Recirculating exhaust gases

B3 the Flue Gas/TCR cycle—mixing the fuel with partially recirculated exhaust gases containing water vapour. 

As the name implies, an EGR system recirculates a portion of the exhaust gases back into the intake manifold. The introduction of exhaust gases helps to reduce the temperature of hot spots, reducing the possibility of pre-ignition. Additionally, recirculating exhaust gases reduce the peak combustion temperature, which reduces NOx emissions. Typically a 25 to 30% recirculation of exhaust gas is effective in eliminating backfire. 

The high rates of NO, formation in hot zones surrounding the head vortex can be offset by introducing a diluent in the form of recirculated exhaust gas. 

For this purpose, in addition to the continuous evolution of CR and exhaust gas recirculation (EGR), novel primary measures are under study, including the long route EGR to cool the recirculated exhaust gas, the use of premixed combustion [which implies, however, higher GO and unburned hydrocarbon (U HG) emissions], the reduction of the compression ratio, the shaping of the injection rate and so on. Still, the after-treatment catalytic technologies for O, removal and for CO/hydro-carbon (HG) and particulate matter (PM) reduction in passenger cars must be improved significantly. 

The pressure of the vessel is controlled by a bypass valve that recirculates exhausted gas to the suction side of the vacuum source, giving the fast response that is required of the pressure loop to compensate for the varying vapor load to the condenser. Nevertheless, the contents temperature responds more slowly to pressure changes due to the time required to mix the surface with the vessel contents and the capacitance of the vessel. To decrease the response time, the contents temperature can be controlled by cascading the temperature to the pressure loop. The master temperature loop will then adjust the pressure set point at a rate commensurate with the temperature process response while maintaining the solution at the surface within the metastable zone the slave pressure loop will react to the pressure fluctuations during boiling. 

Heat and oil resistance coupled with its low swell have led automotive apphcations into laminated tubing and hoses (11) with this material. This resistance to the effects of ASTM No. 3 oil at service temperatures of 200°C makes it competitive with fluorocarbons and with the tetrafluoroethylene—propylene copolymer. Fluorosihcones are used to make exhaust gas recirculation (EGR) diaphragms for some passenger cars. 

The operating air/fuel mixture of the two-stroke engine designs range from 1.3 to 2.0 stoichiometric. This lean mixture plus the characteristic internal exhaust gas recirculation lowers the peak combustion temperatures and results in low NO formation. 

J. J. Gumbleton and co-workers, Optimifing Engine Parameters with Exhaust Gas Recirculation, SAE 740104, Society of Automotive Engineers, Warrendale, Pa., 1974. 

Effective with the 1982 model year, particulate matter from diesel vehicles was regulated by the U.S. Environmental Protection Agency for the first time, at a level of 0.37 gm km . Diesel vehicles were allowed to meet an NO level of 0.93 gm km under an Environmental Protection Agency waiver. These standards were met by a combination of control systems, primarily exhaust gas recirculation and improvements in the combustion process. For the 1985 model year, the standards decreased to 0.12 gm of particulate matter per kilometer and 0.62 gm of NO per kilometer. This required the use of much more extensive control systems (1). The Clean Air Act Amendments of 1990 (2) have kept the emission standards at the 1985 model level with one exception diesel-fueled heavy trucks shall be required to meet an NO standard of 4.0 gm per brake horsepower hour. 

Why might you expect exhaust gas recirculation on a diesel engine to increase the particulate matter emissions ... 

Fig. 8.7 shows a second example (Cycle A2) of carbon dioxide removal by chemical absorption from a CCGT plant, but one in which the semi-closed concept is introduced— exhaust gas leaving the HRSG is partially recirculated. This reduces the flow rate of the gas to be treated in the removal plant, so that less steam is required in the stripper and the extra equipment to be installed is smaller and cheaper. This is also due to the better removal efficiency achievable—for equal reactants flow rate—when the volumetric fraction of CO2 in the exhaust gas is raised from the 4-6% value typical of open cycle gas turbines to about 12% achievable with semi-clo.sed operation. 

Manufacturers added exhaust gas recirculation (EGR) systems to counter the increased in-cylinder NO. formation associated with higher operating temperatures. The EGR recycles a portion of the exhaust stream back into the engine intake air. The relatively inert exhaust gas, containing carbon dioxide and water but little oxygen, serves as a combustion buffer, reducing peak combustion temperatures. 

The strict control of oxides of nitrogen required for 1976 cars can be partially met by operating the engine with rich mixtures, and by using spark retardation and exhaust gas recirculation (EGR) to reduce the peak... 

Embedded in such models, in which variations were developed [12] are further detailed. The laminar burning velocity is expressed as a function of fuel type, fuel/ air ratio, level of exhaust gas recirculation, pressure, temperature, etc. Furthermore, submodels have been developed to describe the impact of engine speed, port-flow control systems, in-cylinder gross-flow motion (i.e., swirl, tumble, squish), and turbulent fluctuations u. Thus, with a wider knowledge base of the parametric impact of external variables, successful modeling of... 

Variations of flame temperatures with exhaust-gas recirculation. Flame temperature maps are obtained by processing images obtained from a combustion chamber of a heavy-duty diesel engine using two-color pyrometry. Images are taken at 2° after the TDC at 1200rpm low-load condition. 

Jacobs, T., Filipi. Z., and Assanis, D., The Impact of Exhaust Gas Recirculation on Performance and Emissions of a Heavy-Duty Diesel Engine, SAE, 2003-01-1068, 2003. 

Figure 1.1. General trend of the NOx and particulate emissions in Europe, Japan and the U.S. for light- and medium-duty engines (ESC test cycle) and effect of engine tuning on NOx/particulate emissions and fuel consumption. EGR exhaust gas recirculation. ESC test cycle European stationary cycle (http //www.dieselnet.com/standards/cycles/esc.html).

Compliance with the EuroIII standards (2000) forced the fitting of Diesel oxidation catalysts (DOC) in the exhaust line [for the after-treatment of unburnt hydrocarbons (HC) and carbon monoxide (CO)]. Additionally, the exhaust gas recirculation (EGR) was adapted to reduce the engine-out emissions of nitrogen oxides (NOx). 

Additionally, the exhaust gas recirculation (EGR) system at the engine intake has been mandated to reduce NO emissions. This device mixes a part of exhaust gases... 

Figure 7.2. Both philosophies of exhaust gas recirculation management.

Exhaust Gas Recirculation (EGR) The mixing of exhaust gas with intake air used in fuel combustion. In the diesel engine, mixing of exhaust gas helps in reducing the NO emissions. This process lowers the combustion temperature and oxygen concentration, thus lowering the total NO. However, excessive EGR leads to the formation of increasing amounts of CO, soot, and hydrocarbon emissions. 

Indicated Mean Effective Difference (IMEP) Exhaust Gas Recirculation (EGR). 

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