Continental looks at new ways to optimize the petrol engine

At the 36th International Vienna Motor Symposium (May 7-8), international automotive supplier Continental will report on further potential for making petrol engines even more economical.

To comply with future exhaust-gas legislation and CO₂ limits, efficiency within the engine must be further increased. "Since the petrol engine is the most widespread drive system for passenger cars worldwide, and will remain so in the foreseeable future, every improvement here will potentially have a large-scale effect. This applies equally to engines with port fuel injection systems as well as to those with direct injection," said José Avila, head of the Powertrain division and member of the Executive Board at Continental. "The central challenges for the automotive industry are first to develop ever more efficient vehicles and second to make these vehicles fun to drive."

In Vienna, Continental will present enhanced technologies that will help to make petrol engines even more efficient. The package of technology on show will consist of leaving the intake valve open longer (the Miller cycle), coupled with a higher compression ratio and low-pressure exhaust-gas recirculation (EGR).

The desired optimization of the radial compressor and use of Continental radial-axial turbine technology (RAAX) demonstrates that modern turbocharger systems can compensate for the disadvantages of a Miller process even with conventional single-stage turbocharging systems.

To further optimise the combustion process itself, the automotive supplier is developing new high-pressure injectors in test engines. "To achieve the European CO₂ targets for 2020, there will also be an increasing proportion of hybridization with electric drives of 48 V and above, particularly in the medium to higher vehicle segments. In the future, systems expertise for all efficiency modules will be even more important when it comes to maximizing vehicle efficiency," said Avila.

Diverse CO₂ technologies
One of the aims of optimization within the engine is to improve the position of the central combustion point in the knock-limited load range of the petrol engine. Continental says it achieves this in a 1.0 l turbocharged engine by keeping the inlet valves open longer and through cooled low-pressure exhaust-gas recirculation, which improves fuel consumption by 3–6 g per kWh.

Forced induction is carried out by a Continental turbocharger with RAAX technology. It improves drivability when using the Miller strategy, because a turbocharger with a RAAX turbine achieves higher boost pressure at lower engine speeds than a standard turbocharger with a conventional turbine. This enables the engine to generate more torque.

Continental is also working on multi-stage forced-induction techniques that use an additional turbocharger and even an electrically powered booster. This can significantly improve the responsiveness of the combustion engine, which in turn improves power output and drivability. The majority of harmful emissions from a modern petrol engine is produced during the cold-start and warm-up phases, which is why the company will also present a dynamic thermal management system that can significantly shorten the time it takes for an engine to warm up in the New European Driving Cycle (NEDC).

Controlling the flow of coolant is also particularly important for hybridization in order to keep the heat in the engine's cooling system during hybrid driving strategies such as coasting (switching off and disconnecting the combustion engine). The integrated electrically heated catalytic converter also supports engine-off strategies. The rapid electric heating of the catalytic converter dispenses with the need to use fuel to heat the catalytic converter and prevents additional consumption and hydrocarbon emissions that would otherwise occur when the combustion engine is restarted due to the catalytic converter not yet being up to operating temperature.

Injection and control for greater efficiency
Fuel injection is key to high efficiency, both in engines with port fuel injection and in gasoline (petrol) direct-injection engines (GDI). The new Deka 10 injectors for port fuel injection (PFI) have a greater spread between the smallest and largest possible flow, which is important for higher-powered engines as well as for turbocharged engines. Deka 10 injectors produce smaller droplets, which leads to better carburetion and thus more efficient combustion.

On the subject of optimization within engines with GDI systems, Continental will report in Vienna on the potential shown by a 1.8-litre test engine.

Increasing the injection pressure from 250 to 350 bar, using the new XL5 injectors with an optimized injector-hole design and the GHP 2.5 high-pressure pump (GHP = gasoline high pressure), could reduce particulate emissions in exhaust gas by 80%, with fuel consumption remaining the same. This will help achieve the urgent objectives for DI engines.

As valve control variability and low-pressure exhaust-gas recirculation become more common, the freedom in engine control will increase. Conversely, this can lead to a significant increase in the number of calibration-data maps in the engine control unit. To limit the need for storage and the cost of calibration, Continental is further developing its EMS3 engine-control and powertrain system platform for use in multi-core processors. These processors can compute powerful polynomial models in real time, for example for engine injection with high precision.