What are new developments in the internal combustion engine

Internal combustion engine development: Many small steps to reduce CO2


The big leaps in the CO2 reduction of the purely internal combustion engine drive are over. In the future, there will be many small steps that, taken together, will result in significant savings. We show examples of measures that still offer potential.

In the European Union (EU), CO2 emissions from new cars are to be reduced to 95 g CO2 / km from 2020/2021. This is the world's strictest CO2 limit and corresponds to fuel consumption of around 4 liters of petrol or around 3.6 liters of diesel per 100 km. The internal combustion engine continues to play the role of the pacemaker for low-CO2 mobility. Due to the low prevalence of purely electrically powered vehicles, their influence on the CO2 balance of the vehicle fleet will hardly be noticeable in the next few years, regardless of how high the CO2 pollution actually is from the generation of electrical energy.

All in all, great potential

Just through modifications to the basic engine, gas exchange, combustion, exhaust gas aftertreatment, engine management and thermal management, experts still expect great potential for reducing CO2 in gasoline and diesel engines. However, there is a small catch, because the optimization measures that bring about large CO2 savings with little effort have mostly already been implemented. For the engine developer, this means making countless small optimizations on many individual systems and components, which together bring about big steps. Overall, however, the CO2 potential is impressive: "I see around 20 percent for gasoline engines and 15 to 20 percent for diesel engines that can be increased using conventional techniques," explains Professor Dr.-Ing. Stefan Pischinger, Director of the Institute for Thermodynamics at RWTH Aachen University and Head of the Chair for Internal Combustion Engines. Below are some examples of developments that will make diesel and gasoline engines cleaner and more economical in the future.

Engine downsizing

A key driver is engine downsizing. On the one hand, the displacement is reduced in order to reduce fuel consumption, on the other hand, the supercharging ensures performance on the level of larger-displacement engines. The degree of downsizing will continue to increase in the future, so the displacements will be even smaller. On the charging side, this leads to complex, multi-stage turbocharger systems, as BMW is showing with the three-stage six-cylinder diesel engine. As an alternative, Audi is working on electrically assisted charging, in which an electric motor briefly increases the boost pressure in acceleration phases, making the notorious "turbo lag" a thing of the past.

Whatever the design of the turbocharging system: The increase in boost pressures leads to a higher load on the pistons. For this reason, pistons made of steel will increasingly find their way into passenger car diesel engines instead of the aluminum that is customary today. Thanks to new design approaches, these are just as heavy as the current pistons made of aluminum. However, switching from aluminum to steel is not in itself a panacea. Rather, the entire engine construction must be designed for the specific advantages of the steel pistons so that they can be lifted.

Friction reduction

In the past few years, developers have once again become more interested in reducing friction in the moving components in the engine. As a result of less friction, the power loss decreases and as a result, fuel consumption drops. The focus here is on the piston system - i.e. pistons, piston rings and cylinder liner - as it accounts for around 50 percent of the main part of the overall friction in the engine. Innovative coatings reduce friction and wear, for example Federal-Mogul promises a CO2 reduction of up to 3 g / km through the new "DuroGlide" piston ring coating.

On the design side, the engine developers try, among other things, to keep the tension with which the piston rings press against the cylinder liner as small as possible. In doing so, they move on a narrow range, because if the piston ring tension is too low, oil can get past the piston into the combustion chamber and negatively affect combustion there. Conversely, blow-by gases from the combustion chamber can age the oil more quickly. Another way to reduce friction is to use the smallest and narrowest possible crankshaft bearings.

Read more about internal combustion engine development on page 2.

Variable valve train

In the valve train of gasoline engines, variable systems with which the gas exchange can be adjusted depending on the map are already widespread. In future, however, variable valve trains will also be used in diesel engines for a wide range of applications.

One of the first representatives is the 1.6-l diesel engine from Volkswagen from the modular transverse matrix, in which the valve timing of the intake camshaft can be changed. The advantage: The adjustment adjusts the compression and creates an air movement in the combustion chamber, which promotes the mixing of air and fuel and thus optimizes the combustion.


On the injection side, very precisely working magnetic or piezo injectors and high injection pressures of currently up to 2500 bar lead to fine fuel atomization and good combustion. Manufacturers of very heavy and powerful diesel vehicles are expected to increase the injection pressure to 2700 bar from 2017 and to 3000 bar after 2020.

As a rule of thumb, experts say that 500 bar more injection pressure results in 2 to 5 percent more power, one to two percent less CO2 emissions or five percent less NOx emissions.

Stratified charge

While most manufacturers use direct injection in gasoline engines for combustion processes with homogeneous mixture formation, which are based on an even distribution of air and fuel in the entire combustion chamber, Mercedes-Benz uses the lean-burn process with stratified charge.

An ignitable mixture is only generated at the spark plug. The fuel concentration decreases with increasing distance from the candle in the combustion chamber. This allows very lean fuel combustion and thus low fuel consumption.

Thermal management

With the help of thermal management measures, the automobile manufacturers optimize the thermal energy balance of the drive system. In particular, the aim is to bring the engine and the exhaust gas aftertreatment system to operating temperature quickly, even in winter temperatures, and to use the engine's heat efficiently. This saves energy and sometimes costs, for example when a catalytic converter can be made simpler because it works more effectively thanks to optimized temperature control. The next step is to improve the networking of the individual drive systems with one another and with the GPS data from the navigation system. The researchers' vision for the future is what is known as the Connected Powertrain, which communicates with other vehicles and the infrastructure in order to adapt the drive systems precisely to the topography of the route and the traffic situation. For example, the upcoming regeneration of the particulate filter could be shifted from stop-and-go operation in the city to driving on the motorway in an energetically sensible way.

Conclusion and outlook

In summary, it can be stated that the developers are approaching the technical limits more and more, be it on the design level, with the material properties as well as the controllability of the systems or in production. This results in new tasks in the entire development process, including completely new collaboration models, for example in the synchronization of simulation and testing of components and systems.

By the way, none of these developments make electrification of the drive unnecessary. At the latest with the next level of 68 to 78 g CO2 / km being planned in Brussels in 2025, no car manufacturer will actually be able to ignore the electrified drive: vehicles of the much-cited Golf class or larger can only manage these limit values ​​according to the current state of the art with a combination Electric and highly efficient combustion engine as a plug-in hybrid drive.