CFD Analysis of 2-Stroke Engines

Abstract 1d and 3d CFD simulation is a standard engineering practice on 4-stroke engines. However, the application to the 2-Stroke cycle is not so trivial, in particular the transition from detailed CFD-3d analyses to simplified 1d engine simulations. A first critical issue is the correlation between the instantaneous cylinder gas composition and the composition of the exhaust flow: such a correlation, required by the 1d software, is very difficult to be determined by experiments, so that CFD-3D analyses remain the only reliable source of information. These CFD analyses must be carefully designed, in order to be representative of the actual operating conditions of the engine, and to provide reliable results. Another problem is the characterization of the ports discharge properties. Conventional experiments at a steady flow bench are affected by several approximations: first of all, flow patterns within the cylinder are quite different from the actual ones; moreover, the real flow is fully transient. Finally, a 3-d analysis on a single whole cycle is not sufficient to accurately predict the evolution of the thermodynamic quantities, as the conditions of the charge at exhaust port opening changes from cycle to cycle, affecting all the internal processes. A robust and cost-effective multi-cycle simulation methodology is therefore required. The paper describes a methodology to perform reliable CFD analyses on 2-Stroke engines, with the support of a conventional steady flow bench. This methodology is applied to a 2-Stroke engine prototype, for which a comprehensive set of experimental data is available. The good agreement between simulation and experiments demonstrates the soundness of the proposed approach

Combustion analysis of a diesel engine running on different biodiesel blends

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

Two-Stage Turbocharging for the Downsizing of SI V-Engines

AbstractOne 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

Combustion System Development of an Opposed Piston 2-Stroke Diesel Engine

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

Design and experimental development of a compact and efficient range extender engine

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

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe

Analisi numerica e sperimentale di processi di combustione non convenzionali nei motori a combustione interna.

Oggigiorno 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

Port Design Criteria for 2-Stroke Loop Scavenged Engines

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