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2024 - Optimization of the Combustion Chamber Design of a Natural Gas-Diesel Dual Fuel Engine Running at Low Load [Relazione in Atti di Convegno]
Scrignoli, Francesco; Savioli, Tommaso; Rinaldini, Carlo Alberto
abstract

2023 - Combustion Chamber Optimization for Dual-Fuel Biogas–Diesel Co-Combustion in Compression Ignition Engines [Articolo su rivista]
Caprioli, Stefano; Volza, Antonello; Scrignoli, Francesco; Savioli, Tommaso; Mattarelli, Enrico; Rinaldini, Carlo Alberto
abstract

Micro-cogeneration with locally produced biogas from waste is a proven technique for supporting the decarbonization process. However, the strongly variable composition of biogas can make its use in internal combustion engines quite challenging. Dual-fuel engines offer advantages over conventional SI and diesel engines, but there are still issues to be addressed, such as the low-load thermodynamic efficiency and nitrogen oxide emissions. In particular, it is highly desirable to reduce NOx directly in the combustion chamber in order to avoid expensive after-treatment systems. This study analyzed the influence of the combustion system, especially the piston bowl geometry and the injector nozzle, on the performance and emissions of a dual-fuel diesel-biogas engine designed for micro-cogeneration (maximum electric power: 50 kW). In detail, four different cylindrical piston bowls characterized by radii of 23, 28, 33 and 38 mm were compared with a conventional omega-shaped diesel bowl. Moreover, the influence of the injector tip position and the jet tilt angle was analyzed over ranges of 2-10 mm and 30-120 degrees, respectively. The goal of the optimization was to find a configuration that was able to reduce the amount of NOx while maintaining high values of brake thermal efficiency at all the engine operating conditions. For this purpose, a 3D-CFD investigation was carried out by means of a customized version of the KIVA-3V code at both full load (BMEP = 8 bar, 3000 rpm, maximum brake power) and partial load (BMEP = 4 bar, 3000 rpm). The novelty of the study consisted of the parametric approach to the problem and the high number of investigated parameters. The results indicated that the standard design of the piston bowl yielded a near-optimal trade-off at full load between the thermodynamic efficiency and pollutant emissions; however, at a lower load, significant advantages could be found by designing a deeper cylindrical bowl with a smaller radius. In particular, a new bowl characterized by a radius of 23 mm was equivalent to the standard one at BMEP = 8 bar, but it yielded a NOx-specific reduction of 38% at BMEP = 4 bar with the same value of BTE.

2023 - Combustion Optimization of a Premixed Ultra-Lean Blend of Natural Gas and Hydrogen in a Dual Fuel Engine Running at Low Load [Articolo su rivista]
Rinaldini, Carlo Alberto; Scrignoli, Francesco; Savioli, Tommaso; Mattarelli, Enrico
abstract

2023 - Hybrid-electric power unit for an ultralight aircraft [Relazione in Atti di Convegno]
Pisapia, A. M.; Volza, A.; Savioli, T.; Martini, P.; Mattarelli, E.
abstract

2022 - Development of a Combustion System for a New Generation of 2-Stroke Spark Ignition Engines [Relazione in Atti di Convegno]
Scrignoli, Francesco; Mattarelli, Enrico; Rinaldini, Carlo; Savioli, Tommaso
abstract

2021 - Design of a Novel 2-Stroke SI Engine for Hybrid Light Aircraft [Relazione in Atti di Convegno]
Caprioli, S.; Rinaldini, C.; Mattarelli, E.; Savioli, T.; Scrignoli, F.
abstract

