This work deals with the impact of operating parameters on fine combustion particles formation in the flue gas of biomass combustion device. The research part of the work describes the properties of fine particles, its basic division, impact on human health and the environment. The basic knowledge of the influence of biomass combustion process on fine particles production up to 1 µm in size is summarized. The main part describes the experimental setup for evaluating the size distribution of fine particles. The following section describes the experimental setup with measured results for various combustion parameters in laboratory combustion, automatic boilers, as well as in the manual wood-burning combustion device. The main parameters which were tested were combustion temperature, oxygen amount, type of fuel and geometry of the burned biomass. The impact of individual parameters on the formation of the fine particles is evaluated. The final part of the thesis summarizes the ways in which it is possible to significantly influence the emissions of fine particles by the appropriate choice of combustion operating parameters.

Soot is a common byproduct of hydrocarbon based combustion systems. It poses a risk to human and environmental health, and can negatively or positively affect combustor performance. As a result, there is significant interest in understanding soot formation in order to better control it. More recently, the need to study soot formation in engine relevant conditions has become apparent. One engine relevant parameter that has had little focus is the ambient pressure. This body of work focuses on the formation of soot in elevated pressure environments, and a number of investigations are carried out with this purpose. Laminar coflow diffusion flames are used as steady, simple soot producers. First, a commonly studied flame configuration is further characterized. Coflow flames are frequently used for fundamental flame studies, particularly at elevated pressures. However, they are more susceptible to buoyancy induced instabilities at elevated pressures. The velocity of the coflow is known to have an effect on flame stability and soot formation, though these have not been characterized at elevated pressures. A series of flames are investigated covering a range of flowrates, pressures, and nozzle diameters. The stability limits of coflow flames in this range is investigated. Additionally, an alternative strategy for scaling these flames to elevated pressures is proposed. Finally, the effect of coflow rate on soot formation is evaluated. Identification of fundamental flames for coordinated research can facilitate our understanding of soot formation. The next study of this work focuses on adding soot concentration and particle size information to an existing fundamental flame dataset for the purpose of numerical model validation. Soot volume fraction and average particle diameters are successfully measured in nitrogen-diluted ethylene-air laminar coflow flames at pressures of 4, 8, 12, and 16 atm. An increase in particle size with pressure is found up to 12 atm, where particle sizes plateau. Particle size in the annulus is more sensitive to pressure. Next, the development of an alternative particle size measuring technique is studied. Time Resolved Laser Induced Incandescence (TiRe-LII) is a commonly used technique to measure soot concentrations and particle size at atmospheric pressure. However, Laser Induced Incandescence (LII) models suffer from an incomplete understanding of the effects of elevated pressures on the absorption, annealing, and cooling of soot. The present study focuses on what affect the laser temporal pulse shape and duration may have on particle sizing. TiRe-LII in flames at 1 and 15 bar is carried out, using laser pulses with tophat or Gaussian temporal profiles of varying duration. Mono-disperse equivalent primary particle diameters are calculated using the KAUST LII model. Little difference in particle sizing is found for different laser pulses. However, this data will be useful for validating the KAUST LII model when absorption and poly-dispersion are accounted for. In an effort to move one step closer to logistical fuel studies, the sooting tendencies of a number of liquid fuels are studied at pressures up to 10. Of parallel relevance, a sooting index for surrogate development is evaluated for elevated pressure applications. The Yield Sooting Index (YSI) methodology is applied to 11 normal, cyclic, and branched alkanes. When referencing to two n-alkane fuels, the YSI of n-alkanes determined at atmospheric pressures accurately reflects the relative sooting tendencies of these fuels at elevated pressures. The relative sooting tendencies of cyclo- and methyl-alkanes have a lower pressure sensitivity than n-alkanes.

La méso-combustion est le régime de combustion où la taille caractéristique du domaine est juste supérieure à la distance de coincement de la flamme , typiquement de l'ordre du centimètre. La difficile réalisation de systèmes de combustion fonctionnant en ce régime de flamme particulier suscite l'intérêt : il devient alors possible de tirer parti de la haute densité énergétique des hydrocarbures pour concevoir des systèmes de production d'énergie plus compacts. Nous nous intéressons à la réalisation de calculs DNS compressibles d'une chambre de combustion cubique de 8 x 10 x 8 mm3. Ce travail présente autant la mise en œuvre des calcules, en particulier la problématique de la condition frontière mur, que les résultats obtenus. Ces derniers nous permettent d'analyser la phénoménologie complexe de cet écoulement réactif confiné et serviront de base à des modélisations futures. / Meso-combustion can be defined as the combustion regime where the involved lenghts scales are close but slightly larger than the quenching distance of the flame, tipically smaller than a cm. By taking advantage of the high energetic density of liquid hydrocarbons, it would become possible to build small-sized combustion-based long-lived lighter electrical power systems. However combsution phenomena at these meso-scales have their own shortcomings. Indeed, by decreasing the system size, the usual phenomenological balance betwenne chemical reactions, mixing, turbulence and heat transfer is changed. In the present work, we focus on the DNS calculation of a cubic meso-combsution chamber of 8 x 10 x 8 mm3. This works presents the implementation of the numerical strategy used, with a specific attention to the no-slip wall compressible boundary condition. We then present an analysis of this particular reactive flow. The results are useful for future modeling of such a combustor.

