Flame propagation through a channel equipped with obstacles was studied experimentally. Two types of obstacle geometries were investigated, i.e., wall-mounted cross-flow cylinders and fence-type obstacles mounted on the top and bottom channel surfaces. The motivation for this research is its applications to both high-speed propulsion and industrial explosion safety. The effect of obstacle distribution and blockage ratio on flame acceleration was investigated in a 2.54cm x 7.6cm “narrow” channel with wall-mounted cross-flow cylindrical obstacles. The cylinders were arranged in a “staggered” or “inline” pattern, with blockage ratios of 0.5 and 0.67. Schlieren images were used to study the flame shape and its leading edge velocity for a range of fuel-air mixtures compositions. It was determined that initial flame propagation occurs faster in higher blockage ratios due to the higher frequency perturbation to the flow. Flame acceleration led to different quasi-steady flame and detonation propagation regimes. In general, higher final steady flame velocities were reached in the lower blockage ratios, and detonation limits were found to be influenced by the geometry. The influence of channel width on flame acceleration was also determined using fence-type obstacles with a single blockage ratio. Experiments were performed in a 2.54cm x 7.6cm and 7.6cm x 7.6cm channel. Schlieren images were again used to study the flame shape and to obtain leading edge velocity. The flame tip was found to have a parabolic profile across the channel width for the narrower channel and flatter profile in the wider channel. It was determined that the channel width has a weak effect on the flame velocity down the channel length. As such, flame acceleration was initially only slightly more pronounced in the narrow channel before the reverse became true later in the wide channel. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-07-18 21:13:40.436

The main focus of this investigation was to get a greater understanding of the effect of combustion frequency, positive pressure amplitude, relative air:fuel ratio (A), water jacket temperature and input firing rates on the emissions of NO from pulse combustors. This study was carried out by a programme of experimental work combined with the development of a one-dimensional model. Results obtained in this study from experimental measurement, revealed evidence that a Schmidt tube has the ability to operate over a wide range of parameters (such as operating frequency, positive pressure amplitude, relative air:fuel ratio, water jacket temperature and input firing rates) with variable NO emissions. It was found that the level of NO emissions became lower with increasing operating frequency and positive pressure amplitude. As an example, when the rig was operated at input firing rate 25 kW and a positive pressure amplitude of 0.12 bar, increasing the frequency from 35 Hz to 73 Hz produced a monotonic reduction in NO emissions from 61 ppm to 29 ppm (dry, 3% O2). An'increase in positive pressure amplitude from 0.05 to 0.12 bar produced a change in NO emissions from 46 ppm to 34 ppm. It was also found that the values of NO emissions fell. with increasing excess air for A> 1.1. However, NO emissions increased with increasing water jacket temperature (Tw) along the length of tail pipe and with increasing input firing rates. Experimental results showed that the positive pressure amplitude was not dependent on the wall jacket temperature. However, the operating range of stable pressure oscillation could be extended from [...continued].

