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Journal Article

Water Injection Benefits in a 3-Cylinder Downsized SI-Engine

2019-01-15
2019-01-0034
With progressing electrification of automotive powertrains and demands to meet increasingly stringent emission regulations, a combination of an electric motor and downsized turbocharged spark-ignited engine has been recognized as a viable solution. The SI engine must be optimized, and preferentially downsized, to reduce tailpipe CO2 and other emissions. However, drives to increase BMEP (Brake Mean Effective Pressure) and compression ratio/thermal efficiency increase propensities of knocking (auto-ignition of residual unburnt charge before the propagating flame reaches it) in downsized engines. Currently, knock is mitigated by retarding the ignition timing, but this has several limitations. Another option identified in the last decade (following trials of similar technology in aircraft combustion engines) is water injection, which suppresses knocking largely by reducing local in-cylinder mixture temperatures due to its latent heat of vaporization.
Technical Paper

Transient Measurements of Discharge Coefficients of Diesel Nozzles

2000-10-16
2000-01-2788
The discharge coefficient is an important functional parameter of an injector characterising the nozzle flow, in terms of cavitation and hydraulic flip, which subsequently play a crucial role in the spray formation and development. Thus it is important to have the possibility of measuring instantaneously the value of the discharge coefficient. The method proposed is based on the measurement of force developed during the impingement of the fuel jet on a normal target. In this study the method was verified experimentally and also the variation of a diesel nozzle discharge coefficient over the entire injection time was studied. The impingement results were in good agreement, when compared with the results from mass flow measurements both at high and low injection pressures. Strong variations of the discharge coefficient during the injector needle opening and closing periods were seen.
Technical Paper

The Structure of Cavitation and its Effect on the Spray Pattern in a Single-Hole Diesel Nozzle

2001-05-07
2001-01-2008
The structure and evolution of cavitation in a transparent scaled-up diesel nozzle having a hole perpendicular to the nozzle axis has been investigated using high-speed motion pictures, flash photography and stroboscopic visualization. Observations revealed that, at the inception stage, cavitation bubbles are dominantly seen in the vortices at the boundary layer shear flow and outside the separation zone. Cavitation bubbles grow intensively in the shear layer and develop into cloud-like coherent structures when viewed from the side of the nozzle. Shedding of the coherent cloud cavitation was observed. When the flow was increased further the cloud like cavitation bubbles developed into a large-scale coherent structure extending downstream of the hole. Under this condition the cavitation starts as a mainly glassy sheet at the entrance of the hole. Until this stage the spray appeared to be symmetric.
Technical Paper

The Influence of PRF and Commercial Fuels with High Octane Number on the Auto-ignition Timing of an Engine Operated in HCCI Combustion Mode with Negative Valve Overlap

2004-06-08
2004-01-1967
A single-cylinder engine was operated in HCCI combustion mode with different kinds of commercial fuels. The HCCI combustion was generated by creating a negative valve overlap (early exhaust valve closing combined with late intake valve opening) thus trapping a large amount of residuals (∼ 55%). Fifteen different fuels with high octane numbers were tested six of which were primary reference fuels (PRF's) and nine were commercial fuels or reference fuels. The engine was operated at constant operational parameters (speed/load, valve timing and equivalence ratio, intake air temperature, compression ratio, etc.) changing only the fuel type while the engine was running. Changing the fuel affected the auto-ignition timing, represented by the 50% mass fraction burned location (CA50). However these changes were not consistent with the classical RON and MON numbers, which are measures of the knock resistance of the fuel. Indeed, no correlation was found between CA50 and the RON or MON numbers.
Technical Paper

The Effect of Elliptical Nozzle Holes on Combustion and Emission Formation in a Heavy Duty Diesel Engine

2000-03-06
2000-01-1251
A serie of experiments were carried out to compare the combustion and emissions characteristics of a diesel engine using non-circular (elliptical) and circular shaped fuel injector nozzle holes. Elliptic nozzle holes have the potential to increase air entrainment into the spray, which could lead to decreased emissions from diesel combustion. Previous work [6,7] has shown some interesting results in a passenger car diesel engine and also in a single cylinder engine with optical access. The idea is based on results from investigations of gas jets, where the air entrainment for elliptical jets was increased substantially compared to circular jets. The present series of experiments were carried out to further investigate these effects. The non-circular holes, which were made with an aspect ratio of close to 2:1, have a similar flow rate as the conventional circular holes. Two different angles of the elliptical major axis to the injector centerline were used.
Technical Paper

