1,721,042 research outputs found
IDENTIFICATION OF CROSS-FLOW LIQUID -JET STRUCTURES BY MEANS OF STATISTICAL IMAGE EVALUATION
No full textAir dilution effects on tetradecane spray autoignition in transcritical and supercritical regimes
No full textAutoignition time delay of tetradecane spray injected in nearly quiescent, high-temperature, high-pressure, diluted and not diluted air has been measured by detecting spontaneous luminous emission. The photodiode location and its spectral sensitivity were carefully tested with preliminary comparison to spectrally resolved measurements hy using a spectrograph equipped with an intensified CCD camera. The measurements were performed starting from a temperature of 873 K, a pressure of 3.6 MPa, and all oxygen molar fraction of 0.21. One of these ambient conditions Ir?asfuced and the other two parameters, were lowered to 873 K ambient temperature, 1.1 MPa, and 0.06 oxygen molar fraction. The results were analyzed in relation to the expected ones, which were based on the available models relative to processes controlled by atomization, evaporation, quenching, and chemical kinetics. The main result of this analysis has been the characterization of the relationship between ignition delay time and oxygen molar fraction in the ambiance that has been found to be well described by a -2 power law. This behavior supports the low-temperature kinetic scheme for paraffin, which hypothesizes oxygen addition on fuel molecules. Moreover, transcritical and supercritical droplet evaporation regimes have been identified as functions of ambient temperature and pressure
Autoignition characteristics of diesel sprays under different injection conditions
No full textAn experimental study analyzing the complex relationship between external thermo fluid dynamic parameters and the ignition of diesel sprays, as well as flame propagation, is presented. The experiments were performed in a high-pressure, high-temperature system simulating the top dead center conditions in the combustion chamber of a diesel engine. The only simplification with respect to real diesel engines is relative to the aerodynamic pattern. In fact, in this case, the air flux is almost quiescent and does not influence significantly the spray evolution or the combustion behavior. The influences of two very different injection regimes on the autoignition characteristics of diesel sprays were investigated using imaging techniques. In order to perform this analysis, a careful choice of injection conditions, obtained with two different types of injection apparatus, was necessary. The spray evolution at both low and high temperatures (at the same air density), the temporal and spatial distributions of the ignition points, and the flame growth velocity were measured for the two cases. Analysis of the results revealed the specular behavior of the ignition spatial distributions ill the two cases. A first attempt to correlate these different behaviors with the spray-flame interaction is presented, and its implications are discussed
Cellulose slow pyrolysis products in a pressurized steam flow reactor
No full textABSTRACT A key strategy to achieve an acceptable degree of matter and energy recovery from vegetal waste disposal is the use of a steam-assisted pyrolysis process that operates at low heating rates and elevated pressure. This procedure, which is different from incineration and fast pyrolysis processes, is expected to reduce the production of secondary hazardous products and produce a residual char with chemical–physical properties comparable to those typical of activated carbon. However, gaseous and condensable products of the process must be demonstrated to allow for a recovery of energy to an extent that can make the process self-sustainable. To clarify these aspects and define the optimal operating conditions of the pro- cess, a multi-plate laboratory reactor was designed and constructed. This paper provides a description of the primary design criteria and operating conditions for a steam pyrolysis process. In addition, the effects of process temperature and pressure on products yields and gas and char characteristics are presented indicating the suitability of the process. In the temperature range examined, steam affects positively char and gas properties. On the other hand, pressure affects, mainly, gas yield and determines only minimal changes in char characteristics
EXPERIMENTAL CHARACTERIZATION OF INTERFACE PROPERTIES IN THE FRAMEWORK OF MultiSECtioning STRATEGY: PRELIMINARY RESULTS
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IDENTIFICATION OF AVERAGE "HIDDEN" FEATURES OF MULTIPHASE FLOWS THROUGH HIGH ORDER STATISTICAL MOMENTA OF QUANTITATIVE IMAGES
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