No description available.

No description available.

The effect of combustion chamber design on combustion rate has been investigated experimentally and theoretically. The experimental work concentrated on the measurement of cylinder pressure and flame speed using a piezo-electric pressure transducer and multiple ionisation probes together with a data acquisition/processing system. A total of twenty one chamber designs of varying shape, compression ratio and spark plug arrangement were tested over a range of operating conditions on a single cylinder S.I. engine. The pressure data were analysed to obtain values of pressure rise rate, cyclic dispersion and combustion (mass burn) rate whilst the ionisation data were processed to yield flame travel angles and flame dispersion. The results obtained show that for a given compression ratio, the flame speed is not significantly affected by chamber design. In contrast, the combustion rate and pressure parameters are highly dependent on the chamber design; more compact arrangements giving higher combustion rates and reduced cyclic dispersion. A computer simulation model of the compression, combustion and expansion phases of the engine cycle was developed to predict the effects of the combustion chamber design parameters. Based on the experimental results, the model assumes that the ratio of laminar to turbulent burning velocity is independent of chamber design. The influence of chamber shape on the burnt volume, flame front surface area and heat transfer surface areas is modelled using a simple but effective geometric integration technique. This technique allows an infinite variation of the design parameters to be specified for a large range of chamber shapes with a minimum of input data being required. The model predicts that chamber design does have a major effect on combustion rate and cylinder pressure but shows that the influence of individual design is highly dependent on the setting of all other parameters. The effect of squish area is shown to be due to it changing the compactness of the chamber, optimum squish area being about 50% for conventional engines with higher areas being suited to higher compression ratio designs. Spark plug arrangement is predicted to be the most effective way of controlling the combustion rate with a single centrally located spark plug or alternatively, dual spark plugs, giving large increases in combustion rate. Computer model predictions have been compared directly with experimental results obtained in this study and with experimental results reported by two other independent workers. Good agreement was obtained thereby giving support to the assumption of the flame speed being unaffected 'by chamber design. The model was also used to predict squish velocities in fired engines. The results show that the velocities and, in particular the reverse squish, can be significantly modified by the combustion process with a strong dependence on ignition timing being evident. The predictive model has been modified to yield a heat release program capable of analysing experimental pressure time data to predict combustion rate, flame speed, turbulent burning velocity and many other variables. The predicted flame speeds were in good agreement with corresponding experimental values obtained from ionisation probes. In conclusion, the study has confirmed the importance of combustion chamber design as a means of improving the combustion rate but has shown that the flame speed is not affected by chamber shape (i.e. squish). The semi-empirical simulation model has been shown to predict the effects of the chamber design parameters to an acceptable degree of accuracy.

Thesis (PhD)--Macquarie University, Division of Environmental and Life Sciences, Department of Chemistry, 2002. / Bibliography: leaves 234-240. / Introduction, theoretical descriptions of spontaneous combustion phenomena and aims of this thesis -- Laboratory measurements of the self-heating phenomenology of bagasse -- Field experiments investigating the self-heating behaviour of large scale stockpiles of low symmetry -- Self-heating and thermal ignition of calcium hypochlorite -- Experimental methods and procedures used for the critical ambient temperature of HCH -- Results of critical ambient temperature measurements upon single containers of hydrated high strength HCH -- Experiments on the interaction of self-heating drums -- Conclusions. / The hazard of spontaneous combustion is a problem that confronts any industry that transports or stores a reactive material. Bagasse is a reactive material that presents an expensive spontaneous combustion hazard for the sugar industry since this material is the principal fuel used at sugar mills. Calcium Hypochlorite is another such material presenting a significant industrial spontaneous combustion hazard for the transport and insurance industry as it has been linked to a number of expensive maritime conflagrations. The investigation of fundamental self-heating phenomenon is critical for the understanding, control and prevention of spontaneous ignition with these materials. -- By way of isothermal calorimetry techniques and fundamental thermal ignition measurements, this study has provided improved understanding into the oxidative self-heating phenomenology of bagasse and thermal ignition phenomenology of calcium hypochlorite. Both substances have been shown to possess unusual and previously unknown self-heating behaviour at temperatures below 100°C, with water being a principal component of each mechanism. -- The outcomes of this study have provided a platform which has enabled current mathematical models to predict large scale self-heating phenomena for industrially stored quantities of these materials. / Mode of access: World Wide Web. / 240 leaves, bound ill

