Exhaust Emission Characteristics of Gasoline Engines with Secondary Air Systems and Electrically Heated Catalysts in Cold-Start WLTC Mode

Abstract Cold-start emissions remain a critical barrier to achieving near-zero tailpipe emissions required by increasingly stringent global regulations. Because gasoline direct-injection (GDI) engines experience incomplete combustion and delayed catalyst activation during the cold phase, effective thermal management of the after-treatment system is essential. This study evaluates the cold-start emission reduction potential of a 1.6-liter gasoline direct injection (GDI) engine equipped with a warm-up catalytic converter (WCC), underfloor catalytic converter (UCC), electrically heated catalyst (EHC), and secondary air injection (SAI) during the cold phase of the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). Various EHC and SAI operating strategies were evaluated to quantify reductions in carbon monoxide (CO), total hydrocarbons (THC), nitrogen oxides (NOx), and particulate number (PN). Simultaneous operation of EHC and SAI during the initial 80 s of the cycle achieved reductions of 69.1% in THC, 65.7% in CO, and 80.6% in NOx, with an additional energy consumption of 26.7 Wh. The most effective strategy involved initiating EHC pre-heating 50 s before mode start and maintaining it for 30 s afterward. In contrast, continuous SAI without EHC led to increased CO emissions due to partial oxidation over an unheated catalyst, underscoring the importance of synchronized thermal management. Cold ambient conditions were simulated by lowering coolant temperature to −7 °C, revealing that higher EHC power and increased SAI flow rates were required to maintain catalyst warm-up effectiveness. Although PN emissions increased sharply under these conditions due to unburned fuel, optimized EHC–SAI coordination reduced PN by more than 30%. These findings demonstrate that coordinated EHC and SAI strategies significantly enhance cold-start emission performance and are essential for achieving ultralow emissions in future regulatory environments.