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Technical Paper

Hypersonic flow simulation towards space propulsion geometries

2019-09-16
2019-01-1873
With the actual tendency of space exploration, hypersonic flight have gain a significant relevance, taking the attention of many researchers over the world. This work aims to present a numerical tool to solve hypersonic gas dynamic flows for space propulsion geometries. This will be done by validating the code using two well-known hypersonic test cases, the double cone and the hollow cylinder flare. These test cases are part of NATO Research and Technology Organization Working Group 10 validation of hypersonic flight for laminar viscous-inviscid interactions. During the validation process several important flow features of hypersonic flow are captured and compared with available CFD and numerical data. Special attention is taken to the phenomenon of vibrational excitation of the molecules. Different vibrational non-equilibrium models are used and compared with the available data. The pressure and the heat flux along the surfaces are also analyzed.
Technical Paper

Large eddy simulation of an ignition wave front in a heavy duty partially premixed combustion engine

2019-08-15
2019-24-0010
In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in an ignition wave-front dominated combustion mode. 3D-CFD modeling of such a combustion mode is challenging as the reaction speed is dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of energetic turbulence scale on the fuel/air mixing and on the propagation of reaction wave. The results are compared with optical experiments to validate both pressure trace and ignition location. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane).
Technical Paper

Intake manifold primary trumpet tuning options for fuel flow limited high performance ICEs

2019-08-15
2019-24-0005
The 2014 change in Formula 1 power units, from naturally aspirated to highly-downsized and heavily-boosted hybridized power units led to a relevant increase of the internal combustion engine brake specific power output in comparison with former V-8 units. The newly designed “down-sized” engines are characterized by a fuel flow limitation and relevant increase in the thermal loads acting on the engine components, in particular on those facing the combustion chamber. Furthermore, efficiency becomes an equivalent paradigm as performance. In the power unit layout, the air path is defined by the compressor, the intercooler and the piping from the intake plenum to the cylinder. Intake duct length is defined from intake plenum to valve seat and it is a key parameter for engine performance.
Technical Paper

Heavy-Duty Compression-Ignition Engines Retrofitted to Spark-Ignition Operation Fueled with Natural Gas

2019-08-15
2019-24-0030
Natural gas is a promising alternative gaseous fuel due to its availability, economic, and environmental benefits. A solution to increase its use in the heavy-duty transportation sector is to convert existing heavy-duty compression ignition engines to spark-ignition operation by replacing the fuel injector with a spark plug and injecting the natural gas inside the intake manifold. The use of numerical simulations to design and optimize the natural gas combustion in such retrofitted engines can benefit both engine efficiency and emission. However, experimental data of natural gas combustion inside a bowl-in-piston chamber is limited. Consequently, the goal of this study was to provide high-quality experimental data from such a converted engine fueled with methane and operated at steady-state conditions, exploring variations in spark timing, engine speed and equivalence ratio.
Technical Paper

Study of fuel octane sensitivity effects on gasoline partially premixed combustion using optical diagnostics

2019-08-15
2019-24-0025
Partially premixed combustion (PPC) is a low-temperature combustion (LTC) concept that could deliver higher engine efficiency, as well as lower NOx and soot emissions. Gasoline-like fuels are beneficial for air/fuel mixing process under PPC mode because they have superior auto-ignition resistance to prolong ignition delay time. In current experiments, the high octane number gasoline fuel E10 (US market used gasoline, RON=91) and low octane number GCI blend fuel (RON=77) were tested respectively in a full-transparent AVL single cylinder optical compression ignition (CI) engine. Aiming at investigating the fuel sensitivity on engine performances under different combustion modes as well as soot particle emissions, the engine operating parameters and emission data were analyzed from CI to HCCI (homogeneous charge compression ignition) via PPC (partially premixed combustion) by changing fuel injection timing.
Technical Paper

HCCI with Wet Ethanol: Investigating the Charge Cooling Effect of a High Latent Heat of Vaporization Fuel.

