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Technical Paper

Large Eddy Simulation of Flow over a Valve in a Simplified Cylinder Geometry

2011-04-12
2011-01-0843
This study focuses on gaining a deeper understanding on the formation of turbulence and other in-cylinder flow structures caused by the intake jets during the intake stroke in internal combustion engines. This is important as the in-cylinder turbulence has a large effect on the mixing of fuel and oxidizer. A fine resolution large eddy simulation (LES) is carried out on an incompressible flow (Re is equivalent to 100,000) over a static valve (lift d = 7 mm) alongside with three other simulations using coarser meshes. The problem is studied in a simplified valve-cylinder geometry on which experimental data by Yasar et al., (2006) is available. The vortex cores, produced by the shear layer of the intake jets, are visualized using the λ₂ definition for vortex cores. The governing flow structures are identified and some features of the flow's mixing capabilities are observed. Additionally, the mixing is studied by releasing a passive scalar into to the flow.
Technical Paper

Interaction of Multiple Fuel Sprays in a Heavy-Duty Diesel Engine

2011-04-12
2011-01-0841
This paper aims to study numerically the influence of the number of fuel sprays in a single-cylinder diesel engine on mixing and combustion. The CFD simulations are carried out for a heavy-duty diesel engine with an 8 hole injector in the standard configuration. The fuel spray mass-flow rate was obtained from 1D-simulations and has been adjusted according to the number of nozzle holes to keep the total injected fuel mass constant. Two cases concerning the modified mass-flow rate are studied. In the first case the injection time was decreased whereas in the second case the nozzle hole diameter was decreased. In both cases the amount of nozzle holes (i.e. fuel sprays) was increased in several steps to 18 holes. Quantitative analyses were performed for the local air-fuel ratio, homogeneity of mixture distribution, heat release rate and the resulting in-cylinder pressure.
Technical Paper

Studying Local Conditions in a Heavy-Duty Diesel Engine by Creating Phi-T Maps

2011-04-12
2011-01-0819
New measurements have been done in order to obtain information concerning the effect of EGR and a paraffinic hydrotreated fuel for the smoke and NO emissions of a heavy-duty diesel engine. Measured smoke number and NO emissions are explained using detailed chemical kinetic calculations and CFD simulations. The local conditions in the research engine are analyzed by creating equivalence ratio - temperature (Phi-T) maps and analyzing the CFD results within these maps. The study uses different amount of EGR and two different diesel fuels; standard EN590 diesel fuel and a paraffinic hydrotreated vegetable oil (HVO). The detailed chemical kinetic calculations take into account the different EGR rates and the properties of the fuels. The residence time in the kinetical calculations is used to explain sooting combustion behavior within diesel combustion. It was observed that NO emission trends can be well captured with the Phi-T maps but the situation is more difficult with the engine smoke.
Journal Article

Characteristics of High Pressure Jets for Direct Injection Gas Engine

2013-04-08
2013-01-1619
The direct injection (DI) natural gas engine is considered as one of the promising technologies to achieve the continuing goals of the higher efficiency and reduced emissions for internal combustion engines. Shock wave phenomena can easily occur near the nozzle exit when high pressure gaseous fuel is injected directly into the engine cylinder. In the present study, high pressure gas issuing from a prototype gas injector was experimentally studied using planar laser-induced fluorescence (PLIF) technique. Acetone was selected as a fuel tracer. The effects of injection pressures on the flow structure and turbulent mixing were investigated based on a series of high resolution images. The jet macroscopic structures, such as jet penetration, cone angle and jet volume, are analyzed under different injection pressures. Results show that barrel shock waves can significantly influence the jet flow structure and turbulent mixing.
Technical Paper

Effect of Intake Channel Design to Cylinder Charge and Initial Swirl

2010-04-12
2010-01-0624
Two different medium-speed diesel engine cylinder head designs have been studied. The focus of the study has been the effect of intake channel design in the in-cylinder flow. The study has been carried out by CFD. The first cylinder head is a standard Wärtsilä 20 cylinder head and the second one is a specially designed head for a single cylinder research engine, called Extreme Value Engine (EVE). The CFD boundary conditions have been simulated by the help of a 1-d simulation code. In the full load cases the maximum cylinder pressure was 300 bar. Simulations have been done at lower load level too. One simulation with the new cylinder head was carried out with one intake valve closed in order to get an idea of the swirl to be generated by this approach. In the study the in-cylinder flow field, the cylinder charge and turbulence kinetic energy have been examined.
Journal Article