Temperature Oscillations in the Wall of a Cooled Multi Pulsejet Propeller for Aeronautic Propulsion

2016-09-20
2016-01-1998
Environmental and economic issues related to the aeronautic transport, with particular reference to the high-speed one are opening new perspectives to pulsejets and derived pulse detonation engines. Their importance relates to high thrust to weight ratio and low cost of manufacturing with very low energy efficiency. This papers presents a preliminary evaluation in the direction of a new family of pulsejets which can be coupled with both an air compression system which is currently in pre-patenting study and a more efficient and enduring valve systems with respect to today ones. This new pulsejet has bee specifically studied to reach three objectives: a better thermodynamic efficiency, a substantial reduction of vibrations by a multi-chamber cooled architecture, a much longer operative life by more affordable valves. Another objective of this research connects directly to the possibility of feeding the pulsejet with hydrogen.
Technical Paper

Supervisory Controller for a Light Duty Diesel Engine with an LNT-SCR After-Treatment System

2018-09-10
2018-01-1767
Look ahead information can be used to improve the powertrain’s fuel consumption while efficiently controlling exhaust emissions. A passenger car propelled by a Euro 6d capable diesel engine is studied. In the conventional approach, the diesel powertrain subsystem control is rule based. It uses no information of future load requests but is operated with the objective of low engine out exhaust emission species until the Exhaust After-Treatment System (EATS) light off has occurred, even if fuel economy is compromised greatly. Upon EATS light off, the engine is operated more fuel efficiently since the EATS system is able to treat emissions effectively. This paper presents a supervisory control structure with the intended purpose to operate the complete powertrain using a minimum of fuel while improving the robustness of exhaust emissions.
Technical Paper

Spray Characterization of Gasoline Direct Injection Sprays Under Fuel Injection Pressures up to 150 MPa with Different Nozzle Geometries

2019-01-15
2019-01-0063
Maximum fuel injection pressures for GDI engines is expected to increase due to positive effects on emissions and engine-efficiency. Current GDI injectors have maximum operating pressures of 35 MPa, but higher injection pressures have yielded promising reductions in particle number (PN) and improved combustion stability. However, the mechanisms responsible for these effects are poorly understood, and there have been few studies on fuel sprays formed at high injection pressures. This paper summarizes experimental studies on the properties of sprays formed at high injection pressures. The results of these experiments can be used as inputs for CFD simulations and studies on combustion behavior, emissions formation, and combustion system design. The experiments were conducted using an injection rate meter and optical methods in a constant volume spray chamber. Injection rate measurements were performed to determine the injectors’ flow characteristics.
Technical Paper

Simulations of Fuel/Air Mixing, Combustion, and Pollutant Formation in a Direct Injection Gasoline Engine

2002-03-04
2002-01-0835
Simulations of a Direct Injection Spark Ignition (DISI) engine have been performed for both early injection with homogeneous charge combustion and for late injection with stratified charge combustion. The purpose has been to study flow characteristics, fuel/air mixing, combustion, and NOx and soot formation. Focus is put on the combustion modeling. Two different full load cases with early injection are simulated, 2000 rpm and 6000 rpm. One load point with late injection is simulated, 2000 rpm and 2.8 bar net MEP. Three different injection timings are simulated at the low load point: 77, 82, and 87 CAD bTDC. The spray simulations are tuned to match measured spray penetrations and droplet size distributions at both atmospheric and elevated pressure. Boundary conditions for the engine simulations are taken from 1-D gas exchange simulations that are tuned to match engine tests.
Technical Paper

Reducing Pressure Fluctuations at High Loads by Means of Charge Stratification in HCCI Combustion with Negative Valve Overlap

