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The use of hydrogen in internal combustion engines is an effective approach to significantly support the reduction of CO2 emissions from the transportation sector using technically affordable solutions. The use of direct injection is the most promising approach to fully exploit hydrogen potential as a clean fuel, while preserving targets in terms of power density and emissions. In this frame, the development of an effective combustion system largely relies on the hydrogen-air mixture formation process, so to adequately control the charge stratification to mitigate pre-ignitions and knock and to minimize NOx formation. Hence, improving capabilities of designing a correct gas jet-air interaction is of paramount importance. In this paper the analysis of the evolution of a high-pressure gas jet produced by a single-hole prototype injector operated with different pressure ratios is presented.

In recent months, the increasing debate within the European Union to review the ban on internal combustion engines has led to the pursuit of environmentally neutral solutions for ICEs, as an attempt to promote greater economic and social sustainability. Interest in internal combustion engines remains strong to uphold the principle of technological neutrality. In this perspective, the present paper proposes a numerical methodology for 3D-CFD in-cylinder simulations of hydrogen-fueled internal combustion engines. The combustion modelling relies on G-equation formulation, along with Damköhler and Verhelst turbulent and laminar flame speeds, respectively. Numerical simulations are validated with in-cylinder pressure traces and images of chemiluminescent hydrogen flames captured through the piston of a single-cylinder optical spark-ignition engine.

Research and development studies regarding the internal combustion engines are, now more than ever, crucial in order to prevent a premature disposal for this application. An innovative technology is analyzed in this paper. The traditional slider-crank mechanism is replaced by a system of two ring-like elements crafted in such a way to transform the rotating motion of one element in the reciprocating motion of the other. This leads both to a less complex engine architecture and to the possibility to obtain a wide range of piston laws by changing the profile of the two cams. The relative motion of the cams is the peculiar feature of this engine and, due to this, alongside with the thermodynamic analysis, also the tribological aspects are investigated. 3D-CFD simulations are performed for several piston laws at different engine speeds to evaluate the cylinder pressure trace to be used as input data for the development of the tribological model.

After-treatment sensors are used in the ECU feedback control to calibrate the engine operating parameters. Due to their contact with exhaust gases, especially NOx sensors are prone to soot deposition with a consequent decay of their performance. Several phenomena occur at the same time leading to sensor contamination: thermophoresis, unburnt hydrocarbons condensation and eddy diffusion of submicron particles. Conversely, soot combustion and shear forces may act in reducing soot deposition. This study proposes a predictive 3D-CFD model for the analysis of the development of soot deposition layer on the sensor surfaces. Alongside with the implementation of deposit and removal mechanisms, the effects on both thermal properties and shape of the surfaces are taken in account. The latter leads to obtain a more accurate and complete modelling of the phenomenon influencing the sensor overall performance.

Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are undergoing a rapid development, due to the ever-growing interest towards their use to decarbonize power generation applications. In the transportation sector, a key technological challenge is their thermal management, i.e. the ability to preserve the membrane at the optimal thermal state to maximize the generated power. This corresponds to a narrow temperature range of 75-80°C, possibly uniformly distributed over the entire active surface. The achievement of such a requirement is complicated by the generation of thermal power, the limited exchange area for radiators, and the poor heat transfer performance of conventional coolants (e.g., ethylene glycol). The interconnection of thermal/fluid/electrochemical processes in PEMFCs renders heat rejection as a potential performance limiter, suggesting its maximization for power density increase.

With growing concern about global warming, alternatives to fossil fuels in internal combustion engines are searched. In this context, hydrogen is one of the most interesting fuels as it shows excellent combustion properties such as laminar flame speed and energy density. In this work a CFD methodology for 3D-CFD in-cylinder simulations of engine combustion is proposed and its predictive capabilities are validated against test-bench data from a direct injection spark-ignition (DISI) prototype. The original engine is a naturally aspirated, single cylinder compression ignition (Diesel fueled) unit. It is modified substituting the Diesel injector with a spark plug, adding two direct gas injectors, and lowering the compression ratio to run with hydrogen fuel. A 3D-CFD model is built, embedding in-house developed ignition and heat transfer models besides G-equation one for combustion.

Increasingly stringent pollutant and CO2 emission standards require the car manufacturers to investigate innovative solutions to further improve the fuel economy and environmental impact of their fleets. Nowadays, NOx emissions standards are stringent for spark-ignition (SI) internal combustion engines (ICEs) and many techniques are investigated to limit these emissions. Among these, an extremely lean combustion has a large potential to simultaneously reduce the NOx raw emissions and the fuel consumption of SI ICEs. Engines with pre-chamber ignition system are promising solutions for realizing a high air-fuel ratio which is both ignitable and with an adequate combustion speed. In this work, the combustion characteristics of an active pre-chamber system are experimentally investigated using a single-cylinder research engine. The engine under exam is a large bore heavy-duty unit with an active pre-chamber fuelled with compressed natural gas.