<div>Chirped-probe pulse femtosecond coherent anti-Stokes Raman scattering (CPP fs CARS) was used to study high pressure gas-phase thermometry. The experimental measurements were</div><div>mostly performed in a static gas cell and in a canonical flat flame burner. The purpose of this study is to provide insights for the future rocket relevant combustion measurements. </div><div><br></div><div><div>Chirped-probe pulse femtosecond coherent anti-Stokes Raman scattering (CPP fs CARS) was used to study high pressure gas-phase thermometry. The experimental measurements were mostly performed in a static gas cell and in a canonical flat flame burner. The purpose of this study is to provide insights for the future rocket relevant combustion measurements. </div></div><div><br></div><div><div>The optical effects associated with ultrashort pulse propagation in the high-pressure system were investigated. For example, the femtosecond pulse can receive large amount of frequency chirp when transmitting through thick glass windows of the optical section in the high-pressure system. The effects of pump and Stokes frequency chirp were investigated both experimentally, by inserting disks of SF11 glass into the pump and Stokes beam paths to study the flame thermometry, and theoretically by incorporating pulse chirp into the TDDM simulations to calculate the Raman excitation efficiency. Meanwhile, the ultrashort pulses can experience self-phase modulation in the high-pressure gas medium. The effects of self-phase modulation (SPM) on the power spectra of femtosecond pulses will have significant impact on the fs CARS profile. On the other hand, the extend and the behavior of SPM reply on the laser intensity and are also species-specific. The optimal laser intensities in high-pressure gas mediums like N2, O2, CO2 and CH4 were investigated.</div></div><div><br></div><div><div>To prepare for future rocket relevant combustion studies, CPP fs CARS thermometry was developed for CO2, O2 and H2. Especially for CO2 and O2, they have close vibrational frequencies but very different coherence dephasing rates. Relative concentration between CO2 and O2 can then be extracted by using a short probe delay, and the temperature information can be determined by using long probe delays and the O2 transitions will not interfere with CO2 and nonresonant contribution of the CARS signal can be suppressed. CO2 CPP fs CARS measurements inside the high-pressure high-temperature gas cell were presented and discussed. Collisional narrowing effects for CO2 especially for high gas number density situation were discussed. </div></div>

Biodiesel has been proposed as a substitute for diesel given that biodiesel has lower net average greenhouse gas emissions than diesel. Additionally, alcohol may be added to biodiesel to improve biodiesel’s performance in a diesel engine as well to reduce engine emissions. This work will study the droplet evaporation process of alcohol-biodiesel blends. Due to alcohol’s polar nature and the fatty acid methyl esters’s (FAME) slightly polar nature, an appropriate method must be chosen to represent the evaporation process of a non-ideal mixture. The vapour-liquid equilibria was modelled in two ways: the first method uses only Raoult’s Law, while the second method uses Raoult’s law modified with activity coefficients calculated using the UNIFAC method. The comparison of the modelled results with experimental vapour-liquid equilibria data has shown that activity coefficients calculated using the UNIFAC method are able to accurately represent alcohol-biodiesel systems. Droplet evaporation experiments have been performed for biodiesel-propanol and biodiesel-pentanol blends at temperatures of 450°C and 700°C with the alcohol concentrations of 5%, 10%, 15%, and 20%. Additionally, the droplet evaporation was numerically modelled using two different models to represent the liquid state: a model with a well-mixed liquid phase and a model which includes component diffusion in the liquid phase. Comparing the experimental droplet temperatures to the numerical models has shown that the diffusion-limited model best represents the droplet evaporation process, suggesting that some of the alcohol components remain in the center of the droplet even when the droplet temperature is greater than the boiling temperature of the alcohol. This was further confirmed by observations of bubbling within the droplet during evaporation of the biodiesel-alcohol blends, in which there were both small bubbles and large bubbles forming. The formation of large bubbles has shown to correspond with the difference between experimental droplet diameter and the diffusion-limited model’s droplet diameter.

