ABSTRACT
Many practical combustor systems such as boilers, gas turbines, diesel engines, rockets, etc., use condensate fuels (liquid and solid fuels) as the energy source. Combustion intensity is then controlled by gasification, mixing, and chemical kinetics processes. The condensate fuel is atomized or pulverized into smaller droplets or particles to increase the surface area of fuel exposed to the hot gases in order to facilitate rapid gasification and mixing with the oxygen-rich ambience; e.g., rocket engine: d
≈
µ
m, diesel engine: 20
µ
m, gas turbines: 30 to 60
µ
m (SMD), and oil-fired heaters: 75
µ
m. The atomization leads to improved ignition and combustion characteristics. Spray ignition and combustion studies are extremely important to determine flame stability behavior at widely varying loads, ensure efficient utilization of fossil energy, and better understand the mechanisms of pollutant formation and destruction. Extensive fundamental and applied research has been conducted on the combustion of oil sprays and pulverized-fuel-particle sprays. Sprays normally involve a large number of drops. Both heterogeneous (drop combustion either in groups or arrays or individually) and homogeneous (small drops less than 10
µ
m) combustion can occur in a spray. The simplest method of analysis is to treat the fuel spray as an aggregate of fuel droplets. Isolated-drop ignition and combustion studies have been conducted in the last three decades. The reader should refer to the extensive reviews and publications by Law [1976,1978], Law and Law [1982,1980], Law et al. [1980], Faeth [1977], Hedley and Williams, and on moving drops, by Ayyaswamy [1989]. Simple drop or particle models yield parameters controlling the combustion characteristics of individual drops or particles. Thus, the spray combustion rate could be estimated to be the sum of combustion rates of isolated drops if interactions between drops are
ignored. However, a drop in the spray does not behave like an isolated drop, because its behavior will be modified owing to the presence of other drops. These interactions will be treated in Chapter 16.
