The design trend for light duty diesel engines is towards lower compression ratio and higher turbocharger boost. This can enable higher specific power and lower pollutant emissions to be achieved, but raises concerns that cold start operation might be adversely affected. This is investigated and quantified through the study of a modern light duty diesel engine at two compression ratios and temperatures down to -20ºC. Key indicators of cold start performance are the magnitude and cycle-to-cycle variation of indicated mean effective pressure. Initial studies were carried out at 300 rpm, a speed representative of post-first-fire conditions. Studies were then conducted at higher engine speeds representative of cold idle. The utility of different injection strategies, timings and quantities is investigated when varying test temperature and engine speed through a range of values encountered during the cold start phase of engine operation. The importance of the glow plug as a cold start aid is also investigated by varying its operating temperature and protrusion into the combustion chamber. The indicated mean effective pressure was used to assess the effects of varying input parameters, and gross heat release rate information is used to identify the phenomena responsible for desirable or undesirable characteristics. Reduction in compression ratio led to no deterioration of initial start performance from speeds just above cranking, provided an appropriate injection strategy was chosen. Higher indicated mean effective pressure was possible at low speeds using low compression ratio due to reduced losses and more complete combustion. Cycle-to-cycle variability in indicated mean effective pressure increased markedly for both compression ratios at engine speeds representative of cold idle, especially when test temperature was reduced. Stability reduction was more severe at low compression ratio. Multiple pilot injections at high compression ratio cold idle resulted in better cycle-to-cycle stability. Analysis of heat release profiles suggested that additional pilots assisted fuel mixing, a conclusion supported by a computational fluid dynamics model. Multiple pilots created a more homogeneous fuel distribution through the bowl at time of main injection. Multiple pilots could not stabilise operation at low compression ratio. Improvement in cold idle at low compression ratio was achieved by increasing glow plug temperature, which significantly increased the rate of fuel preparation. This increased the initial rate of heat release and resulted in significantly less variation in the heat release rate profiles. Small changes in glow plug protrusion rapidly degraded cold idle performance, indicating the importance of correct design.

Partially-premixed Charge Compression Ignition (PCCI) combustion is defined by increased levels of premixed charge whilst retaining control over combustion through injection timing. An experimental investigation has been carried out on a current generation DI diesel engine, equipped with High Pressure Common Rail (HPCR) fuel injection equipment and an external Exhaust Gas Recirculation (EGR) system. The aims of the investigation were to determine the constraints imposed on operating a PCCI combustion strategy with the aim of simultaneously reducing engine-out net soot and NOx emissions. The work was carried out at fully-warm steady-state conditions at engine speeds of 1500 rpm and 1800 rpm, predominantly using a single injection strategy. With a single injection the Start of Injection (SOI), fuel rail pressure, and rate of EGR have been examined with a view to realising PCCI combustion. Timing ranges of -20º to +3ºATDC, rail pressures of 500-1200 bar, and EGR rates of 0-60% have been investigated. The responses looked at have been engine-out soot, NOx, HC, and CO emissions, fuel consumption, and combustion noise. It is shown that variation of the parameters has allowed PCCI combustion to be achieved in a restricted operating region, offering improvement in the NOx-soot trade-off. This region is limited on the available test engine by oxygen availability due to the specifications of the turbocharger and EGR systems. Engine speeds up to 2000 rpm (at 2.5 bar BMEP), and loads of 4.4 bar gross IMEP (at 1500 rpm) have been found to be the limits, beyond which soot and CO emissions rise excessively. It is shown that enhancing the mixing time and intensity are both desirable in achieving PCCI combustion. The net soot reduction mechanism exploited with PCCI combustion strategies is reducing soot formation to outweigh the reduction in oxidation. Enhancing the mixing intensity by increasing injection pressure is highly effective at reducing soot output, but at the expense of brake specific fuel consumption. Increasing the mixing time can also be effective in reducing soot output, but careful parameter selection is required to avoid excessive soot output. Retarded or highly advanced injection timings are shown to reduce net soot output, but both have associated trade-offs and penalties. Retarding combustion is effective at lowering soot and NOx emissions with low associated noise, but a fuel economy penalty is paid. Advanced combustion phasing can result in large peak rates of increase of pressure, which have been shown to correlate well with combustion noise. Overall soot reductions of up to 97% were achieved, but with associated penalties. One of the most acceptable reductions of ~90% came at the cost of a 6% increase in fuel consumption, highlighting that improvements in emissions are achievable with PCCI strategies with acceptable trade-offs.

