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A burning process in a combustion chamber of an internal combustion engine is very important to know the maximum temperature of the gases, the speed of combustion, the ignition delay time of fuel and air mixture exact moment at which ignition will occur. The automobilist industry has invested considerable amounts of resources in numerical modeling and simulations in order to obtain relevant information about the processes in the combustion chamber and then extract the maximum engine performance control the emission of pollutants and formulate new fuels. This study aimed to general construction and instrumentation of a shock tube for measuring shock wave. As specific objective was determined reaction rate and ignition delay time of diesel and ethanol doped with different levels of additive enhancer cetane number. The results are compared with the delays measured for the ignition diesel and biodiesel.

In the present study, ethanol was added in lower proportions to non-edible vegetable oil “Schleichera oleosa” or “Kusum”, to evaluate various performance and emission characteristics of a single cylinder; diesel engine. For engine's trial, four samples were prepared with 5%, 10%, 15% and 20% ethanol in kusum oil (v/v) and the blends were named as E5K95, E10K90, E15K85 and E20K80 respectively. Neat Kusum oil was named as K100. The results indicated that brake thermal efficiency (BTE) was found to increase with increase in volume fraction of ethanol in the kusum oil. E5K95, E10K90, E15K85 and E20K80 test fuels exhibited maximum BTE of 25.4%, 26.4%, 27.4% and 27.7% respectively as compared to 23.6% exhibited by the neat Kusum oil. Similarly, full load brake specific energy consumption (BSEC) decreased from 16.3MJ/kWh in case of neat Kusum oil to 15.1MJ/kWh for E20K80 with an almost linear reduction pattern with increased ethanol composition in the test fuel. Full load carbon monoxide emissions were found to be 0.18% volume for neat Kusum oil which was reduced to 0.1% for E20K80. Similarly, smoke emissions and unburnt hydrocarbons were also found to be reduced by a margin of 7-12% compared to the K100 operation. However, E5K95, E10K90, E15K85 and E20K80 test fuels exhibited 779, 890, 860 and 877 ppm each of NO x emissions as compared to 795 ppm exhibited by the neat Kusum oil.

Vegetable oils have energy content suitable to be used as compression ignition (CI) engine fuel. However, several operational and durability problems of using straight vegetable oils in CI engines are reported in the literature, which are primarily caused by their higher viscosity and low volatility compared to mineral diesel. The viscosity can be brought in acceptable range by (i) chemical process of transesterification, (ii) blending of oil with mineral diesel or (iii) by heating the vegetable oil using exhaust gas waste heat. Reduction of viscosity by blending or exhaust gas heating saves the chemical processing cost of transesterification. Present experimental investigations were carried out for evaluating combustion, performance and emission behavior of Jatropha oil blends in unheated conditions in a direct injection CI engine at different load and constant engine speed (1500 rpm). Analysis of in-cylinder pressure rise, instantaneous heat release and cumulative heat release was carried out. All test blends exhibited similar combustion stages as mineral diesel; however, Jatropha oil blends showed earlier start of combustion but lower heat release rate during premixed combustion phase for all engine loads. The crank angle position of peak cylinder pressure for vegetable oil blends shifts towards top dead center compared to baseline diesel. Combustion duration was found to be comparable with diesel up to 20% concentration of Jatropha oil in the fuel. HC, CO and NO emissions were found to slightly increase with increase in Jatropha oil content in the fuel blends.

A comparison of the NHTSA advanced dummy and the Hybrid III is presented in this paper based on their performance in repeated sled tests under 3 different restraint systems. The restraint systems considered are: the airbag alone, the 3-point belt alone, and a combined use of the airbag and the 3-point belt. Various time-histories pertaining to accelerations, angular velocities, deflections and forces have been compared between the two dummies in order to study their repeatability. The Hybrid III appears to be more repeatable than the NHTSA advanced dummy in its response in one case, that of restraint with the 3-point belt alone. The response of the NHTSA advanced dummy in two other restraint modes, the airbag alone and the combination of 3-point belt and airbag, appears to be no less repeatable than that of Hybrid III in this series of tests. The variability in the sled pulse appears to mask the differences, if any, in the variability of response between the two dummies in two later cases. Under some restraint configurations, for some body segments, the NHTSA advanced dummy appears to show better repeatability. In addition, it appears that the read-out of the chest-deflection measurement system in the NHTSA advanced dummy is not well defined because it is influenced by the rotation of the upper spine relative to the lower spine. (A) For the covering abstract see ITRD E106439.