An experimental investigation of post-start cold idling behaviour has been carried out on a modern single-cylinder HPCR DI light duty diesel engine with a low compression ratio of 15.5:1 at temperatures between 10 and -20°C. The trend toward lower compression ratios from more common values of around 22:1 a few years ago has resulted in lower compression pressures and temperatures, which negatively affects cold idle operation. Improvements in cycle-by-cycle stability of indicated work output through fuel injection strategy and glow plug temperature changes have been explored. This is important to improve NVH and the consumer’s perception of vehicle quality. The key effects on heat release characteristics have been identified and the associated impact on stability discussed. High speed imaging of ignition in a combustion bomb has been used to aid interpretation of engine results. Up to four pilot injections placed in advance of the main have been used. Shorter separation between pilots and pilot-to-main improves stability independent of the number of pilot injections and extends the range of main injection timings to meet target stability of 10% or lower at -20°C. Increasing the number of pilot injections was effective in stabilising combustion at all investigated soak temperatures at fuelling levels producing indicated work required to match friction and ancillary demands. Stability can be susceptible to deterioration at moderate soak temperatures because fuelling demand is relatively low. If a high number of pilot injections are to be avoided to reduce potential wear, then increasing main injection quantity is an effective method to stabilise combustion for a lower pilot number strategy but any increase above target load has to be harnessed by additional ancillary devices. Very high glow plug temperatures of up to 1200°C were examined using a smaller diameter tip ceramic type design. Stable combustion cannot be achieved through higher glow plug temperatures alone. A temperature of 1000°C, which can be achieved using a low voltage metallic type, is adequate to stabilise combustion when combined with a triple-pilot strategy at sub-zero temperatures. The best stability is achieved using 1200°C, which can only be achieved using a more expensive ceramic type, in combination with a triple-pilot strategy producing the desirable target of ~5% or below; the effects are not mutually exclusive. At high glow plug temperatures and using three or four pilot injections, stability improved with warmer soak temperatures. At -5°C, stability was relatively poor when one or two pilots were used irrespective of glow plug temperature. A high premixed contribution to main combustion is associated with improved stability. Minimum threshold values are necessary to stabilise combustion: ~25 J/° at -20°C, ~20 J/° at -5°C and only ~10 J/° at 10°C. A higher number of pilot injections raises pilot induced combustion and improves mixture distribution. These effects subsequently increase the premixed combustion and help sustain a strong main development with less variability. This benefit is maximised when using hotter glow plug temperatures raising IMEPg magnitude and reducing variation.

The research reported in the thesis addresses questions of how engine fuel consumption and carbon dioxide emissions are can be reduced through improvements in thermal management, lubricant design, and energy recovery. The investigations are based on simulation studies using computational models and sub-models developed or revised during the work, and results provided by complementary experimental studies carried out by collaborating investigators. The brake thermal efficiency of the internal combustion engines (ICE) used in cars and light duty commercial vehicles is reduced by frictional losses. These losses vary with engine design, lubricant formulation and thermal state. They are most significant when the engine is running cold or partially warm. Over the New European Drive Cycle (NEDC), engine friction losses raise vehicle fuel consumption by several percentage points. A version of the computational model, PROMETS, has been developed and applied in studies of thermal behaviour, friction and engine lubricant to investigate the performance of a 2.0l, I4 GTDI spark ignition engine and in particular, how these influence fuel consumption over the NEDC. Core parts of PROMETS include a physics-based, empirically calibrated friction model, a cycle averaged description of gas-to-structure heat transfer and a lumped capacity description of thermal behaviour of the engine block and cylinder head. In the thesis, revisions to the description of friction and interactions between friction, local thermal conditions and lubricant are reported. It is shown that the bulk temperature of coolant rather than oil has the stronger influence on friction at the piston-liner interface, whilst bulk oil temperature more strongly influences friction in crankshaft bearings and other lower engine components. However, local oil film temperatures have a direct influence on local friction contribution. To account for this, local values of oil temperature and viscosity are used in describing local friction contributions. Implementation required an oil system model to be developed; an iterative model of the frictional dissipation within the main bearings, and a prediction of piston cooling jet heat transfer coefficients have been added to the oil circuit. Simulations of a range of scenarios and design changes are presented and analysed in the thesis. The size of the fuel savings that could potentially be made through improved thermal management has been demonstrated to be 4.5% for the engine being simulated. Model results show that of the friction contributing surfaces, the piston group is responsible for the highest levels of friction, and also exhibits the largest absolute reduction in friction as the temperature of the engine rises. The relatively low warm-up rate of the lower engine structure gives a correspondingly slow reduction in friction in crankshaft bearings from their cold start values. Measures to accelerate this reduction by raising oil temperature have limited effect unless the strong thermal links between the oil and the surrounding metal are broken. When additional heating is applied to the engine oil, only around 30% is retained to raise the oil temperature due to these thermal links.

