CO2 and Pollutant Emission Reduction using Variable Valve Train in Heavy Duty Diesel Engines

Authors

Ing. P. Traversa, Dr. M. Elicker, Ing. N. Morelli, Dipl.-Ing. S. Hardes, Schaeffler Technologies AG & Co. KG, Herzogenaurach:

Year

2023

Print Info

Production/Publication ÖVK

Summary

The stricter NOx emission limits of the forthcoming EURO7 legislation, along with further reduction of CO2 fleet target values, require additional development steps, especially for heavy-duty Diesel engines. To cope with these ambitious goals, the exhaust gas temperature management will play a pivotal role. Facilitating short warm-up phases of the exhaust gas aftertreatment system, as well as keeping engine-out emissions at a minimum will be part of the major engineering tasks in the heavyduty Diesel engine sector. In addition, unwanted cool-down of the exhaust aftertreatment system during the drive cycles needs to be avoided. In particular, in low load conditions this conflicts with the need to minimize CO2 emissions.

In this context, this Schaeffler study investigates the potential of an innovative valve lift & timing strategy on a heavy-duty in-line six-cylinder engine, in comparison to a state-of-the-art engine architecture.

In a first step, the valve lift & timing design is optimized and validated through 1D- charge cycle simulation at selected operating points. The design and calibration criteria are based on the proposed future EURO7 emission limits for heavy-duty Diesel engines. In a second step, a forecast is made about the fuel economy and the emission performance with the optimized strategies in selected driving cycles. Subsequently, the study compares these results to state-of-the-art engine designs as well as to alternative concepts such as exhaust cam phasing or electric catalyst heating.

The innovative concept of variable intake valve timing & lift combines the abilities to fine dose internal exhaust gas recirculation and to continuously control the cylinder air charge. This allows to increase the exhaust gas temperature at low load operating points while keeping the fuel consumption low, at the same time. With these additional degrees of freedom, engine out emissions can be kept to a minimum. Furthermore, fuel consumption advantages can be leveraged in the medium and high load range (i.e., by high load Miller), as well as in transient operation (cycle-by-cycle control of exhaust gas recirculation rate and air/fuel ratio).

In addition, the study assesses the potential of Schaeffler’s valve train solutions to support ZeroImpact engine concepts. This last part of the investigation includes a virtual transition of a state-ofthe art heavy-duty Diesel engine to an engine with SI combustion process being optimized to be operated with regenerative fuels such as hydrogen by taking benefit from Schaeffler’s continuous variable valve lift systems (CVVL).

In conclusion, fully variable intake valve train systems such as iFlexAir are key technologies to meet upcoming and highly challenging emission targets and efficiency goals for ICEs. Moreover, further flexibility added to the exhaust valve train (e.g., through the switchable iRockAir system), paves the way for additional features like (rolling/dynamic or static) cylinder deactivation (CDA) and compression release brake mode (EB).

ISBN

978-3-9504969-2-5