1,720,973 research outputs found
Analisi numerica e sperimentale di processi di combustione non convenzionali nei motori a combustione interna.
No full textOggigiorno le emissioni inquinanti rappresentano il vincolo più importante nello sviluppo dei motori a combustione interna. Il riscaldamento globale in continuo aumento è causato principalmente dalle emissioni di gas serra, principalmente dalla C02. I motori a combustione interna devono necessariamente aumentare l’efficienza e, allo stesso tempo, migliorare le emissioni inquinanti per poter ottemperare ai limiti imposti dalle leggi.
L’alta efficienza, l’affidabilità, e la flessibilità richiesta nei moderni veicoli per trasporto persone specialmente nei motori diesel rende tali propulsori adottabili su utilizzi quasi stazionari ( e.g. aeromotive, autotrasporto, generatori di energia elettrica) mediante l’utilizzo di combustibili alternativi miscelati con Diesel. Il costo di tali propulsori che è ovviamente più alto degli odierni motori industriali utilizzati per la produzione di energia non determina un grande ostacolo, in quanto la re-ingegnerizzazione di tali propulsori per implementare il funzionamento dual fuel sarebbe limitata, ma permetterebbe di aumentare efficienza e prestazioni.
L’obiettivo di questo lavoro di tesi è quello di esplorare il potenziale di un moderno motore diesel alimentato con differenti miscele di combustibili alternativi (Metano e Benzina) pre-miscelati nella aspirazione . Questo processo di combustione viene chiamato RCCI ( Reactive Controlled Compression Ignition) e permette incrementare il rendimento globale e ridurre le emissioni inquinanti.In particolare le emissioni di CO2 possono diminuire con l’utilizzo di questa tecnologia. In questo contesto è stato preso in considerazione un motore due tempi per aerotrazione; questa tipologia di propulsore non ha limitazioni nella realizzazione della geometria della camera di combustione, a differenza dei quattro tempi, inoltre le minori pressioni in fase di combustione rendono questi motori maggiormente adattabili alla combustione RCCI.
Il presente lavoro è concentrato sulla validazione numerico sperimentale supportando i calcoli CFD di combustione mediante l’utilizzo di una sala prova utilizzando un moderno motore diesel installato sul banco prova dell’Univestità di Modena ed equipaggiato con un sistema si analisi della pressione in camera di combustione; i calcoli CFD sono stati effettuati utilizzando una versione modificata di Kiva 3v. Il motore due tempi è stato studiato con una campagna di calcoli CFD per studiare il potenziale della combustione RCCI applicata a questi propulsori.
Questi differenti processi di combustione possono avere significativi vantaggi in termini di efficienza globale del motore e di emissioni inquinanti, questi risultati pero possono essere raggiunti solamente con un attento processo di calibrazione motore e di una importante campagna sperimentale di calcoli.Nowadays pollutant emission represent the main topic in internal combustion engines development. Global warming is increased due to the high emissions of greenhouse gases, in particular Co2 emissions. Internal combustion engines must increase global efficiency and, at the same time, decrease pollutant emissions in order to be compliant to future legislation constraints.
The high efficiency, reliability and flexibility of modern passenger car Diesel engines makes these power units quite attractive for steady many quasi-steady application ( e.g. aeromotive, truck ,heavy duty, generators) totally or partially running on fuels blends or different combustion process. 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 in order to implement dual fuel operation is limited and that performance and efficiency are enhanced.
The goal of this work is to explore the potential of a current state of the art turbocharged Diesel engine running on both Diesel Fuel and dual fuel combustion with the use of a premixed charge of Methane or Gasoline. This particular combustion process called RCCI ( Reactive Controlled Compression Ignition) can improve engine global efficiency and reduce pollutant emissions. In particular CO2 emissions decreases because of the different nature of the fuel. In this contest an analysis is made also in a two stroke engine for aircraft application. This kind of engine can be quite attractive for the less constraints in combustion chamber design, instead of four stroke; furthermore low combustion pressures lead to fit better RCCI concepts.
The present thesis is focused in experimental and numerical validation supporting CFD combustion calculation with experimental analysis in a modern Diesel Engine by using a test bed equipped with an indicating system for experimental campaign and a custom version of CFD 3D software Kiva 3V. Two stroke engine has been study by several cfd calculation campaign in order to investigate two stroke potential in RCCI application.
