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The transport sector is experiencing a shift to zero-carbon powertrains driven by aggressive international policies aiming to fight climate change. Battery electric vehicles (BEVs) will play the main role in passenger car applications, while diversified solutions are under investigation for the heavy-duty sector. Within this framework, Light Commercial Vehicles (LCVs) impact is not negligible and accountable for about 2.5% of greenhouse gas (GHG) emissions in Europe. In this regard, few LCV comparative assessments on green powertrains are available in the scientific literature and justified by the fact that several factors and limitations should be considered and addressed to define optimal powertrain solutions for specific use cases. The proposed research study deals with a comparative numerical assessment of different zero-carbon powertrain solutions for LCV. BEVs are compared to hydrogen-based fuel cells (FC) and internal combustion engines (ICE) powered vehicles.

An approach for turbocharging automotive engines to reach targeted performance was developed in which the environmental and economic aspects during the turbocharger-engine matching process were considered. Three numerical assessment levels based on output performance, exhaust emissions and techno-economic metrics are established to support users during the decision-making of adequate turbochargers that meets targeted data in terms of boosting and emissions. Satisfactory improvements are measured from a 1.5L, three-cylinders, turbocharged Diesel engine, in terms of brake specific fuel consumption, thermal efficiency and NOx concentrations of about 1.73% (decrease in fuel consumption of around 2.22ml/s), 1.76%, and 4.53% (correspond to a diminution of around 217.54ppm), respectively, at the engine’s extreme conditions (full load and rated power).

Hybrid electric vehicles (HEVs) represent one of the main technological options for reducing vehicle CO2 emissions, helping car manufacturers (OEMs) to meet the stricter targets which are set by the European Green Deal for new passenger cars at 80 g CO2/km by 2025. The optimal power-split between the internal combustion engine (ICE) and the electric motor is a challenge since it depends on many unpredictable variables. In fact, HEV improvements in fuel economy and emissions strongly depend on the energy management strategy (EMS) on-board of the vehicle. Dynamic Programming approach (DP), direct methods and Pontryagin’s minimum principle (PMP) are some of the most used methodologies to optimize the HEV power-split. In this paper two online strategies are evaluated: an Adaptive-RuleBased (A-RB) and an Adaptive-Equivalent Consumption Minimization Strategy (A-ECMS). At first, a description of the P2 HEV model is made.

Over the last decades, internal combustion engines have undergone a continuous evolution to achieve better performance, lower pollutant emissions and reduced fuel consumption. The pursuit of these often-conflicting goals involved changes in engine architecture in order to carry out advanced management strategies. Therefore, Variable Valve Actuation, Exhaust Gas Recirculation, Gasoline Direct Injection, turbocharging and powertrain hybridization have found wide application in the automotive field. However, the effective management of a such complex system is due to the contemporaneous development of the on-board Engine electronic Control Unit. In fact, the additional degrees of freedom available for the engine regulation highly increased the complexity of engine control and management, resulting in a very expensive and long calibration process. To overcome these drawbacks, an effective methodology based on the adoption of 1D thermo-fluid dynamic analysis is proposed in this study.

In the last few years, the automotive industry had to face three main challenges: compliance with more severe pollutant emission limits, better engine performance in terms of torque and drivability and simultaneous demand for a significant reduction in fuel consumption. These conflicting goals have driven the evolution of automotive engines. In particular, the achievement of these mandatory aims, together with the increasingly stringent requirements for carbon dioxide reduction, led to the development of highly complex engine architectures needed to perform advanced operating strategies. Therefore, Variable Valve Actuation (VVA), Exhaust Gas Recirculation (EGR), Gasoline Direct Injection (GDI), turbocharging, powertrain hybridization and other solutions have gradually and widely been introduced into modern internal combustion engines, enhancing the possibilities of achieving the required goals.

It is commonly recognized that the paths for improving fuel consumption (BSFC) in a spark-ignition engine at part-load require more advanced valve actuation strategies, which largely affect the pumping work. Since several years, many different solutions have been proposed, characterized by different levels of complexity, effectiveness, and cost. Valve systems currently available on the market allow for variable phasing (VVT - Variable Valve Timing), and/or lift (VVA - Variable Valve Actuation). Usually VVT devices are applied on intake and exhaust camshafts, in the “phased” or “unphased” configuration, as well. VVA devices are instead commonly mounted on the intake camshaft. More recent VVA systems also allow for a double intake valve lift during a single engine cycle (multi-lift), or may include a small intake pre-lift during the exhaust stroke. The latter solutions may determine further BSFC reductions. Alternatively, an external-EGR circuit can be considered, as well.

