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The abatement of carbon dioxide and pollutant emissions on motorbike spark-ignition (SI) engines is a challenging task, considering the small size, the low cost and the high power-to-weight ratio required by the market for such powertrain. In this context, the passive pre-chamber (PPC) technology is an attractive solution. The combustion duration can be reduced by igniting the air-fuel mixture inside a small volume connected to the cylinder, unfolding the way to high engine efficiencies without penalization of the peak performance. Moreover, no injectors are needed inside the PPC, guaranteeing a cheap and fast retrofitting of the existing fleet. In this work, a 3D computational fluid dynamics (CFD) investigation is carried out over an experimental configuration of motorbike SI engine, operated at fixed operating conditions with both traditional and PPC configurations.

The target of the upcoming automotive emission regulations is to promote a fast transition to near-zero emission vehicles. As such, the range of ambient and operating conditions tested in the homologation cycles is broadening. In this context, the proposed work aims to thoroughly investigate the potential of post-oxidation phenomena in reducing the light-off time of a conventional three-way catalyst. The study is carried out on a turbocharged four-cylinder gasoline engine by means of experimental and numerical activities. Post oxidation is achieved through the oxidation of unburned fuel in the exhaust line, exploiting a rich combustion and a secondary air injection dedicated strategy. The CFD methodology consists of two different approaches: the former relies on a full-engine mesh, the latter on a detailed analysis of the chemical reactions occurring in the exhaust line.

Air pollution is a significant environmental issue, and exhaust emissions from internal combustion engines are one of the primary sources of harmful pollutants. The transportation sector, which includes road vehicles, contributes to a large share of these emissions. In Europe, the latest emission legislation (Euro 7) proposes more stringent limits and testing conditions for vehicle emissions. To meet these limits, the automotive industry is actively developing innovative exhaust emission-control technologies. With the growing prevalence of electrification, internal combustion engines are subject to continuous variations in load and engine speed, including phases where the engine is switched off. The result is an operating condition characterized by successive cold starts. In this context, the challenge in coping with the emission limits is to minimize the light-off time and prevent fast light-out conditions during idling or city driving.

Turbulent Jet Ignition (TJI) represents one of the most effective solution to improve engine efficiency and to reduce fuel consumption and pollutants emission. Even if active prechambers allow a precise control of the air-fuel ratio close to the spark plug and the ignition of ultra-lean mixtures in the main chamber, passive prechambers represent a more attractive solution especially for passenger cars thanks to their simpler and cheaper configuration, which is easier to integrate into existing engines. The main challenge of passive prechambers is to find a geometry that allows to use TJI in the whole engine map, especially in the low load/speed region, without the use of a second sparkplug in the main chamber. To this end, this works reports a CFD study coupled with an experimental investigation to overcome this limitation.

With a view to reducing the environmental impact of fossil fuels, advanced lignin-based biofuels could provide a valuable contribute, since lignin is the most abundant biopolymer on earth after cellulose. However, its thermophysical properties would hamper its use as a pure fuel. In this work we investigated the combustion behavior of sprays of a liquid lignin-methanol blend and evaluated its potential as a low-carbon marine fuel for large two-stroke engines. To this end, an experimental campaign was conducted in an optically accessible combustion chamber whose main dimensions correspond to those of a single cylinder for large two-stroke engines. The chamber is provided with optical accesses for optical diagnostics of the combustion process. The combustion of the mixture was ignited using a diesel pilot jet as the ignition source. Two marine injectors are mounted in the chamber, namely “main” and “pilot” injectors.

The last environmental regulations on passenger vehicles’ emissions harden constraints on designing powertrains. A promising solution consists in vehicle electrification leading to hybrid configurations: the tank-to-wheel pollutant emissions can be drastically reduced combining features of typical battery electric vehicles adding an Internal Combustion Engine (ICE) controlled as a Range Extender (REX). Furthermore, HC and CO/CO2 emissions can be avoided using green hydrogen as fuel for the ICE; moreover, in absence of a mechanical coupling between REX and wheels the best operating conditions in terms of maximum ICE efficiency may be easily achieved. In this work, a light quadricycle (EU L6e, classification) series hybrid vehicle with four in-wheel motors is studied for the application of a range extender system.

The growing concern about Greenhouse Gas (GHG) emissions led institutions to further reduce the limits on vehicle-related CO2 emissions. Therefore, car manufacturers are developing vehicles with low environmental impact, like Hybrid-Electric Vehicles (HEVs), which in the series architecture employ an Internal Combustion Engine (ICE) coupled with an electric generator for battery recharging, thus extending the range of a Battery Electric Vehicle (BEV). For this kind of application, small four-stroke Spark Ignition (SI) engines are preferred, as they are a proven and reliable solution to increase the driving range with very low environmental impact. In series hybrid-electric powertrains, the ICE is decoupled from the drive wheels, then it can operate in a steady-state high-efficiency working point, regardless of the power required by the mission profile. The benefits of lean combustion can be exploited to increase efficiency and reduce CO2 and NOx emissions.