These different combustion process can have several advantages in terms of global efficiency and pollutant emission, but these results can be achieved only with an accurate combustion process calibration and several CFD combustion calculation
Optimization of the Combustion Chamber Design of a Natural Gas-Diesel Dual Fuel Engine Running at Low Load
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Development of a Combustion System for a New Generation of 2-Stroke Spark Ignition Engines
No full textConventional 2-Stroke Spark Ignition engines are characterized by very high power to weight ratios and low manufacturing costs, but also by very low thermal efficiencies and high pollutant emissions. The last issues can be fully addressed by adopting an external scavenging pump and a direct or semi-direct injection system. The implementation of these solutions requires a strong support from CFD simulations, in particular for the optimization of air-fuel mixing and combustion. The paper presents a theoretical study on a new 2-Stroke, three cylinders, 1.3 L, Spark Ignition engine for light aircraft. The power-unit also includes an electric motor connected in parallel with the thermal engine. The latter features a supercharger and a two-stage injection system, made up of a set of low-pressure fuel injectors installed on the transfer ports, and a high-pressure gasoline injector on the cylinder head. While a previous paper [1] describes the general design guidelines and the overall performances predicted for this engine, the current study is focused on the development of the combustion system, driven by 3D-CFD multi-cycle simulations. In particular, the paper reviews the main steps followed for the set-up of the injection and ignition parameters at the condition of maximum power, as well as for the design of an "open"pre-chamber. The simulation results show that the proposed system, with an optimized combination of dual stage injection, piston-controlled ports and open pre-chamber, can be a good basis for achieving a regular and efficient combustion at all the operating conditions of interest for an aircraft piston engine. The concept can be extended also to other types of 2-Stroke high-speed SI engines, suitable for motorcycles, small boats, snow-mobiles et cetera
Combustion Optimization of a Premixed Ultra-Lean Blend of Natural Gas and Hydrogen in a Dual Fuel Engine Running at Low Load
No full textThe numerical study presented in this article is based on an automotive diesel engine (2.8 L, 4-cylinder, turbocharged), considering a NG-H2 blend with 30 vol% of H2, ignited by multiple diesel fuel injections. The 3D-CFD investigation aims at improving BTE, CO, and UHC emissions at low load, by means of an optimization of the diesel fuel injection strategy and of the in-cylinder turbulence (swirl ratio, SR). The operating condition is 3000 rpm - BMEP = 2 bar, corresponding to about 25% of the maximum load of a gen-set engine, able to deliver up to 83 kW at 3000 rpm (rated speed). The reference diesel fuel injection strategy, adopted in all the previous numerical and experimental studies, is a three-shot mode. The numerical optimization carried out in this study consisted in finding the optimal number of injections per cycle, as well as the best timing of each injection and the fuel mass split among the injections. The analysis revealed that combustion can be improved by increasing the local concentration of the more reactive fuel (diesel): in detail, the best strategy is a two-shot mode, with SOI1 = -35°CA AFTDC and SOI2 = -20°CA AFTDC, injecting 70% of the total diesel fuel mass at the first shot. As far as the SR is concerned, the best compromise between performance and emissions was found for a relatively low SR = 1.4. The optimization permitted to extract the full potential of the H2 enrichment in the DF H2/NG-diesel combustion also at low loads: in comparison to the DF NG case, combustion efficiency, and gross indicated thermal efficiency have been improved by 45.7% and 61.0%, respectively; CO- and UHC-specific emissions have been reduced by about 85.0%. Comparing CDC to the optimized DF 30 vol% H2/NG-diesel case, soot emissions are completely canceled, CO2-specific emissions have been reduced by approximately 42.0%, NOx-specific emissions by 33.8%. However, further work has to be done in order to reach comparable values of HC and CO, which are still higher than in a standard diesel combustion
Combustion Analysis of a Diesel Engine Running on Different Biodiesel Blends
No full textRape-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
Port Design Criteria for 2-Stroke Loop Scavenged Engines
No full textInterest 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
Dual Fuel (Natural Gas Diesel) for Light-Duty Industrial Engines: A Numerical and Experimental Investigation
No full textThis 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
Two-Stage Turbocharging for the Downsizing of SI V-Engines
No full textAbstractOne 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 intake-exhaust 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
Performance, emission and combustion characteristics of a IDI engine running on waste plastic oil
Full text linkAn 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
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