Pressure drops Combustion chamber

Smoke (carbon) formation, which apparently is due to incomplete combustion of portions of the fuel-air mixture (i.e., rich combustion), also can pose a serious public relations problem at civilian airports and, by radiant-heat transfer from incandescent carbon particles, can shorten the endurance life of combustion-chamber liners and adjacent parts (0). Smoke would also constitute a serious problem in the case of automotive gas turbines, because accumulation of carbon and other nonvolatile fuel components on the intricate passages of the heat exchanger could reduce turbine and heat-exchanger efficiency by reducing heat-transfer rate and increasing the pressure drop across the... 

Combustion is completed in the chamber and takes place at constant pressure. This simplification must be made because these factors depend upon motor design and not on the propellant system. The pressure drop can be calculated readily when necessary. 

The research was conducted in a cold-flow combustor test rig simulating the exact geometry of the hot combustion rig. This test rig (Fig. 10.1) is set up vertically. The air is introduced at the bottom and is conditioned through an air conditioning section which is composed of perforated cone, screens, and honeycomb is settled in 3.8-inch diameter circular chamber is fed into TARS and then exits to the atmosphere. The pressure drop across TARS is 4%. The TARS features three separate airflow passages and independent liquid fuel supply lines that can be controlled separately (Fig. 10.2). 

Since the flow pressure drop coefficient is twice the Euler number (Equation 10.12), a constant Euler number indicates that the pressure drop coefficient remains a constant at and beyond the critical Reynolds number. However, the critical Re)molds number that ensures selfsimilar flow state is system specific. As a general guide, for combustion air ductwork and FGR ducts, Re, should be maintained at > 5 x 10. For burners and combustion chambers, the recommended Re, is > 2 x 10 . 

Combustion air supply for inductive burners is similar to combustion air supply for natural suction burners. However, the draft in a combustion chamber is created by flue gas fan. This method is used whenever there is insufficient natural suction or if a pressure drop disables suction of a sufficient amount of combustion air (e.g., fhrough convective heat exchangers, filters, etc.). Installation of burners with an inductive supply of combustion air as opposed to natural draft burners is less common. 

A basic requirement of burner combusting liquid fuels is a high-quality fuel atomization [9], necessary for complete evaporation and burnout in the area of the flame. If some fuel drops are not evaporated and combusted in the area of flame, concentrations of carbon monoxide and unburned hydrocarbons (UHCs) in flue gas increase rapidly. For the above mentioned reason most liquid fuel burners are designed as diffusion burners with fuel atomized in the combustion chamber. The fuel atomization system itself is rather dependent on physical and chemical properties of fuel and availability of auxiliary atomizing medium. Thus there are three basic types of atomization [10] (i.e., pressure, pneumatic, and rotary atomization). Besides these, there are other, less frequent types of atomization using vibrational, acoustic, ultrasonic, and electrostatic atomizers or flash liquid atomization. 

Aqueous wastes contain oxidizable compounds within a liquid water stream and may be endothermic or exothermic depending on the concentration of oxidizable compounds. Proper atomization of fhe liquid stream is probably the most critical aspect of handling aqueous wastes. This is because the droplet must be small enough to be capable of completely evaporating within the thermal oxidizer chamber and still allow for sufficient residence time to oxidize the combustible compounds. The fluid nozzle, pressure drop, and atomization fluid (e.g., air or steam) demand (if dual fluid atomization is used) should be matched to what is used in the field to obtain a meaningful simulation. 

The Support - To avoid pressure drop and have a large geometric surface, honeycomb-shape monoliths are used in the gas turbine combustion chamber. The desired properties of the support are ... 

Effect of ducting pressure drop and combustion chamber pressure drop... 

Effect of Ducting Pressure Drop and Combustion Chamber Pressure Drop... 

Between the ontlet of the compressor and the inlet to the turbine there is a small pressure drop caused by the presence of the combustion chamber and the throttling effect of its casing. Let this pressnre drop be AP23. 

For the turbine there are three pressure drops to consider. One for the compressor discharge AP2, one for the practical throttling effect in the combustion chamber AP23 and one for the turbine exhaust pressure due to ducting AP4. The two pressure drops at the inlet to the turbine can be combined as,... 