The paper deals with experimental testing of a natural gas fueled engine. Break Specific fuel Consumption (BSFC), Average Mass Flow Rate, Instantaneous Cylinder Pressure and some wall temperatures have been measured at some full and part load operating conditions. The results of this experimental activity, still in progress, have been used to calibrate a 1D-flow engine's model. Then the effects of some VVA strategies have been theoretically studied through the validated model. With the aim of maximizing the full load engine's torque, a genetic algorithm was used to calculate the optimized intake and exhaust valves timing angles. Various VVA strategies were compared at part-load in order to reduce brake specific fuel consumption.

Modern VVA systems offer new potentialities in improving the fuel consumption for spark-ignition engines at low and medium load, meanwhile they grant a higher volumetric efficiency and performance at high load. Recently introduced systems enhance this concept through the possibility of concurrently modifying the intake valve opening, closing and lift leading to the development of almost "throttle-less" engines. However, at very low loads, the control of the air-flow motion and the turbulence intensity inside the cylinder may require to select a proper combination of the butterfly throttling and the intake valve control, to get the highest BSFC (Brake Specific Fuel Consumption) reduction. Moreover, a low throttling, while improving the fuel consumption, may also produce an increased gas-dynamic noise at the intake mouth. In highly "downsized" engines, the intake valve control is also linked to the turbocharger operating point, which may be changed by acting on the waste-gate valve.

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.

The one-dimensional (1D) modeling of a turbocharged engine requires the availability of the turbine and compressor characteristic maps. This leads to two main problems: performance maps of the turbocharger device are usually limited to a reduced number of rotational speeds, pressure ratios and mass flow rates. Extrapolation of maps’ data is commonly required; performance maps are experimentally derived on stationary test benches, while the turbocharger usually operates under unsteady conditions, when coupled to an internal combustion engine (ICE). To overcome the above problems, in the present paper the flow inside a rotating pipe of a centrifugal compressor is simulated within a 1D modeling approach, with the aim of predicting its characteristic map. The main improvement with respect to the employment of a steady experimental map consists in the absence of data extrapolation and in the possibility of fully characterizing the unsteady operation of the component.

The paper presents a 1D-3D numerical model to simulate the scavenging and combustion processes in a small-size spark-ignition two-stroke engine. The engine is crankcase scavenged and can be operated with both gasoline and Natural Gas (NG). The analysis is performed with a modified version of the KIVA3V code, coupled to an in-house developed 1D model. A time-step based, two-way coupled procedure is fully described and validated against a reference test. Then, a 1D-3D simulation of the whole two-stroke engine is carried out in different operating conditions, for both gasoline and NG fuelling. Results are compared with experimental data including instantaneous pressure signals in the crankcase, in the cylinder and in the exhaust pipe. The procedure allows to characterize the scavenging process and quantify the fresh mixture short-circuiting, as well as to analyze the development of the NG combustion process for a diluted mixture, typically occurring in a two-stroke engine.

This paper presents the results of an experimental activity carried out on a two-stroke SI engine for moped (with a displacement 50 cm3) fueled alternatively by gasoline and natural gas. The effect of the fuel on engine performance and efficiency was evaluated comparing both instantaneous (pressure signal in the crankcase, cylinder and exhaust pipe) and overall data (torque, power, fuel consumption, emissions). Cylinder pressure was measured in order to evaluate the effect of fuel on the optimum ignition timing angle and on cyclic dispersion. Engine emissions were measured by means of a gas analyzer and a gas-chromatograph. Moreover this experimental analysis has been carried out also to validate the 1D-3D numerical model for the simulation of the scavenging and combustion processes in a small-size spark-ignition two-stroke engine. This activity is reported in another paper [1].

An experimental and numerical work has been performed to characterize the performance of a medium-size spark-ignition engine and the related gas-dynamic noise emitted at the intake mouth. The noise attenuation of the main component of the intake system, namely the air flow box, has been experimentally measured and compared to the numerical results obtained using a tri-dimensional code. Then, the 3D-CFD code has been used to improve the noise attenuation of the above component through the introduction of a Helmholtz and a column resonator along the inflow pipe. Both the base and the modified air box have been coupled to the engine, installed inside a vehicle. An experimental analysis has been carried out to measure the engine performance and the gasdynamic noise at the intake. Some comparisons have been then reported with the numerical results derived from a one-dimensional analysis of the whole engine.

