Summary: Combustion engines used as range extenders for electric vehicles promise to optimize fuel consumption and emissions because it is possible to avoid operating the combustion engine under conditions where the efficiency is low. A potential problem with this intermittent operation strategy is that exhaust emissions must be lower than Euro 6 or SULEV. An intermittent operation strategy leads to repeated cold or hot starts. In order to rapidly achieve high catalyst activity, both the start and heating strategy must be optimized, with engine-out emissions as low as possible. An engine for hybrid vehicles must also be able to use future alternative fuels such as methanol, ethanol, butanol and biogas, as EU objectives dictate that 25% of the fuel in 2030 will come from renewable sources.
Within this project, a small direct-injection engine for a plug-in hybrid system will be studied. The project aims to optimize fuel consumption and emissions at acceptable noise, vibration and harshness (NVH) during a driving cycle.
The most obvious way to operate an internal combustion engine as a range extender is to match the engine output power to the vehicle's average power consumption during the test cycle, minus recovered braking energy. An alternative method is to operate the engine intermittently at its maximum efficiency point (start / stop) and let the battery charge status vary over the cycle between a predefined minimum and maximum value. One problem with intermittent start /stop is to maintain sufficiently high catalyst temperatures (active catalyst), and to avoid emission spikes during engine start (especially under low catalyst temperature). Another problem may be noise and vibration (NVH) during high engine load and low vehicle speed. A more likely strategy is to use is a combination of the two, ie. where the combustion engine and electric motor operate together, so that high emission transients occur with electric assist.
With respect to fuels, gasoline and E85 will be studied. Owing to hardware limitations, biogas will be studied exclusively in a single-cylinder engine.
The following will be investigated within this project:
- Gas jets and combustion of methane
- Cold and warm start strategies using E85, for fast catalyst ignition and minimal emissions, including particulates
- Transients – optimization of the combustion engine and electric driveline (in collaboration with the Signal and Systems Department)
The project includes collaboration with Signal and Systems related to transient control.
The Hybrid drivetrain in Chalmers Hybrid Test Cell