a quasi dimensional si combustion model a bi fractal approach

Abstract The main topic of the paper is a detailed description of an extended version of the fractal combustion model (labelled as bi-fractal ) applied for spark ignition (SI) engines, embedded in the commercial software GT-Power as a "user routine". Firstly, a sensitivity analysis has been carried out, with the aim to define a tuning procedure. Subsequently, the combustion model has been calibrated with reference to experimental data of a small-sized two-cylinder SI engine and compared with the traditional version of the fractal approach. Finally, the predictive capability of the bi-fractal approach is assessed over to the whole operating plane, denoting a good agreement for the tested range in terms of both performance and main combustion events

development of a virtual calibration methodology for a downsized si engine by using advanced valve strategies

Abstract The calibration phase of a new engine at test bench is an expensive and time-consuming process. To support the engine development process, in this paper a numerical methodology aiming to define the optimal control parameters is proposed for a downsized VVA SI engine. First, a 1D engine model is build-up in GT-Power and is enhanced with phenomenological sub-models. 1D model is then validated against the experimental findings, at high- and part-load operations. In a second stage, a numerical calibration strategy is defined, to automatically identify, for various engine loads/speeds, the control parameters, ensuring optimal performance and complying with proper system limitations. Complete engine maps are computed for different control strategies ( EIVC and Throttled ). An application example is also presented, where computed maps are embedded in a vehicle model to predict the CO 2 emission produced along a NEDC cycle

development of an on-line energy management strategy for hybrid electric vehicle

Abstract The Hybrid Electric Vehicle (HEV) seems to be one of the most promising short-term solution to improve the sustainability on the transportation sector. As well-known, the numerical analyses can give a substantial contribute during the preliminary vehicle design. In this context, the development of the Energy Management Strategy (EMS) represents the most challenging task. In this paper, an on-line local optimization EMS for a parallel/series hybrid vehicle is proposed to minimize the CO2 emissions. The proposed EMS, implemented in a dynamic simulation platform, is compared to the well-assessed off-line Pontryagin's Minimum Principle (PMP). Firstly, the main differences regarding the energy management are highlighted in detail. Then, the EMSs are assessed in terms of CO2 emissions, putting into evidence that the proposed on-line strategy involves limited penalizations (3-4%) compared to the PMP target

A quasi-dimensional model of pre-chamber spark-ignition engines

Increasingly stringent pollutant and CO2 emission standards require the car manufacturers to investigate innovative solutions to further improve the fuel economy of their fleets. Among these techniques, an extremely lean combustion has a large potential to simultaneously reduce the NOx raw emissions and the fuel consumption of spark-ignition engines. Application of pre-chamber ignition systems is a promising solution to realize a favorable air/fuel mixture ignitability and an adequate combustion speed, even with very lean mixtures. In this work, the combustion characteristics of an active pre-chamber system are experimentally investigated using a single-cylinder research engine. Conventional gasoline fuel is injected into the main chamber, while the pre-chamber is fed with compressed natural gas. In a first stage, an experimental campaign was carried out at various speeds, spark timings and air-fuel ratios. Global engine operating parameters as well as cylinder pressure traces, inside main combustion chamber and pre-chamber, were recorded and analyzed. Based on the available experimental data, a phenomenological model of this unconventional combustion system with divided combustion chambers was developed and validated. The model was then implemented in a 1D code. The proposed numerical approach shows the ability to simulate the experimental data with good accuracy, using a fixed tuning constant set. The model demonstrates to correctly describe the behavior of a pre-chamber combustion system under different operating conditions and to capture the physics behind such an innovative combustion system concept

A Review of Model Predictive Controls Applied to Advanced Driver-Assistance Systems

Advanced Driver-Assistance Systems (ADASs) are currently gaining particular attention in the automotive field, as enablers for vehicle energy consumption, safety, and comfort enhancement. Compelling evidence is in fact provided by the variety of related studies that are to be found in the literature. Moreover, considering the actual technology readiness, larger opportunities might stem from the combination of ADASs and vehicle connectivity. Nevertheless, the definition of a suitable control system is not often trivial, especially when dealing with multiple-objective problems and dynamics complexity. In this scenario, even though diverse strategies are possible (e.g., Equivalent Consumption Minimization Strategy, Rule-based strategy, etc.), the Model Predictive Control (MPC) turned out to be among the most effective ones in fulfilling the aforementioned tasks. Hence, the proposed study is meant to produce a comprehensive review of MPCs applied to scenarios where ADASs are exploited and aims at providing the guidelines to select the appropriate strategy. More precisely, particular attention is paid to the prediction phase, the objective function formulation and the constraints. Subsequently, the interest is shifted to the combination of ADASs and vehicle connectivity to assess for how such information is handled by the MPC. The main results from the literature are presented and discussed, along with the integration of MPC in the optimal management of higher level connection and automation. Current gaps and challenges are addressed to, so as to possibly provide hints on future developments