The trend of powertrain electrification is quickly spreading from the automotive field into many other sectors. For ultra-light aircraft, needing a total installed propulsion power up to 150 kW, the combination of a specifically developed internal combustion engine (ICE) integrated with a state-of-the-art electric system (electric motor, inverter and battery) appears particularly promising. The dimensions and weight of ICE can be strongly reduced (downsizing), so that it can operate at higher efficiency at typical cruise conditions; a large power reserve is available for emergency maneuvers; in comparison to a full electric airplane, the hybrid powertrain makes possible to fly at zero emissions for a much longer time, or with a much heavier payload. On the other hand, the packaging of a hybrid powertrain into existing aircraft requires a specific design of the thermal engine, that must be light, compact, highly reliable and fuel efficient. The last aspect has a direct impact on the performance of the aircraft, since the mission range depends on the capacity of the fuel tanks, which, in turn, is limited by the aircraft total weight. The two-stroke cycle engine is far from a novelty for ultra-light aircraft; unfortunately, the specific fuel consumption and pollutant emissions of the conventional engines is quite high, in comparison to their 4-Stroke (4S) counterparts. The aim of the project presented in this paper is to develop a new type of 2-Stroke SI engine, able to match lightness, fuel efficiency and low pollutant emissions at a reasonable cost. The proposed ICE weights less than 60 kg, it delivers 110 kW@6000 rpm, along with a brake specific fuel consumption lower than 260 g/kWh in all the most relevant operating conditions. The paper describes the design of the new engine, with particular attention to the optimization of the scavenging system (without poppet valves) and the design of a low pressure direct injection system. The process is supported by CFD 1D and 3D simulations. As far as the design of the injection system is concerned, the main goal was to obtain a fuel trapping ratio higher than 95%, along with a properly stratified charge at combustion onset, when considering the most critical operating condition (maximum engine speed and load). The main optimized parameters include the number of injectors, their locations, the injection timing and duration.

2021 - Optimization of a High-Speed Dual-Fuel (Natural Gas-Diesel) Compression Ignition Engine for Gen-sets [Articolo su rivista]
Mattarelli, E.; Rinaldini, C. A.; Savioli, T.; Scrignoli, F.
abstract

The goal of this study is to develop a clean and efficient thermal unit for a generator set (gen-set) rated at 80 kW, exploring the potential of Dual-Fuel (DF) combustion (Natural Gas-Diesel) on high-speed Compression Ignition (CI) engines. Typically, the most comparable commercial gen-sets are made up of Heavy-Duty (HD) Diesel engines, whose cost and complexity will probably increase to meet more stringent emissions standards. The conversion of a light-duty Diesel engine may permit to match the high efficiency of Diesels with the low emissions of DF combustion at an affordable cost. Moreover, the new thermal unit would be more compact and lighter. Running on Natural Gas (NG) is less expensive than using Diesel fuel, and it offers more opportunities to reduce the environmental impact (e.g., NG can be easily obtained from biomass, in the same site where the gen-set is installed). Last but not the least, in case of interruption of NG supply, the system can be easily switched to conventional Diesel operation, offering a higher fuel flexibility. Despite the large number of scientific publications concerning DF engines, very few of them consider high-speed units equipped with modern Common Rail injection systems. Even more limited are the investigations on the combustion process at medium-high loads (BMEP > 10 bar), carried out by measuring in-cylinder pressure and optimizing all the fundamental control parameters (injection strategy for both Diesel fuel and NG, boost pressure, EGR rates, etc.). It should be observed that the use of state-of-the-art injection systems and the accurate calibration of their parameters at each operating condition is the only way to maximize the benefits of NG in terms of reduction of soot emissions while addressing the well-known issues related to the increase of some pollutants (HC, CO, and NOx). This study reviews the results of a theoretical and experimental activity carried out on a four-cylinder, Common Rail, 2.8-liter turbocharged Diesel engine. A gas injection system is installed upstream of the intake plenum, and an open Electronic Control Unit (ECU) is used to calibrate all the most important engine parameters. Thanks to the deep insight into the combustion process provided by in-cylinder pressure analysis and measurement of pollutant emissions, the study presents some general guidelines for setting the control strategy in this type of DF engine. Considering the operating condition at maximum power (BMEP = 12 bar, 3000 rpm, brake power = 83 kW), the following advantages are observed with comparison to the standard Diesel engine: soot is more than halved, NOx emissions are reduced by 32% and CO2 by 31%, and Brake Thermal Efficiency (BTE) increases from 35.8% to 39%. The only drawback is the increase of one order of magnitude of both CO and HC, requiring a specific oxidation catalyst. Another outcome of the study is the limitation on the use of DF NG-Diesel combustion at low loads: the experimental activity demonstrates that it is very difficult to achieve complete combustion of an ultra-lean air-NG premixed charge so that BTE tends to drop. At these conditions, it appears to be more convenient to switch back to standard Diesel operations.