2019-08-15
2019-24-0024
The combustion phasing of Homogeneous Charge Compression Ignition combustion is incredibly sensitive to intake temperature. Controlling the intake temperature on a cycle-to-cycle basis is one-way control combustion phasing, however accomplishing this with an intake air heater/intercooler is unfeasible. One possible way to control the intake temperature is through the direct injection of fuel. The direct injection of fuel during the intake stroke cools the charge via evaporative cooling. Some heat is absorbed from the incoming air, lowering the in-cylinder temperature, while some heat is absorbed from the piston/cylinder walls if the spray reaches the walls. The amount of heat that is absorbed from the air vs. the walls depends on the injection timing during the intake. Therefore, if a high latent heat of vaporization fuel is used, the intake temperature will become very sensitive to injection timing, allowing for cycle-to-cycle control of combustion phasing.
Technical Paper

Cylinder Pressure based Method for In-Cycle Pilot Misfire Detection

2019-08-15
2019-24-0017
For the reduction of emissions and combustion noise in a internal combustion Diesel engine, multiple injections are normally used. A pilot injection reduces the ignition delay of the main injection and hence the combustion noise. However, normal variations of the operating conditions, component tolerances and aging may result in the lack of combustion (misfire) or even the lack of injection (miss-injection) for short on-times. The result is a lower indicated thermal efficiency, higher emissions and louder combustion noise. Closed-loop combustion control techniques aim to monitor in real-time these variations and act accordingly to counteract their effect. To ensure the in-cycle controllability of the main injection, the misfire diagnosis must be performed before the start of the main injection. This paper focuses on the development and evaluation of in-cycle algorithms for the pilot misfire detection.
Technical Paper

Experimental High Temperature Analysis of a Low-Pressure Diesel Spray for DPF Regeneration

2019-08-15
2019-24-0035
In the current automotive scenario, particulate filter technology is mandatory in order to attain emission limits in terms of particulate matter for Diesel engines. Despite DPF is often considered a mature technology, significant issues can derive from the use of the engine fuel injectors to introduce in the exhaust pipe the fuel needed to light on the particulate matter in the filter during its regeneration, primarily the lubricant oil dilution with fuel a consequence of significant spray impact on the cylinder liner. As an alternative, the fuel required to start regeneration can be introduced in the exhaust pipe by an auxiliary low pressure injector spraying in the hot exhaust gas stream. In this conditions, the spray evolution and its possible interaction with the surrounding gas stream are relevant in order to better identify the overall layout of the system, so to have the fuel vaporized at the DPF inlet section.
Technical Paper

Smart cylinder deactivation strategies to improve fuel economy and pollutant emissions for Diesel-powered applications

2019-08-15
2019-24-0055
Further improvement of the trade-off between CO2- and pollutant emissions is the main motivating factor for the development of new diesel engine concepts, from light-duty car applications via medium-duty commercial vehicles up to large long-haul trucks. The deactivation of one or more cylinders of a light-duty diesel engine during low load operation can be a sophisticated method to improve fuel economy and reduce especially NOx emissions at the same time. Dynamic Skip Fire (DSF) is and advanced cylinder deactivation technology, where the decision to fire or skip singular units of a multi-cylinder engine architecture is taken just prior to each firing opportunity, based on a balanced rankling of multiple input parameters.
Technical Paper

Study of Friction Optimization Potential for Lubrication Circuits of Light-duty Diesel Engines

2019-08-15
2019-24-0056
Over the last two decades, engine research has been mainly focused on reducing fuel consumption in view of compliance with stringent homologation targets and customer expectations. As it is well known, the objective of overall engine efficiency optimization can be achieved only through the improvement of each element of the efficiency chain, of which mechanical constitutes one of the two key pillars (together with thermodynamics). In this framework, the friction reduction for each mechanical subsystems has been one of the most important topics of modern diesel engine development. In particular, the present paper analyzes the lubrication circuit potential as contributor to the mechanical efficiency improvement, by investigating the synergistic impact of oil circuit design, oil viscosity characteristics (including new ultra-low formulations) and thermal management. For this purpose, a combination of theoretical and experimental tools were used.
Technical Paper

Piston Bowl Design Selection and Optimization for BS-VI Diesel Engine based on Multi-dimensional Combustion Simulation

