Selected scientific works:

• FVV-No. 1449 "Near-zero Emission Concept for H2 DI Otto Engines"
• FVV-No. 1450 "Assessment of TCs with ejector-bypass for different mobility"
• FVV-No. 1431 "SACI Combustion System with Active Pre-Chamber"
• FVV-No. 1457 "Acoustics of hydrogen piston engines"

Completed projects:

• FVV-No. 1411 "PEM-FC Cold Start Simulation"
• FVV-No. 1357 "Homogenisation Model SI Engines II"
• FVV-No. 1018/1370 "Fast Knocking Prediction"
• FVV-No. 1369 "eMSI - Interference Noise in the Vehicle Compartment with Electrified Drives"
• FVV-No. 1307 "ICE2025+ Ultimate System Efficiency"
• FVV-No. 1214 "Turbocharger damping"
• FVV-No. 1084/1225 "Fuel in Oil I&II"
• FVV-No. 1191 "Exhaust fuel injection"
• FVV-No. 1059/1180 "Fuel characteristic numbers I&II"
• FVV-No. 1092/1207 "Engine noise components I&II"
• FVV-No. 1027/1171 "Potential of valve train variabilities on gas exchange of Diesel engines I&II"
• FVV-No. 1069/1151 "LPG system comparison I&II" (finished 2016)
• FVV-No. 1015/1041/1097 "Downsizing with Biofuels" (pilot, I&II, finished 2014)
• FVV-No. 942 "Future Fuels SI Engines" (finished 2009)
• FVV-No. 660/747 "Akustik Motor-Getriebe I&II" (finished 2001)

The aim of this FVV-funded project is to investigate the potential of a hydrogen combustion engine with direct injection in order to take a further step towards making hydrogen combustion engines for passenger cars ready for series production.

One focus of the project is to investigate the potential for reducing emission reduction. While no CO2 is emitted in a hydrogen combustion process, NOx emissions can be of significant amounts at certain operating points. Therefore, investigations will be performed on both a full engine and a single cylinder engine to derive the potentials and limitations in terms of charge dilution and emission. Furthermore, the anomalous combustion phenomena due to the low ignition energy required will be observed. CFD simulations of the gas exchange and combustion will support the thermodynamic investigations and contribute to a deeper understanding. The high mass diffusivity of hydrogen will affect the homogenization process and is expected to be faster than conventional fuels. The very high laminar burning rate and combustion instabilities pose a challenge for combustion modeling. This will also be considered as part of this project.

As a third pillar, the investigation and evaluation of concepts for exhaust gas aftertreatment of hydrogen combustion engines complements the overall approach of the project. For this purpose, concepts for engines with pure lean hydrogen combustion and lean & stoichiometric combustion control will be investigated. For the conversion of NOx emissions in lean-burn operation, both NSC- and SCR-based approaches as well as reasonable combinations will be considered. In addition, the conversion of carbonaceous emissions especially from oil consumption under stoichiometric conditions at rated power as well as a possible particle aftertreatment will be included.

10/2021 – 09/2024

Assessment of TCs with ejector-bypass for different mobility

Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FVV) - BMWK/AiF - Federal Ministry for Economic Affairs and Climate Action / German Federation of Industrial Research Associations

As part of the FVV project Ejector Bypass TC, a potential analysis of exhaust gas turbochargers (TC) with ejector bypass for different mobility applications is being investigated with a focus on increasing efficiency. It is examined to design the bypass channel as an ejector jet pump to exploit the previously unused thermodynamic potential of the bypass mass flow in the conventional TC with wastegate control. Compared to variable turbine geometry, ejector jet pumps can be designed with a much simplified and more robust structure. This technology could be of particular interest for applications with increased durability requirements (long distance, long haul, enhanced durability).

The use of the ejector jet pump is intended to utilize the exhaust enthalpy mass flow from the bypass path by exchanging momentum with the turbine outlet mass flow (suction mass flow) to produce a pressure drop downstream at the turbine wheel outlet. The lower turbine outlet counterpressure could here have a positive effect on engines and component in terms of efficiency and emissions.

