will be studied and compared to that of natural biomass in atmospheres of air and nitrogen in terms of their ignition behaviour. The results showed that the identified ignition temperatures of cellulose, hemicellulose and lignin are 410 °C, 370 °C and 405 °C, respectively. It has been found that the influence of their interactions on the ignition behaviour of mixtures is insignificant, indicating that the ignition behaviour of various biomass feedstock could be predicted with high accuracy if the mass fractions of cellulose, hemicellulose and lignin are known. While the deficiencies of the determined mutual interactions would be further improved by the analytical results of the activation energies of cellulose, hemicellulose, lignin, their mixtures as well as natural and artificial biomass in air conditions.