he use of lean or ultra-lean ratios is an efficient and proven strategy to reduce fuel consumption and pollutant emissions. However, the lower fuel concentration in the cylinder hinders the mixture ignition, requiring greater energy to start the combustion. The prechamber is an efficient method to provide high energy favoring the ignition process. It presents the potential to reduce the emission levels and the fuel consumption, operating with lean burn mixtures and expressive combustion stability. In this paper the analysis of the combustion process of SI engines equipped with an innovative architecture and operating in different injection modes was described. In particular, the effect of the prechamber ignition on the engine stability and the efficiency was investigated in stoichiometric and leanburn operation conditions. The activity was carried out in two parts. In the first part the investigation was performed in a research small direct injection spark ignition (DISI) engine, running at 2000 rpm WOT, and fueled with Methane. The combustion process was studied using optical diagnostics. Methane was injected both in the prechamber and in the main chamber through the port fuel injection (PFI) mode. The ignition was obtained with a properly designed fueled prechamber prototype. It was equipped with a gas direct injector, used to inject the fuel into the prechamber, and a spark plug used to ignite the mixture. The gaseous fuel in the main chamber was ignited by the plasma jets coming from the prechamber. The combustion of the prechamber mixture generates four plasma jets that quickly ignite the mixture into the combustion chamber, and the flame speed is much faster than the traditional ignition. The optical data were correlated with the engine performance and indicated measurements that showed an increase of the Indicated Mean Effective Pressure (IMEP) and the reduction of the Coefficient of Variation (CoV). In the second part, the optimization of the gasoline combustion by means of a passive prechamber was performed. The investigation was carried out in a commercial small SI engine at 2000 rpm, fueled with gasoline in PFI mode and equipped with the same prechamber used in the first part of the activity. But in this case the prechamber works in passive mode.

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. The experimental data were then used to validate a 1D engine model, integrated with refined sub-models of turbulence, combustion, heat transfer and emissions. The model takes into account the in-cylinder production of noxious species, and their propagation in the exhaust system, up to the three-way catalytic converter. A satisfactory accuracy was reached in reproducing the overall engine performance and the combustion process in the two cylinders. In particular, the emission sub-models confirmed that the variations of the cylinder-out exhaust emissions (NOx, HC and CO) were mainly due to the non-uniform effective in-cylinder A/F ratio. The proposed numerical methodology has the potential to highlight unexpected combustion non-uniformities among different cylinders and represents a powerful support to the engine design and development. It also allows for the prediction of the overall exhaust emissions at different engine operating conditions up to the entire domain, thus assisting the engine calibration phase and reducing the experimental efforts.

The deterioration of automotive diesel oil (ado) in storage has been investigated. The quality of the fuel produced by the refinery was shown to be the major factor determining the amount of chemical degradation which will occur. Ado containing only distillate from the primary distillation unit is a stable fuel. Blending unhydrogenated catalytically cracked or thermally cracked refinery light cycle oil (lco) with the fuel substantially decreased the storage stability. The amount of organic particulate matter formed on storage is dependent upon both the chemical constitution of the lco and the fuel with which it was blended. Chemical additives which are used to reduce soluble gum formation in gasoline were found to be ineffective in ado. Particulate formation in ado was reduced by additives which inhibited acid catalysed processes in the fuel (a).