Real Gas Effects in High-Pressure Engine Environment

2010-04-12
2010-01-0627
Real gas effects are studied during the compression stroke of a diesel engine. Several different real gas models are compared to the ideal gas law and to the experimental pressure history. Comparisons are done with both 1-D and CFD simulations, and reasons and answers are found out for the observed differences between simulations and experimental data. The engine compression ratio was measured for accurate model predictions. In addition, a 300bar extreme pressure case is also analyzed with the real gas model since an engine capable for this performance level is currently being built at the Aalto University School of Science and Technology. Real gas effects are even more important in these extreme conditions than in normal operating pressures. Finally, it is shown that the predicted pressure history during an engine compression stroke by a real gas model is more accurately predicted than by the ideal gas law.
Journal Article

Emission Reduction Using Hydrotreated Vegetable Oil (HVO) With Miller Timing and EGR in Diesel Combustion

2011-08-30
2011-01-1955
Several high-speed diesel engine test runs were carried out during 2010 in Aalto University using a single-cylinder research engine. The main focus was on miller cycle and exhaust gas recirculation (EGR) tests using hydrotreated vegetable oil (HVO) as fuel. But also reference tests were run using both HVO and regular EN590 diesel in normal engine configuration and running parameters. The miller tests included a sweep of three different intake valve closing timings and also a sweep with advanced start of injection. The results showed a reduction in both nitrous oxides (NOx) and smoke emissions. EGR tests showed a significant decrease in NOx emissions as was expected. The lower smoke emissions of HVO compared to EN590 enable higher EGR percentages with similar PM emission and hence bigger NOx emission reduction.
Journal Article

Large-Bore Compression-Ignition Engines: High NOx Reduction Achieved at Low Load with Hydro-Treated Vegetable Oil

2011-08-30
2011-01-1956
The objective of this paper is to analyze the performance and the combustion of a large-bore medium-speed engine running with hydro-treated vegetable oil (HVO) at low engine load. This fuel has a paraffinic chemical structure and high cetane number (CN). The main benefits are thus lower emission compared to diesel fuel and low soot values. The facility used in this study is a research engine, where the conditions before and after the machine, the valve timing and the injection parameters are fully adjustable. Several in-cylinder conditions before the combustion have been tested. The results are promising and show the benefits of HVO compared to diesel fuel. In fact, it has been possible to reduce nitrogen oxides (NOx) emission over 50% running with HVO and opportunely tuned valve timing.
Technical Paper

Experimental Study of Spray Characteristics between Hydrotreated Vegetable Oil (HVO) and Crude Oil Based EN 590 Diesel Fuel

2011-09-11
2011-24-0042
The aim of current study was to compare the global fuel spray characteristics between renewable hydrotreated vegetable oil (HVO) and crude oil-based EN 590 diesel fuel. According to previous studies, the use of HVO enables reductions in carbon monoxide (CO), total hydrocarbon (THC), nitrogen oxide (NOx) and particle matter (PM) emissions without any changes to the engine or its controls. Fuel injection strategies and global fuel spray characteristics affect on engine combustion and exhaust gas emissions. Due to different physical properties of two different fuels, fuel spray characteristics differ. Fuel spray studies were performed with backlight imaging using a pressurized test chamber imitating real engine conditions at the end of compression stroke. However, the measurements were made in non-evaporative conditions. Various injection parameters such as injection pressures and orifice diameter were tested.
Technical Paper

Improving the Accuracy of 1-D Fuel Injection Modeling

2012-04-16
2012-01-1256
In this study, one-dimensional fluid dynamics simulation software was utilized in producing common rail diesel fuel injection for varying injection parameters with enhanced accuracy. Injection modeling refinement is motivated by improved comprehension of the effects of various physical phenomena within the injector. In addition, refined injection results yield boundary conditions for three-dimensional CFD simulations. The criteria for successful simulation results were evaluated upon experimental test run data that have been reliably obtained, primarily total injected mass per cycle. A common rail diesel fuel delivery system and its core mechanics were presented. System factors most critical to fuel delivery were focalized. Models of two solenoid-type common rail injectors of different physical sizes and applications were enhanced.
Technical Paper

