A New Generation of Hydrogen-Fueled Hybrid Propulsion Systems for the Urban Mobility of the Future

The H2-ICE project aims at developing, through numerical simulation, a new generation of hybrid powertrains featuring a hydrogen-fueled Internal Combustion Engine (ICE) suitable for 12 m urban buses in order to provide a reliable and cost-effective solution for the abatement of both CO2 and criteria pollutant emissions. The full exploitation of the potential of such a traction system requires a substantial enhancement of the state of the art since several issues have to be addressed. In particular, the choice of a more suitable fuel injection system and the control of the combustion process are extremely challenging. Firstly, a high-fidelity 3D-CFD model will be exploited to analyze the in-cylinder H2 fuel injection through supersonic flows. Then, after the optimization of the injection and combustion process, a 1D model of the whole engine system will be built and calibrated, allowing the identification of a “sweet spot” in the ultra-lean combustion region, characterized by extremely low NOx emissions and, at the same time, high combustion efficiencies. Moreover, to further enhance the engine efficiency well above 40%, different Waste Heat Recovery (WHR) systems will be carefully scrutinized, including both Organic Rankine Cycle (ORC)-based recovery units as well as electric turbo-compounding. A Selective Catalytic Reduction (SCR) aftertreatment system will be developed to further reduce NOx emissions to near-zero levels. Finally, a dedicated torque-based control strategy for the ICE coupled with the Energy Management Systems (EMSs) of the hybrid powertrain, both optimized by exploiting Vehicle-To-Everything (V2X) connection, allows targeting H2 consumption of 0.1 kg/km. Technologies developed in the H2-ICE project will enhance the know-how necessary to design and build engines and aftertreatment systems for the efficient exploitation of H2 as a fuel, as well as for their integration into hybrid powertrains

Hydrogen mixing and combustion in an SI internal combustion engine: CFD evaluation of premixed and DI strategies

In this study, the effect of start of injection (SOI) timing is investigated on a single cylinder spark ignited (SI) internal combustion engine (ICE) fueled with hydrogen, using Computational Fluid Dynamics (CFD) simulations. Mixing fields and combustion behaviors at different relative air-fuel ratios (λ) and injection strategies are discussed. Direct injection (DI) cases with three different SOI timings for each λ are compared against port-fuel injection (PFI) cases modeled assuming perfectly premixed charge at the intake plenum. Results for the investigated cases show that PFI cases at λ = 2 and λ = 3 have very high combustion efficiency while at λ = 3.5 partial burn occurs (only 70% of the fuel is oxidized). In DI cases, combustion efficiency decreases compared to corresponding premixed situations, as expected, but significant improvements are obtained by advancing the SOI timing towards the end of the intake stroke. In addition, early SOI timings tend to reduce the duration of initial combustion stage, CA0-10, which correlates with ignition repeatability, therefore suggesting potential benefits on combustion stability under very lean conditions. The method and results of this work can be used as a guideline for developing efficient hydrogen injection strategies

Numerical study of ammonia spray with a GDI engine injector

With the aim of expanding the knowledge on liquid ammonia sprays, this paper investigates the injection process of ammonia through Computational Fluid Dynamics (CFD) using the Lagrangian particle method, within the Reynolds Averaged Navier Stokes (RANS) approach for turbulence modeling. Numerical results and experimental data are compared in terms of liquid and vapor tip penetration, local values of Sauter Mean Diameter (SMD) and global spray morphology. This model validation process allows to build a predictive simulation framework for ammonia injection. In order to explore also the flash boiling phenomenon, results of CFD simulations of ammonia spray and the comparison with experimental data are presented for different conditions, ranging from non-flashing regimes to flash boiling conditions. Breakup model constants need to be markedly tuned for each regime, and established values for traditional fuels, like gasoline, appear not to work well with ammonia. Ultimately, this study highlights that capturing spray local details (such as local SMD values) across all the regimes with a single model or setup is still challenging, especially with a new fuel such as ammonia, whose properties differ by a large amount from more established values for hydrocarbons