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

Abstract

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 NOx emission are elevated. Although, NOx emissions are significantly low, a bi-functional after treatment device will be required to control HC, CO and NOx emissions under lean and stoichiometric (oxygen free) engine operating conditions. This paper describes studies on the NOx, 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 4bar (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 NOx 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. NOx, CO and HC concentrations.