Aldehyde and unburned fuel emissions (UBF) were measured from experimental 6V-92TA and 6V-71N methanol-fueled heavy-duty diesel engines. The 6V-71N engine was tested with experimental oxidation catalytic converters. Formaldehyde accounted for 97-99% of the total aldehydes emitted from both engines. Aldehyde and unburned fuel concentrations were highest in the idle modes of the 13-mode test and decreased with increasing engine speed and load. The 13-mode weighted aldehyde and UBF emissions for the 6V-92TA engine were 0.10 G/BHP-HR and 2.01 G/BHP-HR, respectively. The 13-mode aldehyde and UBF emissions from the 6V-71N engine before catalytic treatment were 0.32 G/BHP-HR and 4.51 G/BHP-HR, respectively. These emissions were reduced to 0.19 G/BHP-HR and 1.10 G/BHP-HR with catalytic treatment. Total aldehyde emissions from the methanol-fueled engines compared favorably with the 0.07 to 0.28 G/BHP-HR range reported for heavy-duty conventionally fueld diesel engines. Formaldehyde emissions from these engines were higher than those of conventionally fueled diesel engines but similar to those of other methanol-fueled diesel engines. Particulate and NO/subX/ emissions from these engines were very low and ranged from 0.02-0.22 G/BHP-HR and 1.45-1.66 G/BHP-HR, respectively. These engines show promise for meeting the 1991 urban bus 0.10 G/BHP-HR particulate standard.

Distillation-based waste water pretreatment and recovered water posttreatment methods are proposed for the NASA Space Station. Laboratory investigation results are reported for two nonoxidizing urine pretreatment formulas (hexadecyl trimethyl ammonium bromide and Cu/Cr) which minimize the generation of volatile organics, thereby significantly reducing posttreatment requirements. Three posttreatment methods (multifiltration, reverse osmosis, and UV-assisted ozone oxidation) have been identified which appear promising for the removal of organic contaminants from recovered water.

A line of high-quality multigrade diesel engine oils suitable for long drain applications has been developed using hydrotreated base stock. To meet the growing demand for lubricants in Canada and to offset the high degree of reliance on imports, a new lubricant facility has been constructed in the Toronto area. The facility employs a process in which feedstock undergoes very severe hydrogenation under high pressure. Products are then fractionated, dewaxed, and again hydrogenated under more moderate conditions. Advantages of the hydrotreating process include increased yield, greater flexibility in producing various viscosity grades, and less dependence on selected lubricant crude sources. Two hydrotreated base stocks were used to conduct necessary product development prior to introducing the new lubricant facility. Laboratory and engine dynamometer tests indicated that lubricating oils using hydrotreated base stock had superior control of diesel piston deposits and oxidative viscosity increase. Excellent performance of multigrade diesel engine oils using both hydrotreated and solvent-refined base stock over extended oil change intervals was demonstrated in extensive field trials. Cold weather benefits for multigrade diesel engine oils were defined by cold room studies and outdoor trials. Low volatility, high thermal stability, and good additive response were particular features contributing to overall performance improvements. Finished lubricants formulated from hydrotreated base stocks of similar viscosity index appeared to have similar performance characteristics, regardless of crude source.

Determination de la pression de vapeur et des caracteristiques de distillation d'essences, de melanges alcool-essence et ether-essence

The effect of both soluble gum and insoluble particulate gum from the ageing of automotive diesel oil (ado) has been investigated. The standard experimental procedure has been shown to be a limiting factor in the precision with which soluble gum in diesel fuels may be measured. Greater reproducibility was obtained by extending the steam jet bath heating period to two hours. Filtration characteristics were determined for both laboratory and automotive filtration media with particulate gum from naturally aged fuel and inorganic particulate matter from ac fine test dust. The filtration characteristics were shown to be dependent both on the type of filtration medium and the properties of the particulate matter (a).

Nowadays internal combustion engines can operate under lean combustion conditions to maximize efficiency, as long as combustion stability is guaranteed. The robustness of combustion initiation is one of the main issues of actual spark-ignition engines, especially at high level of excess-air or dilution. The enhancement of the in-cylinder global motion and local turbulence is an effective way to increase the flame velocity. During the ignition process, the excessive charge motion can hinder the spark discharge and eventually cause a misfire. In this perspective, the interaction between the igniter and the flow field is a fundamental aspect which still needs to be explored in more detail to understand how the combustion originates and develops. In this work, a combined experimental and numerical study is carried out to investigate the flow field around the spark gap, and its effect on the spark discharge evolution. Two different velocities of the flow field are explored and compared to the static configuration under ambient conditions in an air flow channel, investigating the effect of the orientation of a conventional J-type spark plug. Results of numerical simulations predict spark stretching that is in close agreement with experimental observations. The model results are used to provide insight into the spatial and temporal development of the spark discharge. This work provides a numerical tool that can be extremely useful to link the interaction between the in-cylinder charge motion and the spark discharge to the engine cycle-to-cycle variability prediction.

