On the relevance of surface growth mechanism in premixed laminar flames

The role of surface growth mechanisms in particle mass accumulation was investigated in rich, premixed, ethylene/air flames from non-sooting to moderately sooting conditions using in situ optical diagnostics and predictions from a detailed chemical kinetic model. Particles formed just after the flame front, which are transparent to the visible light but absorb in the UV range, have been detected in large amounts in non-sooting flames and earlier in the flame than soot particles in sooting-flames, using UV-visible light optical diagnostics. For C/O 0.8, additional soot growth mechanisms need to be included in the mechanism to account for the amount of soot observed in the later part of the flames. interestingly enough, this late growth mechanism occurs almost simultaneously with a strong increase in the coagulation rate of the particles, thus indicating that both effects are related and are probably due to a major change in the chemical nature of the particle surface

Caratteristiche ecofisiologiche di Ruditapes philippinarum nella Sacca di Goro

Lo scopo del lavoro è stata l’analisi delle modificazioni dei parametri fisiologici di Ruditapes. philippinarum al variare delle condizioni ambientali e della disponibilità trofica e la determinazione dello scope for growth, SFG, (energia immediatamente disponibile all’animale per crescere e riprodursi). L’area di studio è la Sacca di Goro, la più meridionale delle baie che appartengono all’area del Delta del Po ed importante centro per la pratica della venericoltura. Sono state eseguite due serie di analisi in due stagioni, inverno ed estate del 2002, utilizzando un sistema a flusso continuo d’acqua ed una camera respirometrica. Sono così stati determinati tasso di clearance, tasso di ingestione, tasso di assorbimento, tasso di respirazione e tasso di escrezione. I risultati hanno messo in evidenza una differenza tra le due stagioni: tutti i tassi fisiologici sono risultati più alti durante l’inverno, ad eccezione del tasso di respirazione il quale, poiché influenzato della temperatura, è risultato più alto in estate. I tassi fisiologici sono stati poi utilizzati, in forma standardizzata ad un grammo di peso secco e convertita in equivalenti energetici, per la determinazione dello SFG, il quale risulta più alto in inverno che in estate. Questo perché durante l’estate l’animale, dopo l’emissione, si trovava in carenza di riserve energetiche, mentre in inverno stava accumulando riserve per la produzione dei gamet

Measurements of ultrafine particles from a gas-turbine burning biofuels

Measurements of ultrafine particles have been performed at the exhaust of a low emission microturbine for power generation. This device has been fuelled with liquid fuels, including a commercial diesel oil, a mixture of the diesel oil with a biodiesel and kerosene, and tested under different loads. Primarily attention has been focused on the measurements of the size distribution functions of the particles emitted from the system by using particle differential mobility analysis. A bimodal size distribution function of the particle emitted has been found in all the examined conditions. Burning diesel oil, the first mode of the size distribution function of the combustion-formed particles is centered at around 2-3 run, whereas the second mode is centered at about 20-30 nm. The increase of the turbine load and the addition of 50% of biodiesel has not caused changes in the shape of size distribution of the particles. A slightly decrease of the amount of particle formed has been found. By using kerosene the amount of emitted particles increases of more than one order of magnitude. Also the shape of the size distribution function changes with the first mode shifted towards larger Particles of the order of 8-10 nm but with a lower emission of larger 20-30 nm particles. Overall, in this conditions, the mass concentration of particles is increased respect to the diesel oil operation. Particle sizes measured with the diesel oil have been compared with the results on a diesel engine operated in the same power conditions and with the same fuel. Measurements have showed that the mean sizes of the formed particles do not change in the two combustion systems. However, diesel engine emits a number concentration of particles more than two orders of magnitude higher in the same conditions of power and with the same fuel. By running the engine in more premixed-like conditions, the size distribution function of the particles approaches that measured by burning kerosene in the microturbine indicating that the distribution function of the sizes of the emitted particles can be strongly affected by combustion conditions. (C) 2009 Elsevier Inc. All rights reserved