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Journal Article

Study of Air Entrainment of Multi-hole Diesel Injection by Particle Image Velocimetry - Effect of Neighboring Jets Interaction and Transient Behavior After End of Injection.

2010-04-12
2010-01-0342
The air entrainment of multi-hole diesel injection is investigated by high speed Particle Image Velocimetry (PIV) using a multi-hole common rail injector with an injection pressure of 100 MPa. The sprays are observed in a high pressure, high temperature cell that reproduces the thermodynamic conditions which exist in the combustion chamber of a diesel engine during injection. Typical ambient temperature of 800K and ambient density of 25 kg/m3 are chosen. The air entrainment is studied with the PIV technique, giving access to the velocity fields in the surrounding air and/or in the interior of two neighboring jets. High acquisition rate of 5000 Hz, corresponding to 200 μs between two consecutive image pairs is obtained by a high-speed camera coupled with a high-speed Nd:YLF laser. The effect of neighboring jets interaction is studied by comparing four injectors with different numbers of holes (4, 6, 8 and 12) with similar static mass flow rate per hole.
Journal Article

Effects of Methane/Hydrogen Blends On Engine Operation: Experimental And Numerical Investigation of Different Combustion Modes

2010-10-25
2010-01-2165
The introduction of alternative fuels is crucial to limit greenhouse gases. CNG is regarded as one of the most promising clean fuels given its worldwide availability, its low price and its intrinsic properties (high knocking resistance, low carbon content...). One way to optimize dedicated natural gas engines is to improve the CNG slow burning velocity compared to gasoline fuel and allow lean burn combustion mode. Besides optimization of the combustion chamber design, hydrogen addition to CNG is a promising solution to boost the combustion thanks to its fast burning rate, its wide flammability limits and its low quenching gap. This paper presents an investigation of different methane/hydrogen blends between 0% and 40 vol. % hydrogen ratio for three different combustion modes: stoichiometric, lean-burn and stoichiometric with EGR.
Journal Article

Towards an Innovative Combination of Natural Gas and Liquid Fuel Injection in Spark Ignition Engines

2010-05-05
2010-01-1513
In order to address the CO₂ emissions issue and to diversify the energy for transportation, CNG (Compressed Natural Gas) is considered as one of the most promising alternative fuels given its high octane number. However, gaseous injection decreases volumetric efficiency, impacting directly the maximal torque through a reduction of the cylinder fill-up. To overcome this drawback, both independent natural gas and gasoline indirect injection systems with dedicated engine control were fitted on a RENAULT 2.0L turbocharged SI (Spark Ignition) engine and were adapted for simultaneous operation. The main objective of this innovative combination of gas and liquid fuel injections is to increase the volumetric efficiency without losing the high knocking resistance of methane.
Technical Paper

Quantifying Benefits of Dual Cam Phasers, Lean Mixture and EGR on the Operating Range and Fuel Economy of a PFI NVO CAI Engine

2010-04-12
2010-01-0844
Among the existing concepts that help to improve the efficiency of spark-ignition engines at part load, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions. This combustion concept is based on the auto-ignition of an air-fuel-mixture highly diluted with hot burnt gases to achieve high indicated efficiency and low pollutant emissions through low temperature combustion. To minimize the costs of conversion of a standard spark-ignition engine into a CAI engine, the present study is restricted to a Port Fuel Injection engine with a cam-profile switching system and a cam phaser on both intake and exhaust sides. In a 4-stroke engine, a large amount of burnt gases can be trapped in the cylinder via early closure of the exhaust valves. This so-called Negative Valve Overlap (NVO) strategy has a key parameter to control the amount of trapped burnt gases and consequently the combustion: the exhaust valve-lift profile.
Technical Paper

A New 0D Approach for Diesel Combustion Modeling Coupling Probability Density Function with Complex Chemistry

2006-10-16
2006-01-3332
The model presented in this paper is an original contribution for two main mechanisms involved in a Diesel combustion chamber: the micro-mixing and the combustion heat release. The micro-mixing phenomenon is modelled thanks to the presumed probability density function theory adapted to the 0D combustion modeling issues in order to take into account the stratification of air / fuel ratio around the spray. The combustion heat release is obtained from complex chemistry look-up tables. These tables are issued from a dedicated use of the Flame Prolongation of ILDM theory and allow a large range of combustion conditions since it includes high EGR rates. Moreover, the spray model including evaporation and turbulent macro-mixing is based on the well-known Siebers theory.
Technical Paper

