After less than two years development time the BMW Group presents the first car in the world whose on-board power is supplied by a petrol operated fuel cell (SOFC). The new type of fuel cell battery can be used in every conventionally operated automobile, reduces fuel consumption and permits a whole range of new safety and comfort functions. The energy system, which was developed together with Delphi Automotives, will feature in coming BMW model generation as the so-called APU (Auxiliary Power Unit). The BMW Group is the world's leader in the development of fuel cells APUs for on-board power supply. Several of the small-series-production 750hL models are already equipped with such a fuel cell APU featuring PEM (Polymer-Electrolyt-Membrane) technology.SOFC fuel cell: effective, robust and reasonably priced
The new fuel cell is a so-called "Solid Oxide Fuel Cell", SOFC in short. In this solid fuel cell, hydrogen is converted into electricity at approx. 800°C via zirconium oxide ceramics. In a start and a main reformer, petrol is evaporated and hydrogen is split off also at 800°C operating temperature. The hydrogen then reacts with the oxygen from the air which is supplied by a fan. In the process electricity is generated and water is produced as a by-product. Non-reacted residual gas is combusted. The heat produced in this way serves to heat the air required for the reaction and the reformer which improves overall efficiency even further.
It is not only this short process chain which makes the SOFC cell so ideally suited for operation in conventionally powered petrol cars. Compared to the currently generally favoured PEM fuel cell (polymer electrolyte membrane) the SOFC is also a lot less sensitive to impurities which are produced in a petrol reforming process since CO can also be converted into electricity and not only hydrogen. In addition it does not require expensive precious metal electrodes.
Efficiency has been doubled compared to conventional concept
The task of the SOFC fuel cell unit for BMW passenger car is to supply the vehicle electrical system with electrical energy. This electrochemical "powerplant" is to take over the function it does best: to generate electricity with a high degree of efficiency - independent of the engine. The conversion of petrol into electricity via SOFC fuel cell is almost twice as efficient as the combination of engine, generator and battery. For driving the car itself, the view held by BMW is that the internal combustion engine offers more benefits.
The autonomous operation of the fuel cell APU makes possible new functions: windows can be defrosted before getting in the car, seats and steering wheel can be warmed. In high outside temperatures the air conditioning can be operated optimally regardless of the engine speed. Air conditioning the car with the engine off can already be carried out using a quarter of the energy required today. With today's electrical consumers in a vehicle, approximated one litre per 100 kilometres can be saved in city traffic. Future "by wire" systems such as electrically operated steering or brakes require far more electrical energy which can then be efficiently provided by the SOFC fuel cell.
The use of Internet and online services in the car and the "mobile office" are facilitated considerably by fuel cell APU technology. The APU developed by BMW is ideally suited for the new 2-voltage electrical system. Existing APU vehicles not only supply the conventional 12V system, but also the newly developed air conditioning system with 42 volts.
APU to be available in a few years: customer benefit with no compromises
The BMW Group wants to offer the fuel cell APU and the benefits involved in approximately five years. This means that BMW customers will be the first to benefit from specific advantages of fuel cell technology without any compromises involved. The aim of series development, which has already begun, is to reduce the size and optimise the overall system even further. Output will be approximately five kilowatts for which the reformer is already designed today. The compact fuel cell battery will only require approximately the space of a conventional lead battery in the future. However, the fuel cell surpasses the power and "endurance" of the lead battery by far. In the long term the fuel cell might even substitute the electric generator in the car. With the APU a new era will begin for the automobile whose electrical power needs are ever increasing.Published 20 February 2001