An Experimental Study on High Pressure Pulsed Jets for DI Gas Engine Using Planar Laser-Induced Fluorescence

2012-09-10
2012-01-1655
Compressed natural gas direct-injection (CNG-DI) engines based on diesel cycle combustion system with pilot ignition have ability to achieve high thermal efficiency and low emissions. Generally, underexpanded jets can be formed when the high pressure natural gas is injected into the combustion chamber. In such conditions, shock wave phenomena are the typical behaviors of the jet, which can significantly influence the downstream flow structure and turbulent mixing. In the present study, the characteristics of high-pressure transient jets were investigated using planar laser-induced fluorescence (PLIF) of acetone as a fuel tracer. The evolution of the pulsed jet shows that there are three typical jet flow patterns (subsonic, moderately underexpanded, and highly underexpanded) during the injection. The full injection process of high-pressure pulsed jets is well described with the help of these shock wave structures.
Technical Paper

Hydrotreated Vegetable Oil and Miller Timing in a Medium-Speed CI Engine

2012-04-16
2012-01-0862
The objective of this paper is to analyse the performance and the combustion of a large-bore single-cylinder medium speed engine running with hydrotreated vegetable oil. This fuel has a paraffinic chemical structure and high Cetane number. These features enable achievement of complete and clean combustion with different engine setups. The main benefits are thus lower soot and nitrogen oxides emissions compared to diesel fuel. The facility used in this study is a research engine, where the conditions upstream the machine, the valve timing and the injection parameters are fully adjustable. In fact, the boundary conditions upstream and downstream the engine are freely controlled by a separated supply air plant and by a throttle valve, located at the end of the exhaust pipe. The injection system is common-rail: rail pressure, injection timing and duration are completely adjustable.
Technical Paper

Large Eddy Simulation of the Intake Flow in a Realistic Single Cylinder Configuration

2012-04-16
2012-01-0137
The present paper focuses on gaining a deeper understanding about the turbulent flow inside an engine cylinder using large eddy simulation. While the main motivation of the current study is to gain a deeper understanding of the flow patterns and especially about the swirl, the background motivation of this study is the development and testing of suitable methods for the large eddy simulation of combustion engines and the validation of the used simulation methodology. In particular, we study the swirl and other flow features generated by the intake jets inside the cylinder. The simulated geometry is the Sisu Diesel 84 engine cylinder where the exhaust valves are closed and the intake valves have constant valve lifts. Furthermore, the piston has been removed so that the flow is able to exit from the opposite end of the cylinder.
Technical Paper

Comparing Breakup Models in a Novel High Injection Pressure SCR System using Polyhedral Meshing

2014-10-13
2014-01-2816
A novel high pressure SCR spray system is investigated both experimentally and numerically. RANS simulations are performed using Star-CD and polyhedral meshing. This is one of the first studies to compare droplet breakup models and AdBlue injection with high injection pressure (Pinj=200 bar). The breakup models compared are the Reitz-Diwakar (RD), the Kelvin-Helmholtz and Rayleigh-Taylor (KHRT), and the Enhanced Taylor Analogy Breakup (ETAB) model. The models are compared with standard model parameters typically used in diesel fuel injection studies to assess their performance without any significant parameter tuning. Experimental evidence from similar systems seems to be scarce on high pressure AdBlue (or water) sprays using plain hole nozzles. Due to this, it is difficult to estimate a realistic droplet size distribution accurately. Thereby, there is potential for new experimental data to be made with high pressure AdBlue or water sprays.
Technical Paper

In-Cylinder Flow Field of a Diesel Engine

2007-10-29
2007-01-4046
The flow through the valves of an engine cylinder head is very complex in nature due to very high gas velocities and strong flow separation. However, it is also the typical situation in almost every engine related flow. In order to gain better understanding of the flow features after the cylinder head, and to gain knowledge of the performance level that can be expected from CFD analysis, flow field measurements and computations were made in an engine rig. Particle image velocimetry (PIV) and paddle wheel measurements have been conducted in a static heavy-duty diesel engine rig to characterize the flow features with different valve lifts and pressure differences. These measurements were compared with CFD predictions of the same engine. The simulations were done with the standard k-ε turbulence model and with the RNG turbulence model using the Star-CD flow solver.
Technical Paper