A Study of Combustion Structure and Implications on Post-Oxidation Under Homogeneous and Stratified Operation in a DISI Engine

2006-04-03
2006-01-1262
An experimental investigation into the structure and flame propagation characteristics of stratified and homogeneous combustion has been performed in an optically-accessible, direct-injection spark ignition (DISI) engine using OH planar laser-induced fluorescence (PLIF) imaging. Homogeneous and stratified operation was achieved by employing either early or late injection timing strategies during the intake or compression stroke respectively. Planar LIF OH images obtained revealed that for stratified operation, the 3D structure of the combustion zone is highly inhomogeneous and is predominantly due to high fuel concentration gradients which are formed as a result of local fuel mixture stratification. The images reveal a combustion structure which suggests that the flame propagation pathway is ultimately determined by the presence of these local fuel mixture inhomogeneities.
Technical Paper

Development of Highly Premixed Combustion Diesel Model: From Simulation to Control Design

2006-04-03
2006-01-1072
In the context of increasingly stringent pollution norms, reduced engine emissions are a great challenge for compressed ignition engines. After-treatment solutions are expensive and very complex to implement, while the NOx/PM trade-off is difficult to optimise for conventional Diesel engines. Therefore, in-cylinder pollutant production limitation by the HPC combustion mode (Highly Premixed Combustion) - including Homogeneous Charge Compression Ignition (HCCI) - represents one of the most promising ways for new generation of CI engine. For this combustion technology, control based on torque estimation is crucial: the objectives are to accurately control the cylinder-individual fuel injected mass and to adapt the fuel injection parameters to the in-cylinder conditions (fresh air and burned gas masses and temperature).
Journal Article

A Comparison of Combustion and Emissions Behaviour in Optical and Metal Single-Cylinder Diesel Engines

2009-06-15
2009-01-1963
Single cylinder optical engines are used for internal combustion (IC) engine research as they allow for the application of qualitative and quantitative non-intrusive, diagnostic techniques to study in-cylinder flow, mixing, combustion and emissions phenomena. Such experimental data is not only important for the validation of computational models but can also provide a detailed insight into the physical processes occurring in-cylinder which is useful for the further development of new combustion strategies such as gasoline homogeneous charge compression ignition (HCCI) and Diesel low temperature combustion (LTC). In this context, it is therefore important to ensure that the performance of optical engines is comparable to standard all-metal engines. A comparison of optical and all-metal engine combustion and emissions performance was performed within the present study.
Journal Article

Advanced Injection Strategies for Controlling Low-Temperature Diesel Combustion and Emissions

2009-06-15
2009-01-1962
The simultaneous reduction of engine-out nitrogen oxide (NOx) and particulate emissions via low-temperature combustion (LTC) strategies for compression-ignition engines is generally achieved via the use of high levels of exhaust gas recirculation (EGR). High EGR rates not only result in a drastic reduction of combustion temperatures to mitigate thermal NOx formation but also increases the level of pre-mixing thereby limiting particulate (soot) formation. However, highly pre-mixed combustion strategies such as LTC are usually limited at higher loads by excessively high heat release rates leading to unacceptable levels of combustion noise and particulate emissions. Further increasing the level of charge dilution (via EGR) can help to reduce combustion noise but maximum EGR rates are ultimately restricted by turbocharger and EGR path technologies.
Journal Article

Formation of Unburned Hydrocarbons in Low Temperature Diesel Combustion

2009-11-02
2009-01-2729
Low temperature combustion is a promising way to reach low NOx emissions in Diesel engines but one of its drawbacks, in comparison to conventional Diesel combustion is the drastic increase of Unburned Hydrocarbons (UHC). In this study, the sources of UHC of a low temperature combustion system were investigated in both a standard, all-metal single-cylinder Diesel engine and an equivalent optically-accessible engine. The investigations were conducted under low load operating conditions (2 and 4 bar IMEP). Two piston bowl geometries were tested: a wall-guided and a more conventional Diesel chamber geometry. Engine parameters such as the start of injection (SOI) timing, the level of charge dilution via exhaust gas re-circulation (EGR), intake temperature, injection pressure and engine coolant temperature were varied. Furthermore, the level of swirl and the diameter of the injector nozzle holes were also varied in order to determine and quantify the sources of UHC.
Journal Article