2019 - Dual Fuel (Natural Gas Diesel) for Light-Duty Industrial Engines: A Numerical and Experimental Investigation [Capitolo/Saggio]
Mattarelli, Enrico; Rinaldini, Carlo Alberto; Savioli, Tommaso
abstract

This paper reviews the main results of a numerical and experimental activity, carried out on an automotive four-cylinder, common rail, 2.8 L turbocharged diesel engine, Euro IV compliant. The purpose of the project is to convert this engine, with minor hardware modifications, in order to operate in compression ignition (CI) dual-fuel (DF) mode, using natural gas (NG) as the main source of energy. The diesel injector will keep the only function to ignite the homogeneous air–NG mixture within the cylinder, injecting just a small quantity of diesel fuel. In this way, soot emissions can be almost completely eliminated, and the after-treatment system can be strongly simplified (then, its cost reduced). Other fundamental advantages in the use of NG instead of diesel are the lower emission of CO2 (provided that brake efficiency is not reduced when running on DF) and the lower concentration of nitrogen oxides (NOx). This DF engine would be particularly suitable for light-duty industrial applications (power generators, small tractors, and off-road vehicles) and boats, where the installation of an additional fuel system is not limited by tight constraints. The experimental activity is supported by a comprehensive theoretical study, carried out through CFD simulation (both 1D and 3D). The numerical models are first calibrated for the standard combustion mode and then applied to get the guidelines for the development and calibration of the physical prototype. The most relevant experimental result is obtained at 3000 rpm, BMEP = 12 bar, where the DF engine can work with just a 20% of the diesel fuel required for standard operations. The following advantages are found: (1) complete elimination of soot; (2) 26% reduction of NOx; (3) 25% reduction of CO2; (4) slight improvement of brake efficiency. The only downside is the strong increase in HC and CO concentrations, which are about ten times higher. However, this issue can be addressed installing a cost-effective oxidation catalyst.

2019 - Experimental investigation on a diesel engine operated in RCCI combustion mode [Relazione in Atti di Convegno]
Legrottaglie, F.; Mattarelli, E.; Rinaldini, C. A.; Savioli, T.; Scrignoli, F.
abstract

Low Temperature Combustion (LTC) concepts have been investigated in many recent studies, aiming to improve engine efficiency and minimize pollutant emissions. One of the most promising techniques is represented by the Reactivity Controlled Compression Ignition (RCCI), that can be obtained combining a low reactivity fuel (such as gasoline, natural gas, ethanol, etc) and a high reactivity fuel (such as Diesel oil). The former is injected in the intake manifold, and it generates a homogeneous mixture before the start of combustion; the latter is injected directly into the combustion chamber. This technology can be easily applied to existent Diesel engines, implementing a low pressure injection system for the low-reactivity fuel. This work presents the most important results of a preliminary experimental study, conducted on a light duty Diesel engine, modified in order to operate in RCCI combustion mode. In particular, four gasoline injectors have been installed between the intercooler and the intake plenum, while the injection strategy of both fuels has been optimized, along with boost pressure. Experiments show that at low loads it is possible to substitute most of Diesel fuel with gasoline, maintaining or even improving brake thermal efficiency. This result was obtained by optimizing the Diesel fuel injection strategy, without the support of EGR. However, at medium loads, it was not possible to achieve relevant reductions of Diesel fuel, due to the high risk of knocking.

