HC, CO and NO_x emissions reduction efficiency of a prototype catalyst in gasoline bi-mode SI/HCCI engine

Lean and highly diluted homogeneous charge compression ignition (HCCI) engines offer great potential in improving vehicle fuel economy and contribute in reducing CO₂ emissions. Hydrocarbons and CO emissions from HCCI engines can be higher than those from spark ignition (SI) engines, especially at low engine load when the residual gas required to control NO_x emission are elevated. Although, NO_x emissions are significantly low, a bi-functional after treatment device will be required to control HC, CO and NO_x emissions under lean and stoichiometric (oxygen free) engine operating conditions. This paper describes studies on the NO_x, HC and CO emissions reduction efficiency of a prototype catalyst, under lean and stoichiometric engine conditions at different loads, speeds, and A/F. A comparative study of catalyst performance will be analysed under HCCI stoichiometric and SI operation under three engine speeds and load of 4 bar (Net Mean Effective Pressure, NMEP). Experimental results indicate that the HC and CO emissions reduction over the prototype catalyst was in the range of 90-95% while the maximum NO_x emissions reduction under lean engine operating conditions was in the range of 35-55%. The catalyst efficiency in reducing the three pollutant emissions is closely related to the exhaust gas conditions (e.g. temperature and space velocity), oxygen and composition i.e. NO_x, CO and HC concentrations.