Effect of Engine Design/Control Parameters and Emission Control Systems on Specific Reactivity of S.I. Engine Exhaust Gases

In 1994, the California Air Resources Board implemented low-emission vehicle (LEV) standards with the aim of improving urban air quality. One feature of the LEV standards is the increasingly tighter regulation of non-methane organic gases (NMOG), taking into account ozone formation, in addition to the existing control of non-methane hydrocarbons (NMHC). Hydrocarbons and other organic gases emitted by S.I. engines have been identified as a cause of atmospheric ozone formation. Since the reactivity of each chemical species in exhaust emissions differs, the effect on ozone formation varies depending on the composition of the exhaust gas components.

This study examined the effect of different engine types, fuel atomization conditions, turbulence and emission control systems on emission species and specific reactivity. This was done using gas chromatographs and a high-performance liquid chromatograph to analyze exhaust emission species that affect ozone formation. It is shown that the chemical species present in engine-out emissions differ depending on the engine design, thereby affecting specific reactivity. To investigate the effect of fuel atomization conditions, evaporation of the fuel was improved. Improved evaporation was found to promote the formation of alkene HCs having high maximum incremental reactivity (MIR) values, which resulted in higher specific reactivity. On the other hand, it had the effect of reducing NMOG mass emissions, there by reducing the quantity of ozone formed. Changes in such engine control parameters as the air-fuel ratio, ignition timing, cooling water temperature and EGR rate were found to affect the specific reactivity of engine-out emissions. The use of a palladium noble metal catalyst systém reduced the specific reactivity of tailpipe emissions owing to the different reaction selectivity of this catalyst system.