In the next future, improvements of direct injection systems for spark-ignited engines are necessary for the potential reductions in fuel consumptions and exhaust emissions. The admission and spread of the fuel in the combustion chamber is strictly related to the injector design and performances, such as to the fuel and environmental pressure and temperature conditions. In this paper the spray characterization of a GDI injector under normal and flash-boiling injection conditions has been investigated. The paper is mainly focused both on the capability of the injection apparatus/temperatures controller system to realize flash-boiling conditions, and the diagnostic setup to catch the peculiarities of the spray behavior. The work aims reporting the spray characterization under normal and flash-boiling conditions. Flash-boiling is a phenomenon that occurs in certain engine conditions when the in-cylinder pressure is lower than the saturation pressure of the fuel, and leads to internal boiling and vapor bubbles creation near the nozzle exit. A customized sensing of the injector nose permitted the temperature control of the nozzle up to 360 K while a remote controlled thermostatic device allowed the fuel heating from ambient to 393 K. An axially-disposed, 0.200 mm in diameter, single-hole injector was used with l/d ratio equal to 1 and static flow@100 bar: 2.45 g/s, using commercial gasoline. A 1.0 ms duration single pulse strategy was adopted at the injection pressure of 10.0 MPa. The spray evolved in a quiescent optically-accessible vessel pressurize at 0.05, and 0.1 MPa at ambient temperature of the gas (N2). Images of the sprays were acquired by Mie-scattering technique using a C-Mos cycle-resolved high speed camera as detector, an off-line processing of the captured images gave tip penetrations and cone-angles vs. time from the start of injection. At flash-boiling conditions clear increasing of the spray-cone angle were observed with respect to the normal one producing consequences on the distribution of the fuel in the combustion vessel.

This paper presents analytical research conducted into the level of fuel consumption improvement that can be expected from turbocompounding a medium-duty opposed-piston 2-stroke engine, which is part of a hybridized vehicle propulsion system. It draws on a successful earlier study which showed a non-compounded opposed-piston engine to be clearly superior to other forms of 2-stroke engine, such as the widely adopted uniflow-scavenged poppet valve configuration. Electrical power transmission is proposed as the method of providing the necessary variable-speed drive to transmit excess turbine power to the system energy storage medium. The work employs one-dimensional engine simulation on a single-cylinder basis, using brake specific fuel consumption (BSFC) as the reportable metric, coupled with positive or negative power flow to the engine from the compounder; this is a variation on an approach successfully used in earlier work. Here it shows the sensitivities of the overall system to cylinder pressure, the compressor and turbine efficiencies, exhaust backpressure and also provides a means to investigate the effect of the power transmission efficiency on the overall benefit. Reheating the air before the turbine is also investigated as a means of providing a “burst” performance facility, albeit at the expense of extra fuel consumption. Positive compounding work is shown to be achievable across all investigated engine operating points under certain conditions. Operating points at lower engine speeds showed an increased propensity for turbocompounding, with 5-6% of the brake torque arising from the compounder, compared to those at higher engine speeds, where a maximum of 4% was seen. BSFC was found to be highly dependent on compounding torque with improvements only arising from reducing backpressure. A better understanding of the flow restrictions of the exhaust aftertreatment and muffler systems, for a given application, would allow for more accurate determination of the possibility for BSFC reduction within realistic operating conditions.

