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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.

Biogas is a gas resulting from biomass, with a volumetric content of methane (CH4) usually ranging between 50% and 70%, and carbon dioxide (CO2) content between 30% and 50%; it can also contain hydrogen (H2) depending on the feedstock. Biogas is generally used to generate electricity or produce heat in cogeneration system. Due to its good efficiency through the rapid combustion and lean air-fuel mixture, Homogeneous Charge Compression Ignition (HCCI) engine is a good candidate for such application. However, the engine load must be kept low to contain the high-pressure gradients caused by the simultaneous premixed combustion of the entire in-cylinder charge. The homogenous charge promotes low particulate emissions, and the dilution helps in containing maximum in-cylinder temperature, hence reducing nitrogen oxide emissions. However, HC and CO levels are in general higher than in SI combustion.

The increased interest in ammonia as a hydrogen carrier and a carbon-free fuel for combustion applications continues to present several challenges to address. Moreover, the high auto-ignition temperature (925 K) for ammonia limits its use in compression ignition engines because excessively high compression ratio are required. One way to retrofit diesel engine is to help the ignition by injecting a pilot injection of reactive fuel, like diesel or biodiesel. In this study, the ammonia engine ignited by a dodecane pilot injection is investigated with a maximum ammonia energy share (until 98.5%). The effect of split diesel injection strategy in two-steps under medium load operating conditions is studied as a function of ammonia/air equivalence ratio. Splitting this injection reduces NOX, CO, UHC and unburnt NH3 emissions at the exhaust, even it remains above the recommended emissions limit, especially at stoichiometric or slightly rich ammonia/air mixture.

Hydrogen-fueled internal combustion engines (H2ICEs) have emerged as a promising technology for reducing greenhouse gas emissions in the transportation sector. However, due to the unique properties of hydrogen, especially under ultra-lean conditions, the combustion characteristics of hydrogen flames differ significantly from those of conventional fuels. This research focuses on evaluating the combustion process and cycle-to-cycle variations (CCVs) in a single-cylinder port-fuel injection H2ICE, as well as their impact on performance parameters. To assess in-cylinder combustion, three indicators of flame development are utilized and compared to the fundamental properties of hydrogen. The study investigates the effects of various factors including fuel-air equivalence ratio (ranging from 0.2 to 0.55), engine load (IMEP between 1 and 4 bar), and engine speed (900 to 1500 rpm).

The goal of mitigating climate change has driven research to the use of carbon-free energy sources. In this regards, green hydrogen appears as one of the best options, however, its storage remains difficult and expensive. Indeed, there is room to consider the use of ammonia (an efficient hydrogen carrier) directly as a fuel for internal combustion engines or gas turbines. Currently, there are very few works in the literature describing liquid ammonia sprays, both from experimental and modeling point of view, and especially dealing with flash-boiling conditions. In this research work, the direct injection ammonia spray is modeled with the Lagrangian particle approach, building up a numerical model within the OpenFOAM framework, for transient analyses using the U-RANS approach.

In the search for zero-carbon emissions and energy supply security, hydrogen is one of the fuels considered for internal combustion engines. The state-of-the-art studies show that a good strategy to mitigate NOx emissions in hydrogen-fueled spark-ignition engines (H2ICE) is burning ultra-lean hydrogen-air mixtures in current diesel architectures, due to their capability of standing high in-cylinder pressures. However, it is well-known that decreasing equivalence ratio leads to higher engine instability and greater cycle-to-cycle variations (CCVs). Nevertheless, hydrogen flames, especially at low equivalence ratios and high pressures, present thermodiffusive instabilities that speed up combustion, changing significantly the flame development and possibly its variability. This work evaluates the hydrogen combustion and their CCVs in two single-cylinder diesel baseline H2ICEs (light-duty and medium-duty) and their influence on performance parameters.

Ammonia is now recognized as a very serious asset in the context of the hydrogen energy economy, thanks to its non-carbon nature, competitive energy density and very mature production, storage and transport processes. If produced from renewable sources, its use as a direct combustion fuel could participate to the flexibility in the power sector as well as help mitigating fossil fuel use in certain sectors, such as long-haul shipping. However, ammonia presents unfavorable combustion properties, requiring further investigation of its combustion characteristics in practical systems. In the present study, a modern single-cylinder spark-ignition engine is fueled with gaseous ammonia/air mixtures at various equivalence ratios and intake pressures. The results are compared with methane/air and previous ammonia/hydrogen/air measurements, where hydrogen is used as combustion promoter. In-cylinder pressure and exhaust concentrations of selected species are measured and analyzed.

The present social context imposes effective reductions of transport greenhouse gases and pollutant emissions. To answer to this demand, car manufacturers adopted technologies such as downsizing, turbocharging, intense in-cylinder aerodynamics and diluted combustion process. In this context, to master mixture ignition is crucial to ensure an efficient heat release. To get to a clearer knowledge about the physics holding early stages of premixed mixture combustion, the PRISME institute in the framework of the French government research project ANR MACDOC generated a consistent experimental database to study ignition and spherical flame propagation processes in a constant volume vessel in laminar and turbulent environment.

While the optimization of the internal combustion engine (ICE) remains a very important topic, alternative fuels are also expected to play a significant role in the reduction of CO2 emissions. High energy densities and handling ease are their main advantages amongst other energy carriers. Ammonia (NH3) additionally contains no carbon and has a worldwide existing transport and storage infrastructure. It could be produced directly from renewable electricity, water and air, and is thus currently considered as a smart energy carrier and combustion fuel. However, ammonia presents a low combustion intensity and the risk of elevated nitrogen-based emissions, thus rendering in-depth investigation of its suitability as an ICE fuel necessary. In the present study, a recent single-cylinder spark-ignition engine is fueled with gaseous ammonia/hydrogen/air mixtures at various hydrogen fractions, equivalence ratios and intake pressures.

In Spark Ignition engines, the heat release rate is not only piloted by the mixture reactivity but also by its sensitivity to stretch effects. Only few results can be found in the literature about flame stretch effect in SI engine configurations. For this study, three different fuels (Methane, Propane, Iso-octane) were studied, but at different air-fuel lean mixture conditions, to present almost equivalent laminar flame speeds and thermo-dynamical properties at ignition timing condition. Besides those mixtures present different Lewis numbers which are relevant parameters to describe flame-stretch interactions. Mie-scattering tomography was then performed in an optical Spark Ignition (S.I.) engine. Using a high speed camera, flame propagation images were acquired through the piston. Thermodynamic analyses based on in-cylinder pressure traces were performed to estimate in-cylinder temperature and burnt mass fraction during the engine cycle.

The current decrease in fossil energy resources requires a diversification of the liquid and gaseous fuels potentially consumable in internal combustion engines. The use of these fuels modifies the combustion process and the heat released as well. In a Spark Ignition (SI) engine, the heat released is mainly piloted not only by the mixture reactivity but also by its sensitivity to stretch effects. Only a few results can be found in the literature about stretch effects for SI engine configurations. The purpose of the present paper is to evaluate stretch effects on the flame front propagation in an optical SI engine and to investigate the relative importance of these effects depending on the fuel considered. Different air-fuel mixtures presenting different flame stretch sensitivities were selected. Four different engine regimes (1400, 1600, 1800 and 2000 rpm) were studied for all the mixtures in order to evaluate the impact of different turbulence intensities.