In future decarbonized scenarios, hydrogen is widely considered as one of the best alternative fuels for internal combustion engines, allowing to achieve zero CO2 emissions at the tailpipe. However, NOx emissions represent the predominant pollutants and their production has to be controlled. In this work different strategies for the control and abatement of pollutant emissions on a H2-fueled high-performance V8 twin turbo 3.9L IC engine are tested. The characterization of pollutant production on a single-cylinder configuration is carried out by means of the 1D code Gasdyn, considering lean and homogeneous conditions. The NOx are extremely low in lean conditions with respect to the emissions legislation limits, while the maximum mass flow rate remains below the turbocharger technical constraint limit at λ=1 only.

Focusing on coastal or inland navigation cities, where emissions from ships are not negligible concerning global ones, the possibility of reducing exhaust gas pollution would have more benefits for public health and air quality. Therefore, in recent years, increasing attention on environmental sustainability is driving the shipbuilding industry towards greener propulsion based on full-electric or hybrid-electric propulsion systems. This work is presented a parallel hybrid system composed of two electric motors, one internal combustion engine, and lithium battery storage. All motors are coupled to the propeller through a specially designed transmission system based on the High Sliding Gear theory (HSG). The hybrid-electric propulsion system is designed to extender the battery pack durability, ensuring a smooth profile of the required current, through the complementary action of the batteries and the internal combustion engine.

The urban mobility electrification has been proposed as the main solution to the vehicle emission issues in the next years. However, internal combustion engines have still great potential to decarbonize the transport sector through the use of low/zero-carbon fuels. Alcohols such us methanol, have long been considered attractive alternative fuels for spark ignition engines. They have properties similar to those of gasoline, are easy to transport and store. Recently, great attention has been devoted to gaseous fuels that can be used in existing engine after minor modification allowing to drastically reduce the pollutant emissions. In this regard, this study tries to provide an overview on the use of alternative fuels, both liquid and gaseous in spark ignition engines, highlighting the benefits as well as the criticalities. The investigation was carried out on a small displacement spark ignition engine capable to operate both in port fuel and direct injection mode.

SI engines fueled with hydrogen represent a promising powertrain solution to meet the ambitious target of carbon-free emissions at the tailpipe. Therefore, fast and reliable numerical tools can significantly support the automotive industry in the optimization of such technology. In this work, a 1D-3D methodology is presented to simulate in detail the combustion process with minimal computational effort. First, a 1D analysis of the complete engine cycle is carried out on the user-defined powertrain configuration. The purpose is to achieve reliable boundary conditions for the combustion chamber, based on realistic engine parameters. Then, a 3D simulation of the power-cycle is performed to mimic the combustion process. The flow velocity and turbulence distributions are initialized without the need of simulating the gas exchange process, according to a validated technique.

This work has the objective to present the extension of a novel quasi-dimensional model, developed to simulate the combustion process in diesel Compression Ignition (CI) engines, to describe this process when Dimethyl ether (DME) is used as fuel. DME is a promising fuel in heavy-duty CI engines application thanks to its high Cetane Number (CN), volatility, high reactivity, almost smokeless combustion, lower CO2 emission and the possibility to be produced with renewable energy sources. In this paper, a brief description of the thermodynamic model will be presented, with particular attention to the implementation of the Tabulated Kinetic Ignition (TKI) model, and how the various models interact to simulate the combustion process. The model has been validated against experimental data derived from constant-volume DME combustion, in this case the most important parameters analyzed and compared were the Ignition Delay (ID) and Flame Lift Off Length (FLOL).

The tightening trend of regulations on the levels of admitted pollutant emissions has given a great spur to the research work in the field of combustion and after-treatment devices. Despite the improvements that can be applied to the development of the combustion process, pollutant emissions cannot be reduced to zero; for this reason, the aftertreatment system will become a key component in the path to achieving near-zero emission levels. This study focuses on the numerical analysis and optimization of different metallic substrates, specifically developed for three-way catalyst (TWC) and Diesel oxidation catalyst (DOC) applications, to improve their thermal efficiency by reducing radial thermal losses through the outer mantle. The optimization process relies on computational fluid dynamics (CFD) simulations supported by experimental measurements to validate the numerical models carried out under uncoated conditions, where chemical reactions do not occur.