This paper aims to correlate the in-cylinder soot formation and the exhaust particle emissions for different methods of gasoline/ethanol fueling in spark ignition engine. In particular, the engine was fueled with gasoline and ethanol separately and not, in this latter case both blended (E30) and dual fueled (EDF). For E30 the bend was direct injected and for EDF, the ethanol was injected in the combustion chamber and the gasoline into the intake duct. For both the injection configurations, the same percentage of ethanol in gasoline was supplied: 30%v/v. The measurements were carried out at 2000 and 4000 rpm, under full load, and stoichiometric condition, in small single cylinder optical engine. 2D-digital imaging was performed to follow the combustion process with a high spatial and temporal resolution through a full-bore optical piston. The two-color pyrometry was applied for the analysis of the in cylinder soot formation in the combustion chamber. Particle mass concentration was evaluated at the exhaust by means of a smoke meter. The particle size distribution function was measured in the range from 5.6 to 560 nm by an Engine Exhaust Particle Sizer (EEPS). It was observed that the use of ethanol allows the reduction of soot formation and particles emission in DI configuration. However, for E30 the in-cylinder soot formation and emissions are larger than EDF. This result is mainly due to the different contribution of gasoline. Optical analysis shows that in E30 the direct injected gasoline causes wide diffusive flames where soot formation is promoted; whereas for EDF the better evaporation and mixing of gasoline, typical of PFI configuration, results in few, small, and localized diffusive flames producing smaller particle emissions.

Today, the contribution of the transportation sector on greenhouse gases is evident. The fast consumption of fossil fuels and its impact on the environment have given a strong impetus to the development of vehicles with better fuel economy. Hybrid electric vehicles fit into this context with different targets, starting from the reduction of emissions and fuel consumption, but also for performance and comfort enhancement. Lamborghini has recently invested in the development of a hybrid super sport car, due to performance and comfort reasons. Aventador series gearbox is an Independent Shift Rod gearbox with a single clutch and during gear shifts, as all the single clutch gearbox do, it generates a torque gap. To avoid the additional weight of a Dual Clutch Transmission, a 48V Electric Motor has been connected to the wheels, in a P3 configuration, to fill the torque gap, and to habilitate regenerative braking and electric boost functions. This paper discusses the usage of a control-oriented vehicle and powertrain model to analyze the performance of the first Lithium Ion Capacitor-based hybrid V12 by Automobili Lamborghini. The internal combustion engine, the gearbox, the LiC and the vehicle longitudinal dynamics models have been initially validated through the comparison with experimental data from chassis dynamometer testing, in addition to experimental results from specific components' testing. As shown in the paper, the validated model has then been used to develop control strategies aimed at increasing comfort and performance, but also to expand the hybrid system capabilities by widening the LiC working range, and to study the possibility of implementing CO2 reduction-oriented control functions.

International audience

Development processes for modern combustion engines already make substantial use of more or less sophisticated simulation approaches. The enhancement of computational resources additionally allows the increasing use of simulation tools in terms of time-consuming three-dimensional CFD approaches. In particular, the preliminary estimation of feasible operating ranges and strategies requires a vast multitude of single simulations. Here, multi-zone simulation approaches incorporate the advantages of comparably short simulation durations. Nevertheless, the combination with more detailed sub-models allows these rather simple modeling approaches to offer considerable insight into relevant engine operation phenomena. In the context of combustion process development, this paper describes a phenomenological model approach for the prediction of operating point characteristics of a dual-fuel pilot injection combustion process. In order to describe the ignition initiated by pilot fuel injection, the present model approach uses the package-based multi-zone approach as presented by Hiroyasu et al. Therefore, physical phenomena such as spray breakup, atomization, and evaporation are considered. The governing entrainment of premixed cylinder charge into the individual package zones is based on the conservation of momentum. In addition, measured pilot fuel injection profiles are implemented. The calculation of the characteristic ignition delay time applies an Arrhenius-based one-step mechanism taking local gas properties as well as the particular composition within the packages into account. Eventually, the identification of the ignition event triggers a transition process from the combustion within the spray cone to the hemispherical flame propagation of the premixed cylinder filling. Besides the detailed description of the model approach, this paper discusses crucial influences originating from quasi-dimensional discretization. In particular, the radial discretization of the spray jet indicates a considerable influence on the prediction of spray breakup as well as fresh gas mixing into the package zones and thus eventually on the calculation of the ignition delay time. The validation of the phenomenological model approach regarding its ability to predict different operating characteristics uses experimental data. Here, variations of timing and the quantity of the pilot fuel injection as well as variations of injection pressure and global air-fuel equivalence ratio have been taken into account. The model approach indicates plausible prediction with regard to both the basic phenomenology of the combustion process and the characteristic two-stage ignition behavior. In particular, cylinder pressure curves and combustion rates as well as peak pressures and the overall released heat quantities are correctly calculated.