2019 - Numerical optimization of the injection strategy on a light duty diesel engine operating in dual fuel (CNG/diesel) mode [Articolo su rivista]
Cantore, G.; Mattarelli, E.; Rinaldini, C. A.; Savioli, T.; Scrignoli, Francesco
abstract

The next generation of light duty Diesel engines will face increasingly stringent emissions regulations, as well as the restrictions enforced by some local administrations. As a result, many manufacturers are starting to abandon this technology, because of the high costs and the reduced appeal on customers. On the other hand, Spark Ignition (SI) engines are not able to match the thermal efficiency of diesels, as well as their low emission of carbon dioxide (CO2): therefore, it would be highly desirable to identify cost effective solutions that permit to overcome the limits of Diesel engines, in particular soot emissions, while maintaining all the above-mentioned advantages. Dual fuel combustion, combining Natural Gas and Diesel fuel, is a well-proven technique for reducing soot emissions, while maintaining, or even increasing fuel efficiency. Moreover, this technology can be directly applied to existent Diesel engines with a few hardware modifications. However, to achieve the best results, a brand new calibration of the engine control parameters is needed. CFD-3D combustion simulation is the most cost effective tool to drive the experimental calibration process. Obviously, the numerical models must be previously calibrated against a first set of experimental data.The first part of this study, based on a previous work [9], reviews the building and experimental validation of a CFD 3D model, able to analyze this type of Dual Fuel concept applied to a current production light duty turbocharged Diesel engine, suitable for many different applications. A good agreement between simulation and experiments is found. In the second part of the paper, the calibrated model is used to investigate Dual Fuel combustion, analyzing the effects of Diesel oil injection strategies.

2018 - An Innovative Hybrid Powertrain for Small and Medium Boats [Relazione in Atti di Convegno]
Mattarelli, Enrico; Rinaldini, Carlo Alberto; Savioli, Tommaso; Warey, Alok; Gopalakrishnan, Venkatesh; Potter, Michael
abstract

Hybridization is a mainstream technology for automobiles, and its application is rapidly expanding in other fields. Marine propulsion is one such field that could benefit from electrification of the powertrain. In particular, for boats to sail in enclosed waterways, such as harbors, channels, lagoons, a pure electric mode would be highly desirable. The main challenge to accomplish hybridization is the additional weight of the electric components, in particular the batteries. The goal of this project is to replace a conventional 4-stroke turbocharged Diesel engine with a hybrid powertrain, without any penalty in terms of weight, overall dimensions, fuel efficiency, and pollutant emissions. This can be achieved by developing a new generation of 2-Stroke Diesel engines, and coupling them to a state-of-the art electric system. For the thermal units, two alternative designs without active valve train are considered: opposed piston and loop scavenged engines. The design of the alternative engines is carried out through CFD simulations. The CFD has been calibrated and validated using experimental data from single-cylinder loop scavenged engine. The study demonstrates that the new Loop scavenged engine with a 23 kWh battery pack and an Opposed Piston design with a 15 kWh battery pack can meet the goals of the project while providing 5% and 10% fuel efficiency improvement at cruise conditions respectively, in comparison to the reference 4-stroke engine.

2018 - MOTORE A DUE TEMPI E A PISTONI CONTRAPPOSTI [Brevetto]
Mattarelli, Enrico; Rinaldini, Carlo Alberto; Savioli, Tommaso
abstract

2017 - Combustion System Development of an Opposed Piston 2-Stroke Diesel Engine [Relazione in Atti di Convegno]
Mattarelli, Enrico; Cantore, Giuseppe; Rinaldini, Carlo Alberto; Savioli, Tommaso
abstract

Today, the interest towards 2-stroke, opposed-piston compression-ignition engines is higher than ever, after the announcement of imminent production of a 2.7L 3-cylinder light truck engine by Achates Powers. In comparison to other 2-stroke designs, the advantages in terms of scavenge and thermal efficiency are indisputable: a perfect "uniflow" scavenge mode can be achieved with inexpensive and efficient piston controlled ports, while heat losses are strongly reduced by the relatively small transfer area. Unfortunately, the design of the combustion system is completely different from a 4-stroke DI Diesel engine, since the injectors must be installed on the cylinder liners: however, this challenge can be converted into a further opportunity to improve fuel efficiency, adopting advanced combustion concepts. This paper is based on a previous study, where the main geometric parameters of an opposed piston engine rated at 270 kW (3200 rpm) were defined with the support of CFD 1D-3D simulations. The current work will focus on the influence of an innovative combustion system, developed by the authors by means of further CFD-3D analyses, holding constant the boundary conditions of the scavenging process. The numerical study eventually demonstrates that an optimized 2-S OP Diesel engine can achieve a 10% improvement on brake efficiency at full load, in comparison to an equivalent conventional 4-stroke engine, while reducing in-cylinder peak pressures and turbine inlet temperatures.