The reduction of the catalyst light-off time at the engine cold start represents a key factor for the pollutant emissions control from vehicles tested on homologation cycles and real drive conditions. The adoption of heating strategies to increase the temperature of the catalytic substrate in the early phase of the engine start is regarded as a promising solution. The present study focuses on the application of electrical heated catalyst (EHC) in an after-treatment line for a spark-ignition gasoline engine. The analysis is carried out by means of an advanced CFD framework, which includes the modeling of catalytic reactions in the substrates and accounts for the thermal evolution of all the components included in the after-treatment system.

Hybrid electric vehicles are a suitable solution for the transition from fossil fuels-based transportation to electric mobility. They have the benefits of zero-emissions operation when only the electric engine is used preventing the typical range anxiety of full-electric vehicles. Also, they can have a low battery pack capacity and weight thanks to the continuous recharge from the internal combustion engine that becomes the only responsible for exhaust emissions. A practical solution to limit the combustion engine emissions is represented by the range extender configuration, where the engine works at a fixed operating point with the highest efficiency serving uniquely as a battery charger. In the face of the current world situation and future changes, research for alternative energy sources is crucial. Hydrogen can be used as an alternative fuel for common internal combustion engines; moreover, it has the great advantage of high efficiency (about 44%).

Direct injection spark ignition engines represent an effective technology to achieve the goal of carbon dioxide emission reduction. Further reduction of the carbon footprint can be achieved by using carbon-neutral fuels. Oxygenated alcohols are well consolidated fuels for spark ignition engines providing also the advantages of knock resistance and low soot tendency production. Methanol and ethanol are possible candidates as alternative fuels to gasoline due to their similar properties. In this study a blend at 25 % v/v of ethanol in gasoline (E25) and a blend with 80% gasoline, 5 % v/v ethanol and 15% v/v of methanol (GEM) were tested. These blends were considered since E25 is already available at fuel pump in some countries. The GEM blend, instead, could represent a valid alternative in the next future. Experiments were carried out on a high performance, turbocharged 1.8 L direct injection spark ignition engine over the Worldwide Harmonized Light Vehicles Test Cycle.

The paper illustrates and validates a novel predictive combustion model for the estimation of performances and pollutant production in CI engines. The numerical methodology was developed by the authors for near real-time applications, while aiming at an accurate description of the air mixing process by means of a multi-zone approach of the air-fuel mass. Charge stratification is estimated via a 2D representation of the fuel spray distribution that is numerically derived by an axial one-dimensional control-volume description of the direct injection. The radial coordinate of each control volume is reconstructed a posteriori by means of a local distribution function. Fuel mass clustered in each zone is further split in ‘liquid’, ‘unburnt’ and ‘burnt’ sub-zones, given the local properties of the fuel spray control volumes with respect to space-time location of modelled ignition delay, liquid length, and flame lift-off.

In the intermediate stage towards zero-emissions, use of methane-hydrogen blends in spark ignition (SI) engines could represent an attractive application. The present work investigated the relevance of empirical base rules for choosing maximum brake torque spark timing settings when using methane-hydrogen blends. A 0D/1D model was used for investigating the optimized ignition for maximizing engine output. Calibration was performed by using in-cylinder pressure data recorded on a methane fueled small size SI engine for two-wheel applications. After adaptations of the model such as valves timing, for rendering it more representative for power generation applications, the investigation was focused on how MBT spark advance was correlated to the 50% mass fraction burned mark (CA50) and peak pressure location. The fact that they were optimized for methane was found to be essential only for high concentrations of hydrogen.

In the next years, the upcoming emission legislations are expected to introduce further restrictions on the admittable level of pollutants from vehicles measured on homologation cycles and real drive tests. In this context, the strict control of pollutant emissions at the cold start will become a crucial point to comply with the new regulation standards. This will necessarily require the implementation of novel strategies to speed-up the light-off of the reactions occurring in the after-treatment system, since the cold start conditions are the most critical one for cumulative emissions. Among the different possible technological solutions, this paper focuses on the evaluation of the potential of a burner system, which is activated before the engine start. The hypothetical burner exploits the lean combustion of an air-gasoline mixture to generate a high temperature gas stream which is directed to the catalyst section promoting a fast heating of the substrate.

Within the context of environmental impact reduction for small size spark ignition (SI) engines, especially green-house gas emissions, this study looked at laminar flame speed as an optimization parameter for hydrogen-methane fueled micro-generators. To this aim, SI engine operation was modeled in a 0D/1D simulation framework, so as to identify the best choice of methane-hydrogen ratios in different conditions. Starting from experimental data recorded on a small size engine, an optimization method was implemented for achieving the proposed goal. One of the main conclusions is that high concentrations of hydrogen and resulting fast burn rates are beneficial at high engine speed settings, while the opposite is true at low engine speed. Hydrogen addition was also considered as an additional control margin during lean operation, given that stable combustion can be achieved even with very low equivalence ratios.