Secondary air injection

Serious research in catalytic reduction of automotive exhaust was begun in 1949 by Eugene Houdry, who developed mufflers for fork lift trucks used in confined spaces such as mines and warehouses (18). One of the supports used was the monolith—porcelain rods covered with films of alumina, on which platinum was deposited. California enacted laws in 1959 and 1960 on air quality and motor vehicle emission standards, which would be operative when at least two devices were developed that could meet the requirements. This gave the impetus for a greater effort in automotive catalysis research (19). Catalyst developments and fleet tests involved the partnership of catalyst manufacturers and muffler manufacturers. Three of these teams were certified by the California Motor Vehicle Pollution Control Board in 1964-65 American Cyanamid and Walker, W. R. Grace and Norris-Thermador, and Universal Oil Products and Arvin. At the same time, Detroit announced that engine modifications by lean carburation and secondary air injection enabled them to meet the California standard without the use of catalysts. This then delayed the use of catalysts in automobiles. 

Figure 6.9 Temperature distribution along an enclosed flame centerhne for different control conditions 1 — low soot, no secondary air 2 — low soot, with secondary air injection 3 — high soot, no secondary air and 4 — high soot, with secondary air injection...

In enclosed combustors, external air is not readily available at the flame base and the gases entrained at this region are t3rpically burned, air-depleted reaction products. The possibility to recover the control authority by the secondary air injection at the flame base is important for... 

The lean operating boundary shown in Figure 1 (to its interception of the lean limit line) represents the line of constant turbine inlet gas temperature (1407 K or 2073°F) typically required for cruise power. This boundary line shows that there is a minimum allowable premixed equivalence ratio that satisfies power requirements. But, since air-film cooling and perhaps secondary air injection for temperature pattern factor adjustment (at the turbine inlet) will be required in an engine combustor, the useful lean boundary will lie possibly 20-30% to the right of that shown. Cooling requirements should be much reduced from current practice because of the ultralean (cooler) burning zone. 

There is a secondary air injection. It decreases the tar content in the produced gas (23). Total air is split thus m primary and secondary air flows (there would be a possibility for a tertiary air injection). Besides, it is considered that both primary and secondary air flows are well (homogeneously) distributed along with cross-sectional area of the gasifier. 

The comparison of the different concentration levels for the respective measuring position shows a considerable reduction of the CO concentration between the positions 11 and 9 which is possibly due to the effect of the secondary air injection by the three nozzles, see Figure 5. The marginal differences of CO concentration for the positions 6 and 9 can be put down to differences during the two test burn cycles. For the positions 6 and 9 the subdivision into the different burn phases is not as obvious than for the position 11. 

The comparison of the velocity values shows that the characteristics as well as the computed and measured absolute values are in good accordance. The flow field characteristics in areas with high velocity gradients, for example the secondary air injection by the nozzles (z = -90 mm), are qualitatively well predicted. However, deviations between calculated and measured absolute velocity values can be found, especially for the prediction of the recirculation zone in the upper left part of the burnout zone (z = 100 mm). 

Prior to each test, the reactor was preheated to a temperature of SOO°C and primary air was preheated to 350 - 400°C. In combustion, secondary air injection was started immediately after initiating friel feed to the reactor. Temperature equilibrium and uniform temperature distribution were achieved typically within IS min from start. Sampling was conducted only after reaching steady operating conditions. 

All of these NOx-reducing reactions are much more rapid and effective than the catalyzed direct redox reaction (Eq. 3.9), and hence convert most of the NOx to innocuous gases. After NOx reduction, secondary air injection. 

Pd or Pt/Pd with other means of reducing NOx emissions, e.g. exhaust gas recirculation. This strategy normally entails a slightly lean tune and secondary air injection. The extent of NOx reduction is determined by driveability considerations, limiting applicability to less demanding requirements. 

Gasoline emission tests were conducted on a 1.6 1 Ford Escort car on a rolling road dynamometer. The vehicle was modified to incorporate secondary air Injection into the exhaust to ensure an exhaust composition which was consistently oxygen rich. The car was driven over the European ECE-15 test cycle, and throughout the cycle exhaust gas was sampled at a... 

Consider the circulating fluidized bed (CFB) boiler. Figure 1 where typical operating conditions might be 3-5 m/s up to the secondary air injection level and 5-8 m/s above that level at a bed temperature of 1,173 K. Coal with a top size of 6 mm is fed at the bottom of the bed consisting of coal-ash particles of mean diameter 0.3 mm. Entrained particles are collected in a cyclone and recycled to the combustor via a non-mechanical return valve. Part of the heat released from the carbon burning in the bed is extracted by water wall tubes placed in the furnace. The remaining heat leaves the furnace as sensible heat in the flue gas. 

Cho YJ, Namkung W, Kim SD, Park S. Effect of secondary air injection on axial solid holdup distribution in a circulating fluidized bed. J Chem Eng Japan 27 158 164, 1996. 

Kim J. Hydrodynamic behavior of solid transport for a closed loop circulating fluidized bed with secondary air injection. Korean J Chem Eng 16 840-842, 1999. 

Wang XS, Gibbs, BM. Hydrodynamics of a circulating fluidized bed with secondary air injection. In Basu P, Horio M, Hasatani M, eds. Circulating Fluidized Bed Technology III. Oxford Pergamon Press, 1991, pp 225-230. 

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