Performance and Emissions of an Advanced Multi-Cylinder SI Engine Operating in Ultra-Lean Conditions

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

Serum Albumin Is Inversely Associated With Portal Vein Thrombosis in Cirrhosis

We analyzed whether serum albumin is independently associated with portal vein thrombosis (PVT) in liver cirrhosis (LC) and if a biologic plausibility exists. This study was divided into three parts. In part 1 (retrospective analysis), 753 consecutive patients with LC with ultrasound-detected PVT were retrospectively analyzed. In part 2, 112 patients with LC and 56 matched controls were entered in the cross-sectional study. In part 3, 5 patients with cirrhosis were entered in the in vivo study and 4 healthy subjects (HSs) were entered in the in vitro study to explore if albumin may affect platelet activation by modulating oxidative stress. In the 753 patients with LC, the prevalence of PVT was 16.7%; logistic analysis showed that only age (odds ratio [OR], 1.024; P = 0.012) and serum albumin (OR, -0.422; P = 0.0001) significantly predicted patients with PVT. Analyzing the 112 patients with LC and controls, soluble clusters of differentiation (CD)40-ligand (P = 0.0238), soluble Nox2-derived peptide (sNox2-dp; P < 0.0001), and urinary excretion of isoprostanes (P = 0.0078) were higher in patients with LC. In LC, albumin was correlated with sCD4OL (Spearman's rank correlation coefficient [r(s)], -0.33; P < 0.001), sNox2-dp (r(s), -0.57; P < 0.0001), and urinary excretion of isoprostanes (r(s), -0.48; P < 0.0001) levels. The in vivo study showed a progressive decrease in platelet aggregation, sNox2-dp, and urinary 8-iso prostaglandin F2 alpha-III formation 2 hours and 3 days after albumin infusion. Finally, platelet aggregation, sNox2-dp, and isoprostane formation significantly decreased in platelets from HSs incubated with scalar concentrations of albumin. Conclusion: Low serum albumin in LC is associated with PVT, suggesting that albumin could be a modulator of the hemostatic system through interference with mechanisms regulating platelet activation

Comparison of seven prognostic tools to identify low-risk pulmonary embolism in patients aged <50 years

publishersversionPeer reviewe

Association Between Preexisting Versus Newly Identified Atrial Fibrillation and Outcomes of Patients With Acute Pulmonary Embolism

Background Atrial fibrillation (AF) may exist before or occur early in the course of pulmonary embolism (PE). We determined the PE outcomes based on the presence and timing of AF. Methods and Results Using the data from a multicenter PE registry, we identified 3 groups: (1) those with preexisting AF, (2) patients with new AF within 2 days from acute PE (incident AF), and (3) patients without AF. We assessed the 90-day and 1-year risk of mortality and stroke in patients with AF, compared with those without AF (reference group). Among 16 497 patients with PE, 792 had preexisting AF. These patients had increased odds of 90-day all-cause (odds ratio [OR], 2.81; 95% CI, 2.33-3.38) and PE-related mortality (OR, 2.38; 95% CI, 1.37-4.14) and increased 1-year hazard for ischemic stroke (hazard ratio, 5.48; 95% CI, 3.10-9.69) compared with those without AF. After multivariable adjustment, preexisting AF was associated with significantly increased odds of all-cause mortality (OR, 1.91; 95% CI, 1.57-2.32) but not PE-related mortality (OR, 1.50; 95% CI, 0.85-2.66). Among 16 497 patients with PE, 445 developed new incident AF within 2 days of acute PE. Incident AF was associated with increased odds of 90-day all-cause (OR, 2.28; 95% CI, 1.75-2.97) and PE-related (OR, 3.64; 95% CI, 2.01-6.59) mortality but not stroke. Findings were similar in multivariable analyses. Conclusions In patients with acute symptomatic PE, both preexisting AF and incident AF predict adverse clinical outcomes. The type of adverse outcomes may differ depending on the timing of AF onset.info:eu-repo/semantics/publishedVersio

Numerical Investigations of Innovative SI engines suitable for hybrid powertrains with reduced CO2

