Fuel air ratio control

The discussion below will focus briefly on the design of the graphic displays in order to illustrate the methodology used. The aim of the furnace operation (see Figure 7.15) is to achieve a specified output temperature of the crude oil. This is done by means of a master temperature controller which regulates the pressures of the fuels used. An air/fuel ratio controller regulates the flow of the combustion air, receiving as input the flow rates of the fuels... 

The development of reliable zirconia cells which can measure the gas analysis in situ without recourse to gas-sampling techniques has led to systems which provide feedback to the air/fuel ratio control system. 

A. J. Beumont, A. D. Noble, and A. Scariobrick, "Adaptive Transient Air Fuel Ratio Control to Minimize Gasoline Engine Emissions," Fisita Congress, London, 1992. 

Chemical Sensors for Oxygen Detection and Air/Fuel Ratio Control... 

In order to provide the proper stoichiometrically balanced exhaust gas composition required for use of the three-way catalyst, an air/fuel ratio control system had to be developed for the vehicle. Closed-loop electronic air-fuel ratio control required the installation of an exhaust oxygen sensor and an on-board microprocessor to provide the necessary control capability. 

The operation of warmed-up automotive three-way catalysts is considered. Special emphasis is given to the observation that significant fractions of CO, hydrocarbon, and NO emissions in urban driving tests occur during vehicle acceleration. The increased emissions during acceleration occur as a result of increased exhaust flow rates and rich air-fuel ratio excursions of the air-fuel ratio control system. A method is presented for displaying and analyzing... 

Fig. 2. Comparision of air-fuel ratio control, exhaust flow rate, and CO and NO emission rates during constant speed driving and variable speed driving through a selected segment of a U.S. FTP test (ref.4).

The use of zeolite-hosted semiconductor oxides as chemicai sensors towards oxidizing or reducing gases might be attractive. Since the alteration of the conductivity depends on changes of the oxide stoichiometry [93,94], shorter diffusion distances in smaller clusters should result in shorter response times of the sensors. Fast response is a prerequisite for the application of sensors based on changes of the bulk composition, e.g. in air/fuel ratio control devices. 

Take safety Close burner valve and inject Burner flame has been Steam injection for y Forgets to put air/fuel ratio control and furnace... 

Use a quality air/fuel ratio controller set as close to stoichiometric as practical, but erring on the oxidizing side (because dross is easier to remove than absorbed hydrogen)... 

Sensible heat carried out of the furnace by the furnace gases (poc) is often the largest loss from high-temperature furnaces and kilns. It is evaluated by the available heat charts mentioned in section 5.1 100% — %available heat = %heat carried out through the flue. It can be reduced by careful air/fuel ratio control, use of oxy-fuel firing, and good furnace pressure control. 

Air/fuel ratio control also prevents excessive lean burning, which results in extra unused air passing through the furnace, absorbing heat, and carrying that heat out the flue, unabsorbed by the loads. Chapter 7 of reference 52 describes how a variety of air/fuel ratio control systems work and how to evaluate the savings from their use. 

Air/Fuel Ratio Control. Air flows may differ to burners in parallel in the same zone on the inside and outside of a rotary hearth furnace donut because of the long runs of air duct and the large number of tees and elbows. High design air velocity creates very different air flows to burners in a zone. One such furnace was designed for an air flow of 70 ft/sec (21 m/s) with three elbows and four tees to each burner. The fan s discharge pressure was 14"wc (3.5 kPa), but the pressure delivered to one burner... 

If the furnace will have sophisticated automatic air/fuel ratio control, and is constructed with a steel outer shell so that tramp air will be minimal—say 5% excess air, then extrapolating at 5% XS air from figure 5.1 at 2060 F flue gas exit temperature and 400 F preheated air, read 49% available heat. 

Find The %fuel saved by preheating the air to 900 F (427 C) (using an air temperature compensator in the air/fuel ratio controller to continue to hold only 10% excess air at all firing rates). 

The chain of command for air/fuel ratio controls is usually as follows The burner or zone input control responds to a T-sensor (or steam pressure sensor in the case of a boiler). The burner input control (also termed furnace input control, kiln input control, etc.) may actuate a burner or zone air valve ( air primary air/fuel ratio control ) or a burner or zone fuel valve ( fuel primary air/fuel ratio control ). Air primary air/fuel ratio control is more common with smaller burners. Many problems are avoided if each burner is equipped with its own ratio control. Where multiple burners are ganged in parallel downstream from a single air/fuel ratio control, if one burner has a problem with its ratio, all parallel burners of that zone will have the opposite difficulty, the intensity of which will be divided by the number of burners in the zone. 

Furnaee engineers and operators must understand the many aspects of air/fuel ratio control for safety and for equality. Mass flow control is essential if the combustion air is preheated. Changing air temperature affects the weight of air passing through... 

The upper time-line diagram of figure 6.11 shows a burner startup situation where the air/fuel ratio control has erroneously been set too rich. The burner may have lighted as it entered the flammable zone (about 5% gas in a gas-air mixture, for natural gas), but its mixture soon became too rich to burn, exceeding the upper limit of flammability (about 15% gas in a natural gas-air mixture), exiting the flammable zone, with the flame going out. The pilot has its own controlled air and fuel supply, set at an air/fuel ratio between the flammability limits thus, it stays lighted even... 

Oxides of iron, aluminum, copper, zinc, and glass often form on their molten surfaces, becoming inclusions in the final casting, probably causing it to be a reject. It is therefore desirable to minimize excess oxygen in contact with a molten metal bath thus, a quality air/fuel ratio controller can be a major help in controlling product quality. 

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