2017 - Design and experimental development of a compact and efficient range extender engine [Articolo su rivista]
Borghi, Massimo; Mattarelli, Enrico; Muscoloni, Jarin; Rinaldini, Carlo Alberto; Savioli, Tommaso; Zardin, Barbara
abstract

The paper reviews the design and experimental development of an original range-extender single-cylinder two-stroke gasoline engine, rated at 30 kW (maximum engine speed: 4500 rpm). The goal of the project is to get most of the benefits of the two-stroke cycle (compactness, high power density, low cost), while addressing the typical issues affecting the conventional engines of this type. Among many recent similar propositions, the peculiarities of this engine, besides the cycle, are: external scavenging by means of an electric supercharger, piston controlled scavenge and exhaust ports (no poppet valves), gasoline direct injection (GDI), and a patented rotary valve for the optimization of the scavenging process, of the loop type. Lubrication is identical to a conventional four-stroke engine, and the rotary valve, connected to the crankshaft, helps to improve the balance of the piston reciprocating forces, yielding an excellent NVH behavior. It should be noted that, except the patented rotary valve, all the engine parts are standard automotive commercial components, that don’t require any specific expensive technology. In fact, the originality of the engine consists in the optimum combination of existing well assessed concepts. The scavenging and combustion systems of the engine are developed in the first phase of the project, including the construction and the experimental testing of a prototype. In the second phase, the air metering system of the prototype is completely modified: the piston pump is replaced by an electric supercharger, and engine load is now controlled by the supercharger speed, without throttle valve. The new engine is compared to a standard 4-stroke engine, developed in a previous project for the same application. The main advantages of the two-stroke engine may be summarized as follows: lower weight (−35%), higher brake efficiency (+6%, on average), less heat rejected (−18%), lower thermal and mechanical loads within the cylinder (−40%). The only concern, that will be addressed in a future phase of the study, is the compliance with very low NOx limits: in the worst scenario, the 2-stroke engine could be forced to adopt a well assessed but expensive after-treatment device.

2017 - Development of a 2-Stroke GDI Engine [Relazione in Atti di Convegno]
Savioli, Tommaso; Zardin, Barbara; Borghi, Massimo
abstract

Nowadays, high-pressure gasoline direct injection (GDI) can be considered a standard technology, due to the wide application on 4-stroke turbocharged engines. This technology - in combination with other specific solutions - has been successfully applied to a 500 cc, 30 kW 2-stroke engine, initially developed as a range extender. The engine is valve-less and cam-less, being the scavenge and exhaust ports controlled by the piston. An electric supercharger delivers the required airflow rate, without need of a throttle valve; the lubrication is identical to a 4-stroke. The current study reviews the development process, assisted by CFD simulation, that has brought to the construction of a prototype, tested at the dynamometer bed of the University of Modena and Reggio Emilia (Engineering Department "Enzo Ferrari"). An experimentally calibrated CFD-1d model is applied to predict full load engine performance. The results show an excellent fuel efficiency and a very low level of thermal and mechanical stress despite the high power density.

