Exhaust gas recirculation

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 ... 

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.

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. 

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). 

In commercial vehicle engines, by means of cooled exhaust gas recirculation, in-cylinder temperatures are reduced, leading to lower NOx, but mostly also to higher particulate emissions. To fulfill future emission standards, a combination of raw emission reduction and exhaust gas aftertreatment is necessary. Decreasing fuel economy with raw emission reduction has to be weighed against catalyst—and especially noble metal—price for exhaust gas aftertreatment. 

Exhaust Gas Recirculation. In one method of NO emission control, exhaust gas is fed back into the inlet manifold and mixed with the fuel and inlet air. The resultant mixture upon combustion in the cylinder results in lower peak combustion temperature and lower NO formation because the reaction of N2 + 0-, — NOx is strongly dependent on the combustion flame temperature (99,109—112). The degree of NO depression is dependent on the amount of exhaust gas recirculation (EGR) as shown in Figure 13. EGR provides a diluent gas having high molecular weight and C02 which absorbs heat. Also, EGR affects the flame speed of the mixture, and thus provides a certain antiknock quality to the combustion process. The impact of EGR on engine parameters has been detailed (113). 

---