2019-08-15
2019-24-0086
Stringent emission norms imposed by the recent changes due to implementation of BS-VI emission regulation requires additional focus on improving in-cylinder combustion and emission behavior. These behaviors are in general influenced by piston bowl shape and design. Properties like local AF ratio inside the cylinder and in-cylinder fuel air mixing are influenced by piston bowl shape and design. These properties in turn affect NOx and soot emission. The load on after treatment system like DPF can thus be decreased by optimizing the piston bowl design such that in-cylinder soot emission is reduced. In this study CFD combustion analysis has been carried out to arrive at a piston bowl geometry design with least soot emission for a 3.76-Liter BS-VI CRDI engine. In this work commercially available CFD code AVL FIRE is used for the combustion simulation.
Technical Paper

Effects of Droplet Behaviors on Fuel Adhesion of Flat Wall Impinging Spray injected by a DISI Injector

2019-08-15
2019-24-0034
Owing to the short impingement distance and high injection pressure, it is difficult to avoid the fuel spray impingement on the combustion cylinder wall and piston head in Direct Injection Spark Ignition (DISI) engine, which is a possible source of hydrocarbons and soot emission. For better understanding of the mechanisms behind the spray-wall impingement, the fuel spray and adhesion on a flat wall using a mini-sac injector with a single hole was examined. The microscopic characteristics of impinging spray were investigated through Particle Image Analysis (PIA). The droplet size and velocity were compared before and after impingement. The adhered fuel on the wall was measured by Refractive Index Match-ing (RIM). Time-resolved fuel adhesion evolution as well as adhesion mass, area, and thickness were discussed. Moreover, the relationships between droplets behaviors and fuel adhesion on the wall were discussed.
Technical Paper

Dynamic thermal behavior of a GDI spray impacting on a heated thin foil by phase-averaged infrared thermography

2019-08-15
2019-24-0036
The regulations about pollutant emissions imposed by Community’s laws encourage the investigation on the optimization of the combustion in modern engines and in particular in those adopting the Gasoline Direct Injection (GDI) configuration. It is known that the piston head and cylinder surface temperatures, coupled with the fuel injection pressure, strongly influence the interaction between droplets of injected fluid and the impinged wall. In the present study, the Infrared (IR) thermography is applied to investigate the thermal footprint of an iso-octane spray generated by a multi-hole GDI injector impinging on a heated thin foil. The experimental apparatus includes an invar foil (50 μm in thickness), clamped within a rigid frame heated at a fixed temperature (373 K) by Joule effect, and the GDI injector located 11 mm over the surface.
Technical Paper

Integrated CFD-Experimental Methodology for the Study of a Dual Fuel Heavy Duty Diesel Engine

2019-08-15
2019-24-0093
This paper deals with the experimental and numerical investigation of a 2.0 litre single cylinder Heavy Duty Diesel Engine fuelled by natural gas and diesel oil in Dual Fuel mode. Due to the gaseous nature of the main fuel and to the high compression ratio of the diesel engine, reduced emissions can be obtained. An experimental study has been carried out at three different load level (25%, 50% and 75% of full engine load). Basing on experimental data, the authors’ methodology is based on the use of one-dimensional and 3-dimensional models. The former is able to perform the whole engine with faster simulations while the latter can study deeply the even more complex phenomena (turbulence, combustion, etc.), due to the presence and to the interaction of the two fuels, which occur in the cylinder for the most interesting operating conditions.
Technical Paper

Effects of the domain zonal decomposition on the hybrid URANS/LES modeling of the TCC-III motored engine flow

2019-08-15
2019-24-0097
Hybrid URANS/LES turbulence modeling is rapidly emerging as a valuable complement to standard LES for full-engine multi-cycle simulation. Among the available approaches, zonal hybrids are potentially attractive due to the possibility of clearly identify URANS and LES zones, eventually introducing further zone types with dynamically switching behavior. The present work aims at evaluating the impact of different zonal configurations on the simulated flow statistics using the well-assessed TCC-III experimental engine setup. More specifically, different methods (URANS, LES or seamless DES) are applied inside the cylinder volume, as well as into the intake/exhaust ports and plenums. For each of the five tested configurations, in-cylinder flow features are compared against the reference TCC-III experimental measurements, in terms of ensemble-averaged, RMS fields and flow alignment.
Technical Paper