The purpose of this research is to develop a dataset for some of the most important fire characteristics, namely CO2 yield, CO yield, HCN yield, soot yield and heat of combustion for probabilistic analysis and modelling. Raw data in time series are required to mechanically reduce experimental data into yields (kg/kg) and effective heats of combustion (MJ/kg), which are expressions for the amount of products generated per unit mass of fuel. Mass loss rate thresholds were applied to all tests to define the beginning and end of tests. These species yields and heat of combustions were then grouped by material compositions and fitted with distribution functions to produce distributions curves. As fire species productions and heat of combustions are dependent on the fire conditions as it develops, different yields are expected at different fire stages. These have been identified as the growth (G), transition (T), and smouldering (S) stages in this research. These values are also compared against, and are generally in agreement with, other research data. Nonetheless, some discrepancies have occurred and require further information to ascertain the material characteristics and combustion conditions. In conclusion, design recommendations for these fire characteristics have been made for several material groupings and verified against other research results. Certain physical and chemical limitations exist for combustions and have not been reflected in the fitted distribution, including stoichiometric yields and unlimited air yields. As such, species yields and heat of combustions beyond these values should not be considered in fire engineering design and analysis. Research results on HCN including all required data parameters for yield conversions were difficult to obtain and require further research efforts. Tube furnace results were initially investigated. Unfortunately, without a continuous mass record, has proved to be challenging in producing reliable mass loss rate profiles for yield conversions. A semi-automated data reduction application UCFIRE was also used. However, certain technical difficulties were encountered and require modifications to broaden its applicability.

No description available.

A model of premixed lean Hydrogen-Oxygen flame is studied by singular perturbation techniques based on high activation energy. The model is built from four reaction steps consisting of two chain branching steps, a chain propagating step, and a recombination step. The analysis, in this case, gives rise to a layer phenomenon different from what is currently seen in combustion literature. First, there is a basic layer similar to those obtained for the one step reaction model. Then embedded in the first layer is a thinner layer giving rise to an interesting system of nonlinear boundary value problems. This system of nonlinear problems does not meet standard existence criterium and also involves an unknown parameter. Hence existence results are called for. Existence is proved for both the boundary value problem and the unknown parameter, and numerical solutions are obtained in support of the existence results. A numerical estimate of the unknown parameter is obtained. A generalization of the model for different reaction parameter ranges is made. Two new thin layers emerge. The structure of one of the new thin layers turns out to be exactly the same as that just described, hence the existence results do carry over. The boundary value problem resulting from the second of the new thin layers turned out to be quite simple and a solution could be written down explicitly.

Fouling, slagging, corrosion, and emission of submicron particulate from pulverized coal combustors have been linked to vapor alkali. Size segregated fly ash samples extracted from a 17 kW down-fired pulverized coal combustor showed strong evidence of alkali vaporization. The fraction of sodium in sizes smaller than 0.65 μm (f(8A)) showed a correlation with acid soluble sodium divided by total silicates in the parent coal. Addition of silicates to coal reduced f(8A) for sodium. Potassium existing primarily in the mineral matter, did not show a similar correlation, but f(8A) for potassium did correlate with f(8A) for sodium. Bench scale experiments indicated potassium does not vaporize in the presence of Na or Cl alone, but requires both, and was only released when sodium was captured. Additional of sodium acetate to coal increased f(8A) for potassium. Equilibrium calculations, experiment, and modelling of sodium capture by silicates during pulverized coal combustion identified several important mechanisms governing alkali behavior. The mode of occurrence of alkali in the parent coal dictates its ability to vaporize, its release kinetics, and its sate as it diffuses to the char surface. Other species such as chlorine, sulfur, moisture, and other metals influence alkali stability in the vapor, its reactivity, and its condensation characteristics. Char oxidation can influence alkali vaporization, and capture by affecting included silicate surface area. Sodium reaction with silicates captures from 70 to over 95% of total sodium for typical coals. Silicate additive appears to be a viable technique for reducing the fraction of alkali in the vapor during combustion.

This project documents the multi-scalar formation processes of two northern Levantine coastal Paleolithic cave sites using field geology, archaeological micromorphology and sediment geochemistry. Located in within several hundred meters of each other, the sequences from Üçağızlı I and II present an opportunity to compare late Middle and early Upper Paleolithic hominin adaptations to a similar coastal environment. The morphologies of the sites and the suite of coastal geomorphic features available to the area's Paleolithic occupants were impacted by fluctuations in sea level as well as tectonic events. The sites share similar formation histories that include active karstic processes, marine inundation, occupation by hominins, partial collapse of the cave vaults, and erosion of the uppermost archaeological deposits. Mousterian occupation of Üçağızlı II began after the formation of a series of stable sea level features that date to Marine Isotope Stage (MIS) 5a. Hominin utilization of the highly eroded portions of the cave continued at least through the middle of MIS 3, although the cultural attribution of the youngest materials is presently unknown. Üçağızlı I contains a sequence of Initial Upper Paleolithic, Ahmarian and Epipaleolithic materials dating to MIS 3 and 2. Micromorphology of the archaeological sediments reveals strong anthropogenic contributions to the infilling of both caves, in particular the deposition of abundant, well-preserved wood ashes. In both sequences, post-depositional insect bioturbation has negatively impacted the combustion features, resulting in alteration of the original sedimentary fabrics and loss of information regarding hominin activities such as sweeping, rake-out and dumping of ashes. In Üçağızlı II, the dominant mode of sedimentation is anthropogenic; a series of intact and cemented combustion features located beneath the highest point of the cave ceiling is surrounded by sediment exhibiting evidence of both rodent and insect bioturbation. In Üçağızlı I, phases of human activity alternated with periods of natural sedimentation. Combustion features in the site include isolated hearths, stacks of hearths, rake-out or sweeping deposits, ash dumps, and mixed burned materials that have been impacted by colluvial reworking and bioturbation. In sum, the two sites contain similar types of anthropogenic sediments despite differing cultural affiliation.

No description available.

No description available.

No description available.