Cold Operation with Optical and Numerical Investigations on a Low Compression Ratio Diesel Engine

2009-11-02
2009-01-2714
With a high thermal efficiency and low CO2 (carbon dioxide) emissions, Diesel engines become leader of transport market. However, the exhaust-gas legislation evolution leads to a drastic reduction of NOx (nitrogen oxide) standards with very low particulate, HC (unburned hydrocarbons) and CO (carbon monoxide) emissions, while combustion noise and fuel consumption must be kept under control. The reduction of the volumetric compression ratio (CR) is a key factor to reach this challenge, but it is today limited by the capabilities to provide acceptable performances during very cold operation: start and idle below −10°C. This paper focuses on the understanding of the main parameter’s impacts on cold operation. Effects of parameters like hardware configuration and calibration optimization are investigated on a real 4 cylinder Diesel 14:1 CR engine, with a combination of specific advanced tools.
Technical Paper

Study of the Correlation Between Mixing and Auto-Ignition Processes in High Pressure Diesel Jets

2007-04-16
2007-01-0650
A tracer laser-induced fluorescence (LIF) technique for the visualisation of fuel distribution in the presence of oxygen was developed and then used sequentially with high speed chemiluminescence imaging to study the correlation between the mixing and auto-ignition processes of high pressure Diesel jets. A single hole common rail Diesel injector allowing high injection pressures up to 150MPa was used. The reacting fuel spray was observed in a high pressure, high temperature cell that reproduces the thermodynamic conditions which exist in the combustion chamber of a Diesel engine during injection. Both free jet and flat wall impinging jet configurations were studied. Several tracers were first considered with the objective of developing a tracer-LIF technique in the presence of oxygen. 5-nonanone was selected for its higher fluorescence efficiency.
Technical Paper

Tracer LIF Visualisation Studies of Piston-Top Fuel Films in a Wall-Guided, Low-NOx Diesel Engine

2008-10-06
2008-01-2474
Tracer laser induced fluorescence (LIF) imaging of piston-top fuel films has been performed within the combustion chamber of an optically-accessible, single cylinder Diesel engine. The first objective of the study was to adapt the tracer LIF technique so as to perform in-cylinder imaging of the fuel films under reacting (i.e. combustion) conditions. The results obtained in a wall-guided, combustion chamber operating under highly dilute, Diesel low temperature combustion (LTC) conditions reveal the significant presence of late-cycle piston-top fuel films. Furthermore, it is believed that these fuel films contribute to engine-out hydrocarbon (HC) emissions via a mechanism of flash boiling. An attempt was also made to evaluate the role of fuel volatility on fuel film lifetimes. This was achieved by using a 50/50 fuel mixture of two single component fuels whose boiling points correspond to moderately high and low volatility components of standard Diesel fuel.
Technical Paper

On the origin of Unburned Hydrocarbon Emissions in a Wall Guided, Low NOx Diesel Combustion System

2007-07-23
2007-01-1836
The formation mechanisms of unburned hydrocarbons (HC) in low NOx, homogeneous type Diesel combustion have been investigated in both standard and optical access single cylinder engines operating under low load (2 and 4 bar IMEP) conditions. In the standard (i.e. non-optical) engine, parameters such as injection timing, intake temperature and global equivalence ratio were varied in order to analyse the role of bulk quenching on HC emissions formation. Laser-induced fluorescence (LIF) imaging of in-cylinder unburned HC within the bulk gases was performed on the optical-access engine. Furthermore, studies were performed in order to ascertain whether the piston top-land crevice volume contributes significantly to engine-out HC emissions. Finally, the role of piston-top fuel films and their impact on HC emissions was studied. This was investigated on the all-metal engine using two fuels of different volatilities.
Journal Article

System Approach for Compliance with Full Load Targets on a Wall Guided Diesel Combustion System

2008-04-14
2008-01-0840
Low temperature combustion concept as HCCI is one of the most promising research ways to comply future emission regulations of Diesel passenger vehicles. IFP promoted this concept with NADI™ (Narrow Angle Direct Injection) combustion design whose original approach lies on a fuel spray guided by the bowl central tip to the re-entrant. For full load operating range, one of the key issue for success is to use as much as possible available air in the combustion chamber in order to reach low value of air fuel ratio, and therefore high value of specific power and specific torque. In this study, engine tests on a single cylinder engine with NADI™ concept are performed at full load; 3-D calculations as well as air/fuel mixing process visualizations in a constant volume vessel with optical access allowed to establish criteria for helping future combustion system design for full load operation.
Journal Article

