Local burning rate

Equation (54) gives the local burning rate in physical variables. The ratio (Po oV(Poo oo) is local dimensionless burning rate or mass-transfer coefficient. An average dimensionless burning rate for a plate of length / can be defined as... 

One of the most challenging aspects of modeling turbulent combustion is the accurate prediction of finite-rate chemistry effects. In highly turbulent flames, the local transport rates for the removal of combustion radicals and heat may be comparable to or larger than the production rates of radicals and heat from combustion reactions. As a result, the chemistry cannot keep up with the transport and the flame is quenched. To illustrate these finite-rate chemistry effects, we compare temperature measurements in two piloted, partially premixed CH4/air (1/3 by vol.) jet flames with different turbulence levels. Figure 7.2.4 shows scatter plots of temperature as a function of mixture fraction for a fully burning flame (Flame C) and a flame with significant local extinction (Flame F) at a downstream location of xld = 15 [16]. These scatter plots provide a qualitative indication of the probability of local extinction, which is characterized... 

Some considerations relevant to public health concerns about modern and effective incineration systems have been described. However, local health officials and citizens of communities with hazardous waste incinerators have expressed to ATSDR their concern that they may not be able to judge a good operation, or that, once the initial trial burns and inspections are completed, the system may not be operated in the same manner as during the testing phase. Citizens have also expressed concern that burning rates will be exceeded or monitoring systems will be overridden. 

The soot temperature was found to exceed the gas temperature as measured by thermocouples in the absence of droplet injection but decayed at a similar rate. This is attributed to bulk heating effects associated with the localized burning of vaporized material. A detailed diffusion flame calculation for a cylindrical source of reactants and relative velocity on the same order as these experimental data, indicate that this bulk heating effect is reasonable. 

Specific examples of such bistable behavior arise in models of combustion. In the simplest case, a two-component system, that includes the distribution of the fuel and of the temperature field, is appropriate. The reaction takes place only when the temperature is above a certain ignition temperature, with a burning rate that is an increasing function of the local temperature following the Arrhenius law (Eq. (3.43)). The burning of fuel is an exothermic reaction that increases the local temperature and results in even higher reaction rates. This leads to the autocatalytic character of the system, while the ignition temperature acts as a threshold, responsible for the bistability. 

Pressure waves of local explosions can accelerate a preceding slower flame front leading to a sudden increase of burning rate and flame velocity,... 

Statistical information on strain-rate, curvature, local burning ratio and displacement speed along the flame surface explored in these simulations support earlier findings of Ref. 10. We refer to Ref. 8 for more details. 

In most cases, pool size is fixed by the size of the release and by local physical barriers (e.g., dikes, sloped drainage areas). For a continuous leak, on an infinite flat plane, the maximvun diameter is reached when the product of burning rate and surface area equals the leakage rate. 

The pool size must be defined, either based on local containment systems or on some model for a flat surface. Burning rates can be obtained from tabulations or may be estimated from fuel physical properties. Surface emitted flux measurements are available for many common fuels or are calculated using empirical radiation fractions or solid flame radiation models. An estimate for atmospheric humidity is necessary for transmissivity. All other parameters can be calculated. 

---