Oscillatory Behavior in Methane Combustion: Influence of the Operating Parameters

The influence of the main process parameters on the oscillatory behavior of methane oxidation was analyzed in conditions relevant for low-temperature combustion processes. The investigation was performed by means of direct comparisons between experimental measurements realized in two jet-stirred flow reactors used at atmospheric pressure. With the operating conditions of the two systems coupled, wide ranges of the inlet temperature (790-1225 K), equivalence ratio (0.5 < Φ < 1.5), methane mole fraction (XCH4 from 0.01 to 0.05), bath gases (i.e., He, N2, CO2, or H2O) and different overall mixture dilution levels were exploited in relation to the identification of oscillatory regimes. Although the reference systems mainly differ in thermal conditions (i.e., heat exchange to the surroundings), temperature measurements suggested that the oscillatory phenomena occurred when the system working temperature accessed a well-identifiable temperature range. Experimental results were simulated by means of a detailed kinetic scheme and commercial codes developed for complex chemistry processes. Simulations were also extended considering systems with different heat losses to the surroundings, thus passing from adiabatic to isothermal systems. Results highlighted the kinetic nature of the dynamic behavior. Because predictions were consistent with experimental tests, further numerical analyses were realized to identify the kinetics responsible for the establishment of oscillatory phenomena. Temperature oscillations were predicted for a significant reactor working temperature range, where oxidation and recombination kinetic routes, involving carbon C1-2 species as well as reactions of the H2/O2 sub-scheme, become competitive, thus boosting limit cycle behaviors. Oscillatory phenomena cease when the system working temperatures exceed characteristic threshold values with the promotion of faster oxidation routes that diminish the inhibiting effects of recombination reactions

The influence of ammonia on the laminar burning velocities of methylcyclohexane and toluene: An experimental and kinetic modeling study

Laminar burning velocities of methylcyclohexane and toluene blended with ammonia have been determined using the heat flux method at atmospheric pressure and initial temperature of 338 K, over equivalence ratios ranging from 0.7 to 1.3 and ammonia blending fractions in the binary fuel mixtures from 0 to 90%. It was observed that the addition of ammonia to methylcyclohexane and toluene leads to a decrease in laminar burning velocity that is not proportional to the ammonia mole fraction. Such a burning velocity reduction is due to synergistic thermal and kinetic effects. In addition, ammonia has a slightly higher impact on the burning velocities of toluene due to fuel structure effects. The CRECK detailed kinetic model has been used to interpret the experimental measurements and minor modifications on methylcyclohexane, toluene, and methyl-phenoxy radical chemistry allowed even improved agreement. New experimental results have been compared with predictions of this refined kinetic mechanism. The model provided good predictions of the measurements capturing the effect of equivalence ratio and ammonia fraction ranges investigated. Finally, a mass fraction-based mixing rule was shown to be predictive for binary blends of NH3 with methane and several hydrocarbons typically used to formulate surrogates for practical fuels

Knowledge networks and dynamic capabilities as the new regional policy milieu. A social network analysis of the Campania biotechnology community in southern Italy

A new definition of regional milieu is emerging from the recent innovation policy framework inspired by the notion of a ‘knowledge economy’. It is grounded in a theoretical context where the emphasis is on the interactive character of innovation, involving the sharing and exchange of different forms of knowledge among the actors. Identifying regional positioning within the global knowledge value chain is a current preoccupation of both policy and empirical research. This study tries to measure the degree of involvement of a (follower) regional community of biotechnology actors in the global knowledge value chain. It applies inductive research and exploratory case studies to analyse local relational behaviour within the knowledge network (KN) structure. Our description of a regional bio-community highlights the distinctiveness of regional knowledge in relation to the distribution of KN capabilities. The critical nodes in the KN structure are the intra-regional actors, represented by public basic research organizations. These actors bridge between local basic research groups and the international scientific community, although the ability of local actors to collaborate can affect the strength of the links among them. This aspect, which is not addressed by regional strategies, should be the focus of new regional policies