Conference report: 46th International Vienna Motor Symposium
29 May 2025
The 46th International Vienna Motor Symposium was held May 14-16, 2025. As happened last year, a “Virtual Event” option was offered again this year. Virtual attendees could access the symposium material starting May 14th. Topics covered included new engine concepts and emission reduction, driveline technologies, powertrain electrification, hybrid technologies, fuels, battery technologies, fuel cell technologies, and hydrogen engines.
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Heavy-Duty Hybrids
Cummins evaluated two heavy-duty plug-in hybrid powertrain architectures for North American truck applications, a P2 and a P4 configuration. In the P4 architecture, they called it a through the road (TTR) hybrid, the 2nd rear axle in a 6×4 axle configuration is a Cummins e-axle while the front axle is a conventional mechanical axle connected to the internal combustion engine through a drive shaft and gearbox. No electric machine is connected to the engine so the battery is charged either by plugging in or collecting regenerative braking energy. Both architectures used a 220 kW electric machine and 208 kWh battery with the electric machine being large enough to capture all the vehicle braking energy in the ARB transient cycle for a 70,500 lb GVW truck equipped with a Cummins X15 engine. They conclude that both architectures could help OEMs meet their CO2 targets in late 2020s. For hybrid powertrains to offer an OPEX benefit in line-haul duty cycles, either the duty cycle should have higher energy recuperation potential (e.g., ARB Transient cycle) when operated in CS mode, or the application should have access to cheaper ($0.08/kWh) electricity for CD mode operation [6446].
SwRI also concluded that hybrid drivetrains with diesel fueled internal combustion engines could satisfy EPA Phase 3 GHG standards. In a demonstration for a Class-8 vocational truck, a 13-L diesel engine was replaced with a 6.8-L engine equipped with cylinder deactivation (CDA) and a 305 hp e-motor in the P2 configuration, yielding a total powertrain output of 490 hp. This powertrain was complemented by a copper zeolite SCR-based aftertreatment system using a 48 V electric heater for thermal management. The combination of CDA and electric heating yielded tailpipe NOx emissions well below the EPA 2027 standards (0.035 g/bhp-hr). The strong downsizing and e-motor yielded powertrain CO2 emissions of 455 g/bhp-hr on the FTP cycle. This offers estimated vehicle-level CO2 emissions of 150-160 g/ton-mi, which can satisfy the 2030-31 EPA Phase 3 Greenhouse Gas standard for vocational trucks [6447].
Heavy-Duty Engines
MAN provided a more detailed look at their 30 L V12 engine. The design objectives for this engine were a peak pressure capability of at least 250 bar and torque of at least 8000 Nm. The major challenge was to implement all this within the same installation space as the existing 24 L V12. The 30 L displacement was achieved with a stroke extension from 157 mm to 165 mm and bore enlargement from 128 mm to 138 mm. Bainitic cylinder liners spaced at 170 mm were used and careful attention to crankshaft design were required to maximize main and connecting rod diameter and width to achieve sufficient bearing area. The cylinder head design needed to meet conflicting requirements for charge motion for diesel and Otto cycle applications. A design using two tangential intake ducts was chosen that allows the swirl to increase almost linearly with increasing valve lifts. The resulting swirl can be adapted to the requirements of the combustion process using the valve lift and timing. A squish piston together with high valve lift and late intake closing are used in the gas engine while the diesel engine uses early intake closing. In addition to the 1213 kW workboat engine (D3872LE432) announced in 2023, a single charger gas engine (E3872LE201, 735 kW @ 50 Hz and 840 kW @ 60 Hz) for stationary power generation with natural gas or biogas as well as a 1618 kW diesel yacht engine (D3872LE433) have gone into production. A heavy-duty 919 kW diesel for marine applications such as tugboats and commercial fishing will also be offered. For hydrogen and methanol applications, a dual fuel approach is planned while ammonia capability is not being planned as no significant demand for it in vessels powered by engines such as the D3872 is expected [6448].
Several papers were presented that detailed heavy-duty hydrogen engine developments.
A spark ignited, low pressure direct injection, hydrogen combustion concept by FEV is based on a diesel engine and its flat cylinder head design. The cylinder head incorporates a dedicated tumble port to achieve high charge movement. The cylinder head design in combination with an improved piston ring design, a special engine oil formulation and an increased injection pressure enables a mean effective pressure (IMEP) of 28 bar without and 30 bar with tolerably low pre-ignition events. Even with the different intake port, a high degree of commonality with the base cylinder head is maintained [6449].
Cummins prototype 6.7 L direct injection, lean burn hydrogen engine, the B6.7H, utilizes the latest base engine technologies from Cummins’ current 6.7 L gasoline spark-ignited platform. These include a tumble-based charge motion system with a pent-roof combustion chamber and dual overhead cams (DOHC) with cam phasers. A sequential two-stage boosting system without EGR uses fixed geometry turbochargers with the high pressure (HP) turbine having a twin entry and dual wastegates. A low-pressure direct injection (DI) fuel system and an ignition system with dedicated inductive ignition coil and super-flat, cold-type spark plug are also used. A maximum engine load of 22.5 bar BMEP and a maximum power output of 290 hp with transient performance competitive with the NG variant are achieved. The initial launch is expected for India and BS-VI compliant emissions with a simplified aftertreatment system are expected [6450].
Daimler Truck AG provided details on a prototype 15.6 liters commercial vehicle hydrogen engine that shares over 80% of its parts with the existing OM473 diesel engine. The engine is equipped with a port fuel injection (PFI), a single-stage exhaust turbocharger, and an EGR system. A maximum power of 350 kW is available that would be typical for a fleet rating. An SCR catalyst would be required for NOx control. The EGR system is primarily used to displace air and enable the simplified charging system –at rated power, λ = 1.6. However, EGR can introduce significant amounts of water into the intake system that can lead to icing—especially after extended idling at low temperature [6451].
Emission Reduction
In an analysis of passenger car propulsion options for the EU in 2035, FEV examined the potential of eFuels to provide significant GHG reductions as an alternative to 100% BEV sales—the latter is looking increasingly unlikely. They concluded that there will be massive lack of availability of eFuel even if all productions sites currently planned are realized. Since there is a period of 8 to 10 years from planning to production, they conclude that eFuel must be treated as a very limited resource and any scenario based on the assumption that eFuel will be available for all ICE-driven vehicles is highly unrealistic for the next decade and beyond. They suggest that PHEVs with a range of about 200 km might be a viable alternative to BEVs—even if fueled by fossil fuels [6457].
Emitec summarized aftertreatment options for PHEVs. They have two solutions that could be used to achieve a more rapid light-off and improved catalyst performance. The Crossversal Structure (CS substrate) uses a corrugated foil placed at a 7° angle to eliminate the flat layer of foil that can achieve a 20% material reduction that reduces the thermal mass, enables some gas mixing between the channels and enables some cost reduction. In the “Belt Mantle” (BM), an insulating air gap is provided between the catalyst substrate and the can that requires only a very small brazing stripe to attach the substrate to the can and provides a more uniform temperature distribution across the substrate with outer edge temperatures as much as 47 K higher than with a standard mantle [6456].
Conference website: wiener-motorensymposium.at