Impact of multi-mode range and location on fuel economy on a light-duty spark-ignition based powertrain using vehicle system simulations 2020-01-1018
Advanced compression ignition (ACI) modes have been shown to offer higher brake thermal efficiency than conventional spark ignition combustion with gasoline range fuels. The goal of a full-time ACI in which an ACI mode can be operated in over the entire speed and load map in a conventional passenger vehicle have been limited to date. The benefits of running ACI modes in a portion of the engine operating map have been shown in a number of studies to have potential benefits on improving fuel economy and reducing emissions. An engine that runs in two different combustion modes is known as a multi-mode strategy. Different multi-mode strategies have been proposed and demonstrated in laboratory and in demo vehicle settings. Multi-mode combustion strategies for vehicle applications offer the ability to maintain functionality expected for the real-world and certification driving cycles but offer part-time higher-efficiency/ lower emissions operation during a sufficient portion of the expected drive/duty cycle to offer significant fuel economy benefits as well as potential emissions controls benefits. There are challenges as well in both combustion controls and emissions controls that are multi-mode strategy dependent. The potential fuel economy benefits of such multi-mode strategies are not well understood.
To estimate the potential fuel economy benefits of multimode engines in light-duty vehicles, the researchers performed a systematic study of the effect of ACI engine-map location, load range, and efficiency within the Autonomie vehicle system simulation tool. They used data from a 2.2-L direct-injection SI engine to simulate the baseline fuel economy of a mid-sized passenger vehicle over the U.S. Environmental Protection Agency’s (EPA’s) Urban Dynamometer Driving Schedule (UDDS). The analysis highlights the magnitude of urban fuel economy improvement that might be realized through multimode engine strategies. It also identifies the low-load engine-map regions where urban ACI operation likely will be most impactful, suggesting prime opportunities for research and development. The researchers also explored the effects of changing the location of the ACI load ranges within the engine map, and those results underscore the dominance of low-load ACI operation in improving urban fuel economy.