Approved for public release, distribution unlimited / An existing freejet facility was upgraded and its range of operation extended into the high subsonic regime for operation as a test rig for the development of a combined-cycle, turbo-ramjet engine. A combustor was designed, developed, and tested as the afterburner for the turbo-ramjet engine. At subsonic speeds with the afterburner running, an increase in thrust of 40% was measured over the baseline turbojet running at 80% spool speed. A Computational Fluid Dynamics model of the flow through the shrouded turbojet engine was developed and successfully used to assist in predicting the bypass ratio of the engine at different Mach numbers. Numerous recommendations were made to improve the operation of the test rig, to improve the performance of the turbo-ramjet engine, and refine the numerical models. These recommended improvements will extend the present capabilities to design and analyze small combined cycle engines which have an application in unmanned aerial vehicles and missiles. / Lieutenant, United States Navy

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Donald Fenton / Combustion turbine performance deterioration, quantified by loss of system power, is an artifact of increased inlet air temperature and continuous degradation of the machine. Furthermore, the combustion turbine operator has to meet ever changing stricter emission levels. Different technologies exist to mitigate the impact of performance loss and meeting the emission standard. However an upgrade using one or more of the available technologies has associated capital and operating costs. Thus, there is a need for a tool that can evaluate power boosting and emission control technologies in concert with the machine maintenance strategy. This dissertation provides the turbine operator with a new and novel tool to examine each of the upgrades and determine its suitability both from the cost and technical stand point. The main contribution of this dissertation is a tool-kit called the Combustion Turbine Operation and Optimization Model (CTOOM) that can evaluate both power-boosting and emission control technologies. It also includes a machine maintenance model to account for degradation recovery. The tool-kit is made up a system level thermodynamic optimization solver (CTOOM-OPTIMIZE) and two one-dimensional, mean-line, aero-thermodynamic component level solvers for the compressor (CTOOMCOMP1DPERF) and the turbine (CTOOMTURB1DPERF) sections. In this work, the cogeneration system as given by the classical CGAM problem was used for system level optimization. The cost function was modified to include the cost of emissions while the maintenance cost of the combustion turbine was separated from the capital cost to include a degradation recovery model. Steam injection was evaluated for NO[subscript]x abatement, power boosting was examined by both the use of inlet air cooling and steam injection, and online washing was used for degradation recovery. Based on the cost coefficients used, it was seen that including the cost of emissions impact resulted in a significant increase in the operational cost. The outcomes of the component level solvers were compressor and turbine performance maps. It was demonstrated that these maps could be used to integrate the components with the system level information.

The aim of the present work was to experimentally investigate the influence of atomizing medium on combustion properties of methyl-ester of rapeseed oil. The experiments were carried out in a water-cooled horizontal combustion chamber. The pneumatic atomization using effervescent atomizer was used in test. As atomizing medium compressed air and superheated steam was chosen. The tests were performed at GLR = 15, 20 and 25 %. The experiments were focused on the investigation of the flame characteristics, quality of combustion, emissions, temperature of flue gas, distribution of heat fluxes and stability of combustion. Results revealed that atomization by compressed air is more efficient (approximately by 6 %), on the other hand it leads to higher NO emissions (for 13 mg/mN3 due to higher in-flame temperature).

