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C. Six:
"Development of an exhaust emission and CO2 measurement test procedure for heavy-duty hybrids (HDH), Final Report of the Institutes";
Report No. B14030, 2014.

For engines installed in hybrid vehicles, the hybrid system offers a wide and rather specific engine operation range since the engine not necessarily delivers the power needed for propelling the vehicle directly. Applying the WHTC engine test cycle for emission certification and type approval, which is proven to be representative for conventional heavy duty operation, for hybrid engine applications as well is thus hardly justifiable. To meet the requirement of an engine test cycle representative of real-world engine operation also in a hybrid vehicle, the entire vehicle and its control systems need to be considered for the engine certification.
This document presents two test procedures considering the entire hybrid vehicle setup:
- Hardware in the loop simulation (HiLS method) and
- Hybrid powertrain testing (Powertrain method)
Both aim to reflect a vehicle chassis dyno test to derive the in-vehicle engine operation pattern for the emission certification.
To nevertheless ensure the comparability between hybrid and conventional vehicles in terms of emissions and to allow to keep the existing emission limit values also for engines installed in hybrid vehicles, extensive complementary measures needed to be taken and can be summarized as follows:
- The WHVC vehicle and the WHTC engine schedule were aligned in terms of power and cycle work demand
- A method to account for the propulsion work delivered by the entire hybrid system was developed, which defines the basis for calculation of specific emissions in g/kWh of hybrid propulsion systems
- A procedure to determine a representative power rating for a hybrid system with variable power capabilities during operation was developed
- Generic vehicle parameters were established which in first place enable the alignment of conventional and hybrid vehicle testing and allow a test procedure with moderate effort simultaneously
- A hybrid family concept similar to the engine family concept in gtr No. 4 [2] was introduced
However, due to the complexity and novelty of the developed procedures, further development may be needed when the methods have been applied by a higher number of stakeholders.
Accompanying the development of amendment 3 to gtr No.4 a validation test program of the proposed procedures was performed where three European OEMs provided hybrid vehicles and heavily supported the research activates of the group.
Even if indicated in the title of the document, CO2 determination procedures had to be left out of scope of the performed work.