The shift toward electrification and limitations in battery electric vehicle technology have led to high demand for hybrid vehicles (HEVs) that utilize a battery and an internal combustion engine (ICE) for propulsion. Although HEVs enable lower fuel consumption and emissions compared to conventional vehicles, they still require combustion of fuels for ICE operation. Thus, emissions from hybrid vehicles are still a major concern.
Engine starts are a major source of emissions during any driving event, especially before the three-way catalyst (TWC) reaches its light-off temperature. Since the engine is subjected to multiple starts during most driving events, it is important to mitigate and better understand the impact of these emissions.
In this study, experiments were conducted to analyze engine starts in a hybrid powertrain on different experimental setup. First, the tests were conducted on a hybrid system at powertrain test bed where emissions and fuel consumption for various engine starting events were investigated under different drive cycles, including WLTC and RTS95. The start events were categorized based on the initial engine and TWC temperature. In the second campaign, the focus was given to electric assisted-warm engine starts to identify optimal starting conditions for more efficient engine starts.
The hardware used for the first experimental campaign comprised of a three-cylinder, 1.5 L turbo-charged SI engine with PFI system installed in P2.5 hybrid powertrain. The HEV powertrain was installed and operated on a powertrain testbed. Experiments in the second campaign were conducted on a 4-cylinder GDI engine, installed on an engine testbed. Results from both campaigns were post-processed using AVL Concerto and Python programming language. As a result, optimal engine starting point was identified for the 4-cylinder GDI engine and a methodology was developed to extend similar analysis for different engine setup.