In this work the combustion characteristics of coal, charcoal, microalgae biomass and blends between these three components were evaluated by means of non-isothermal thermogravimetry. Blends between coal, charcoal and microalgae biomass were made according to the specifications of a D-optimal mixture design so as to be able to model interactions between the three components with maximum precision despite multiple constraints built into the design. These constraints specified that coal can have a minimum value of 70 mass percent in any blend, while microalgae can have a maximum value of 20 mass percent. While coal and charcoal were blended by mixing the two respective dry components, microalgae biomass was incorporated into the blends by first absorbing microalgae onto fine coal from concentrated slurry of the microalgae in water. The microalgae in these blends were therefore intimately associated with the coal. This approach differed substantially from the normal practice of preparing coal – biomass blends (which are usually dry-mixed as for coal – charcoal blends). Proximate analyses of the starting materials showed that the microalgae biomass has a significantly higher volatile matter: fixed carbon content than both coal and charcoal, which should improve the combustion of these materials by providing a more stable combustion flame. Analyses of the thermogravimetric data obtained showed that coal and charcoal have much simpler combustion profiles than microalgae biomass for which five different thermal events could be observed in the DTG combustion profile. Qualitative kinetic analyses showed that the combustion of coal and charcoal follows first-order kinetics, but for microalgae biomass combustion, the first two combustion stages appear to follow first-order kinetics. The TG and DTG profiles for coal, charcoal, microalgae and blends of these three components were used to derive values for the so-called comprehensive combustion property index (S-value), which provides a combined measure of the ease of ignition, rate of combustion, and burn-out temperature. The S-values so obtained were used as response variable for the construction of a response surface model in the experimental domain investigated. Following statistical validation of the response surface model, the model was used to predict an optimum S-value or a blend that would display optimum combustion behaviour. Two optimum blends were obtained from the optimisation process, one in which only charcoal is added to coal, and one in which only microalgae is added to coal. Adding both charcoal and microalgae produced an antagonistic effect compared to when only one of these are used. Qualitative kinetic analyses of the combustion data of blends indicate that blends of coal and charcoal combust in a manner similar to the individual components (hence following first-order kinetics), but blends of coal and microalgae follow more complex kinetics despite the fact that the combustion profile is visibly more simple compared to the combustion profile for microalgae alone.