2017 - Experimental investigation on a Common Rail Diesel engine partially fuelled by syngas [Articolo su rivista]
Rinaldini, Carlo Alberto; Allesina, Giulio; Pedrazzi, Simone; Mattarelli, Enrico; Savioli, Tommaso; Morselli, Nicolo'; Puglia, Marco; Tartarini, Paolo
abstract

The high efficiency, reliability and flexibility of modern passenger car Diesel engines makes these power units quite attractive for steady power plants totally or partially running on fuels derived from biomass, in particular on syngas. The engine cost, which is obviously higher than that of current industrial engines, may not be a big obstacle, provided that the re-engineering work is limited and that performance and efficiency are enhanced. The goal of this work is to explore the potential of a current automotive turbocharged Diesel engine running on both Diesel fuel and syngas, by means of a comprehensive experimental investigation focused on the combustion process. The engine is operated at the most typical speed employed in steady power plants (3000 rpm), considering three different loads (50–100–300 Nm/16–31–94 kW). For each operating condition, the syngas rate is progressively increased until it provides a maximum heating power of 85 kW, while contemporarily reducing the amount of injected Diesel oil. Maximum care is applied to guarantee a constant quality of the syngas flow throughout the tests, as well as to maintain the same engine control parameters, in particular the boost pressure. It is found that in-cylinder pressure traces do not change very much, even when drastically reducing the amount of Diesel fuel: this is a very encouraging result, because it demonstrates that there is no need to radically modify the standard stock engine design. Another promising outcome is the slight but consistent enhancement of the engine brake efficiency: the use of syngas not only reduces the consumption of Diesel oil, but it also improves the combustion quality. The authors acknowledge that this study is only a starting basis: further investigation is required to cover all the aspects related to the industrial application of this syngas-Diesel combustion concept, in particular the impact on pollutant emission and on engine durability.

2017 - Scavenge Ports Ooptimization of a 2-Stroke Opposed Piston Diesel Engine [Relazione in Atti di Convegno]
Mattarelli, Enrico; Rinaldini, Carlo; Savioli, Tommaso; Cantore, Giuseppe; Warey, Alok; Potter, Michael; Gopalakrishnan, Venkatesh; Balestrino, Sandro
abstract

This work reports a CFD study on a 2-stroke (2-S) opposed piston high speed direct injection (HSDI) Diesel engine. The engine main features (bore, stroke, port timings, et cetera) are defined in a previous stage of the project, while the current analysis is focused on the assembly made up of scavenge ports, manifold and cylinder. The first step of the study consists in the construction of a parametric mesh on a simplified geometry. Two geometric parameters and three different operating conditions are considered. A CFD-3D simulation by using a customized version of the KIVA-4 code is performed on a set of 243 different cases, sweeping all the most interesting combinations of geometric parameters and operating conditions. The post-processing of this huge amount of data allow us to define the most effective geometric configuration, named baseline. In the second step of the study, the baseline is further optimized, keeping into account some fundamental design constraints, such as the overall dimensions of the manifold. The evolved geometry is then simulated by using KIVA, adopting a refined grid and realistic boundary conditions. The paper presents the calculated scavenging patterns, offering a detailed insight of the process. Finally, the influence of the offset between the crankshafts is analyzed, by using a calibrated CFD-1D engine model.

2016 - Modified diesel engine fueled by syngas: Modeling and experimental validation [Relazione in Atti di Convegno]
Pedrazzi, Simone; Allesina, Giulio; Morselli, Nicolò; Puglia, Marco; Rinaldini, Carlo Alberto; Savioli, Tommaso; Mattarelli, Enrico; Giorgini, Loris; Tartarini, Paolo
abstract

