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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.

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.

Knock occurrence is a widely recognized phenomenon to be controlled during the development and optimization of S.I. engines, since it bounds both compression ratio and spark advance, hence reducing the potential in gaining a lower fuel consumption. As a consequence, a clear understanding of the engine parameters affecting the onset of auto-ignition is mandatory for the engine setup. In view of the complexity of the phenomena, the use of combined experimental and numerical investigations is very promising. The paper reports such a combined activity, targeted at characterizing the combustion behavior of a small unit displacement two-stroke SI engine operated with either Gasoline or Natural Gas (CNG). In the paper, detailed multi-cycle 3D-CFD analyses, starting for preliminary 1D computed boundary conditions, are performed to accurately characterize the engine behavior in terms of scavenging efficiency and combustion.

Despite syngas is a promising alternative fuel for internal combustion engines (ICEs), its extensive adoption has not been adequately investigated so far. The dedicated literature offers several fundamental studies dealing with H2/CO blends burning at high pressure and room temperature, as well as preheated mixture at low pressure. However, these thermodynamic states are far from the operational conditions typical of ICEs. Therefore, it is essential to investigate the syngas combustion process at engine-like conditions to shed light on this fuel performance, in order to fully benefit from syngas characteristics in ICE application. One of the key properties to characterize a combustion process is laminar flame speed, which is also used by the most widespread turbulent combustion models.

Conventional fossil fuels are more and more regulated in terms of both engine-out emissions and fuel consumption. Moreover, oil price and political instabilities in oil-producer countries are pushing towards the use of alternative fuels compatible with the existing units. N-Butanol is an attractive candidate as conventional gasoline replacement, given its ease of production from bio-mass and key physico-chemical properties similar to their gasoline counterpart. A comparison in terms of combustion behavior of gasoline and n-Butanol is here presented by means of experiments and 3D-CFD simulations. The fuels are tested on a single-cylinder direct-injection spark-ignition (DISI) unit with an optically accessible flat piston. The analysis is carried out at stoichiometric undiluted condition and lean-diluted mixture for both pure fuels.

A new generation of highly downsized SI engines with specific power output around or above 150 HP/liter is emerging in the sport car market sector. Technologies such as high-boosting, direct injection and downsizing are adopted to increase power density and reduce fuel consumption. To counterbalance the increased risks of pre-ignition, knock or mega-knock, currently made turbocharged SI engines usually operate with high fuel enrichments and delayed (sometimes negative) spark advances. The former is responsible for high fuel consumption levels, while the latter induce an even lower A/F ratio (below 11), to limit the turbine inlet temperature, with huge negative effects on BSFC. A possible solution to increase knock resistance is investigated in the paper by means of 3D-CFD analyses: water/methanol emulsion is port-fuel injected to replace mixture enrichment while preserving, if not improving, indicated mean effective pressure and knock safety margins.

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.

The paper investigates the low-temperature cranking operation of a current production automotive Gasoline Direct Injected (GDI) by means of 3D-CFD simulations. Particular care is devoted to the analysis of the hollow cone spray evolution within the combustion chamber and to the formation of fuel film deposits on the combustion chamber walls. Due to the high injected fuel amount and the strongly reduced fuel vaporization, wall wetting is a critical issue and plays a fundamental role on both the early combustion stages and the amount of unburnt hydrocarbons formation. In fact, it is commonly recognized that most of the unburnt hydrocarbon emissions from 4-stroke gasoline engines occur during cold start operations, when fuel film in the cylinder vaporize slowly and fuel can persist until the exhaust stroke.