The efficiency of an internal combustion engine is highly dependent on the peak pressure at which the engine operates. A new compound engine concept, the double compression expansion engine (DCEE), utilizes a two-stage compression and expansion cycle to reach ultrahigh efficiencies. This engine takes advantage of its high-integrity structure, which is adapted to high pressures, and the peak motored pressure reaches up to 300 bar. However, this makes the use of conventional combustion cycles, such as the Seiliger–Sabathe (mixed) or Otto (isochoric) cycles, not feasible as they involve a further pressure rise due to combustion. This study investigates the concept of isobaric combustion at relatively high peak pressures and compares this concept with traditional diesel combustion cycles in terms of efficiency and emissions. Multiple consecutive injections through a single injector are used for controlling the heat release rate profile to achieve isobaric heat addition. In this study, the intake pressure is varied to enable a comparison between the isobaric cases with different peak pressures, up to 150 bar, and the mixed cycle cases. Tests are performed at several different levels of EGR. The experiments are performed on a 12.8 L displacement 6-cylinder Volvo D13C500 engine utilizing a single cylinder with a standard 17-compression-ratio piston. In this study, the cylinder represents the high-pressure unit of the DCEE. The fuel used in all the experiments is a standard EU diesel. In each target condition, the different injection strategies are compared with the total amount of fuel kept relatively constant. The results prove that the isobaric combustion concept is feasible with a traditional injection system and can achieve gross indicated efficiencies close to or higher than those of a conventional diesel combustion cycle. Moreover, the results show that with an isobaric cycle, heat transfer losses can be reduced by over 20%. However, the exhaust energy is higher, which can eventually be recovered in the second stage of expansion. Thus, this cycle could be suitable for the DCEE concept. The CO, UHC and soot emission levels are proven to be fairly similar to those of the conventional diesel combustion. However, the NOx emissions are significantly lower for the isobaric combustion.

No description available.

Thesis: M.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1976 / Includes bibliographical references. / by Gordon D. Marsh. / M.S. / M.S. Massachusetts Institute of Technology, Department of Mechanical Engineering

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of requirements for the degree of Master of Science. October 2014. / Domestic fuel burning activities have become a major source of urban air pollution. Studies have indicated that domestic burning activities, specifically in low-income settlements and townships, contribute greatly to the air quality problems experienced by most developing urban centres. Low-income households that exist within townships in South Africa, house a large portion of the South African population. These households burn vast quantities of coal, wood, paraffin as well as other substances in order to provide for their energy needs. Pollution emitted as a result of domestic burning activities is estimated to be one of the leading causes of respiratory illnesses, prevalent in inhabitants of low-income settlements. To better understand the relationship that exists between domestic burning and the resultant pollutants, a method of quantifying these pollutants has been developed for a completely un-electrified settlement, near Johannesburg, using the quantities and type of fuel consumed. A study, carried out in Zenzele during the winter months, in addition to a month before and a month after this period, allowed for the analysis of some of the more harmful winter fuels. Common fuel types consumed were identified through the analysis of census data and information gathered from questionnaires. In un-electrified households, paraffin and liquid petroleum gas (LPG), used specifically for cooking and lighting, are the most commonly used fuel types during the warmer months. During the colder months, however, residents of households in low-income settlements prefer to use solid fuels such as wood and coal. Factors such as seasonality, the availability and price of fuels as well as cultural aspects all have a bearing on residents’ fuel choices and the quantity consumed. Emissions were quantified based on the quantities of wood and coal burnt in 15 households in Zenzele, using emission factors for SO2, PM10, CO2 and CO. As the temperature declines, the rate at which these solid fuels are consumed increases. The most significant observations identified in this study are the diurnal and seasonal trends associated with domestic burning.

Various sub models of a multi-zone phenomenological model are developed by incorporating Dec’s conceptual model and Siebers’ mixing limited theory and validated with experiments. The spray penetration model, liquid length model and lift-off length model are verified with experiment data. The ignition delay model is then validated with experiment data at different injection timings and loads. The air entrainment model is based on Siebers’ jet theory. Sub models for the premixed heat release rate and diffusion burn rate are also included. The overall phenomenological model is at first used to match the motoring pressure curve. The important sub models are well validated independently and the phenomenological model is useful in simulating diesel spray combustion. Future work is needed to integrate these sub models and to resolve existing issues in temperature profiles of the preparing zone and liquid zone.