Diesel engines are robust and reliable machine for stationary electrical energy production. In fact, these engines are designed to run continuously for thousands of hours and with low maintenance. However, several issues affect the application of syngas as fuel in this kind of engines. The full conversion from diesel to gas fuel need the presence of the spark plug instead of the diesel injection. Therefore, the high compression ratio in this kind of engines increase the possibility of the knocking phenomenon inside the combustion chamber. The knocking damages the engine mechanical structure and reduce the engine reliability. Several works set the limit of the compression ratio to 17 in order to overcome this issue. In addition, the velocity of the syngas combustion flame is higher compared to the diesel one as result to the presence of hydrogen in the syngas. This difference forces to reduce the spark ignition time from 0 to 15 ° in advance respect the Bottom Top Dead Center (BTDC) in order to limit the peak pressure inside the cylinders to the design value of the engine. Aim of this work is to compare results of a 0D mathematical model of a converted diesel engine with the results obtained in an experimental campaign. For the tests a Fiat Power Train (FPT) 4.5 liters commercial diesel engine converted to syngas is used. The model calculates the maximum power output of the engine at different rpm starting from syngas composition, airsyngas mixture temperature and diesel nominal power. The model takes into account the friction losses, air to fuel ratio and intake manifold pressure. Experimental tests were run on a gasification facility consisting in a fixed bed wood chip downdraft gasifier that generates syngas to fuel the FPT engine. The engine is connected to a MeccAlte generator for electrical power production. An Arduino based controller sets the position of the air valve in order to stabilize the lambda value of the exhaust of the engine to 1.05. A variable electrical load was applied and it was increased as long as the engine was able to drag the generator at 1500 rpm. During the tests, the following parameters were monitored: syngas volumetric flow rate and composition, syngas pollutants concentration (tar, particulate and water), air-gas mixture temperature and intake manifold pressure. An HT electrical circuit analyzer recorded the power output of the generator. Several tests were run at 1500 rpm varying the air-syngas mixture temperature and the intake manifold pressure and experimental results was compared to 0D model predictions. A good agreement of the model to experimental data was achieved. Syngas conversion reduces the maximum electrical power output of the engine generator from 49.7 kW to about 22 kW as result of the lower air-syngas mixture calorific value and density compared to diesel-air mixture. However, the engine mechanical efficiency is comparable using syngas or diesel fuel (about 30%) and pollutant emissions are strongly lower with syngas fuel.

2016 - Performance, emission and combustion characteristics of a IDI engine running on waste plastic oil [Articolo su rivista]
Rinaldini, Carlo Alberto; Mattarelli, Enrico; Savioli, Tommaso; Cantore, Giuseppe; Garbero, M.; Bologna, A.
abstract

An interesting alternative to fossil fuel for Diesel engines is the use of Diesel-like oil from plastic wastes: such a solution yields the double advantage of recovering the valuable energy content of wastes, as well as of mitigating the disposal problem of the very large amount of plastic wastes produced by both domestic and industrial activities. The present paper describes the experimental campaign carried out on a current production indirect injection, naturally aspirated diesel engine, running on standard Commercial Diesel Oil (CDO) and on a Waste Plastic Oil (WPO) derived from the pyrolysis of plastics. Tests have been carried out at both full and partial load, while in-cylinder pressure traces have been measured in order to analyze the combustion phase. The results of the experimental campaign showed a slight reduction of engine performance for the WPO, basically due to a lower volumetric fuel rating, but better brake specific fuel consumption and brake fuel conversion efficiency (differences up to 8%). In-cylinder pressure traces, measured at the same load, revealed some difference in the first part of the combustion process, in particular at high speeds, where for WPO heat release is smoother. Engine soot emissions are always lower running on WPO, with difference up to 50% at full load.

2016 - Port Design Criteria for 2-Stroke Loop Scavenged Engines [Relazione in Atti di Convegno]
Mattarelli, Enrico; Rinaldini, Carlo Alberto; Savioli, Tommaso
abstract

Interest in 2-stroke engines has been recently renewed by several prototypes, developed for the automotive and/or the aircraft field. Loop scavenging, with piston controlled ports is particularly attractive, but the configurations successfully developed in the past for motorbike racing (in particular, the 125cc unit displacement, crankcase pump engines), are not suitable for automotive applications. Therefore, new criteria are necessary to address the scavenging system design of the new generation of 2-stroke automobile/aircraft engines. The paper reviews the transfer ports optimization of a loop scavenged 2-stroke cylinder, whose main parameters were defined in a previous study. The optimization has been carried by means of a parametric grid, considering 3 parameters (2 tilt angles, and the focus distance), and 3 different engine speeds (2000-3000-4000 rpm, assuming a Diesel engine). A set of scavenging CFD-3d simulations have been performed by using a customized version of KIVA-3V. The numerical approach was experimentally calibrated in a previous project (see appendix 1) The simulations results are presented by means of maps showing the influence of the geometrical parameters on the main scavenging coefficients. Finally, a refined mesh has been constructed for the optimum configuration found in the previous parametric analysis, and a set of multi-cycle simulations have been performed. The results demonstrated the very good efficiency of the scavenging process, close to a perfect displacement for delivery ratio up to 1.5, or for residuals fraction higher than 50%