The paper reports the application of LES multi-cycle analysis for the characterization of cycle to cycle variability (hereafter CCV) of a highly downsized DISI engine for sport car applications. The analysis covers several subsequent engine cycles operating the engine at full load, peak power engine speed. Despite the chosen engine operation is usually considered relatively stable, relevant fluctuations were experimentally measured in terms of in-cylinder pressure evolution and combustion phasing. On one hand, despite the complex architecture of the V-8 engine, the origin of such CCV is considered to be poorly related to cyclic fluctuations of the gas-dynamics within the intake and exhaust pipes, since acquisitions of the instantaneous pressure traces at both the intake port entrance and exhaust port junction by fast-response pressure measurements over 250 subsequent engine cycles showed almost negligible differences in both amplitude and phasing compared to those within the cylinder.

In order to improve fuel conversion efficiency, currently made spark-ignited engines are characterized by the adoption of gasoline direct injection, supercharging and/or turbocharging, complex variable valve actuation strategies. The resulting increase in power/size ratios is responsible for substantially higher average thermal loads on the engine components, which in turn result in increased risks of both thermo-mechanical failures and abnormal combustion events such as surface ignition or knock. The paper presents a comprehensive numerical methodology for the accurate estimation of knock tendency of SI engines, based on the integration of different modeling frameworks and tools. Full-cycle in-cylinder analyses are used to estimate the point-wise heat flux acting on the engine components facing the combustion chamber.

New SI engine generations are characterized by a simultaneous reduction of the engine displacement and an increase of the brake power; such targets are achieved through the adoption of several techniques such as turbocharging, direct fuel injection, variable valve timing and variable port lengths. This design approach, called “downsizing”, leads to a marked increase in the thermal loads acting on the engine components, in particular on those facing the combustion chamber. Hence, an accurate evaluation of the thermal field is of primary importance in order to avoid mechanical failures. Moreover, the correct evaluation of the temperature distribution improves the prediction of pointwise abnormal combustion onset.

The paper investigates the idle operating condition of a current production turbocharged Gasoline Direct Injected (GDI) high performance engine both from an experimental and a numerical perspective. Due to the low engine speed, to the low injection pressure and to the null contribution of the turbocharger, the engine condition is far from the standard points of investigation. According to the low heat flux due to combustion, temperature levels are low and reduced fuel evaporation is expected. Consequently, fuel spray evolution within the combustion chamber and spray/wall interaction are key points for the understanding of the combustion process. In order to properly investigate and understand the many complex phenomena, a wide set of engine speeds was experimentally investigated and, as far as the understanding of the physics of spray/wall interaction is concerned, many different injection strategies are tested.

Hybrid URANS/LES turbulence modeling is rapidly emerging as a valuable complement to standard LES for full-engine multi-cycle simulation. Among the available approaches, zonal hybrids are potentially attractive due to the possibility of clearly identify URANS and LES zones, eventually introducing further zone types with dynamically switching behavior. The present work aims at evaluating the impact of different zonal configurations on the simulated flow statistics using the well-assessed TCC-III experimental engine setup. More specifically, different methods (URANS, LES or seamless DES) are applied inside the cylinder volume, as well as into the intake/exhaust ports and plenums. For each of the five tested configurations, in-cylinder flow features are compared against the reference TCC-III experimental measurements, in terms of velocity field statistics and quality indices.

The paper aims at providing information about the in-cylinder flow structure and its evolution of a high speed direct injection (HSDI) four valve per cylinder engine for off-highway applications. Fully transient CFD analyses by means of state-of-the-art tools and methodologies are carried out for the whole intake and compression strokes, in order to evaluate port effects on both engine permability and in-cylinder flow field evolution. Organized mean motions (i.e., swirl, tumble and squish) are investigated, trying to establish general rules in the port design optimization process, addressing relationships between the relative port orientation and the in-cylinder flow structure. Different port configurations are compared, each deriving from the rotation of the BASE port configuration on two different planes, the former being perpendicular to the cylinder axis, while the latter being parallel to the cylinder axis.

