Engine operating conditions

Beyond the catalytic ignition point there is a rapid increase in catalytic performance with small increases in temperature. A measure of catalyst performance has been the temperature at which 50% conversion of reactant is achieved. For carbon monoxide this is often referred to as CO. The catalyst light-off property is important for exhaust emission control because the catalyst light-off must occur rehably every time the engine is started, even after extreme in-use engine operating conditions. 

C is the minimal temperature necessary for DPF regeneration in the case of non additivated soot. In nominal engine operating conditions, the temperature at the DPF inlet remains widely lower than 600°C. In the case of an additivated soot (additives added directly within the fuel), the temperature to be reached to burn the soot is decreased by about 50°C to 100°C even in that case, the temperature target is always difficult to reach in nominal engine operating conditions. 

These engine operating conditions allow the generation of compounds in the exhaust line, which are able to reduce the NO accumulated during the storage phase on the NOtTrap surface. 

Results clearly indicated effects of diesel exhausts from different engine operating conditions on the cells already after 1 h of exposure. However, a 1-h continuous exposure to a therapeutic aerosol is probably of limited clinical relevance. To study the effect of drugs administered by typical pharmaceutical single-dose inhalers (MDI, DPI) effective deposition of one puff within the time of one breathing maneuver ( 5 s) is probably more relevant. 

Table 8 Exhaust Gas Temperature and Composition (%voL, dry basis) at Different Diesel Engine Operating Conditions ...

Effect of Engine Operating Conditions. The interdependence of the operating variables again renders the direct determination of the influence of one variable on combustor deposits difficult. The situation is similar to the determination of the effect of these variables on combustion efficiency and limits. 

Smoke formation and coke deposition General reviews Theory of formation Effect of engine operating conditions... 

The fourth emission control concept is the oxidation catalyst. Secondary air is added to the exhaust gas to assure a lean composition, independent on the engine operation condition. The catalyst is designed to promote reactions between oxygen and both carbon monoxide and hydrocarbons, which can be removed to a high extent. However, nitrogen oxides cannot be removed in this manner. 

Engine tests offer the additional advantage over vehicle tests that several catalysts can be evaluated at about the same time under real identical engine operation conditions. This is achieved with a multichamber converter, in which small cores drilled out of a full size converter are used (Fig. 43). The sizes of the cores is such that each is operated at the same space velocity as the full size catalyst would experience. 

Quite the opposite is true for automotive catalytic converters. None of the operating conditions can be chosen to guarantee optimal conversion at minimal deactivation, as the operating conditions are fixed by engine speed and load. Further, the engine operation conditions depend upon the driving conditions. Table 17 gives a... 

Table 17. Influence of engine operation conditions upon the reaction conditions over a ceramic monolithic three-way catalyst (gasoline fueled spark ignition engine with four cylinders and a total displacement of 1.81 ceramic monolith catalyst with 62 cells cm total volume 1.241).

Table 17 also shows that the exhaust gas flow is laminar inside the channels of a ceramic monolith with 62 cells cm at all engine operation conditions. With a Reynolds number in the range of about 10 up to about 300, it is no surprise that both the limiting Sherwood and Nusselt numbers assume low values as well, which means that there is only a limited contribution of convection to the transfer of heat and mass from the gas phase to the catalyst surface. 

Figure 45. Comparison between the operating range of catalyst temperature and reactant space time for a three-way catalyst at two engine operation conditions (idling and full load operation), and for various heterogeneous catalytic processes used in the chemical and petrochemical industries. Reprinted with permission from ref. [34], 1994 Society of Automotive Engineers, Inc.

The extent to which this maximum occurs depends on the type of hydrocarbon and on the oxygen content (Fig. 53). It should be emphasized that the hydrocarbon fraction in the exhaust gas is composed out of typically more than 100 different individual hydrocarbons (Fig. 54). The composition of the hydrocarbon fraction depends on numerous parameters, such as the composition of the fuel, the engine operating conditions and the design of the engine (Fig. 55). 

Figure 99. Amount and composition of particulates in the exhaust gas of a heavy duty DI diesel engine at various engine operation conditions in the AVL-8-mode engine test cycle. Reprinted with permission from ref [68], 1991 Society of Automotive Engineers, Inc.

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