In Pursuit of a Dedicated Hydrogen ICE for Heavy-Duty Vehicles

Experimental hydrogen combustion engine for commercial vehicles designed and optimized with computational fluid dynamics (CFD).

July 30, 2024

Kami Buchholz

The CFD optimization process to improve the mixing by choosing the best engine aerodynamic architecture and injector targeting. Good matching was observed between simulation and experiments for a mid-load operating point. (IFPEN)

Heavy-duty vehicle regulations from the European Union specify a 43% carbon emissions reduction by 2030. The EU’s carbon emissions reduction mandate climbs to 64% by 2035 before soaring to 90% by 2040. “The hydrogen combustion engine has a role to play to reduce CO₂ emissions,” said Vincent Giuffrida, CFD engineer for IFP Energies novellas (IFPEN), a Rueil-Malmaison, France-headquartered public research and innovation organization.

Comparison between experimental (dotted line) and simulated (full line) in-cylinder pressure for a spark advance sweep at 1200 rpm and 9 bar Indicated Mean Effective Pressure (IMEP), showing good accordance in all variation spectra of the spark advance variation. (IFPEN)

Giuffrida and IFPEN colleague and research engineer Olivier Colin were the presenters for a webinar addressing the “Development of a Dedicated Hydrogen Combustion System for Heavy-Duty Applications” in July. The webinar was hosted by Madison, Wisconsin-headquartered Convergent Science, whose CONVERGE CFD software simulates three-dimensional fluid flows. Features of the CFD software include autonomous meshing, complex moving geometries, a detailed chemical kinetics solver, advanced physical models, conjugate heat transfer model, fluid structure interaction/FSI (including rigid and non-rigid body FSI), and a volume of fluid (VOF) tool to model multi-phase flows.

CONVERGE CFD tools played a major role in the development, simulation and optimization of IFPEN’s experimental heavy-duty hydrogen combustion engine. Specific software models developed in collaboration with IFPEN were used to simulate combustion in a hydrogen engine that underwent experimental testing. Those tools include: ISSIM (Imposed Stretch Spark Ignition Model) for ignition, TKI (Tabulated Kinetic Ignition) for auto-ignition and knock prediction, as well as ECFM (Extended Coherent Flame Model) for premixed flame propagation.

A new turbulent stretch model, LPF (Low Pass Filter), showed very good agreement with DNS (Direct Numerical Simulation) results for both Le>1 and Le<1 mixtures – “Le” stands for Lewis number – in the flamelet as well as in the Thickened Reaction Zone (TRZ) regimes, according to IFPEN’s Colin. In addition, the multi-fuel capability of ECFM, implemented in CONVERGE, makes hydrogen or ammonia simulations possible with this model.

The design and optimization process with the CONVERGE CFD software showed that a high turbulence level is required for better hydrogen/air gaseous mixing, which is achievable via a Tumble aerodynamic motion approach. CFD simulations also showed that the hydrogen injector definition (location and targeting) “is of first interest” to achieve further improvements relating to hydrogen/air mixing and engine performance, the experts said.

IFPEN’s engine research team spearheaded the development of an in-house-designed engine test bench: a 2.1-liter displacement single-cylinder, direct injection engine with a maximum injection pressure of 40 bar (580 psi). IFPEN’s partners in building the test engine were Tenneco Powertrain (supplier of the spark plug), Phinia (supplier of the hydrogen injector), and Danielson Engineering (manufacturer of the hydrogen combustion engine).

A priori tests against Direct Numerical Simulation (DNS) of the new turbulent stretch model LPF (Low Pass Filter) for the CFM turbulent premixed flame model. X-axis: variation of turbulence intensity from the flamelet regime (lowest Ka) to the Thickened Reaction Zone (TRZ) regime (two other Ka). Left: stoichiometry iso-octane/air flame. Right: lean hydrogen/air flame (phi=0.4). (IFPEN)

“In the end, it was possible for us to realize a full engine map based on the proposed CFD design,” Giuffrida said, noting that an indicated efficiency of 47% was predicted by CFD and confirmed experimentally on the test bench with the 2.1-liter hydrogen engine. A maximum efficiency of 48% is possible with a lambda ratio ranging from 1.8 to 3.

Three-dimensional combustion modeling of a hydrogen engine still presents challenges for engineers. For example, the supersonic hydrogen jet occurring in the combustion chamber with hydrogen direct injection is difficult to model due to unaccounted hydrogen specific properties, namely vortices and diffusion. The CFD team also noted significant differences in the hydrogen/air mixing function of turbulence modeling approaches via RANS (Reynolds-Averaged Navier-Stokes) and LES (Large Eddy Simulation).

Another software modeling challenge for the hydrogen combustion engine relates to wall heat transfers, especially considering the inherent differences of physical properties, such as quenching distance, between hydrogen and other conventional fuels, such as gasoline and methane. The bottom line is the need for additional research work to identify the causes of pre-ignition and knock so that those unwanted phenomena can be addressed in the modeling process.

Various challenges related to a hydrogen internal combustion engine are being addressed at IFPEN with ongoing research, according to Giuffrida. IFPEN engineers and researchers are also working with Convergent Science to improve CFD modeling of hydrogen combustion via different research programs, including projects focused on advanced experimental tools.