Fuel control strategies

A lean NOx trap (LNT) (or NOx adsorber) is similar to a three-way catalyst. However, part of the catalyst contains some sorbent components which can store NOx. Unlike catalysts, which involve continuous conversion, a trap stores NO and (primarily) N02 under lean exhaust conditions and releases and catalytically reduces them to nitrogen under rich conditions. The shift from lean to rich combustion, and vice versa, is achieved by a dedicated fuel control strategy. Typical sorbents include barium and rare earth metals (e.g. yttrium). An LNT does not require a separate reagent (urea) for NOx reduction and hence has an advantage over SCR. However, the urea infrastructure has now developed in Europe and USA, and SCR has become the system of choice for diesel vehicles because of its easier control and better long-term performance compared with LNT. NOx adsorbers have, however, found application in GDI engines where lower NOx-reduction efficiencies are required, and the switch between the lean and rich modes for regeneration is easier to achieve. 

Both of the vehicle-aged catalysts were driven a total of 80,450 km on the AMA 223 durability driving cycle. Note, however, that the vehicles were different makes - the Pt/Rh catalyst came from a 1990 5.0L Crown Victoria, while the Pd/Rh catalyst came from a 1989 3.8L Thunderbird. Despite the same durability schedule, the thermal histories of the two catalysts may have been quite different due to differences in engine load factors, catalyst mounting locations, air-fuel control strategy, etc. Consequently, no conclusions can be drawn regarding the relative sintering rates of Pt/Rh and Pd/Rh TWCs. 

Schemes to control the outlet temperature of a process furnace by adjusting the fuel gas flow are shown in Figure 13. In the scheme without cascade control (Fig. 13a), if a disturbance has occurred in the fuel gas supply pressure, a disturbance occurs in the fuel gas flow rate, hence, in the energy transferred to the process fluid and eventually to the process fluid furnace outlet temperature. At that point, the outlet temperature controller senses the deviation from setpoint and adjusts the valve in the fuel gas line. In the meantime, other disturbances may have occurred in the fuel gas pressure, etc. In the cascade control strategy (Fig. 13b), when the fuel gas pressure is disturbed, it causes the fuel gas flow rate to be disturbed. The secondary controller, ie, the fuel gas flow controller, immediately senses the deviation and adjusts the valve in the fuel gas line to maintain the set fuel gas rate. If the fuel gas flow controller is well tuned, the furnace outlet temperature experiences only a small disturbance owing to a fuel gas supply pressure disturbance.

Both control schemes react in a similar manner to disturbances in process fluid feed rate, feed temperature, feed composition, fuel gas heating value, etc. In fact, if the secondary controller is not properly tuned, the cascade control strategy can actually worsen control performance. Therefore, the key to an effective cascade control strategy is the proper selection of the secondary controlled variable considering the source and impact of particular disturbances and the associated process dynamics. 

Fouling organisms attach themselves to the underwater portions of ships and have a severe impact on operating costs. They can increase fuel consumption and decrease ship speed by more than 20%. Warships are particularly concerned about the loss of speed and maneuverabiHty caused by fouling. Because fouling is controUed best by use of antifouHng paints, it is important that these paints be compatible with the system used for corrosion control and become a part of the total corrosion control strategy. 

The DPF regenerations done by specific engine control strategies lead to a fuel overconsumption. 

To regenerate the NOxTrap, the engine must create rich conditions in the exhaust line and the car manufacturers must deal with specific engine control strategies to increase the reductant quantity (H2, CO and HC). These strategies lead to fuel over-consumption. 

To accommodate the wide variations in fuel moisture content while maintaining close bed temperature control, two control strategies are used. 

Without doubt, the top-priority application of air quality models is the determination of emission controls needed to achieve ambient air quality standards. With the re-examination of transportation control strategies and with the pressures of fuel substitutions, refinements well bqrond the traditional proportional models are imperative. Where validated diffusion models are available, they should be used to recalculate the emission requirements that came from initial hasty efforts to implement the Qean Air Act Amendments of 1970. This is the greatest national service that could be performed by the air quality modelers at present. Before this can be achieved, however, the institutional apparatus must provide the impetus and resources called for in a recent National Academy of Sciences report to the U.S. Senate. 

Combustion control is currently a hot area of research in the U.S. and abroad. In addition to basic research at a number of universities, joint industry-university S T efforts are also underway to implement the control strategies developed by researchers in industry applications. Though some of the demonstrations have been made using gaseous fuels, the techniques can be extended to liquid fuels as well, and efforts are underway to accomplish this. It is hoped that future engines will perform equally well in off-design conditions, with improved reliability and easier maintenance, and reduced operational costs. 

Active control was implemented by imposing the oscillations at the dominant frequency but with a difference in phase, and the control strategy was similar to that of [8] and only essential details are provided here. The actuators used to impose oscillations on the flow of fuel have been characterized in [f4], and the details given here are limited to those most relevant to the present experiments. 

Hence, a feasible control strategy should be the use of fuels with smaller mass emissions, reduced reactivity of the emissions, or both. We discuss briefly some of the chemical implications of the use of some of these alternate fuels. For a more comprehensive treatment of the advantages and disadvantages of alternate fuels and technologies, see the National Research Council report (1991), and for a discussion of a variety of issues associated with motor vehicle emissions, see Cadle et al. (1996, 1997a, 1997b) and Chang et al. (1991). 

The control systems for CNG refueling systems have evolved from being only mechanically controlled to some that are completely computer controlled today. Computer control offers flexibility not possible with mechanical systems and the ability to change the control strategy of the refueling system. Computer-controlled systems can also provide functions such as accounting of the amount of fuel dispensed into vehicles and billing functions. It is also possible to incorporate safety shut-down of the system if certain conditions are present. 

To perform simulation and optimisation of a power system using the HOMER tool, information and data on natural resources (such as wind and solar irradiance data), electric and thermal loads, economic constraints, current and future equipment costs, user behaviour and control strategies are required. The main purpose of the techno-economic analysis presented in this chapter was to investigate the impact of diesel generators and batteries replacement with hydrogen technologies, including fuel cells both in technical and financial terms. 

Catalytic converters were first installed in U.S. cars in 1976.20 21 They were passive devices in that they were simply placed in the exhaust with no communication with the engine or its control strategy. It catalyzed the oxidation of the unburned hydrocarbons (CyHn) and carbon monoxide (CO) emitted during the incomplete combustion of the fuel. In some vehicles excess air was pumped into the exhaust to ensure sufficient oxygen to complete the catalytic oxidation. This resulted in about a 90% reduction of these two pollutants relative to the uncontrolled uncatalyzed vehicle. 

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