Combustion cycle

A second type of CRGT plant involving modification of the fuel before combustion (Cycle B3) is shown in Fig. 8.14. Now some part of the exhaust from the turbine (which contains water vapour) is recirculated to the reformer where the fuel is modified. Thus this FG/TCR cycle has an element of the semi-closed cycle plus modification of the combustion process. The chemical process involved in this cycle has been described in Section 8.5.4, but there is now no simple comparison that can be made between the FG/ TCR cycle and the basic STIG cycle, as de.scribed in Section 8.6.2.1. 

Fuel cells such as the one shown on Fig. 3.4a convert H2 to H20 and produce electrical power with no intermediate combustion cycle. Thus their thermodynamic efficiency compares favorably with thermal power generation which is limited by Carnot-type constraints. One important advantage of solid electrolyte fuel cells is that, due to their high operating temperature (typically 700° to 1100°C), they offer the possibility of "internal reforming" which permits the use of fuels such as methane without a separate external reformer.33 36... 

Volume changes also can be mechanically determined, as in the combustion cycle of a piston engine. If V=V(i) is an explicit function of time. Equations like (2.32) are then variable-separable and are relatively easy to integrate, either alone or simultaneously with other component balances. Note, however, that reaction rates can become dependent on pressure under extreme conditions. See Problem 5.4. Also, the results will not really apply to car engines since mixing of air and fuel is relatively slow, flame propagation is important, and the spatial distribution of the reaction must be considered. The cylinder head is not perfectly mixed. 

Substances applied to or incorporated in a combustible material (e.g. organic polymers, nylon, vinyl and rubber, etc.) to reduce flammability. Act by retarding ignition, control/douse burning, reduce smoke evolution. Slow down or interrupt the self-sustained combustion cycle when the heat-flux is limited. Flame retardants (FRs) improve the combustion behaviour and alter the combustion process (cool, shield, dilute, react) so that decomposition products will differ from nonflame retarded articles. FRs are usually divided into three classes ... 

For direct injection of hydrogen, the power density is roughly 120% that of an equivalent gasoline engine. Because of the easy combustion property, researchers are experimenting with a multiple injection approach, where hydrogen is injected directly into the cylinder once or twice during each combustion cycle [25,28,36]. 

The operation of the reciprocating internal combustion engines represents a compromise between the Otto and the Diesel cycles, and can be described as a dual combustion cycle. Heat transfer to the system may be considered to occur first at constant volume and then at constant pressure. Such a cycle is called a dual cycle. 

When the combustion cycle takes place, the components, hydrogen and oxygen, recombine to once again form water molecules. Thus only water and extra air exit the exhaust pipe. Next, being that this water is in a highly excited state, very hot steam, it exits as something similar to very moist air. Ever driven your car in the rain Doesn t kill or rust it does it And there you have a car that runs on water. Just needs the right modifications performed. 

Thus, it is evident that as of the early 1980s, the panacea for stack gas treatment was yet to be realized. Difficulties in treating stack gases have provided incentives at the other end of the combustion cycle, namely, in the treatment of the fuels prior to combustion. Various means for treating coal are described in detail in the entry on Coal and desulfurization of petroleum fuels is described under Petroleum. 

After combustion furnaces have come to thermal equilibrium, turn combustion cycle control to START and let it proceed normally through the cycle. Observe indicated temperature on pyrometer of both upper and lower combustion furnaces at the end of the combustion portion of cycle. 

Add 2 min more to combustion portion of cycle by turning auxiliary timer to setting 3. Turn combustion cycle control to START. Let analyzer proceed through its cycle. After cycle is complete and combustion cycle control has entered STAND-BY... 

In petrol engines the internal EGR concept is often implemented. This involves adjusting the exhaust valve timing so that some of the combusted gas is trapped in the cylinder [16]. This residual gas acts as a diluent for the next combustion cycle, hence lowering the combustion temperature. Internal EGR can only reduce NOx slightly, because no more than 5-10% of the exhaust gas can be trapped without significantly affecting combustion. 

Then, the influences by which the presence of oxygen can affect these processes are discussed. The different structures of the various polymer types influence the end consequence of any decomposition, and this may affect the resistance, if any, to combustion. At this point, the polymer combustion cycle will be described. 

FIGURE 2.2 Schematic representation of the polymer combustion cycle main approaches to flame retardancy are shown in italics. 

This scheme may now be used to understand how different flame-retardant strategies may be designed and adopted to break the combustion cycle. For a given polymer, the strategy to be adopted will be largely dictated by its particular thermal degradative chemistry, which has been briefly reviewed in Section 2.3 earlier, for all the significant polymer types. 

FIGURE 4.1 Self-sustained polymer combustion cycle. 

The burning rate (kg fuel/h) is not constant over the combustion cycle. However, since a fan is used for the air supply to the boiler the actual flue gas flow does not vary too much with time. Based on calculations from the total fuel consunqition and oxygen content in the flue gas and on measurements using a Prandtl-tube in the chimney, the average flue gas flow was estimated to be 100 m /h. 

The catalyst starts to deactivate immediately when it is exposed to the flue gases. The activity has an exponential decline versus the numbers of combustion cycles, Figure 3. The conversion falls from 80 % down to 40 %, after 17 cycles, were it seems to level... 

Figure 3 The conversion of CO over 12 nets, fresh and regenerated net-catalyst, versus the number of combustion cycles.

When the catalyst is exposed to the flue gas in a biofuel-fu ed boiler, it starts to deactivate immediately. The conversion (figure 3) declines exponentially from 80% down to about 40 %, where it seems to levels out, after about 17 combustion cycles. The reason for the deactivation is a loss of specific surface area. Washing in a water solution of citric acid can restore this area and the activity (ftgure 3 and 4). The catalyst cannot be restored by thermal treatment, at least not by heating to 700-800°C. This means that the poison is non-organic and easily soluble in slightly acidic solution compound, probably a salt. 

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