OCR Text |
Show KINETIC MODEL The kinetic model is mostly based on those for tetrachlormethane combustion in a methane/air mixture[ll] and the high temperature oxidation of l,l,l,trichloroethane [12]. The C|-C2 combustion model was from the work of Noto et al [13]. Also included in the data base are a number of reactions from the NIST Chemical Kinetics Data Base [14] and from a number of other sources. [15-18]. Altogether the model contains 632 reactions and 83n species. They include the following set of reactions. H/Cl species (CI, Cl2, HC1), H7C1/0 species (CIO, HOC1), Ci/Hx/Cly species, except CC1 radical, C,/H/Cl/0 species (CH2C10, CHCIO, C O C l 2 , COC1) C2/Hx/Cly species, except C2C1 radical. Oxygenated C 2 chlorohydrocarbon species and their reactions are not considered. The absence of experimental data prevents extensive tests. However, calculations of ignition delays with chlorohydrocarbon additives behind shock tubes show satisfactory agreement[19] Subsets of the model have however been tested [11,15,20] The fuel we chose was a mixture of ethylene and dichloromethane and was selected mainly to have the C/H ratio that is typical of a hydrocarbon fuel. The ratio of fuel and chlorine compound was set at 2 % which is not too far from that found in waste mixtures. The Chemkin suite of program was used. The specific subroutines excerised were those for a steady premixed flame and a plug flow reactor, RESULTS Since the present interest is in the consequences of imperfections in combustion systems, there is an almost infinite set of scenarios that should be investigated. In the following w e report on the results of a few test cases. The present work must therefore be consider an initial exploratory attempt at determining the key parameters that should be considered. The main intention is to lay the basis for further work. Figure 1 contains plots of the concentration profiles under lean conditions upon the passage of the flame front across the mixture. The flame speed was about 15 cm/sec. Thus the time scale is of the order of milliseconds. At the flame front there is the expected sudden increase in temperature and the corresponding decrease in fuel and oxygen concentration. Water, HC1 and C O and subsequently carbon dioxide all show large increases as one traverses the flame front and are the expected main products. Of particular interest is the behavior of the organics. As the fuel, ethylene, is consumed, acetylene, the next breakdown product, concentration increases through a maximum and then is ultimately destroyed as it must be in a lean system. Chlorinated organics are formed immediately behind the flame front. However at the high temperature where the fuel is ignited its concentration is never very high and they are rapidly destroyed. It will be |