The goal will be to develop a design process for turbines with downstream ejectors in exhaust gas turbochargers. CFD-based geometry-based optimization methodology through experimentally validated results will be used to create a predictive 1D model for an application-specific ejector jet pump design. The research results could not only be used in charging, but by using the ejector, the inflow behavior of downstream components such as catalyst inflow can be conditioned.

The further development of the fuel cell is currently the focus of many research projects. The results generated via the ejector jet pump, for example, could provide added value for turbine development for combustion engines and fuel cells. These are not only useful for small and medium-sized enterprises in the turbocharger industry, but could also be used, for example, by compressed air system technology for their own research and development.

10/2021 – 09/2023

The project is aimed at investigating the interaction between turbulence-controlled premixed and reaction-controlled combustion for a spark assisted compression ignition (SACI) system in combination with an active pre-chamber. This type of combustion system is expected to improve the thermal efficiency at part load as well as the peak efficiency due to a high dilution level and increased combustion stability.

First, the fundamental ignition behavior is investigated on a rapid compression machine (RCM). The RCM is equipped with an active pre-chamber, which houses both a spark plug and a direct fuel injector. The ignition process is triggered by the spark discharge inside the pre-chamber. The pre-chamber is fueled with gasoline pump fuel or alternative fuels, such as methanol, using the direct injector. The air-fuel mixture for the main chamber is externally provided to the main chamber before the compression stroke starts. Different fuel-air mixtures, i.e., relative air/fuel ratios, are considered at various initial boundary conditions, such as temperature and pressure. The resulting pressure curves are evaluated regarding their ignition delay times to assess the combustion in terms of a conventional pre-chamber combustion and an auto-ignition in the main chamber triggered by the pre-chamber jets. In addition, the RCM is equipped with optical accesses in both the pre-chamber and the main chamber. Thus, the mixing behavior inside the pre-chamber and the location of auto-ignition in the main chamber is assessed.

Second, the active pre-chamber system is thermodynamically investigated on a single-cylinder engine (SCE). The selected operating conditions are derived from the findings of the RCM investigations. In particular, variations of the relative air/fuel ratio at different engine speeds and net indicated mean effective pressures are considered. The pre-chamber layout in the SCE is identical to that of the RCM, despite the optical accesses. The SCE main chamber is fueled by a lateral direct injector located between the intake valves. Similar to the RCM investigations, the SCE is fueled with gasoline pump fuel or with alternative fuels. The ignition and combustion process of the main chamber is evaluated using the indicated pressure traces.

Third, computational fluid dynamics simulations are performed for both the RCM and the SCE to link their combustion mechanisms and to transfer the specific findings. In addition, 0D/1D simulations of the SCE are performed to further describe the combustion system. To this end, combustion models for spark-ignition and auto-ignition are implemented in a pre-chamber setup to create a holistic simulation tool.

01/2021-06/2023

The subject of this FVV-funded research project is the investigation of hydrogen combustion processes in internal combustion engines to establish systematic understanding of hydrogen-specific combustion noise characteristics and measures of positively influencing such noise.

Despite the challenging NVH aspects of hydrogen combustion (high pressure peaks and gradients, high tendency of instability and knocking, etc.), analysis of the current state of the art shows that research is mainly focused on the thermodynamic conversion and implementation of hydrogen combustion in the internal combustion engine while the important acoustical optimization is rarely considered. Thus, the first focus of the project is to investigate the combustion noise of hydrogen combustion engine. With the aid of estimated/predicted sound pressure level with respective calculation models, an initial assessment of the acoustic performance of hydrogen combustion engines using only the data from thermodynamic measurements of the other research projects will be performed. The potential influence factors on the noise excitation of hydrogen combustion engines will be analyzed with the data from variational engine parameters, in order to identify relevant levers to reduce such noise. Characteristic parameters for the combustion process will be worked out which can be used to optimize the combustion noise emission.

Secondly, based on the knowledge gained above, a comparison of hydrogen combustion process characteristics to combustion processes with conventional fuels (Otto / Diesel – CAI; SI, Dual Fuel etc.) will be made. Similarities and differences will be investigated. As a result, optimization strategies currently followed during combustion system development for conventionally fueled engines will be evaluated for their applicability during hydrogen combustion system development. Potentials and limitations will be compared and rated.

06/2022 – 05/2023