Technology: alternatives to the combustion engine

D he rescue package for the mobility of the future, for security of supply in matters Energy and fuel or even for the global climate are rich in alternatives. Never before have so many drive technologies been discussed as at present. And yet: the combustion engine will continue to dominate as a drive source for the next two to three decades.

Diesel and gasoline engines should become even more effective

Admittedly will he not stay who he is today - any more than he is today, what he used to be. It is worth looking back at the development of the diesel engine, for example: were the key data of a VW Golf GTD with a 1.6-liter engine, 70 hp, 133 Nm and a consumption of eight liters /100 km in 1982, it looks downright antiquated compared to a TDI of the same displacement from 2009 (105 hp, 250 Nm and 4.5 liters) - and that with a reduction in pollutant emissions of over 90 percent. Modern common rail direct injection and an abundance of detail improvements made it possible. No wonder that Bernd Bohr, Head of the Automotive Technology Division at Bosch, does not want to know anything about the end of the development: 'We still see considerable efficiency potential for both diesel and gasoline.'

Diesotto - diesel and gasoline engine in one

Experts name downsizing with turbocharging and spray-guided direct gasoline injection as the building blocks for gasoline engines. In the case of diesel engines, even higher injection pressures and an injection that is precisely adapted to the combustion process ('rate shaping') should ensure further savings. It is also the task of the engine developers in the coming years to combine the advantages of both combustion processes wherever possible. It is therefore more than symbolic when the engine presented for the first time in the F700 research car is from Mercedes was given the name Diesotto. Engineers around the world are working on the combustion processes summarized under the collective term HCCI (Homegenous Charge Compression Ignition). This homogeneous compression ignition in the partial load range is intended to make petrol engines similar to diesel onesHelp consumption with greatly minimized nitrogen oxide emissions.

CCS system from VW requires diesel-like fuel

GM developer Uwe Grebe expects consumption savings of up to 15 percent with the GM HCCI concept. VW is driving a comparable development under the term CCS (Combined Combustion System), but requires tailor-made, diesel-like fuel for this. Although these optimized combustion processes have not yet been used in series production, they have first priority among the alternatives, since the internal combustion engine, as mentioned, remains indispensable for the time being. Such combustion concepts are also interesting because of their flexibility: permanent monitoring of the combustion chamber with the help of pressure sensors allows HCCI engines to be fed with practically any mixture ratio of gasoline and /or ethanol. This not only reduces the current dependence on fossil fuels, but also paves the way for future fuels based on bio-ethanol. Especially in second-generation biofuels, in which the entire biomass can be used, experts see a noticeable relief for the climate in the future, even if at least initially hardly under economic conditions can also be fed with gas

It looks cheaper - if only because of the tax relief - with gaseous alternative fuels for internal combustion engines. You can also feed with natural gas (CNG) or autogas (LPG) without any major changes. With regard to the climate, the gas alternatives, which are currently state of the art, have advantages, but because of their fossil origin they are not CO2-neutral. Only the main natural gas component, methane, can also be obtained as biogas from decomposition processes - a process that is, however, complex and hardly suitable for large-scale use. In addition, methane, when released unburned into the atmosphere, is an extremely effective greenhouse gas, 20 to 30 times more effective than CO2.

Micro-hybrids should save costs

Since the internal combustion engine is indispensable, at least for the time being, fuel can also be saved by choosing it one size smaller and allowing it to work in peaceful coexistence with an electric motor and a storage battery. Because the combustion engine is inefficient especially where electric motors have their strength: when starting up and in the partial load range. Such hybrids are now available in an abundance of varieties with advantages and disadvantages of very different forms. A general shortcoming when combining two engine concepts is the additional technical and thus financial effort. Keeping it within narrow limits is one of the goals of micro-hybrids, which have recently become increasingly popular as start-stop systems.Either belt-driven or designed as a pinion starter, three to five kW electric units ensure that motors start quickly and are automatically switched off when they are not running. This results in their main savings effect. This is measured in the standardized consumption cycle in the range of around three to four percent, but can increase by a factor of two or three in extreme traffic jams in congested city centers, especially when limited kinetic energy is also recovered, which, however, only in the belt-driven design is possible.

Mild hybrids save fuel, especially in traffic jams

This results in a clear priority of such cost-effective systems for urban traffic. The longer the stationary phases, the greater the savings effect: this fundamental finding naturally also applies to mild hybrids, in which electric motors with an output of around ten to 20 kW support the combustion engine in its most inefficient phases - i.e. in the idle to medium speed range. The space-saving connection between the electric unit and the crankshaft is becoming more and more common in this application. Because the electric motor is both a starter and a generator, there are additional savings effects by returning kinetic energy to the battery as soon as the vehicle coasts or brakes.

Together that can add up to 15 to 18 percent - depending on the application profile. Full hybrids go one - costly - step further in terms of their performance bonus (between 30 and 60 kW) and thus also the battery size. The decisive difference to the mild hybrids with this concept is the possibility of more or less short, purely electric driving routes. They often have a symbolic character, but such complex concepts can save up to 25 percent and more. Above all, of course, in stop-and-go traffic, the savings effect is close to zero on long distances that are driven evenly.

