Due to benefits from the use of electric power, Hybrid Electric Vehicles (HEVs) and Plug-in Hybrid Electric Vehicles (PHEVs) are regarded to be superior over conventional Internal Combustion Engine (ICE) only vehicles in fuel economy and emissions. However, recent studies find out that this is not always true. On certain conditions, hybrid vehicles can be even more polluted.
In order to identify these challenges and develop catalysts to meet more stringent emission requirement in the future, e.g. Euro 7, for hybrid application, as a part of our xHEV project, this study includes exclusively extensive investigation on a latest Euro 6d temp Parallel PHEV.
Key parameters including driving modes, Status of Charge (SOC), were investigated under World harmonized Light vehicles Test Cycle (WLTC) and Real Driving Emission (RDE) tests on the chassis dyno, and their influences on engine behaviours and emissions were studied, in comparison with emissions from the ICE only counterpart under the same legislation. Besides regulated emissions, secondary emissions and Particle Number (PN) and size distribution, including those under 23 nm were also analysed. It was found out cold start and hot restart emission control were critical for PHEV in order to fulfil our assumed Euro 7 legislation. Particle emissions were worst when the engine kicked in during the acceleration in the high-speed phase, i.e. cold catalyst under high space velocity exhaust and gas emissions were worst in the “Battery Control” mode when the ICE had to propel the vehicle while charging the battery.
Two new and improved aftertreatment systems were then proposed and evaluated that addressed the hybrid emission challenges without modifying the current vehicle calibration: The first was designed for overall best emission performance and the second was designed to meet the emission target at a lower cost. Both can reduce the hybrid vehicle emissions further and have the potential to meet the Euro 7 requirements for all gaseous and PN requirements.