Applying Soot Phi-T Maps for Engineering CFD Applications in Diesel Engines

2005-10-24
2005-01-3856
Soot modeling has become increasingly important as diesel engine manufacturers are faced with constantly tightening soot emission limits. As such the accuracy of the soot models used is more and more important but at the same time 3-D CFD engine studies require models that are computationally not too demanding. In this study, soot Phi-T maps created with detailed chemistry code have been used to develop a soot model for engineering purposes. The proposed soot model was first validated against detailed chemistry results in premixed laminar environment. As turbulence in engines is of major importance, it was taken into account in the soot oxidation part of the model with the laminar and turbulent characteristic time- type of approach. Finally, the model was tested in a large bore Diesel engine with varying loads. Within the steps described above, the proposed model was also compared with the well-known Hiroyasu-Magnussen soot model.
Technical Paper

NOx Reduction in a Medium-Speed Single-Cylinder Diesel Engine using Miller Cycle with Very Advanced Valve Timing

2009-09-13
2009-24-0112
The objective of this study is to achieve high reduction of NOx emissions in a medium-speed single-cylinder research engine. The main feature of this research engine is that the gas exchange valve timing is completely adjustable with electro-hydraulic actuators. The study is carried out at high engine load and using a very advanced Miller valve timing. Since the engine has no turbocharger, but a separate charge air system, 1-D simulations are carried out to find the engine setup, which would be close to the operating points of a real engine. The obtained NOx reduction is over 40% with no penalty in fuel consumption.
Technical Paper

Fuel Injection System Simulation with Renewable Diesel Fuels

2009-09-13
2009-24-0105
Renewable diesel-type fuels and their compatibility with a single-cylinder medium-speed research diesel engine were studied. The report consists of a literature study on the fuels, introduction of the simulation model designed and simulations made, and of the results and summary sections. The fuels studied were traditional biodiesel (fatty acid methyl ester, FAME), hydrotreated vegetable oil (HVO), Fischer-Tropsch (FT) diesel fuels and dimethyl ether (DME). According to the simulations, the behaviors of different renewable diesel fuels in the fuel injection system are quite similar to one another, with the greatest deviations found with DME. The main differences in the physical properties are fuel densities and viscosities and especially with DME compressibility, which have some predictable effect. The chemical properties of the fuels are more critical for a common rail fuel injection system.
Technical Paper

Liquid Spray Data from an Optical Medium-Speed Diesel Engine and Its Comparison with CFD

2009-11-02
2009-01-2676
Experimental spray tip penetrations obtained from a large-bore medium-speed optical diesel engine were compared to CFD simulations. The optical spray results are unique as they are obtained from a running large-bore (200mm) diesel engine. The experimental spray tip penetration measurements were obtained during the early spray development period when the spray evaporation had not yet reached the quasi steady-state phase. The CFD simulations were conducted in both static chamber environment and in engine conditions. The fuel injection boundary conditions were obtained from 1-D simulations. Within the error margins associated with the experimental and computational data, relatively good accuracy was obtained between measured and simulated spray tip penetration. It was also observed that it is very important to have accurate fuel injection mass flow rate data. This was observed after a sensitivity analysis was made for the injection duration and fuel mass quantity.
Journal Article

Hydrotreated Vegetable Oil (HVO) as a Renewable Diesel Fuel: Trade-off between NOx, Particulate Emission, and Fuel Consumption of a Heavy Duty Engine

2008-10-06
2008-01-2500
Hydrotreating of vegetable oils or animal fats is an alternative process to esterification for producing biobased diesel fuels. Hydrotreated products are also called renewable diesel fuels. Hydrotreated vegetable oils (HVO) do not have the detrimental effects of ester-type biodiesel fuels, like increased NOx emission, deposit formation, storage stability problems, more rapid aging of engine oil or poor cold properties. HVOs are straight chain paraffinic hydrocarbons that are free of aromatics, oxygen and sulfur and have high cetane numbers. In this paper, NOx - particulate emission trade-off and NOx - fuel consumption trade-off are studied using different fuel injection timings in a turbocharged charge air cooled common rail heavy duty diesel engine. Tested fuels were sulfur free diesel fuel, neat HVO, and a 30% HVO + 70% diesel fuel blend. The study shows that there is potential for optimizing engine settings together with enhanced fuel composition.
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