The detailed study of part-load conditions is essential to characterize engine-out emissions in key operating conditions. The relevance of part-load operations is further emphasized by the recent regulations such as the new WLTP standard. Combustion development at part-load operations depends on a complex interplay between moderate turbulence levels (low engine speed and tumble ratio), low in-cylinder pressure and temperature, and stoichiometric-to-lean mixture quality (to maximize fuel efficiency). From a modelling standpoint, the reduced turbulence intensity compared to full-load operations complicates the interaction between different sub-models (e.g., reconsideration of the flamelet hypothesis adopted by common combustion models). In this article, the authors focus on chemistry-based simulations for laminar flame speed of gasoline surrogates at conditions typical of part-load operations. The analysis is an extension of a previous study focused on full-load operations.

The paper describes an integrated methodology for the accurate characterization of the thermal behavior of internal combustion engines, with particular reference to a high performance direct injected SI engine for sport car applications. The engine is operated at full load and maximum power revving speed, which is known to be critical from the point of view of thermal stresses on the engine components. In particular, two different sets of 3D-CFD calculations are adopted: on one side, full-cycle in-cylinder analyses are carried out to estimate the point wise thermal heat flux due to combustion on the engine components facing the combustion chamber. On the other side, full-engine multi-region CHT calculations covering the engine coolant jacket and the surrounding metal components are used to compute the point wise temperature distribution within the engine head, liner and block.

The paper aims at providing information about the influence of the combustion chamber shape on the combustion process evolution in a high speed direct injection (HSDI) small unit displacement engine for off-highway applications. Small HSDI Diesel engines require a deep optimisation process in order to maximize specific power output, while limiting pollutant emissions without additional expensive pollutant aftertreatment equipments. Making reference to a current production engine, the purpose of this paper is to investigate the influence of combustion chamber design on both engine performances and combustion efficiency. The actual piston omega-shape is progressively distorted in order to assess the influence of some of the main bowl-features on both mean-flow evolution, mixture formation and pollutants.

The recent interest in alternative non-fossil fuels has led researchers to evaluate several alcohol-based formulations. However, one of the main requirements for innovative fuels is to be compatible with existing units’ hardware, so that full replacement or smart flexible-fuel strategies can be smoothly adopted. n-Butanol is considered as a promising candidate to replace commercial gasoline, given its ease of production from bio-mass and its main physical and chemical properties similar to those of Gasoline. The compared behavior of n-butanol and gasoline was analyzed in an optically-accessible DISI engine in a previous paper [1]. CFD simulations explained the main outcomes of the experimental campaign in terms of combustion behavior for two operating conditions. In particular, the first-order role of the slower evaporation rate of n-butanol compared to gasoline was highlighted when the two fuels were operated under the same injection phasing.

In spark-ignited direct-injected engines, the formation of fuel pools on the piston is one of the major promoters of unburnt hydrocarbons and soot: in order to comply with the increasingly stringent emission regulations (EU6 and forthcoming), it is therefore necessary to limit fuel deposit formation. The combined use of advanced experimental techniques and detailed 3D-CFD simulations can help to understand the mechanisms driving fuel pool formation. In the paper, a combined experimental and numerical characterization of pool formation in a GDI engine is carried out to investigate and understand the complex interplay of all the mentioned factors. In particular, a low-load low-rpm engine operation is investigated for different ignition phasing, and the impact of both fuel formulation and instantaneous piston temperature variations in the CFD analyses are evaluated.

The paper aims at defining a methodology for the prediction and understanding of knock tendency in internal combustion engine piston crevices by means of CFD simulations. The motivation for the analysis comes from a real design requirement which appeared during the development of a new high performance SI unit: it is in fact widely known that, in high performance engines (especially the turbocharged ones), the high values of pressure and temperature inside the combustion chamber during the engine cycle may cause knocking phenomena. “Standard” knock can be easily recognized by direct observation of the in-cylinder measured pressure trace; it is then possible to undertake proper actions and implement design and control improvements to prevent it with relatively standard 3D-CFD analyses.