The controlled emissions limits defined to passenger cars are becoming very stringent. Therefore, the first minutes of the emissions test cycles gained importance. This work deals with a strategy to reduce the emissions of NMHC, CO and NOx in the cold phase of the test cycle, while the engine and catalyst are cold.
Leaving the engine, the exhaust gases pass through a three- way catalyst to reduce controlled pollutant gases, but the catalyst is effective only above 300°C (the so-called light-off temperature). When the catalyst is not hot enough, the gases pass through the catalyst without any beneficial effect. In modern engines, most of the NMHC emissions occur in the cold phase; then, reducing this pollutant in the cold phase is the main objective of the adopted strategy. Besides, significant amounts of CO and NOx are formed during this phase and this must also be considered.
The strategy adopted in this work is to retard the ignition timing, so the exhaust gases leave the engine hotter, reducing the time to increase the catalyst temperature and, as a consequence, reducing the time to attain the light-off temperature. This strategy was implemented in a passenger car engine, which was tested according to Brazilian Code ABNT NBR 6601. The obtained results proved this strategy is viable and can reduce the cold phase emissions.