2015 - Combustion analysis of a diesel engine running on different biodiesel blends [Articolo su rivista]
Mattarelli, Enrico; Rinaldini, Carlo Alberto; Savioli, Tommaso
abstract

Rape-seed biodiesel is an interesting option to address the problem of decreasing availability of conventional fossil fuels, as well as to reduce the CO2 emissions of internal combustion engines. The present paper describes an experimental campaign carried out on a current production 4-cylinder, 4-stroke naturally aspirated diesel engine, running on standard diesel fuel and on three different blends of rape-seed biodiesel (20%-50%-100%). Performance, emissions and in-cylinder pressure traces were measured at full load. It was found that the influence of rape-seed biodiesel in the fuel blend is not constant at each operating condition. However, as the biodiesel content increases, full load performance tends to drop, in particular brake specific fuel consumption (maximum worsening: +18%), while soot emission goes down. The maximum improvement observed in terms of soot concentration is 37.5%, at 1200 rpm. The combustion analysis revealed that the main differences among the fuels occur in the first phase of combustion: the burn rate is slower for biodiesel blends at low speeds, and faster at high.

2015 - Experimental-analytical evaluation of sustainable syngasbiodiesel CHP systems based on oleaginous crop rotation [Relazione in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; Rinaldini, Carlo Alberto; Savioli, Tommaso; Morselli, Nicolo'; Mattarelli, Enrico; Tartarini, Paolo
abstract

This work is aimed at investigating how the solutions adopted for the SRF (short rotational forestry) can be applied to oleaginous cultures for bioenergy production with a dual fuel diesel engine. The method is based on four sub-systems: a seed press for oil production, a downdraft gasifier, a biodiesel conversion plant and a dual fuel biodiesel IC engine for CHP (combined heat and power) production. The plant is analytically modeled except for the IC engine that was tested via experimental analysis. Results showed that, in the hypothesis of 8000 hours/year of power plant run, a surface of 27 hectares can supply enough syngas and biodiesel to run a CHP unit with nominal electrical power of 13.61 kW. Moreover, the experimental analysis outlined how the engine running with dual fuel is not almost affected by significant losses in its performance. Besides, the use of syngas yields strong benefits in terms of soot emissions (measured by an opacimeter), as well as in terms of brake fuel conversion efficiency.

2015 - Two-stage turbocharging for the downsizing of SI V-engines [Relazione in Atti di Convegno]
Rinaldini, Carlo Alberto; Breda, Sebastiano; Fontanesi, Stefano; Savioli, Tommaso
abstract

One of the most critical challenges for the specific power increase of turbocharged SI engines is the low end torque, limited by two aspects. First, the big size of the compressor necessary to deliver the maximum airflow does not allow high boost pressures at low speed, due to the surge line proximity. Second, the flame front velocity may become slower than the end gas auto-ignition rate, thus increasing the risk of knocking. This study is based on a current SI GDI V8 turbocharged engine, modeled by means of CFD tools, both 1d and 3d. The goal of the activity is to lower by 20% the displacement, without reducing brake torque, all over the engine speed range. It was decided to adopt a smaller bore, keeping stroke constant. Obviously, the combustion chamber, the valves and the intakeexhaust ports have been re-designed, as well as the whole intake and exhaust system. Instead of the two turbochargers, one for each bank of cylinders, a triple-turbocharger layout has been considered. The development of the engine has been carried out by means of 1D engine cycle simulations, using predictive knock models, calibrated with the support of both experiments and CFD-3d simulations. A few operating conditions for the final configuration have been also analyzed by means of a 3-d CFD tool. The paper presents the results of this activity, and describes in details the guidelines followed for the development of the engine.