The paper reports the research activity related to the development of a “downsized” turbocharged Spark-Ignition (SI) engine. Both experimental and theoretical analyses are carried out to characterize the performance of this engine architecture, and particularly to analyze the matching conditions with the turbocharger and the combustion process at wide-open-throttle conditions. To this aim, a quasi-dimensional model for the simulation of the burning process is included as an external user-defined routine in a commercial 1D simulation code (GT-Power®). The rate of heat release is computed through a two-zone model, based on a “fractal” representation of the turbulent flame front. A turbulence sub-model is included and it is properly tuned with respect to turbulence results computed by a 3D CFD code. A CAD procedure evaluating, at each crank-angle and flame radius, the intersections between the flame surface and the actual combustion chamber walls, is also presented.

The paper summarizes the activities related to the characterization of the noise sources and related sound emission levels emitted by a single cylinder diesel engine. A deep analysis is carried out aiming to clearly define the various noise sources, through the employment of numerical and experimental techniques. In particular, an intensimetric analysis is carried out to define a bi-dimensional noise level map around the engine. In addition, the gasdynamic noise, at the different engine speeds, is measured through a microphone mounted near the intake and exhaust mouth. Contemporarily to the experimental activity, a theoretical one dimensional simulation of the whole engine, is also carried out. The presented one-dimensional analysis is able to characterize the wave propagation phenomena in the external ducts and provide the estimation of both engine performance and gasdynamic noise emission too.

The paper is focused on the development of a fractal combustion model, included within a whole-engine one-dimensional model (1Dime code). An extensive validation is carried out through the comparison with experimental data. The experimental activity was carried out in the combustion chamber of an optically accessible one-cylinder engine, equipped with a commercial head. Experimental data basically consisted on optical measurements which were also correlated to the instantaneous pressure inside the cylinder. Optical measurements were based on 2D digital imaging and UV chemiluminescence of radical species. The rate of chemical energy release and related parameters were evaluated from the in-cylinder pressure data using interpretation models for heat release analysis. Moreover a post-processing of the optical measurements allowed to define the mean flame radius, and propagation speeds as well, as a function of the crank angle.

The paper details recent results concerning the design of a new intake system for a 1.4 liter displacement ELASIS-FIAT engine. A classical approach, based on theoretical one-dimensional characterization of the whole system, is presented. This approach, however, requires a relevant number of geometrical information which are usually unavailable in the first phase of the design process. For this reason, a statistical analysis on a number of existing devices was also carried out to the aim of providing such initial data as a function of prescribed levels of pressure losses and noise emission for the device. The methodology allows then to define a base configuration of the system, to start the 1D analyses. The base geometry is further refined taking into account the layout constraints and the presence of resonators for the reduction of the noise emission. Experimental data collected on a prototype of the designed system have confirmed the robustness of the whole design procedure.

The paper reports the research activity related to the development of a twin-spark SI engine equipped with a variable valve timing (VVT) device. Improvements on the fuel consumption at part load are expected when an high internal exhaust gas recirculation (internal EGR) level is realized with a proper phasing of the VVT device. The twin-spark solution is implemented to improve the burning speed at low load, and to increase the EGR tolerance levels. Both experimental and theoretical analyses are carried out to investigate the real advantages of the proposed engine architecture. In particular an original quasi-dimensional model for the simulation of the burning process in a twin-spark engine is presented. The model is mainly utilized to find the proper combination of VVT device position (and hence EGR level) and spark advance for different engine operating conditions. A comparison with the single-spark solution is also provided.

The paper describes preliminary results of a research activity finalized to the development of a new scavenging concept for the reduction of the HC emitted by a small-size two-stroke carbureted crankcase-scavenged SI engine. Further developments of a well-established model (1Dime code) are presented, with particular emphasis on combustion and scavenging processes simulation. The rate of heat release is computed through a two-zone model, based on a “fractal” representation of the turbulent flame front. A CAD procedure evaluating, at each crank-angle and flame radius, the intersections between the flame surface and the actual combustion chamber walls, has been developed. Scavenging is modeled through an original two-zone approach which accounts for mixing and short-circuiting processes. The latter are directly related to the in-cylinder turbulent flow regime, inlet and exhaust flow velocities, and engine speed.

A theoretical-experimental analysis of a VVT engine and a methodology for the definition of its optimal control is presented. The analyses are based on the employment of a very accurate 1D simulation model of the engine, developed by the authors. The code is validated by comparison with experimental data collected on a traditionally fixed- and a variable-valve timing engine as well. The model is then linked to an efficient optimization procedure, which is able to select - for each assigned operating condition - the most appropriate values of control parameters (spark advance, intake/exhaust valve opening/closing, and valve lift), with the objective of pursuing part-load BSFC improvements. Various VVT or VVA arrangements are analyzed and compared.