The problem of atmospheric air pollution, caused by the Internal Combustion Engines (ICEs), has never been greater than today. Car manufacturers, driven by more and more stringent legislations, are continuously forced to find proper technical solutions to deal with this challenge, without giving up on the high standards regarding engine performance. In particular, the new emission limit for the CO2 recently set for the 2026, with a target of 80 g/km of CO2 along the WLTC, has never pushed so much the automotive manufacturers in developing innovative and clean solutions to improve the fuel economy of the vehicle fleets. However, how to solve this problem is still an open debate. On the one hand, the complete disappearance in few years of the ICE-based propulsion systems in the automotive sector, replaced by fuel cell and/or Battery Electric Vehicles (BEVs) seems to be expected. On the other hand, several analyses declare that potential benefits of a BEV cannot be easily defined. Indeed, if the CO2 formed during the entire vehicle life cycle is considered, the emissions from the two antagonist vehicles become comparable, to such an extent that ICE-based vehicles could be even better than the “zero-emission” alternatives. As often happen, the truth is somewhere in-between, hence, it should be expected in the years to come rather than a pure electric or ICE-based mobility a scenario characterized by variegated technologies that are best suited to the contest in which they are employed. This means that ICE-based vehicles, HEVs, PHEVs, BEVs or even Fuel Cell based vehicles, will coexist in the market for a long time, pushing car manufactures to overcome the limits related to each technology. On the light of the above concerns, the topic of this research activity is to numerically investigate, through a hierarchical simulation-level approach, innovative SI engines, eventually suitable for hybrid powertrains, with a strongly reduced CO2 impact. To this aim, two different ICEs are analyzed, assessing their CO2 emission along the WLTC. The former is a downsized turbocharged VVA 2-cylinder engine, for a conventional vehicle application, defining the reference for the state of art of ICE-based propulsion system. The latter is an innovative 4-cylinder SI engine, equipped with an active pre-chamber ignition system, which guarantees an ultra-lean operation all over the engine operating range. Here, HEV/PHEV architectures are considered for the vehicle simulation. Additionally, the potential fuel economy as well as CO2 benefits, coming from Connected and Automated Vehicles (CAV), are investigated through a numerical methodology able to benchmark these last on a real world-scenario. The simulation efforts carried out to assess the previous objectives is mainly effected in a 0D/1D modelling environment, where the whole engine system is schematized through a network of 1D pipes and 0D cylinders, the latter described in term of in-house developed quasi-dimensional models of the in-cylinder phenomena. In particular, the flame propagation in the conventional engine is modeled according to a well-assessed version of the fractal combustion model developed at the University of Naples Federico II. Whereas, for the pre-chamber engine, a dedicated and innovative procedure, still based on the fractal theory, is developed, since, differently from conventional SI ICEs, only a few predictive combustion models were available in the current literature at the beginning of this activity. The reliability of the overall simulation models is checked for both the engines through the comparisons with 3D or experimental data, using a unique engine-dependent set of tuning constants. Once verified that the physics included in the model is accurate enough to guarantee a good agreement, the model is utilized as a predictive tool for deriving the complete performance maps of both a conventional and a pre-chamber engine. To this aim, a Rule-Based (RB) calibration strategy is also implemented in both the models to identify the optimal values of each control variable in whole operating plane. Of course, the reliability of the RB calibration is demonstrated, too, through the comparison with the outcomes of a general-purpose optimizer, for both the engine architectures. The RB methodology demonstrates to furnish control parameter close to the optimizer, in a very limited computational time. Finally, the engine maps are embedded in vehicle simulations to quantify the CO2 emission over a WLTC, for many different engine and vehicles architectures. In parallel to the above activities, a dedicated off-line Energy Management Strategy, named ETESS, for the HEV is also developed aiming to minimize the CO2 emission along a prescribed mission. The ETESS is compared with the well-known Pontryagin Minimum Principle (PMP) in terms of management of the control units and vehicle performance outcomes. Although the ETESS can only furnish a sub-optimal solution, the reduced computational time to the respect of the PMP suggests the possibility to implement it for an on-line application, with limited penalization. The results carried out in this research activity show that the ICE-based system can reach 94.81g/km CO2 along the WTLC. However, this value is still far away from the EU target of 80 g/km CO2 of 2026. On the contrary, PHEV architecture combined with a pre-chamber engine, able to achieve a maximum Indicted Thermal Efficiency (ITE) around 50%, attains a CO2 emission equal to 43.0 g/km along the same regulatory driving cycle. Although this impressive result, it has to remark that in the current regulation the CO2 emissions necessary for charging the battery is not included, leading to a not representative enough results of the real condition. On the contrary, the HEV configuration reaches 88.8 g/km CO2, very close to the EU ambitious target, suggesting that the combination of these two technologies could be a suitable solution for the years to come. Additionally, connected and autonomous vehicle, thanks to the possibility to use the look-ahead information from the route can further improve the CO2 reduction of about 15-17%, respect to a vehicle not equipped with this technology