2009-06-15
2009-01-1785
Future demands for improvements in the fuel economy of gasoline passenger car engines will require the development and implementation of advanced combustion strategies, to replace, or combine with the conventional spark ignition strategy. One possible strategy is homogeneous charge compression ignition (HCCI) achieved using negative valve overlap (NVO). However, several issues need to be addressed before this combustion strategy can be fully implemented in a production vehicle, one being to increase the upper load limit. One constraint at high loads is the combustion becoming too rapid, leading to excessive pressure-rise rates and large pressure fluctuations (ringing), causing noise. In this work, efforts were made to reduce these pressure fluctuations by using a late injection during the later part of the compression. A more appropriate acronym than HCCI for such combustion is SCCI (Stratified Charge Compression Ignition).
Technical Paper

Pressure Drop of Monolithic Catalytic Converters Experiments and Modeling

2002-03-04
2002-01-1010
The pressure drop behavior of catalytic converters has been investigated for a number of different substrates, suitable for high performance IC-engines, regarding cell density, wall thickness and coating. The measurements have been performed on an experimental rig with room-air flow and hot-air flow. The data has been used to develop an empirical model for pressure drop in catalytic converters. The sources of pressure drop, such as viscous and inertial effects, have been separated in the model. The influence of turbulence on the pressure drop has been experimentally investigated. The model agrees well with experimental data and previous literature models and can be applied for 1D predictions as well as 3D CFD calculations.
Technical Paper

Performance of a Heavy Duty DME Engine - the Influence of Nozzle Parameters on Combustion and Spray Development

2009-04-20
2009-01-0841
DME was tested in a heavy duty diesel engine and in an optically accessible high-temperature and pressure spray chamber in order to investigate and understand the effect of nozzle parameters on emissions, combustion and fuel spray concentration. The engine study clearly showed that smaller nozzle orifices were advantageous from combustion, efficiency and emissions considerations. Heat release analysis and fuel concentration images indicate that smaller orifices result in higher mixing rate between fuel and air due to reductions in the turbulence length scale, which reduce both the magnitude of fuel-rich regions and the steepness of fuel gradients in the spray, which enable more fuel to burn and thereby shorten the combustion duration.
Journal Article

Performance Studies and Correlation between Vehicle- and Rapid- Aged Commercial Lean NOx Trap Catalysts

2017-03-28
2017-01-0940
Even though substantial improvements have been made for the lean NOx trap (LNT) catalyst in recent years, the durability still remains problematic because of the sulfur poisoning and sintering of the precious metals at high operating temperatures. Hence, commercial LNT catalysts were aged and tested in order to investigate their performance and activity degradation compared to the fresh catalyst, and establish a proper correlation between the aging methods used. The target of this study is to provide useful information for regeneration strategies and optimize the catalyst management for better performance and durability. With this goal in mind, two different aging procedures were implemented in this investigation. A catalyst was vehicle-aged in the vehicle chassis dynamometer for 100000 km, thus exposed to real conditions. Whereas, an accelerated aging method was used by subjecting a fresh LNT catalyst at 800 °C for 24 hours in an oven under controlled conditions.
Technical Paper

Particulate Emissions in a GDI with an Upstream Fuel Source

2019-04-02
2019-01-1180
Public health risk and resulting stringent emission regulations for internal combustion engines pose a need for solutions to reduce particle emissions (PN). Current PN control approaches include increasing fuel injection pressure, optimizing spray targeting, multiple injection strategies, and the use of tumble flaps together with gasoline particulate filters (GPF). Experiments were performed using a single-cylinder spark-ignited GDI engine equipped with a custom inlet manifold and a port fuel injector located 500 mm upstream. Particulate emissions were measured during stationary medium/high load operation to evaluate the effect of varying the mass split between the direct and upstream injectors. Mixing quality is improved substantially by upstream injection and can thus be controlled by altering the mass split between the injectors.
Journal Article

Multi-hole Injectors for DISI Engines: Nozzle Hole Configuration Influence on Spray Formation

2008-04-14
2008-01-0136
High-pressure multi-hole injectors are one candidate injector type for closed-spaced direct injection (DI) gasoline engines. In such a system, the spark plug must be located close to the spray and, during stratified operation, the spray is ignited very soon after the fuel droplets have been vaporized. Thus there are very high demands on the sprays used in such a system. An additional challenge is the positioning of the spark plug relative to the spray; both consistent ignitability and the absence of liquid fuel droplets must be achieved. Many injector parameters influence spray formation; for example, hole diameter, length to hole diameter ratio, nozzle hole configuration etc. This paper investigates the spray formation and spray induced air movement associated with rotational symmetrical and asymmetrical nozzle hole configurations.
Technical Paper