There is an urgent call for action to address the energy efficiency, climate, and local air quality concerns associated with transport because of CO2, particulates, nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) emissions. This has driven the international policy agenda towards reducing greenhouse gas (GHG) with a major emphasis on CO2 emission. Fossil fuel combustion is considered a main contributor to the emission of CO2. The transport sector with a particular emphasis on ground transport is considered the fastest growing sector among all emission sources. To meet climate change goals, governments around the world may need to implement strict regulations on the transport sector. Governments around the world have indeed set stricter emissions standards for vehicles as a way to reduce greenhouse gas emissions from the transport sector. These standards can be achieved through various methods, such as requiring more efficient engines, alternative fuels, or the adoption of electric vehicles. On the other hand, in recent years, a lot of effort was put into promotion of electric vehicles as zero emissions vehicles. This statement should be reconsidered, since the greenhouse impact of electrical vehicles is not negligible. Conversely, in some cases, an electrical vehicle can have an even higher emission impact than modern vehicles with sophisticated internal combustion engines. In fact, the pollutant emissions discharged at the tailpipe outlet will be so low as to be hardly measurable, and their practical impact on air quality will be negligible. In terms of particulate matter emission for example, the impact of tire and brake wearing is already much higher than that due to the ICE (tire wear produces around 50 mg/km of particulates), reaching values around 10 times the emission from the engine (5 mg/km). This implies that today’s conventional ICE-powered-car is equivalent to fully electric and hybrid cars with regard to particulate emissions, when tire and brake and other contributions (e.g. road dust) are accounted for. All the data indicate that ICEs will never cease to exist and the majority of cars will be powered by ICEs in the future. These factors sparked my work on the simulation of ICEs. The first project was mainly focused on high-pressure isobaric combustion, which is a promising concept that has the potential to introduce high efficiency. This work started with the development and validation of the computational models for full cycle combustion engine simulations to capture the flow and combustion characteristics and their interactions with the intake and exhaust flows through the valves and ports. The computational models were extensively validated against the optical engine experiment data, to ensure the fidelity needed for predictive simulations. Upon identifying the numerical models, a comparative study of isobaric and conventional diesel combustion was conducted. The results revealed the superiority of the isobaric combustion mode compared to the conventional diesel combustion especially at high load conditions. On the other hand, the isobaric combustion led to high soot levels compared to the conventional diesel combustion due to the undesirable spray-to-spray interactions resulting from a single central injector with multiple consecutive injections which introduced a fuel-rich zones. For the same injection technique, a study of the effect of injection pressure and the number of holes were numerically investigated as means to reduce the soot levels. To further decrease the soot emissions, multiple injector configurations were used and the results showed more than 50% drop in the soot levels and an increase in the indicated thermal efficiency due to the lower heat transfer losses. The successful injection strategies for low-emission isobaric combustion mode have further motivated research about fuel flexibility. The potential of using fuels from different sources with varying reactivity was explored by utilizing the high pressure combustion. Various primary reference fuels (PRFs) were employed at the same middle engine load, varying from PRF0 up to PRF100. Different injection methods from a single to four injections were studied. The results demonstrated that various PRFs showed significant discrepancies when using a single injection method, owing to the different fuel auto-ignition capability. On the other hand, excellent fuel flexibility was achieved by employing a small pilot injection, under this condition various fuels led to similar engine combustion performance and emissions. Exhaust gas recirculation (EGR) was used as a way to reduce NOx emissions where 50% EGR was employed. To reduce soot emissions, various volume fractions of three shorter-chain alcohols (methanol, ethanol, and n-butanol) were blended with the baseline fuel (n-heptane). The methanol-blended fuels yielded the lowest soot emissions, but the worst fuel economy was obtained due to the highest heat transfer losses. By increasing the nozzle number and introducing an adequate amount of isochoric combustion, the fuel economy for pure methanol combustion was effectively promoted. The second project was focused on ultra-lean hydrogen combustion using CONVERGE CFD as computational framework. The problem of numerically detecting engine knock and the methods to mitigate such a problem were addressed. Different combustion modes such as port fuel injection spark ignition (PFI SI), homogenous charge compression ignition (HCCI), and pre-chamber (PC) were investigated. The effects of the chemical mechanisms in terms of ignition delay time and laminar flame speed were studied. Starting with the simple combustion mode using PFI SI, high engine knock tendency was observed. The effects of compression ratio, air-fuel-ratio, and spark time were examined as means to reduce engine knock. Upon mitigating the engine knock issue, a comparative study of the PFI spark ignition and the PC modes was conducted. The results revealed that the current used design of the PC introduced high turbulence levels, which resulted in high heat transfer losses to the engine piston. In general , all of these studies (isobaric and hydrogen combustion) were aimed to increase the overall engine efficiency and reduce the emissions.

No description available.

Thesis (Ph.D.), University of the Witwatersrand, Faculty of Engineering (Chemical Engineering), 1983

Conventional combustion processes are known to be highly irreversible processes. The potential to obtain useful work from the fuel is degraded during the combustion process. For example, for a reciprocating internal combustion engine, about 20% or more of the potential work from the fuel is destroyed during the combustion process. This potential work is known as availability (a thermodynamic property). The motivation for the current work was to develop a conceptual model of a set of processes related to reciprocating engines that would eliminate this destruction of availability. One conceptual model, proposed by Keenan, suggested that a preselected set of “reactants” could be compressed (at constant composition) to a high temperature and pressure. At this high temperature and pressure, the “reactants” would be in chemical equilibrium. At this point, the “reactants” would be expanded back to the original volume. The expansion process would consist of a “shifting” chemical equilibrium such that the composition during expansion would continue to change. At the end of the compression and expansion, net work would be available without destroying any of the work potential of the fuel. The purpose of the current work was to develop a quantitative model of this concept, and to use the model in a series of computations to examine the effects of temperature, pressure, and other parameters on the work production capability of the concept. The concept was studied for eight different fuels for various conditions. In general, the net work output increased as the temperature, pressure and compression ratio increased. For low compression temperatures and pressures, the concept resulted in a small amount of net work produced without destroying any fuel availability. For sufficiently high compression pressure and temperature (e.g., 10 MPa and 6000 K, respectively), however, the thermal efficiency was ~28% for isooctane and was ~40% for hydrogen and methane, for air as the oxidant, an equivalence ratio of 1.0, and a compression ratio of 18. Although the temperatures and pressures considered are well beyond practical values for the materials and designs of today, the general result of the study is that conditions can be identified to eliminate the combustion irreversibility.

Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Brophy, Christopher M. Second Reader: Sinibaldi, Jose O. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: Transient Plasma Ignition, Pulse Detonation Engine, Flame Kernel Growth. Includes bibliographical references (p. 83-84). Also available in print.