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Potential combustion engine: 95 grams thanks to downsizing and hybrid

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S since Chancellor Merkel proclaimed Germany the future lead market for electromobility, at the latest Electric drive predicts brilliant prospects. But it is now clear: the future has to wait a little longer. Only 4,500 electric cars are currently lost in the mass of around 43 million cars in Germany. And experts expect a maximum global market share of three percent by 2020. The automotive world will not change fundamentally yet, and there is no avoiding the fact that the global target values ​​for reducing CO2 emissions have to be achieved for the most part by internal combustion engines.

Of course, car manufacturers have that Consumption and CO2 reductions have long been recognized as advertising arguments and send messages of success - often wrapped in percentage improvement margins - into the world. Without a defined starting point, however, they are hardly meaningful. What does this mean for the European market?

CO2 emissions should be reduced to 95 g /km by 2020

The EU Commission has committed its member states to a CO2 emissions target of an average of 130 grams per kilometer by 2015, which is an eleven percent reduction compared to the decision year 2009 - when the CO2 emissions of new cars were 146 g /km means. The goal is to achieve a margin of just 95 grams per kilometer by 2020, which would then correspond to around 35 percent. And by 2025, the EU Commission has already envisaged a reduction of around 50 percent to 70 grams of CO2 emissions per kilometer for an average new vehicle. That would correspond to a consumption of around three with gasoline engines, with diesels only 2.6 liters per 100 kilometers. These are ambitious goals that were still considered utopian a few years ago.

But engineers like Jürgen Gerhardt, Head of Development at Bosch, are sending out a clear message: with a package of technical measures up to partial hybridization 95 gram goal achievable. Only beyond that will the air for gasoline and diesel engines become thin. There will then be no getting around gradual electrification and, above all, additional consumption-reducing measures in the vehicle concept. But the resolution is not really clear here.

Direct injection as a prerequisite for effectiveDownsizing

Market scenarios in Europe assume a 50:50 share for gasoline and diesel engines in 2020. Both combustion concepts must therefore make their contribution to the fleet consumption target. The most effective and therefore central recipe is engine downsizing. This is based on the knowledge that combustion engines achieve their best efficiency when their main operating range is shifted towards higher specific power. The consequence are engines with smaller displacement that have to run in a higher load range. If the displacement is also reduced with fewer cylinders than before, friction losses and thermal losses are also smaller, as are the moving masses - another plus in terms of efficiency. The loss of performance with a reduced displacement is compensated for by means of a turbocharger, which artificially increases the air supply. With downsizing, turbocharging and displacement reduction become inseparable siblings, which alone are good for a fuel consumption improvement of ten to twelve percent Fuel, good cooling of the reduced combustion chambers can be achieved and, moreover, effective cylinder scavenging without fuel loss during gas exchange. In this way, good torque values ​​can be achieved even at low engine speeds, as is known from diesel. In addition, this effect (downspeeding) can be used to save fuel with wider gear ratios.

Six cylinders become four

A large part of the savings potential of compression-ignition engines, which today are almost all turbodiesels, can ultimately be interpreted as a downsizing concept. But its possibilities have not yet been exhausted either: Higher boost pressure in combination with injection pressures of up to 2,500 bar promises further improvements in power output and combustion quality.

When it comes to downsizing, the trend from six- to four-cylinder - for example BMW - and more and more often, as with Ford, Peugeot, Renault or VW, from four to three-cylinder as the basic engine. Only Fiat is more consistent with its supercharged two-cylinder, which in the Fiat 500 already achieves the 95-gram CO2 target.

Cylinder deactivation is practiced, so to speak, temporarily downsizing. The latest, if not really new, trend is now being followed by Audi, VW and even AMG-Mercedes. This cure is less surprising for V8 engines, which mutate into part-time four-cylinder engines, but rather for the 1.4 TSI from VW, where two cylinders are deactivated in the partial load range. This should save around 0.4 liters of fuel per 100 kilometers, and even more when driving at a moderate speed.

The secret lies in the details

Further savings potentialis hidden where ventilation of the motor is hindered and its efficiency is reduced. The developers therefore endeavor to resolve the compromise of fixed valve timing and to adapt them to different load and speed points. In the case of a gasoline engine, this can be achieved through variable valve timing on the intake and exhaust valves. This not only has a positive effect on fuel consumption, but also on torque behavior. The independent phase adjustment of the valves, as implemented by BMW with double vanos, for example, requires two separately, steplessly adjustable camshafts. Concepts such as the BMW Valvetronic or Univalve from KS also vary the valve lift. This dethrottles the gas exchange further, can make the throttle valve superfluous in the medium term and thus contribute to consumption savings in the single-digit percentage range in practice.

Further optimization could be achieved by cylinder-selective, fully electric valve control, a complex and therefore expensive technological step . However, like the other components, it has to be subjected to a cost-benefit analysis. One thing is clear: The last steps to the summit are always the most expensive.

The precision of the processes must be further improved

This also applies to variable valve control in diesel, which is to be used primarily for the exhaust valves in order to achieve a higher exhaust gas temperature for faster activation of the exhaust gas aftertreatment. In general, with the still possible optimization in the combustion process, the top priority is to further improve the precision of the processes and narrow tolerances. In diesel engines, we will therefore increasingly see glow plugs that also act as pressure sensors during combustion. Only in this way, together with fast processors, will the upstream precise control be successful in the future.

In addition to the core topics mentioned, however, other technical components flank the optimization of the combustion engine. This includes a sophisticated thermal management system, a generator that primarily uses overrun mode to charge the battery, as well as ancillary units that are electrically controlled as required, such as oil and coolant pumps, air conditioning compressors or power steering - elements that are already appearing bit by bit in new models. And even friction-optimized piston rings or needle roller bearings make their small but not insignificant contribution to reducing CO2.

Based on the status in 2009, the 2020 CO2 target and thus a savings potential of 30 percent for combustion engines is a very realistic target. Additional savings potential through hybrid drive concepts can bring in another ten percentage points. Even more ambitious goals that aim to halve consumption are currently inconceivable without conceptual interventions in the car itself.

The fight againstthe driving resistances

Almost three quarters of the fuel-saving potential can be attributed to engine and drive technology. But it is also clear that the driving resistances have a significant influence on consumption. Reducing them is therefore part of the strategy to reduce CO2. The rolling resistance, which is mainly caused by the flexing of the tires while driving, plays a decisive role. However, the weight of the car is also indirectly included. Smooth running tires with improved rolling resistance are therefore just as important as the vehicle weight. A rule of thumb states that 100 kilograms less reduce consumption by 0.2 to 0.3 liters per 100 kilometers.

The rolling resistance increases slightly with speed, but decreases from around 75 km /h constantly increasing air resistance exceeded, which then makes up the lion's share of the driving resistance. Improved aerodynamics are therefore one of the decisive factors for the consumption-optimized car of the future.

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