Abstract
A range extender (RE) is a device used in electric vehicles (EVs) to generate electricity on-board, enabling them to significantly reduce the number of required batteries and/or extend the vehicle driving range to allow occasional long trips. In the present work, an efficiency-oriented RE based on a small motorcycle engine modified to the efficient over-expanded cycle, was analyzed, tested and simulated in a driving cycle. The RE was developed to have two points of operation, ECO: 3000 rpm, very high efficiency with only 15 kW; and BOOST: 7000 rpm with 35 kW. While the ECO strategy was a straightforward development for the over-expansion concept (less trapped air and a much higher compression ratio) the BOOST strategy was more complicated to implement and involved the need for throttle operation. Initially the concepts were evaluated in an in-house model and AVL Boost® (AVL List Gmbh, Graz, Austria), and proved feasible. Then, a BMW K75 engine was altered and tested on a brake dynamometer. The running engine proved the initial concept, by improving the efficiency for the ECO condition in almost 40% in relation to the stock engine and getting well over the required BOOST power, getting to 35 kW, while keeping an efficiency similar to the stock engine at the wide open throttle (WOT). In order to protect the engine during BOOST, the mixture was enriched, while at ECO the mixture was leaned to further improve efficiency. The fixed operation configuration allows the reduction, not only of complexity and cost of the RE, but also the set point optimization for the engine and generator. When integrated as a RE into a typical European light duty vehicle, it provided a breakthrough consumption reduction relatively to existing plug-in hybrid electric vehicles (PHEVs) in the market in the charge sustaining mode. The very high efficiency of the power generation seems to compensate for the loss of efficiency due to the excess electricity production, which must be stored in the battery. The results indicate that indeed it is possible to have an efficient solution, in-line with the electric mobility sustainability paradigm, which can solve most of the shortcomings of current EVs, notably those associated with batteries (range, cost and charging time) in a sustainable way.
Highlights
Electric vehicles (EVs) have an enormous potential for enabling the quest for sustainable urban transportation
The results indicate that it is possible to have an efficient solution, in-line with the electric mobility sustainability paradigm, which can solve most of the shortcomings of current EVs, notably those associated with batteries in a sustainable way
While subsidies support the competitiveness of Battery electric vehicles (BEVs), they still seem to fail to lead to favorable total costs of ownership (TCOs) within most vehicle segments and for a wide range of annual mileages according to some authors [6]
Summary
Electric vehicles (EVs) have an enormous potential for enabling the quest for sustainable urban transportation. 450 kW [3] often during peak demand schedules and will be extremely expensive, both to manufacture and to use and tend to increase the battery degradation rate This sometimes brings the running costs of electric vehicles in pair, if not more expensive, than conventional fuelled cars [4,5]. Some solutions have been proposed to reduce the cost of fast charging during hours of peak electricity demand such as through load shifting. Such a solution was assessed by the authors using stationary energy storage to store energy during low electricity demand periods and supplying to the EV fast charging stations during the day [7]. It seems clear that there is a need for practical solutions that may circumvent the limitations of current EV storage
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