Prospects for the future: Alternative drive systems more important than ever
Which alternative drive gets preference at which point in time depends on various factors: on the availability of the particular fuel, on legal requirements and tax privileges, on the state of the art of each system, and on the emotive issues of the environmental debate. By now there are diesel engines which with the right aftertreatment meet the EEV standards no less than natural gas engines do. And the question arises whether it makes any sense at all to fix increasingly lower limits for nitrogen oxide and particulate emissions where there are so many old vehicles which emit many times these emissions.
There are essentially two reasons that call for doing further research on alternative drive systems. One is that the supply of fossil energy sources is limited. The mathematical models for computing the range of these stocks differ and are influenced by the discovery of new reserves as well as by the additional consumption caused by new, rapidly growing economies. All the same, at the end of this century at least petroleum production, and perhaps also natural gas production, will have passed its zenith. Continuing to ensure mobility therefore means keeping a lookout for new drive system alternatives.
Moreover, we increasingly see that along with the emissions on which attention has centered to date the handling of the greenhouse gas CO2 will play a more and more important role in future. But carbon dioxide emissions can only be reduced on balance if, instead of fossil fuels, renewable sources of energy, so-called BTL (biomass-to-liquid) fuels, are used, since the growing of the plants binds exactly the amount of CO2 which is released afterwards during combustion.
Along with biodiesel from rape seed oil, which, however, will never be available in adequate quantities, ethanol and methanol are possibilities which again could become attractive. Making this unlikely – leaving aside special cases like Brazil and recently Sweden – is that a special filling station system would have to be built up, which would be economically viable probably only in very few countries. The same can be said about other possible fuels such as dimethyl ether.
In addition, synthetic diesel oil manufactured from lumber industry and agricultural wastes soon will be available on a larger scale. Daimler AG has been working in this field together with the Choren company, Freiberg, since 2002. Before long, Choren will be manufacturing this fuel, known by the brand name SunDiesel, on a large scale. Like biodiesel, synthetic diesel fuel does not require the development of separate engines, but can be admixed with conventional diesel or used alone in a normal diesel engine. There is no need for a separate infrastructure.
Of course, at the present time no one can say whether in the long run enough fuel will be on hand to replace the fossil sources of energy. It would therefore be ill-considered to refrain from investigating other possible solutions, and Daimler AG as world market leader has a special responsibility in this respect. If we succeed in manufacturing enough hydrogen by electrolysis with regenerative electricity, then the fuel cell indeed may have a great future in store for it.
However, the hopes raised by the rapid progress from NECAR 1 to NEBUS and through to NECAR 5 meanwhile have given way to a certain disillusionment. Fundamentally, a conclusive energy balance and lifecycle assessment must consider the overall system. The vision of new bus transport systems of the 1970s unexpectedly gains present-day relevance here.
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Finally, we see that it is precisely the synergies from the development of different systems that lead to new solutions. The fuel-cell buses benefited from the development of new high-pressure tanks which had previously been used in natural gas buses. To make the fuel cell drive system fit for production, it would have to be integrated into an uncompromising energy management system of the kind developed in the area of hybrid drives.
At the same time, new storage systems like the lithium-ion battery and the fuel cell enter into a competition whose outcome is undecided yet. Future developments consequently will depend not least of all on whether we consistently pursue all possible options further and, where indicated, develop new solutions from their combination.