Using Multiple Injection Strategies in Diesel Combustion: Potential to Improve Emissions, Noise and Fuel Economy Trade-Off in Low CR Engines

2008-04-14
2008-01-1329
In former high compression ratio Diesel engines a single injection was used to introduce the fuel into the combustion chamber. With actual direct injection engines which exhibit a compression ratio between 17:1 and 18:1 single or multiple early injections called “pilot injections” are also added in order to reduce the combustion noise. For after-treatment reasons a late injection during the expansion stroke named “post injection” may also be used in some operating conditions. Investigations have been conducted on lower compression ratio Diesel engine and in high EGR rate operating conditions to evaluate the benefits of multiple injection strategies to improve the trade off between engine emissions, noise and fuel economy.
Journal Article

Cold Start on Diesel Engine: Is Low Compression Ratio Compatible with Cold Start Requirements?

2008-04-14
2008-01-1310
Future emission standards for Diesel engine will require a drastic reduction of engine-out NOx emissions with very low level of particulate matter (PM), HC and CO, and keeping under control fuel consumption and combustion noise. One of the most promising way to reach this challenge is to reduce compression ratio (CR). A stringent limitation of reducing Diesel CR is currently cold start requirements. Indeed, reduction of ambient temperature leads to penalties in fuel vaporization and auto ignition capabilities, even more at very low temperature (-20°C and below). In this paper, we present the work operated on an HSDI Common rail Diesel 4-cyl engine in three area: engine tests till very low temperature (down to -25°C); in cylinder imaging (videoscope) and CFD code development for cold start operation. First, combustion chamber is adapted in order to reach low compression ratio (CR 13.7:1).
Technical Paper

Potential to Improve Specific Power Using Very High Injection Pressure In HSDI Diesel Engines

2009-04-20
2009-01-1524
Engine downsizing is one of the most promising engine solutions to improve efficiency, but requires higher specific performance because of a lower engine displacement. The study is based on experimental work performed with an IFP prototype single cylinder engine, representative of passenger car applications. This engine enables very high specific power, with a high level of thermal and mechanical constraints. Tests were carried out on both full load and part load operation with a prototype common rail equipment capable of very high fuel pressure (up to 250 MPa). Results show that increasing fuel flow rate using fuel injection pressure instead of increasing nozzle hole diameter is more advantageous at full load, mainly because a lower nozzle hole diameter improves air entrainment. Benefits observed with increased injection pressure are enhanced when associated with upgraded engine thermo-mechanical limits, and advanced turbo charging system.
Journal Article

Study of the Mixing and Combustion Processes of Consecutive Short Double Diesel Injections

2009-04-20
2009-01-1352
The mixing and combustion processes of short double Diesel injections are investigated by optical diagnostics. A single hole Common Rail Diesel injector allowing high injection pressure up to 120MPa is used. The spray is observed in a high pressure, high temperature cell that reproduces the thermodynamic conditions which exist in the combustion chamber of a Diesel engine during injection. Three configurations are studied: a single short injection serving as a reference case and two double short injections with short and long dwell time (time between the injections). Several optical diagnostics were performed successively. The mixing process is studied by normalized Laser Induced Exciplex Fluorescence giving access to the vapor fuel concentration fields. In addition, the flow fields both inside and outside the jets are characterized by Particle Imaging Velocimetry.
Technical Paper

Which Fuel Properties for Improved CAI Combustion? Study of Fuel Impacts on the Operating Range of a CAI PFI Engine

2009-04-20
2009-01-1100
This paper presents the major results of an International Consortium study carried out by IFP and focused on the evaluation of fuel impacts on Controlled Auto Ignition (CAI) combustion. The formulation and tests of two adapted fuel matrix have allowed identifying and evaluating the main fuel properties that can improve CAI combustion for a maximum enlargement of the CAI operating range. CAI combustion mode appears as one promising solution for the development of low CO2 gasoline engines. Fuel properties can then be key parameters to improve the performances of CAI engines. During a first step of the study, steady state tests have been performed on a single cylinder Port Fuel Injection Spark Ignition (PFI SI) engine, with real fuels.
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