Combustion early studies

Aircraft turbines in jet engines are usually fabricated from nickel-based alloys, and these are subject to combustion products containing compounds of sulphur, such as S02, and oxides of vanadium. Early studies of the corrosion of pure nickel by a 1 1 mixture of S02 and 02 showed that the rate of attack increased substantially between 922 K and 961 K. The nickel-sulphur phase diagram shows that a eutectic is formed at 910 K, and hence a liquid phase could play a significant role in the process. Microscopic observation of corroded samples showed islands of a separate phase in the nickel oxide formed by oxidation, which were concentrated near the nickel/oxide interface. The islands were shown by electron microprobe analysis to contain between 30 and 40 atom per cent of sulphur, hence suggesting the composition Ni3S2 when the composition of the corroding gas was varied between S02 02 equal to 12 1 to 1 9. The rate of corrosion decreased at temperatures above 922 K. 

Early studies in this field [35, 36] indicated that a high surface-to-volume ratio, which represents a hurdle for gas-phase combustion, is instead an advantage for catalytic combustion. In fact the small scale enhances considerably the rate of gas-solid mass transfer, which favors the kinetics of the combustion process and compensates for the short residence time. Also, as is well established for large-scale systems, the presence of a catalytic phase allows for stable combustion at significantly lower temperature than traditional homogeneous burners [55, 56]. This makes the design and operation of microcombustors more fiexible. Several recent studies have explored the potential of catalytic microcombustors using H2 [37, 38, 50], methane [37], propane [52,53,57] and mixtures of H2 with propane [57], butane [38,47,52] and dimethyl ether [52]. 

Although the prediction of N0X emissions under lean and stoichiometric combustion with the extended Zeldovich mechanism is adequate for certain applications, predictive methods for fuels containing bound nitrogen and for rich combustion conditions require substantial improvement. However, the early studies of Fenimore (13, 14) demonstrated the potential importance of HCN and NH type species in fuel-nitrogen interactions. To illustrate the critical importance of the coupling of nitrogenous species reactions in rich combustion, predictions of NO emissions from rich iso-octane combustion in a jet-stirred combustor are shown in Table III. C2 hydrocarbon fragmentation and oxidation creates... 

For heterogeneous propellants, the current situation is much less satisfactory. The complexity of the combustion process was discussed in Section 7.7. To employ a result like equation (66) directly is questionable, although attempts have been made to evaluate parameters like A and B of equations (67) and (68) from complicated combustion models for use in response-function calculations [81], [82]. Relatively few theories have been addressed specifically to the acoustic response of heterogeneous propellants [82]. Applications of time-lag concepts to account for various aspects of heterogeneity have been made [60], [83], a simplified model—including transient variations in stoichiometry—has been developed [84], and the sideways sandwich model, described in Section 7,7, has been explored for calculating the acoustic response [85], There are reviews of the early studies [7] and of more recent work [82],... 

Early studies of slow combustion and ignition characteristics of organic compounds showed that although methanol, ethanol and propanol are more readily oxidized than methane, ethane and propane, the situation is reversed with butanol and the higher homologues [1—4]. 

As stated above. It has been established that carboxylate Ions are the true Initiators in B lactone polymerization. In an early study. Hall ( ) stated that In Intermediate pH ranges anions or water Itself attack the CH2 group with alkyl-oxygen cleavage by SN2 reaction that proceeds most rapidly In anhydrous acetonitrile or tetrahydrofuran. From heats of combustion he determined the heat of polymerization of plvalolactone AH j. to be -20.1 kcal mol l. 

The possibility of extinguishing a polymer flame depends on the mechanism of thermal decomposition of the polymer. Whereas ignition of a polymer correlates primarily with the initial temperatnre of decomposition, steady combustion is related to the tendency of the polymer to yield a char, which is produced at the expense of combnstible volatile fragments. Therefore, the dependence of steady combnstion on the amonnt of char seems to be simple, and in an early study it was established that the oxygen index shows a very good correlation with the char yield. In reality, char also serves as a physical barrier for heat flux from the flame to the polymer surface, as weU as a diffusion barrier for gas transport to the flame. Therefore, the contribution of the char can be more significant than is expected from a simple reduction in combustible gases. 

The original formulation and verification of the Zeldovich mechanism is attributed to Zeldovich (1946), who studied explosions of gases within a combustion bomb. By assuming equilibrium between O and O2, that O and N were in steady state, and that only reactions (1) and (2) were important, Zeldovich was able to obtain an approximate Arrhenius expression for k. Another early study was performed by Click et al (1957), who used a singlepulse shock tube technique. Their study was intended as an investigation of the overall reaction N2 + O2 2NO, and an explicit expression for was not reported. They did, however, report a steric factor and activation energy for ki based on a model that assumed N-atom steady state and O/O2 partial equilibrium. 

Fly ashes from coal combustion have been used in various animal studies, with only modest effects (183). However, coal fly ash contrasts with fly ashes from oil combustion, from which the metals can be considerably more bioavailable (water- or acid-soluble). Early studies of residual oil fly ash have shown enhancement of pulmonary infections in mice and cytotoxicity to alveolar macrophages (180). The degree of acute inflammation (as measured by PMNs, lactic... 

The chronology of the most remarkable contributions to combustion in the early stages of its development is as follows. In 1815, Sir Humphry Davy developed the miner s safety lamp. In 1826, Michael Faraday gave a series of lectures and wrote The Chemical History of Candle. In 1855, Robert Bunsen developed his premixed gas burner and measured flame temperatures and flame speed. Francois-Ernest Mallard and Emile Le Chatelier studied flame propagation and proposed the first flame structure theory in 1883. At the same time, the first evidence of detonation was discovered in 1879-1881 by Marcellin Berthelot and Paul Vieille this was immediately confirmed in 1881 by Mallard and Le Chatelier. In 1899-1905, David Chapman and Emile Jouguet developed the theory of deflagration and detonation and calculated the speed of detonation. In 1900, Paul Vieille provided the physical explanation of detonation... 

Nakaya, S., et al., A numerical study on early stage of flame kernel development in spark ignition process for methane/air combustible mixtures, Trans. Jpn. Soc. Mech. Eng.(B), 73-732, 1745,2007 (in Japanese). 

The propagation of premixed flames in closed vessels has been a subject of combustion research since its inception as a defined field of study in the late 1800s, when Mallard and LeChatelier [1] explored the behavior of explosions in the tunnels of coal mines. In the early decades of the twentieth century, experimenters used streak cameras to monitor the progress of premixed flame fronts propagating in tubes and channels without... 

As briefly discussed in Section 1.2, chemical-reaction engineers recognized early on the need to predict the influence of reactant segregation on the yield of complex reactions. Indeed, the competitive-consecutive and parallel reaction systems analyzed in the previous section have been studied experimentally by numerous research groups (Baldyga and Bourne 1999). However, unlike the mechanical-engineering community, who mainly focused on the fluid-dynamics approach to combustion problems, chemical-reaction... 

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