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ABSTRACT: To burn dense, viscous combustibles like Heavy Fuel-Oil as a water-in-oil emulsified combustible enables to decrease the emission of solid carbonaceous residue, in comparison with raw, non-emulsified combustible. This is due to the phenomenon of micro-explosion, meaning the rapid (<0.1 ms) vaporization of the inside water droplets ofcthe emulsion, breaking up the initial emulsion droplet. This phenomenon is also called the "second atomisation" among the spray of emulsified combustible. The present work is based on a small-scale furnace (~200 kW) feed with Heavy Fuel-oil mixed with 10% of diesel, with and without emulsion of water. The emulsification of combustible enables to record a reproducible lowering in emission of carbonaceous residue from combustion of emulsion, in comparison with raw Fuel, added with a variation in granulometry of carbonaceous residue, indicating the second atomisation.
01/2008;
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ABSTRACT: This paper presents the determination of knock rating of gaseous fuels in a single cylinder engine. The first part of the work deals with an application of a standard method for the knock rating of gaseous fuels. The Service Methane Number (SMN) is compared with the standard Methane Number (MN) calculated from the standard AVL software METHANE (which corresponds to the MN measured on a Cooperative Fuel Research engine). Then, in the second part, the 'mechanical' resistance to knock of our engine is highlighted by means of the Methane Number Requirement (MNR). A single cylinder LISTER PETTER engine was modified to run as a spark ignition engine with a fixed compression ratio and an adjustable spark advance. Effects of engine settings on the MNR are deduced from experimental data and compared extensively with previous studies. Using the above, it is then possible to adapt the engine settings for optimal knock control and performances. The error on the SMN and MNR stands beneath ^ 2 MN units over the gases and engine settings considered.
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ABSTRACT: In a combined heat and power (CHP) plant, spark ignition engines must operate at their maximum power to reduce the pay back time. Because of environmental and economic concerns, engines are set with high compression ratios. Consequently, optimal operating conditions are generally very close to those of knock occurrence and heavy knock can severely damage the engine piston.There are two main protection techniques: the curative one commonly used by engine manufacturers and well documented in the literature and the preventive one based on a knock prediction according to the quality of the supplied gas. The indicator used to describe gas quality is the methane number (MN). The methane number requirement (MNR) of the engine is defined, for an engine set (spark advance, air–fuel ratio, and load), as the minimum value of MN above which knock free operation is ensured. To prevent knock occurrence, it is necessary to adapt the engine tuning according to variable gas composition. The objective of the present work is to validate the concept of knock preventive protection. First, a prediction of MNR according to engine settings (ES) is computed through a combustion simulator composed of a thermodynamic 2-zone model. Predicted MNR are compared to experimental results performed on a single-cylinder SI gas engine and show good agreement with numerical results (uncertainty below 1 point). Then, the combustion simulator is used to generate a protection mapping. At last, the knock preventive protection was successfully tested.
Fuel Processing Technology 91(6):641-652. · 2.94 Impact Factor
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ABSTRACT: Burning a water-in-oil emulsion enables reduction in solid and gaseous pollutants in comparison with neat oil. In the emulsion, Heavy Fuel-Oil and water lie in distinct phases, having a high difference in boiling point (up to 200 K). In an emulsion droplet injected and subsequently heated inside a flame, the internal water droplets are enclosed inside the emulsion and do not systematically vaporise at boiling point. They are known to reach a metastable state, breaking up at a temperature below the spinodal limit of water. From this moment, the surrounding Fuel-Oil is fragmented into numerous faster and smaller droplets by the suddenly expanding steam. This physical phenomenon is called “micro-explosion”. This work demonstrates a numerical modelisation of unsteady heat and mass transfer at the surface and inside of the emulsion droplet, and provides a prediction of its micro-explosion delay, using homogeneous nucleation hypothesis. This assumption of homogeneous nucleation for internal water droplets matches the use of a “drop tower” experimental facility. Finally, comparisons between predicted ranges for micro-explosion delays and experimental delays from literature are discussed, along with combustion parameters (ambient temperature, relative velocity) and combustible emulsion parameters. As a result, the experimental and numerical micro-explosion delays decrease with liquid or ambient temperature and relative velocity, and increase with water content and radius of emulsion droplet. Their low average deviation reveals the accuracy of the assumption of homogeneous nucleation in the considered situations.
International Journal of Thermal Sciences 48(2):449-460. · 2.14 Impact Factor
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ABSTRACT: This paper presents a methodology for the determination and measurement of important natural gas combustion properties (Higher heating value, Wobbe index and Stoichiometric Air–fuel ratio). A pseudo-gas formulation is used to determine an equivalent gas composition to the real natural gas tested. The pseudo-composition, made up of the most influent constituents of the natural gas, is determined by solving a system of non-linear equations. The input parameters to the procedure are: the thermal conductivity of the natural gas at 333 K and 383 K, the speed of sound at 303 K and the concentration of CO2. A combustion properties measurement sensor has been developed and tested for many natural gas compositions. The tested natural gases are chosen to represent typical European gases as well as to account for large variations of individual components (heavy hydrocarbons, inert gases). With the developed sensor, combustion properties measured at standard conditions agree with gas chromatographic analysis, to within 0.5%.
Fuel.
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ABSTRACT: Knock is a major problem when running combined heat and power (CHP) gas engines because of the variation in the network natural gas composition. A curative solution is widely applied, using an accelerometer to detect knock when it occurs. The engine load is then reduced until knock disappears. The present paper deals with a knock preventive device. It is based on the knock prediction following the engine operating conditions and the fuel gas methane number, and it acts on the engine load before knock happens. A state of the art about knock prediction models is carried out. The maximum of the knock criterion is selected as knock risk estimator, and a limit value above which knock may occur is defined. The estimator is calculated using a two-zone thermodynamic model. This model is specifically based on existing formulas for the calculation of the combustion progress, modified to integrate the effect of the methane number. A chemical kinetic model with 53 species and 325 equilibrium reactions is used to calculate unburned and burned gases composition. The different parameters of the model are fitted with a least squares method from an experimental data base. Errors less than 8% are achieved. The knock risks predicted for various natural gases and operating conditions are in agreement with previous work. Nevertheless, the knock risk estimator is overestimated for natural gases with high concentrations of inert gases such as nitrogen and carbon dioxide. The definition of a methane number limit based on the engine manufacturer's recommendation is then required to eliminate unwarranted alerts. Safe operating conditions are thus calculated and gathered in the form of a map. This map, combined with the real time measurement of the fuel gas methane number, can be integrated to the control device of the CHP engine in order to guarantee a safe running towards fuel gas quality variation.
Fuel Processing Technology.
