Deriving in-use PHEV fuel economy predictions from standardized test cycle results

Plug-in hybrid electric vehicles (PHEVs) have potential to reduce or eliminate the United States' dependence on foreign oil. Quantifying the amount of petroleum each uses, however, is challenging. To estimate in-use fuel economy for conventional vehicles, the U.S. Environmental Protection Agency (EPA) conducts chassis dynamometer tests on standard historic drive cycles and then adjusts the resulting "raw" fuel economy measurements downward. Various publications, such as the forthcoming update to the SAE J1711 recommended practice for PHEV fuel economy testing, address the challenges of applying standard test procedures to PHEVs. This paper explores the issue of how to apply an adjustment method to such raw PHEV dynamometer test results in order to more closely estimate the inuse fuel and electricity consumption characteristics of these vehicles. The paper discusses two possible adjustment methods, and evaluates one method by applying it to dynamometer data and comparing the result to in-use fleet data (on an aftermarket conversion (PHEV). The paper also presents the methodologies used to collect the data needed for this comparison. The predictions using the proposed method are shown to provide close agreement with the in-use observations when the actual fleet charging characteristics are included.