International audience; Recent internal combustion (IC) engine developments focus on gasoline fuel. This requires a better understanding of fuel reactivity at different thermodynamic conditions. Gasoline fuel reactivity control by additives is an efficient method to get better IC engine performances. 2-Ethylhexyl nitrate (EHN) promoting effect (0.1-1% mol.) on combustion has been investigated experimentally and numerically. Rapid compression machine (RCM) experiments were carried out at equivalence ratio 0.5 at 10 bar, from 675 to 995 K. The targeted surrogate fuel is a mixture of toluene and n-heptane in order to capture the additive effect on both cool flame and main ignition. A kinetic model was developed from literature data assembly and validated upon a large set of variations including species profiles and ignition delays of pure compounds as well as mixtures. At the experimental conditions, it was found that the EHN reduces the ignition delay time (IDT) of the surrogate fuel in the whole temperature range. EHN effectiveness tends to be minimum around 705 K and increases with temperature. The results also indicate that EHN effect increases nonlinearly with EHN doping levels. Numerical analyses revealed that the EHN effect is linked to NO2-NO loops, which enhances fuel reactivity. The methodology proposed here enable to simulate the EHN effect with simple compounds rather than the full EHN chemistry set. This strategy could simplify the consideration of additive effect when computational fluid dynamics (CFD) simulations are performed on engine. Finally, the study also highlights the EHN effectiveness on several thermodynamic conditions as well as equivalence ratios. The objective is to assess its performance upon large operating conditions which appears to be of interest with novel combustion systems targeting low temperature as well as lean combustion.

In this paper, computation fluid dynamics (CFD) simulations are performed to describe the effect of in-cylinder flow structures on the formation and oxidation of soot in a swirl-supported light-duty diesel engine. The focus of the paper is on the effect of swirl motion and injection pressure on late cycle soot oxidation. The structure of the flow at different swirl numbers is studied to investigate the effect of varying swirl number on the coherent flow structures. These coherent flow structures are studied to understand the mechanism that leads to efficient soot oxidation in late cycle. Effect of varying injection pressure at different swirl numbers and the interaction between spray and swirl motions are discussed. The complexity of diesel combustion, especially when soot and other emissions are of interest, requires using a detailed chemical mechanism to have a correct estimation of temperature and species distribution. In this work, Representative Interactive Flamelets (RIF) method is employed to describe the chemical reactions, ignition, flame propagation and emissions in the engine. The CFD simulations are validated using experimental measurement of light-duty diesel engine at two different loads. A good agreement is achieved between the model results and the pressure, heat release rates and emissions from the experiment. These cases are considered as the base-line for the parameter study cases.

In this work the performance and noxious emissions of a prototype Spark Ignition (SI) engine, working in ultra-lean conditions, are investigated. It is a four-cylinder engine, having a very high compression ratio, and an active pre-chamber. The required amount of air is provided by a low-pressure variable geometry turbocharger, coupled to a high-pressure E-compressor. The engine is equipped with a variable valve timing device on the intake camshaft. The goal of this activity is to support the development and the calibration of the described engine, and to exploit the full potential of the ultra-lean concept. To this aim, a combustion model for a pre-chamber engine, set up and validated in a previous paper for a similar single-cylinder unit, is utilized. It is coupled to additional in-house developed sub-models, employed for the prediction of the in-cylinder turbulence, heat transfer, knock and pollutant emissions. Such a complex architecture, schematized in a commercial 1D modeling framework, presents several control parameters which have to be properly selected to maximize the engine efficiency and minimize the noxious emissions over its whole operating domain. A Rule-Based (RB) calibration strategy is hence implemented in the 1D model to identify the optimal values of each control variable. The reliability of the RB calibration is also demonstrated through the comparison with the outcomes of a general-purpose optimizer, over a load sweep at a constant speed. The 1D model and the RB methodology are then applied for the performance prediction over the whole engine operating domain. The predicted performances show the possibility to achieve a wide zone of very high efficiency, with limited penalizations only at very low loads. Main advantages of the lean-combustion concept are highlighted, concerning a higher specific heat ratio, reduced heat losses, improved knock mitigation, and abatement of pollutant emissions, especially regarding CO and NOx. The presented methodology demonstrates to be a valuable tool to support the development and calibration of the considered high-efficiency engine architecture.

