Fuel Economy of Plug-In Hybrid Electric and Hybrid Electric Vehicles: Effects of Vehicle Weight, Hybridization Ratio and Ambient Temperature

Hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) are evolving rapidly since the introduction of Toyota Prius into the market in 1997. As the world needs more fuel-efficient vehicles to mitigate climate change, the role of HEVs and PHEVs are becoming ever more important. While fuel economies of HEVs and PHEVs are superior to those of internal combustion engine (ICE) powered vehicles, they are partially powered by batteries and therefore they resemble characteristics of battery electric vehicles (BEVs) such as dependence of fuel economy on ambient temperatures. It is also important to understand how different extent of hybridization (a.k.a., hybridization ratio) affects fuel economy under various driving conditions. In addition, it is of interest to understand how HEVs and PHEVs compare with BEVs at a similar vehicle weight. This study investigated the relationship between vehicle mass and vehicle performance parameters, mainly fuel economy and driving range of PHEVs focused on 2018 and 2019 model years using the test data available from fuel economy website of the US Environmental Protection Agency (EPA). Previous studies relied on modeling to understand mass impact on fuel economy for HEV as there were not enough number of HEVs in the market to draw a trendline at the time. The study also investigated the effect of ambient temperature for HEVs and PHEVs and kinetic energy recovery of the regenerative braking using the vehicle testing data for model year 2013 and 2015 from Idaho National Lab (INL). The current study assesses current state-of-art for PHEVs. It also provides analysis of experimental results for validation of vehicle dynamic and other models for PHEVs and HEVs.

The Gas Turbine Hybrid Vehicle Prototype of the University of Roma 1: Status Review

In 1999, the University of Roma 1 launched a project to study the theoretical and practical feasibility of a hybrid passenger car in which the thermal engine is a Gas Turbine unit. The feasibility was demonstrated on paper, and some experimental tests were conducted at the ENEACasaccia Laboratories on a small (45 kW) gas turbine set, to investigate the performance of the propulsive unit (turbine plus batteries and electrical motor) under the standard european ECE emission tests. After successful completion of these tests, a further analysis was carried out to identify an “optimal” hybridization ratio with respect both to driveability and to fuel consumption: the results indicate that an absolute “optimal” configuration does not exist, because not only the system performance, but also the absolute and relative sizes (i.e., nameplate power) of the turbine and of the battery pack depend substantially on the type of driving mission the car is called to perform. The present status report describes all the above activities in some detail, and constitutes an attempt to put into perspective the entire Project. Using commercially available data for the components, the preliminary design of a road prototype is described and briefly discussed. For practical reasons the first prototype is likely to be equipped with a sub-optimal propulsion system: the differences and their implications are discussed as well.