Large-Eddy Simulation of the Flow Around a Ground Vehicle Body

2001-03-05
2001-01-0702
Large Eddy Simulation of the the flow around bus-like ground vehicle body is presented. Both the time-averaged and instantaneous aspects of this flow are studied. Time-averaged velocity profiles are computed and compared with the experiments [1] and show good agreement. The separation length and the base pressure coefficient are presented. The predicted pumping process in the near wake occurs with a Strouhal number St = 0.073, compared with St = 0.069 in the experiment. Unsteady results at two points are presented and compared with the experiments. The coherent structures are studied and show good agreement with the experiments.
Technical Paper

LES Investigation of ECN Spray G2 with an Eulerian Stochastic Field Cavitation Model

2018-04-03
2018-01-0291
Due to an ongoing trend of high injection pressures in the realm of internal combustion engines, the role of cavitation that typically happens inside the injector nozzle has become increasingly important. In this work, a large Eddy Simulation (LES) with cavitation modeled on the basis of an Eulerian Stochastic Field (ESF) method and a homogeneous mixture model is performed to investigate the role of cavitation on the Engine Combustion Network (ECN) spray G2. The Eulerian stochastic field cavitation model is coupled to a pressure based solver for the flow, which lowers the computational cost, thereby making the methodology highly applicable to realistic injector geometries. Moreover, the nature of the Eulerian stochastic field method makes it more convenient to achieve a high scalability when applied to parallel cases, which gives the method the edge over cavitation models that are based on Lagrangian tracking.
Technical Paper

Ion Current Sensing in an Optical HCCI Engine with Negative Valve Overlap

2007-01-23
2007-01-0009
Ion current sensors have high potential utility for obtaining feedback signals directly from the combustion chamber in internal combustion engines. This paper describes experiments performed in a single-cylinder optical engine operated in HCCI mode with negative valve overlap to explore this potential. A high-speed CCD camera was used to visualize the combustion progress in the cylinder, and the photographs obtained were compared with the ion current signals. The optical data indicate that the ions responsible for the chemiluminescence from the HCCI combustion have to be in contact with the sensing electrode for an ion current to start flowing through the measurement circuit. This also means that there will be an offset between the time at which 50% of the fuel mass has burned and 50% of the ion current peak value is reached, which is readily explained by the results presented in the paper.
Technical Paper

Injection Orifice Shape: Effects on Spray Characteristics and Heat-Release Rate in a Large-Size Single-Cylinder Diesel Engine

1999-10-25
1999-01-3490
A series of experimental studies of diesel spray and combustion characteristics was carried out using circular, elliptic and step orifices. The experiment was performed on a 3-litre single-cylinder engine with optical access. In the engine tests, an elliptic-orifice nozzle with an aspect ratio of approximately 2:1, and a step-orifice nozzle were compared with circular-orifice nozzles. All orifices had sharp-edged inlets. The nozzles were tested at injection pressures extending from 300 to 1300 bar. The nozzles were evaluated in respect of initial spray tip velocity, penetration, spray cone angle, spray width, intermittency and heat-release. Substantial differences were observed in the spray characteristics: At an injection pressure of 300 bar, the spray width increased twice as fast in the minor axis plane of the elliptic orifice and step orifice than the circular orifices.
Technical Paper

Inertia Collection Applied to Vehicle Emissions

1989-09-01
892092
The INCOLL or INertia COLLection system described in this paper, should meet the requirements for a short transient test, without using any chassis dynamometer. To prove this point not only the background of its principles are described, but also results from its application both to S I engines with and without catalytic converters and to truck diesel engines. Special interest has been devoted to the oxygen sensor and converter efficiency and their response both during warm up and under transient conditions. The simplification of the analyzing equipment and the direct interpretation of the results, have been dealt with, as well as the repeativity of the results achieved. The INCOLL test may also have a potential use as quality test at the end of the production line and as a tool for reliability development as well as research and development within the field. The cost for an INCOLL test is estimated to be around one (1) percent of a normal FTP certification procedure.
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