Study on first-cycle combustion and emissions during cold start in a TSDI gasoline engine

The combustion characteristics in the first cycle are very important for all kinds of spark ignition engines, regardless of port fuel injection (PFI) or direct injection spark ignition (DISI) engines; Due to the fact the worse combustion during cold start results in an increase of misfiring events and HC emissions. To solve the reliable cold start, a total stoichiometric air/fuel ratio and local richer mixture start-up strategy was put forward. Also, the effect of boundary parameters (ignition timing, injection pressure, total air fuel ratio and local air fuel ratio) on the first cycle combustion (in-cylinder pressure, heat release rate and combustion) and emissions (HC and NO) during cold start were investigated experimentally for a two-stage direct injection (TSDI) engine. The engine-out HC and NO emissions were measured by means of a fast response Cambustion FID500 HC detector and a fast response Cambustion CLD500 NOx detector. The results show that, as far as combustion and emissions concerned, there exists a proper the ignition timing of 10 °CA BTDC. Increasing the injection pressure and the 2nd fuel injection amount is favorable to improving the first cycle firing performance. In addition, with the increase in the total A/F ratio from 11.4 to 26.7, the HC emissions decreased firstly and increased afterward, but the NO emissions decreased. The study provides a more detailed understanding of the combustion and emission characteristics in the first cycle during the start-up.