Electronic emission controls

Exhaust emissions of HC, CO, and NOx—the products of incomplete combustion—are controlled primarily by a catalytic converter, in conjunction with exhaust gas recirculation and increasingly sophisticated technology for improving combustion efficiency, including electronic emission controls. See emissions (stationary source),... 

The initial mechanical system was cmde, but the advancement of engine and emission controls, in particular the use of electronics and computers, has brought about substantial refinement (36). 

The results of several studies were interpreted by the Poole-Erenkel mechanism of field-assisted release of electrons from traps in the bulk of the oxide. In other studies, the Schottky mechanism of electron flow controlled by a thermionic emission over a field-lowered barrier at the counter electrode oxide interface was used to explain the conduction process. Some results suggested a space charge-limited conduction mechanism operates. The general lack of agreement between the results of various studies has been summari2ed (57). 

Minimization of pollutants from the combustion chamber. This approach consists of designing the engine with improved fuel-air distribution systems, ignition timing, fuel-air ratios, coolant and mixture temperatures, and engine speeds for minimum emissions. The majority of automobiles sold in the United States now use an electronic sensor/control system to adjust these variables for maximum engine performance with minimum pollutant emissions. 

Noise emission control is another area where the application of electronics goes hand in hand with environment protection. Special electronic circuits on DC motors ensure that the noise level can be reduced at the source rather than through costly insulation. 

To achieve a more stable mode of operation, in modem instruments the heating current for the filament is emission-controlled, i.e., the current of the electron trap is used to keep emission comparatively independent from actual ion source conditions. Typical emission currents are in the range of 50-400 pA. 

Schulten, H.-R. Nibbeiing, N.M.M. An Emission-Controlled Field Desorption and Electron Impact Spectrometry Study of Some A-Substituted Propane and Butane... 

Promoters are added to Pt catalysts because the promoted catalyst with modified electronic properties leads to a decrease in the activity for coke formation and also in the rate of metal sintering. Several promoted systems have been reported in the literature including for environmnetal pollution (vehicle exhaust emission) control and some are summarized here. 

The theoretical relation, Ve — hv, has been abundantly checked in measurements of spectroscopy and physics but its direct application to complex molecules in chemical reactions has not been established. Bombardment of mercury atoms or other simple atoms at low pressures by electrons under controlled voltages causes the emission of monochromatic light at the wave lengths predicted by this formula. Moreover, the ionization potential, at which the electron is completely separated from its atom, corresponds directly to the wave length at which the discrete lines of the spectrum merge into a continuous spectrum. This continuous spectrum is due to the fact that the kinetic energy of the expelled electron and ion is not quantized. The close agreement between the ionization potential and the lowest frequency of continuous absorption, where ionization first starts, constitutes another proof of the relation Ve — hv. 

Double-walled carbon nanotubes (DWNTs), first observed in 1996, constitute a unique family of carbon nanotubes (CNTs). -2 DWNTs occupy a position between the single-walled carbon nanotubes (SWNTs) and the multiwalled carbon nanotubes (MWNTs), as they consist of two concentric cylinders of rolled graphene. DWNTs possess useful electrical and mechanical properties with potential applications. Thus, DWNTs and SWNTs have similar threshold voltages in field electron emission, but the DWNTs exhibit longer lifetimes.3 Unlike SWNTs, which get modified structurally and electronically upon functionalization, chemical functionalization of DWNTs surfaces would lead to novel carbon nanotube materials where the inner tubes are intact. The stability of DWNTs is controlled by the spacing of the inner and outer layers but not by the chirality of the tubes 4 therefore, one obtains a mixture of DWNTs with varying diameters and chirality indices of the inner and outer tubes. DWNTs have been prepared by several techniques, such as arc discharge5 and chemical vapor depo-... 

Thermionic converters are high temperature devices which utilize electron emission and collection with two electrodes at different temperatures to convert heat into electric power directly with no moving parts. Most thermionic converters operate with a plasma of positive ions in the interelectrode space to neutralize space charge and permit electron current flow. Both the plasma characteristics and the surface properties of the electrodes are controlled by the use of cesium vapor in thermionic diodes. 

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