An experimental and numerical investigation into the influence of intake port preheating on cold-start THC emissions of a scooter engine

Compared with the Euro 4 emission standard (L3e) for two-wheelers, the Euro 5 implemented in 2020 requires a 73% reduction in THC emissions. To meet this standard, the cost of the catalytic converter and the effort required to tune the engine have increased. The current challenge is reducing cold-start THC emissions, which are generated at 80% during cold-start. Intake port preheating (IPP) could be a potential approach to address this issue. A self-designed strip heater and a controller were set up on the intake port of a commercial scooter to preheat the engine to 37 °C before cranking. The experiment and CFD simulation were then performed to understand the IPP effects on mixture preparation, combustion, and THC emissions. The numerical results indicated that 32.9% of the injected fuel was in the wall film at the end of the third cycle during cold start, which was mostly located at the intake port of 53.9% and the intake valve of 18.4%. By applying IPP, the wall film was reduced from 32.9% to 28.2% at the end of the third cycle, which improved the mixture conditions. The experiment confirmed this finding with a richer equivalence ratio (EQR) of 1.070 after 10 s, allowing the engine to enter the closed loop 35 s earlier. This slightly improved the engine fuel economy by 5.25% during the first 80 s of operation. Consequently, 49.53% reduction of the cumulative THC concentration could be achieved for 10 s operating under open loop and 29.3% overall for 80 s.