Argon replacing nitrogen has been examined as a new engine cycle to reach high efficiency. Experiments were carried out under Homogeneous Charge Compression Ignition (HCCI) conditions using a single cylinder variable compression ratio Cooperative Fuel Research (CFR) engine. Isooctane has been used as the fuel for this study. All the parameters were kept fixed but the compression ratio to make the combustion phasing constant. Typical engine outputs and emissions were compared to conventional cycles with both air and synthetic air. It has been found that the compression ratio of the engine must be significantly reduced while using argon due to its higher specific heat ratio. The resulting in-cylinder pressure was lower but combustion remains aggressive. However, greater in-cylinder temperatures were reached. To an end, argon allows gains in fuel efficiency, in unburned hydrocarbon and carbon monoxide, as well as in indicated efficiency. A higher nitrogen oxide concentration while replacing nitrogen by argon was observed but the origin remains to be identified. The concept should therefore be able to reach zero-NOx emissions as no nitrogen should be present.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Master of Science. Johannesburg, 2015. / Fly ash is a by-product generated during the combustion of coal for electricity gen- eration. Previous studies have shown that various waste fly-ashes (Japanese, Saudi Arabian, and Australian) contain trace quantities of transition metal elements which can be used in the synthesis of shaped carbon nanomaterials. A survey of the litera- ture has shown that no attempts to correlate the composition of a particular coal fly ash and the type or quantity of carbon nanomaterials (CNMs) that can be synthesized has been made. Neither has the effect of leached fly ash been tested for the synthesis of CNMs. Hence a study on the effect of the chemical composition of South African fly ash (collected from ESKOM’s Duvha power station in Mpumalanga) upon the chemical vapour deposition (CVD) synthesis of carbon nanostructures is justified. Untreated and chemically treated fly ash samples were used as catalysts in the CVD method to synthesize CNMs. In the latter case selective leaching experiments were conducted on the fly ash samples under acidic, basic and neutral conditions. Op- timal CNM synthetic conditions were achieved by initially flowing H2 gas to re- duce the metal oxides within the fly ash catalyst followed by the introduction of the carbon source (C2H2) at a temperature range of 600 - 800 ◦C. All samples were quantitatively and/or qualitatively characterized. Inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray fluorescence (XRF) techniques were used to quantify the metal ions which were removed from the fly ash samples. Fur- thermore, qualitative studies were conducted with (PXRD, and laser Raman spec- troscopy), morphological and surface area characterization techniques (SEM, TEM and BET) were used to investigate the synthesis of CNMs from the untreated and chemically treated fly ash samples. Results have shown that carbon nanofibers (CNFs) of different geometric morpholo- gies were synthesized at an optimal yield temperature of 700◦C. A combination of smooth, thin, wide, spiral platelet-like, stacked cup, and fishbone morphologies were reported when the untreated fly ash catalyst was used. Fly ash catalysts under acidic, basic and neutral treatments showed CNFs of varying sizes and specific morpholo- gies. Smooth graphitic platelet-like, stacked cup and platelet-like CNFs were re- ported when the fly ash catalyst was leached with neutral, basic and acidic solutions. Carbon nanofibre sizes with the IG ID ratios were reported as follows 115 nm (1.092), 52 nm (0.799), and 200 nm (0.960) under neutral, basic and acidic mediums respec- tively. Surface areas (41, 14 and 7) m2/g for the CNFs that were synthesised from the neutral, basic and acidic treated fly ash catalysts were related to the selective leaching of metals. The quality and quantity of CNFs obtained under acidic medium were associated with the leaching of iron (5.6%), cobalt (1.7%), calcium (20.4%), copper (12.5%), chromium (4.6%), magnesium (23.3%), manganese (15.2%) and nickel (2%) from the fly ash catalyst. Under a basic medium only chromium (0.2%), calcium (0.3%) and copper (7.4%) were removed. Significantly the best quality of CNFs was ob- tained when fly ash was treated under neutral conditions. Metal ions such as: cal- cium (3.7%), copper (3.8%), chromium (0.1%), and magnesium (1.3%) were mod- erately removed from the ash matrix. Therefore, composition and quantity of the fly ash catalyst had an effect on the synthesis of CNFs.

Resumo: Este trabalho tem a finalidade de investigar a incineração de resíduos sólidos na presença de ondas acústicas para incrementar o processo de combustão. Para tanto foi projetado e construído um forno rotativo para incineração de resíduo sólido industrial. Um combustor do tipo sintonizável foi desenvolvido e acoplado ao forno rotativo para indução de oscilações acústicas, além de outros acessórios utilizados no processo de combustão (alimentador de resíduos, ejetor, sonda para análise de gases). Os resultados obtidos mostram que a presença do campo acústico melhora o processo de combustão. Estes resultados foram avaliados principalmente através da análise de gases de combustão, permitindo uma redução da quantidade de combustível utilizado. / Abstract: This work has the objective of investigating the incineration of solid wastes with acoustics oscillations to improve the combustion process. A rotary kiln was designed and built for the research. A tunable combustor was developed and connected to the rotary kiln for induction of the acoustics oscillations. Accessories were also built and used in the combustion process (feeder of waste, air ejector, probe for gas analysis). The results show that the presence of the acoustic field improves the combustion process. These results had been evaluated mainly through the analysis of gas combustion, allowing a reduction of the amount of used fuel. / Orientador: João Andrade de Carvalho Junior / Coorientador: Galdenoro Botura Júnior / Banca: Marco Aurélio Ferreira / Banca: Cristiane Aparecida Martins Andraus / Banca: José Antonio Perrella Balestieri / Banca: Luiz Roberto Carrocci / Doutor