The interest towards hydrogen fueling in internal combustion engines (ICEs) is rapidly growing, due to its potential impact on the reduction of the carbon footprint of the road transportation sector in a short-term scenario. While the conversion of the existing fleet to a battery-electric counterpart is highly debated in terms of both technical feasibility and life-cycle-based environmental impact, automotive researchers and technicians are exploring other solutions to reduce, if not to nullify, the carbon footprint of the existing ICE fleet. Indeed, ICE conversion to “green” fuels is seen as a promising short-term solution which does not require massive changes in powertrain production and end-of-life waste management. To better evaluate potentials and challenges of hydrogen fueling, a clear understanding of fuel injection and mixture formation prior to combustion is mandatory.

In the last years, pushed by a combination of environmental concerns and technological competition with alternative powertrain architectures, internal combustion engines (ICEs) have seen a growing interest in the adoption of greener fuels. Due to increasing restrictions on ICE tailpipe emissions and loudly advertised bans of ICEs from the passenger car market, OEMs find themselves at a very important crossroad: a complete electrification of their car fleet or the adoption of disruptive solutions in the existing ICE technology, such as the use of carbon-neutral or carbon-free fuels. In this paper the authors provide a CFD assessment of both potentials and limitations of the conversion of an existing direct-injected spark-ignited (DISI) engine for high-performance applications to a hydrogen-fuelled unit. A preliminary validation of the modelling framework for the conventional gasoline fuelling is performed to reduce modelling uncertainties.

Polymer Electrolyte Membrane Fuel Cell (PEMFC) are among the most promising technologies as energy conversion devices for the transportation sector due to their potential to eliminate, or greatly reduce, the production of greenhouse gases. One of the current issues with this type of technology is thermal management, which is a key aspect in the design and optimization of PEMFC, whose main aim is an effective and balanced heat removal, thus avoiding thermal gradients leading to a cell lifetime reduction as well as a decrease in the output performance. In addition, a uniform temperature distribution contributes to the achievement of a uniform current density, as it affects the rate of the electrochemical reaction. This is made even more challenging due to the low operating temperature (80°C), reducing the temperature difference for heat dissipation, and leaving a critical role to the design and optimization of the cooling circuit design.

In the recent years, the interest in heavy-duty engines fueled with Compressed Natural Gas (CNG) is increasing due to the necessity to comply with the stringent CO2 limitation imposed by national and international regulations. Indeed, the reduced number of carbon atoms of the NG molecule allows to reduce the CO2 emissions compared to a conventional fuel. The possibility to produce synthetic methane from renewable energy sources, or bio-methane from agricultural biomass and/or animal waste, contributes to support the switch from conventional liquid fuels to CNG. To drive the engine development and reduce the time-to-market, the employment of numerical analysis is mandatory. This requires a continuous improvement of the simulation models toward real predictive analyses able to reduce the experimental R&D efforts. In this framework, 1D numerical codes are fundamental tools for system design, energy management optimization, and so on.

Aiming at meeting the stringent regulations imposed by the EU and other legislators in the transport sector, various advanced combustion modes for Internal Combustion Engines (ICEs) are currently under investigation. Among those, Homogeneous Charge Compression Ignition (HCCI) appears a promising solution, simultaneously reducing pollutant emission and enhancing thermal efficiency. Hence, to simulate HCCI combustion mode, a general multi-zone model has been developed and implemented through user coding into a commercial software (GT-Power™). This model is based on a control mass Lagrangian multi-zone approach, and it incorporates a procedure based on an off-line tabulation of chemical kinetics (Tabulated Kinetic of Ignition - TKI). It performs an accurate and fast prediction of the air/fuel mixture auto-ignition, combining the accuracy of detailed chemistry with a lighter computational effort.

Knock is one of the main limitations on Spark-Ignited (SI) Internal Combustion Engine (ICE) performance and efficiency and so has been the object of study for over one hundred years. Great strides have been made in terms of understanding in that time, but certain rather elementary practical problems remain. One of these is how to interpret if a running engine is knocking and how likely this is to result in damage. Knocking in a development environment is typically quantified based on numerical descriptions of the high frequency content of a cylinder pressure signal. Certain key frequencies are observed, which Draper [1] explained with fundamental acoustic theory back in 1935. Since then, a number of approaches of varying complexity have been employed to correlate what is happening within the chamber with what is measured by a pressure transducer.