Development and validation of SI combustion models for natural-gas heavy-duty engines

2019-08-15
2019-24-0096
Flexible, reliable and consistent combustion models are necessary for the improvement of the next generation spark-ignition engines. Different approaches have been proposed and widely applied in the past. However, the complexity of the process involving ignition, laminar flame propagation and transition to turbulent combustion need further investigations. Purpose of this paper is to compare two different approaches describing turbulent flame propagation. The first approach is the one-equation flame wrinkling model by Weller, while the second is the Coherent Flamelet Model (CFM). Ignition is described by a simplified deposition model while the correlation from Herweg and Maly is used for the transition from the laminar to turbulent flame propagation. Validation of the proposed models was performed with experimental data of a natural-gas, heavy duty engine running at different operating conditions.
Technical Paper

PIV and DBI Experimental Characterization of Air flow-Spray Interaction and Soot Formation in a Single Cylinder Optical Diesel Engine using a Real Bowl Geometry Piston

2019-08-15
2019-24-0100
With demanding emissions legislations and the need for higher efficiency, new technologies for compression ignition engines are in development. One of them relies on reducing the heat losses of the engine during the combustion process as well as to devise injection strategies that reduce soot formation. Therefore, it is necessary a better comprehension about the turbulent kinetic energy (TKE) distribution inside the cylinder and how it is affected by the interaction between air flow motion and fuel spray. Furthermore, new diesel engines are characterized by massive decrease of NOx emissions. Therefore, considering the well-known NOx-soot trade-off, it is necessary a better comprehension and overall quantification of soot formation and how the different injection strategies can impact it.
Technical Paper

Fuel-Lubricant Interactions on Stochastic Pre-Ignition Tendency

2019-08-15
2019-24-0103
This work explores the interaction of lubricant and fuel properties on stochastic pre-ignition (SPI). Findings are based statistically significant measurements of cylinder pressure to SPI tendency and magnitude. Specifically, lubricant detergents, lubricant volatility, fuel volatility, fuel chemical composition, fuel-wall impingement, and engine load were varied to study the physical-chemistry effects of fuel-lubricant interactions on SPI tendency. The work illustrates that at low loads, with fuels susceptible to SPI events, lubricant detergent package effects on SPI were non-significant. However, with changes to fuel distillation, fuel-wall impingement or fuel chemistry, lubricant detergent effects could be observed even at reduced loads.
Technical Paper

Numerical and Experimental Investigation into Brake Thermal Efficiency Optimum Heat Release Rate for a Diesel Engine

2019-08-15
2019-24-0109
Although theoretical thermal efficiency is the best with ideal Otto cycle, brake thermal efficiency (BTE) with a diesel engine was projected to be higher with Sabathe (or Seilliger) like cycle than Otto or Diesel like cycle by a zero-dimensional calculation merged empirical energy loss models and mechanical constraints. To pursue the confirmation of the calculated result with the real engine, three injectors (center and two sides) were installed to a cylinder to achieve more degrees of freedom to control heat release rate (HRR) profile. The experimental result was well consistent with the calculated results, namely BTE with Sabathe like cycle was higher than other cycles even though its HRR had less peak and longer duration than ideal. On the other hand, several papers have concluded with a series of numerical simulation parameterized by the DoE technique that the simple delta-shaped HRR is the optimum for BTE under the realistic exhaust emissions’ and/or mechanical constraints.
Technical Paper

Optical investigation of mixture formation in a small bore DISI engine by laser induced exciplex fluorescence (LIEF)

2019-08-15
2019-24-0133
Legislative and customer demands in terms of fuel consumption and emissions are an enormous challenge for the development of modern combustion engines. Downsizing in combination with turbocharging and direct injection is one way to increase efficiency and therefore meet the requirements. This results in a reduction of the displacement and thus the bore diameter. The application of direct injection with small cylinder dimensions increases the probability of the interaction of liquid fuel with the cylinder walls, which may result in disadvantages concerning especially particulate emissions. This leads to the question which bore diameter is feasible without drawbacks concerning emissions as a result of wall wetting. The emerging trends towards long-stroke engine design and hybridization make the use of small bore diameters in future gasoline engines a realistic scenario.
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