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Show conditions is correspondingly sparse. Consequently, modelling of flames, which is now extensive, has substantially outrun the experimental data-base that can be used to test and validate the modelling, particularly in the fuel rich region, although modelling is of little value without such validation. Herein lies the incentive for this paper. As a logical extension of our current studies of experimental and model-predicted behavior of p.c. flames, the importance of the fuel-rich region was as evident as was the lack of systematic information in this region as a target for the modelling studies. In the process of assembling the relevant information, obtained from our own past records, we found that there was a systematic pattern of experimental behavior that was clearly of value in its own right in addition to being a usefully- coherent description of behavior that, as a working data base, is independently valuable as a target for future modelling. Thus, presentation of this experimental pattern is the primary objective of this paper; but we also show that the pattern of behavior mostly follows some surprisingly simple theoretical considerations which alone have utility in immediate practical applications which, after all, is the primary incentive for coal combustion research. 2. EXPERIMENTAL METHODS The two experimental devices referred to in the Introduction are: the plug flow furnace [1-5]; and the high-intensity reactors [6,7] and furnaces [8-11]. 2.1 Plue-flow Furnace. Figure 1 illustrates the furnace in its most commonly- used form [3]. It is a vertical combustion tunnel of refractory brick, standing about 2.5 m high, of 64 mm (2.5") wall thickness, and of square crosssection, of 165 mm (6.5") on the side. The tunnel is topped by a cone with fuel and air supplied at the apex of the cone. For easier independent control of firing rate (fuel supply rate) and stoichiometry (air rate at fixed firing rate) the total air is split into conveying (primary) air and supplementary (secondary) air. The cone then has two functions: it provides for the total mixing of the primary and secondary streams at the apex of the cone by using opposed jets; and provides for expansion of the totally mixed cloud uniformly across the full width (165 mm) of the furnace proper. At the connec- |