Performance and emissions characteristics of a direct injection diesel engine from compressing producer gas in a dual fuel mode

This research highlights the impact of compressed producer gas combined with diesel fuel in a dual fuel mode on performance and emission characteristics of a three-cylinder diesel engine connected to an AC generator. Producer gas was generated from a small downdraft gasifier using charcoal, and sent into the engine using a supercharger to increase the gas flow rate from 76 to 125 lpm. The engine speed was adjusted from 1,000 to 1,600 rpm, while operating at full load. All results of this investigation indicate that supercharging producer gas improved the diesel economy and engine performance characteristics, but it increased the amount of various pollutants. Engine performance testing results from compressing producer gas showed that the use of gas flow rates of 116 to 125 lpm increased the maximum diesel saving by 41%, electrical power by 1.88%, and thermal efficiency by 35.76% as compared to a diesel fuel only mode. Additionally, specific energy consumption decreased with increasing producer gas flow rate and engine speed. For measuring the emissions of the engine, exhaust gas temperature increased from 223 to 276 oC, CO2 emissions increased from 21.59 to 33.90%, CO emissions increased from 0.36 to 0.59%, HC emissions increased from 23 to 58 ppm, and smoke opacity increased from 4.00 to 6.07 K.m-1 compared with the diesel fuel only mode

Forced Convection Heat Transfer from a Finite-Height Cylinder

[EN] This paper presents a large eddy simulation of forced convection heat transfer in the flow around a surface-mounted finite-height circular cylinder. The study was carried out for a cylinder with height-to-diameter ratio of 2.5, a Reynolds number based on the cylinder diameter of 44 000 and a Prandtl number of 1. Only the surface of the cylinder is heated while the bottom wall and the inflow are kept at a lower fixed temperature. The approach flow boundary layer had a thickness of about 10% of the cylinder height. Local and averaged heat transfer coefficients are presented. The heat transfer coefficient is strongly affected by the free-end of the cylinder. As a result of the flow over the top being downwashed behind the cylinder, a vortex-shedding process does not occur in the upper part, leading to a lower value of the local heat transfer coefficient in that region. In the lower region, vortex-shedding takes place leading to higher values of the local heat transfer coefficient. The circumferentially averaged heat transfer coefficient is 20 % higher near the ground than near the top of the cylinder. The spreading and dilution of the mean temperature field in the wake of the cylinder are also discussed.The simulation was carried out using the supercomputing facilities of the Steinbuch Centre for Computing (SCC) of the Karlsruhe Institute of Technology. MGV has been partially supported by grant TRA2012-37714 of the Spanish Ministry of Economy and Competitiveness.García Villalba, M.; Palau-Salvador, G.; Rodi, W. (2014). Forced Convection Heat Transfer from a Finite-Height Cylinder. Flow, Turbulence and Combustion. 93(1):171-187. https://doi.org/10.1007/s10494-014-9543-7S171187931Ames, F., Dvorak, L.: Turbulent transport in pin fin arrays: experimental data and predictions. J. Turbomach. 128(1), 71–81 (2006)Armstrong, J., Winstanley, D.: A review of staggered array pin fin heat transfer for turbine cooling applications. J. 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Satellite image analysis and frozen cylinder experiments on thermal erosion of periglacial fluvial islands

International audienceFrozen islands in the Lena River, Siberia, experience rates of fluvial thermal erosion exceeding 10m/year. The islands erode differentially, with rates of frontal retreat exceeding those on island sides. We define the erosion ratio (ER) between the front and sides to estimate this differential erosion. A GIS‐based study of 19 islands from 1967 to 2010 indicated average erosion rates of 19.7 and 3.7 m/year for the island heads and sides, respectively. The average ER over the period was 4.7. An analytical model of local thermal erosion for a frozen cylinder of sand in a turbulent water flow is proposed, assuming an ablation process. Thermal erosion of 19 frozen cylinders was measured for water flows of different temperature and velocity in a cold chamber. As observed in the field, frontal erosion always exceeded lateral erosion, with an average ER of 1.6. The ER decreased with increasing temperature from 5 to 15°C. The higher value of ER in the field may be due to interactions with neighboring islands and banks. An empirical law including phase change and the process of erosion is proposed, and validates our model compared with previous laws that do not account for erosion. The erosion process enhances heat transfer

Forced convection and heat transfer around a bounded cylinder

The article deals with the heat transfer solution in the fluid flow inside a pipe, the small tube is inserted into the pipe and its axis is perpendicular to the axis of the pipe. The fluid is water, the regime of the fluid flow is turbulent. The small tube is loaded by the internal source of the heat, the power of the source is constant and homogenous over the small tube surface and the cold water cools down the small tube. The analysis of the described problem helps to design the experimental model (the heat source above all) to validate the CFD results. The work included the numeric and analytic method. The model was prepared with the aim to investigate large amount of the variants of the geometric set up (the tube and pipe diameters ratio, the geometrical aspect ratio, corresponding stabilization length of the pipe for given diameter), the flow properties (variation of the velocity values, Reynolds number) and the power of the heat source (ensuring the measurable differences of the temperatures on the tube surface, large Nusselt number). The effect of the constrained space has been observed and described, compare to the free fluid flow