Alternative fuels: Project Green Rex

Markus Kremer talks about the collaborative “Green Rex” project

11. May 2015 | Engineering Service, Software & Testing Solutions

Development of a light commercial vehicle that is operated purely with renewable energy is the goal of the collaborative project called “Green Rex”. Experts from FEV GmbH, and a group of renowned partners, are revising a “range extender” for operation with compressed natural Gas. The basis of this development is the V2 range extender with the FEVCom© system developed by FEV and KSPG, which has already been operated in a Fiat 500 e-car from FEV’s e-car fleet since 2012. FEV project leader Markus Kremer talked with SPECTRUM about the project, its tasks and roadmap.

Mr. Kremer, could you please explain the advantages of a range extender?

Range extenders are a central concept for vehicle electrification because they offset the disadvantage of the low energy density of traction batteries. In the case of a near-empty traction battery, the combustion engine supplies it with electrical energy via a driven generator.



The majority of existing range extenders consist of petrol SI engines. Why?

This is usually due to cost-efficient manufacturing. The obvious disadvantage of this concept is that the range extender is dependent on a fuel supply from crude oil. Natural Gas engines that meet the requirements of a range extender – including low production cost, compact size and good NVH attributes – are currently not available. This is why we are trying to determine, in the Green Rex project, if a marketable vehicle that is completely operated with renewable energy can be manufactured through a new combination of available mass production technologies.

Markus Kremer talks about the collaborative

Markus Kremer talks about the collaborative “Green Rex” project

Why did you decide for the CNG instead of LPG technology?

We decided in favor of biogas instead of Liquefied Petroleum Gas (LPG) as the latter is not produced sustainably. Biogas offers greater potential for reduced emissions of harmful CO2. There is a potential of around 24 percent, which is similar to gasoline engines, and, even in comparison with LPG, savings of up to 15 percent are still possible. Finally, methane can be stored easily in the natural Gas network.


What is the roadmap of the project?

In a first step, the petrol-fueled range extender developed by FEV and KSPG was integrated into a StreetScooter commercial vehicle (model “Work”) and presented to the public at the IAA Commercial Vehicles exhibition in Hannover. At the moment, the V2 KSPG range extender is being revised and optimized for operation with processed biogas by the Fraunhofer Institute in Karlsruhe, Germany, in close cooperation with FEV GmbH. The revised range extender will then be thoroughly checked on the test bench and subsequently integrated in another Street­Scooter Work commercial vehicle.

What results can be expected upon completion of this project?

Due to the early involvement of production specialists, we expect, by the end of the project, to be able to accurately estimate the additional cost of the biogas version in comparison to the base variant. The project includes MOT approval, initial driving tests to document the CO2 savings for demonstration purposes, and illustration of the concept feasibility. Differential Dynamic Programming is being used to develop an optimized operating strategy for delivery vehicles. This strategy will be utilized in FEV’s range extender control system to further decrease fuel consumption of the delivery vehicle.

The Green Rex project is funded by the German Federal Ministry of Economics and Technology while the Deutsche Zentrum für Luft- und Raumfahrt (DLR) is the project executing organization. Green Rex was initiated by the State Agency for Electric Mobility and Fuel Cell technology Baden-Württemberg GmbH (e-mobil BW) and is listed in the German cluster "Electric mobility South-West". Partners include: KSPG AG, StreetScooter GmbH, the Institute for Internal Combustion Engines (VKA) at the RWTH Aachen, Fraunhofer ICT and KIT (wbk Institute for Production Technology).


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