First, we shall use a quasi-stationary approach already mentioned earlier, based on the assumption that characteristic times of heat and mass transfer in the gaseous phase are much shorter than in the liquid phase, since the coefficients of diffusion and thermal conductivity are much greater in the gas than in the liquid. Therefore the distribution of parameters in the gas may be considered as stationary, while they are non-stationary in the liquid. On the other hand, small volume of the drop allows us to assume that the temperature and concentration distributions are constant within the drop, while in the gas they depend on coordinates. Another assumption is that the drop s center does not move relative to the gas. Actually, this assumption is too strong, because in real processes, for example, when a liquid is sprayed in a combustion chamber, drops move relative to the gas due to inertia and the gravity force. However, if the size of drops is small (less than 1 pm) and the processes of heat and mass exchange are fast enough, then this assumption is permissible. As usual, we assume the existence of local thermodynamic equilibrium at the drop s surface, as well as equal pressures in both phases. The last condition was formulated at the end of Section 6.7. 

Under ideal operating conditions, the compressions 0-2 and 2-3 are supposed to be isentropic, and so are the expansions 4-5 and 5-7. In practice, the two compressions (0-2 and 2-3) and the two expansions (4-5 and 5-7) are not isentropic. During the actual combustion, there is a pressure drop in the combustion chamber (P4 < P3). The temperature of the gases feeding the turbine lies between 1000 and 1600 K to avoid it being damaged. 

A number of papers have been published [5.5,6] about the complex equilibria resulting from the different sulfur modifications these papers show that complete reaction of the sulfur components to elemental sulfur cannot be expected until the temperature is reduced to less than 140° C. Figure 5.9 shows the sulfur yield versus temperamre at an overall pressure of 1 bar. It is obvious that the conversion rate drops in the area of purely thermal incineration (combustion chamber) and then rises steeply again as the temperatures decrease. As the reaction velocity is very small at temperatures of less than 350° C, catalysts have to be used for low temperatures. Reactions in this temperature range are accelerated by highly active AI2O3 catalysts which are normally doped with cobalt and molybdenum to improve CS2 and COS conversion. 

Typically, pulse combustors operate at frequencies from 20 to 250 Hz. Pressure oscillation in the combustion chamber of 10 kPa produces velocity oscillation in the tailpipe of about 100 m/s, so the instantaneous velocity of a gas jet at the tailpipe exit varies from 0 to 100 m/s (Keller et al., 1992). Although pulse combustors deliver flue gases at a higher pressure than the inlet air pressure, the resulting increase in stagnation pressure is relatively small. This restricts practical applications of pulse combustors to the systems where pressure drop is not critical. The amplitude of the pressure rise may vary from 10% (domestic heating applications) to 100% as for heavy-duty pulse combustors for industrial use (Kentfleld, 1993). The output power for commercially available pulse combustors ranges from 70 to 1000 kW. 

Analysis procedures for Brayton cycles are similar to the previous examples of Rankine cycles with the exception that properties are determined from gas fables. The gas turbine in Figure 23.21 is analyzed using air standard assumptions, which consider the working fluid to be air and treat combustion as a heat addition process. A more accurate analysis could employ tables that account for combustion products, such as Keenan and Kay (1960). The heat to the combustion chamber is assumed to be available at 2500°F. In the example, air from the dead state (14.7 psia, 75°F) enters the intake structure. Pressure drops before the turbine inlet in the intake ducting to 14.5 psia. It is compressed in a compressor with a... 

Table 23.3 summarizes the conditions at each state point. (Points 2s and 4s represent points the conditions for isentropic processes input properties in the table are underlined.) Point a is at atmospheric conditions (the dead state). Point 1, the compressor inlet, is reached after the atmospheric air undergoes a throttling process (constant enthalpy) and experiences a 0.2 psi pressure drop, and point 2s would be achieved in an isentropic compressor. The ratio of the reduced pressure equals the ratio of the actual pressures for an isentropic process. In point 2, the enthalpy is calculated from the compressor isentropic efficiency. In the combustion chamber, the pressure drops 2 psi and the temperature is increased to 1800°F. Point 4s and 4 are analyzed similarly to 2s and 2. Finally, the pressure drops to point 5 where the air enters the atmosphere. The accompanying h-s (or T-s) diagram shows the cycle and includes all of the pressure drops and turbine and compressor inefficiencies. 

The air blower produces a pressure of about 0.3 bar above atmospheric pressure and this is sufficient to push the air and all of the product gases formed through the drying tower, the combustion chamber, the reactor, the absorbers, the filters in the top of the absorbers and up the chimney stack at the end of the plant. Quite clearly, techniques to calculate pressure drops are important because the correct sizing of the inlet air blower is vital. 

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