Increasingly stringent regulations in the field of pollutant are forcing engine manufacturers to adopt new solutions to contain exhaust emissions, such as Hybrid Electric Vehicles (HEV) or Full Electric Vehicles (FEV). Still far from the wide diffusion of FEV limited from electrochemical storage systems together with the difficulty of creating adequate infrastructure distributed throughout the territory to recharging batteries, the HEV seems to be actually a better solution. The hybrid vehicle is already able to guarantee satisfactory autonomy and low pollution levels by combining the advantages offered by the two technologies of thermal and electric propulsion. Currently on the market there are several types of hybrid vehicles, with different degree of hybridization (electric motor power versus propulsion total power), capacity to store electricity and type of scheme constructive adopted for the integration between the thermal engine and the electric machine. A particular interest is getting the mild-hybrid (or light hybridization) and the micro-hybrid (or minimum hybridization) with 48V electrical system added to the classic 12V one. A possible solution could be the electric turbo-compounding system where a turbine coupled to a generator (turbo-generator) uses the exhaust gas flow of a reciprocating engine to harvest waste heat energy and convert it into electrical power. In this way, the power generated from the system can be used to feed local electrical loads such as engine auxiliaries, increasing the whole system efficiency. The present study deals with the simulation of a spark ignition engine, present in a test room of Istituto Motori (CNR), including a turbo-generator at the exhaust to evaluate the advantages in terms of overall efficiency. The internal combustion engine model was developed by using a 1D code (GT-Power software), while the turbo-generator and the electric system are described in the Matlab/Simulink environment. The results obtained showed an appreciable increase in the overall efficiency.

This paper evaluates a thermodynamic ice crystal icing model that has been previously presented to describe the possible mechanisms of icing within the core of a turbofan jet engine. The model functions between two distinct ice accretions based on a surface energy balance: freeze-dominated icing and melt-dominated icing. Freeze-dominated icing occurs when liquid water (from melted ice crystals) freezes and accretes on a surface along with the existing ice of the impinging water and ice mass. This freeze-dominated icing is characterized as having strong adhesion to the surface. The amount of ice accretion is partially dictated by a freeze fraction, which is the fraction of impinging liquid water that freezes. Melt-dominated icing occurs as unmelted ice on a surface accumulates. This melt-dominated icing is characterized by weakly bonded surface adhesion. The amount of ice accumulation is partially dictated by a melt fraction, which is the fraction of impinging ice crystals that melts. Experimentally observed ice growth rates suggest that only a small fraction of the impinging ice remains on the surface, implying a mass loss mechanism such as splash, runback, bounce, or erosion. The fraction of mass loss must be determined in conjunction with the fraction of freezing liquid water or fraction of melting ice on an icing surface for a given ice growth rate. This mass loss parameter, however, along with the freeze fraction and melt fraction, are the only experimental parameters that are currently not measured directly. Using icing growth rates from ice crystal icing experiments, a methodology that has been previously proposed is used to determine these unknown parameters. This work takes ice accretion data from tests conducted by the National Aeronautics and Space Administration (NASA) at the Glenn Research Center in 2018 that examined the fundamental physics of ice crystal icing. This paper continues evaluation of the thermodynamic model from a previous effort, with additions to the model that account for sub-freezing temperatures that have been observed at the leading edge of the airfoil during icing. The predicted temperatures were generally in good agreement with measured temperatures. Other key findings include the total wet-bulb temperature being a good first order indicator of whether icing is freeze-dominated (sub-freezing values) or melt-dominated (above freezing). Maximum sticking efficiency values, the fraction of impinging mass that adheres to a surface, was calculated to be about 0.2, and retained this maximum value for a range of melt ratios (0.3 to 0.65 and possibly higher), which is defined as the ratio of liquid water content to total water content. Higher air velocities reduced the maximum sticking efficiency and shifted the icing regime to higher melt ratio values. Finally, the leading edge ice accretion angle was found to be related to ice growth (lower growth rates for smaller angles) and melt ratio (smaller melt ratios resulted in smaller angles, likely due to erosion effects).