Opel Ampera or Mercedes Blue Zero with Range Extender

If car experts see the different variants of the hybrid drive as bridging technology in the gradual transition to the electric car, then So-called plug-in hybrids or those series hybrids in the form of a range extender (range extension) are already closer to the electric drive. Hybrid pioneer Toyota plans to introduce the The first plug-in hybrid vehicles have already been field-tested for some time. With the use of more energy-rich lithium-ion batteries, which can also be recharged via sockets, the operational routes should be shifted even further to an electric range that is roughly doubled. The petrol engine then only intervenes when the charge level is low. Go one step furtherSeries hybrid concepts (range extender) à la Opel Ampera or Mercedes Blue Zero E-Cell Plus, where the electric motor and battery are good for ranges of 50 to 70 kilometers.

High costs prevent competitiveness

The concept is based on the knowledge that 80 percent of daily driving distances are shorter than 60 kilometers and therefore with one battery charge removed from the socket could be covered. In order not to limit the car to such an electric range, there is a generator on board, which, if necessary, is moved by a small internal combustion engine fed with gasoline or bio-ethanol. There is no longer a mechanical connection to the drive, the generator and motor are, so to speak, provided as an auxiliary device to combat possible range fears. So the Opel Ampera , if he because it will be launched on the market in 2011 as planned, expanding its range to over 500 kilometers. Such detours are only necessary because the energy content of the batteries and thus purely electrical ranges are still the limiting factor despite all technological advances. The other is the currently excessive costs that stand in the way of competitiveness with conventional cars.

A battery costs at least 8,000 euros

At Bosch, with a targeted minimum range of 200 kilometers, it is assumed that even with optimized power consumption, a battery capacity of around 35 kilowatt hours is required. With the technology available today, this would require a lithium-ion battery weighing a good 250 kilograms. The clear development goal for the next few years is to increase energy density and reduce weight - and of course battery costs too. In a few years' time, they will still be between 8,000 and 12,000 euros, estimates Bernd Bohr and therefore sees the urgent need for large-scale production within the framework of cooperation partnerships. This seems to be paying off for Bosch. The SB LiMotive joint venture entered into with Samsung is now bearing fruit, the first customer is called BMW .

Development is being strongly promoted in China in particular

Like other manufacturers, the Munich-based company is aiming for series production of a megacity vehicle within six years at the latest , because despite the range handicap, the global trend towards further urbanization gives the electric car new opportunities. By 2015 at least 60 megacities will grow to a population of more than five million - mainly in Asia. No wonder, then, that especially in ChinaIs strongly advancing the development of e-cars. The mobility needs in such metropolitan regions - short distances and local emissions free - make it appear attractive from the Chinese point of view to invest more in a technology that is on the rise than in conventional concepts.

Only BMW and Mazda rely on hydrogen

However, this shifts the question of power generation, its efficiency and its consequences for the climate to the power plants. Because electricity generation is largely climate-neutral only when using renewable sources such as solar, wind or water power. In Germany, however, with a renewable share of primary energy consumption of a good seven percent, this is a long way off, and globally even further. Even the advocates of a hydrogen future cannot ignore this knowledge, who see the gas as a final energy source at the latest after the end of the petroleum age, which would also be free of pollutants and climate-relevant CO2 emissions on site. Two directions open up for the use of hydrogen: Molecular hydrogen (H2) is flammable and therefore allows it to be fed directly to the combustion engine. However, BMW and Mazda are pretty much alone with this idea . The second way, the utilization of hydrogen in fuel cell drives, is considered to be the technological mainstream.

Fuel cell cars are currently far too expensive

In theory, the combination of fuel cells and electric motors has a clear advantage over the combustion engine in terms of efficiency. In addition, the fuel cell car has other efficiency advantages in its lap, as braking energy can be recuperated in conjunction with a storage battery. The range problem of pure electric cars can certainly be alleviated with the fuel cell drive. But then there is the storage problem that costs both money and efficiency points. Because the H2 energy content is not intoxicating under atmospheric conditions, which is why the gas liquefies by cooling it to minus 253 degrees or usually compressed to 700 bar and stored in pressure tanks. However, the fact that fuel cell cars are still much too expensive small series products at the planned launch of the Mercedes B-Class F-Cell, although they are now technically highly mature, does not make their introduction any easier. Skeptics therefore do not expect real large-scale production before the year 2025.

Until then, however, there are still a few crucial questions to be clarified - for example that of a functioning hydrogen infrastructure. Or that of an environmentally friendly production of the energy carrier, which has really not been possible until now with the production of natural gas. And it would not be it even then, if you used hydrogen in the current power plant mixObtain with an efficiency of 36 percent by electrolysis. Critics consider the hydrogen detour to be far too lossy anyway, because - as they calculate - the efficiency chain would be at least three times cheaper in purely battery-electric operation than with fuel cells.