In recent years, internal combustion engine (ICE) downsizing coupled with turbocharging was considered the most effective path to improve engine efficiency at low load, without penalizing rated power/torque performance at full load. On the other side, issues related to knocking combustion and excessive exhaust gas temperatures obliged adopting countermeasures that highly affect the efficiency, such as fuel enrichment and delayed combustion. Powertrain electrification allows operating the ICE mostly at medium/high loads, shifting design needs and constraints towards targeting high efficiency under those operating conditions. Conversely, engine efficiency at low loads becomes a less important issue. In this track, the aim of this work is the investigation of the potential of the oversizing of a small Variable Valve ActuationSpark Ignition gasoline engine towards efficiency increase and tailpipe emission reduction.

The paper reports a wide numerical analysis of the well-known “Darmstadt engine” operated under motored condition. The engine, which features multiple optical accesses and is representative of currently made four-valve pentroof GDI production engines, is simulated using computational grids of increasing density and two widely adopted approaches to model turbulence, Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES). In the first part of the paper, attention is focused on the increase of grid density within the RANS modelling framework: both bulk-flow grid density and near-wall grid density are varied in order to analyse potentials and limitations of the different grid strategies and evaluate the trade-off between accuracy and computational cost.

Recently, the car manufacturers are moving towards innovative Spark Ignition (SI) engine architectures with unconventional combustion concepts, aiming to comply with the stringent regulation imposed by EU and other legislators. The introduction of burdensome cycles for vehicle homologation, indeed, requires an engine characterized by a high efficiency in the most of its operating conditions, for which a conventional SI engine results to be ineffective. Combustion systems which work with very lean air/fuel mixture have demonstrated to be a promising solution to this concern. Higher specific heat ratio, minor heat losses and increased knock resistance indeed allow improving fuel consumption. Additionally, the lower combustion temperatures enable to reduce NOX production. Since conventional SI engines can work with a limited amount of excess air, alternative solutions are being developed to overcome this constraint and reach the above benefit.

The establishment of highly-diluted combustion strategies is one of the major challenges that the next generation of sustainable internal combustion engines must face. The desirable use of high EGR rates and of lean mixtures clashes with the tolerable combustion stability. To this aim, the development of numerical models able to reproduce the degree of combustion variability is crucial to allow the virtual exploration and optimization of a wide number of innovative combustion strategies. In this study ignition experiments using a conventional coil system are carried out in a closed volume combustion vessel with side-oriented flow generated by a speed-controlled fan. Acquisitions for four combinations of premixed propane/air mixture quality (Φ=0.9,1.2), dilution rate (20%-30%) and lateral flow velocity (1-5 m/s) are used to assess the modelling capabilities of a newly developed spark-ignition model for large-eddy simulation (GLIM, GruMo-UniMORE LES Ignition Model).

In the recent years, the interest in heavy-duty engines fueled with Compressed Natural Gas (CNG) is increasing due to the necessity to comply with the stringent CO2 limitation imposed by national and international regulations. Indeed, the reduced number of carbon atoms of the NG molecule allows to reduce the CO2 emissions compared to a conventional fuel. The possibility to produce synthetic methane from renewable energy sources, or bio-methane from agricultural biomass and/or animal waste, contributes to support the switch from conventional fuel to CNG. To drive the engine development and reduce the time-to-market, the employment of numerical analysis is mandatory. This requires a continuous improvement of the simulation models toward real predictive analyses able to reduce the experimental R&D efforts. In this framework, 1D numerical codes are fundamental tools for system design, energy management optimization, and so on.

The optimal control of hybrid powertrains represents one of the most challenging tasks for the compliance with the legislation concerning CO2 and pollutant emission of vehicles. Most common off-line optimization strategies (Pontryagin minimum principle - PMP - or dynamic programming) allow to identify the optimal control along a predefined driving mission at the expense of a quite relevant computational effort. On-line strategies, suitable for on-vehicle implementation, involve a certain performance degradation depending on their degree of simplification and computational effort. In this work, a simplified control strategy is presented, where the conventional power-split logics, typical of the above-mentioned strategies, is here replaced with an alternative utilization of the thermal and electric units for the vehicle driving (Efficient Thermal Electric Skipping Strategy - ETESS).

This paper reports a numerical and experimental analysis on a twin-cylinder turbocharged Spark Ignition engine carried out to investigate the cylinder-to-cylinder variability in terms of performance, combustion evolution and exhaust emissions. The engine was tested at 3000 rpm in 20 different steady-state operating conditions, selected with the purpose of observing the influence of cylinder-by-cylinder A/F ratio variations and the EGR effects on the combustion process and exhaust emissions for low to medium/high loads. The experimental outcomes showed relevant differences in the combustion evolution (characteristic combustion angles) between cylinders and not negligible variations in the emissions of the single cylinder exhaust and the overall engine one. This misalignment resulted to be due to differences in the injected fuel amount by the port injectors in the two cylinders, mainly deriving from the specific fuel rail geometry.