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Technical Paper

Laminar Flame Speeds of Premixed Iso-Octane/Air Flames at High Temperatures with CO2 Dilution

2019-04-02
2019-01-0572
Spherically expanding flames are employed to measure the laminar flame speed of premixed iso-octane/air mixtures at elevated temperatures through both experiments and numerical simulations. Iso-octane (2,2,4-trimethlypentane) is an important gasoline primary reference fuel (PRF). While most studies on laminar burning velocity of iso-octane focus on low temperatures (less than 400 K), the experiments here were conducted in an optically accessible constant volume combustion chamber between 373 K-473 K, at a pressure of 1 bar, and from ϕ=0.8 to ϕ=1.6. The effect of diluent is investigated through the addition of 15% CO2 dilution in order to simulate the effect of exhaust gas recirculation. The decreased reactivity with diluent addition reduces mixture reactivity, which can reduce the propensity for knock in spark ignition engines. All laminar flame speeds were calculated using the constant pressure method enabled via schlieren visualization of the spherically propagating flame front.
Technical Paper

Impact of CO2 Dilution on Ignition Delay Times of Iso-Octane at 15% and 30% Dilution Levels in a Rapid Compression Machine

2019-04-02
2019-01-0569
Iso-Octane (2,2,4-trimethlypentane) is an important gasoline primary reference fuel (PRF) surrogate. Auto ignition of iso-octane was examined using a rapid compression machine (RCM) with iso-octane, air and carbon dioxide (CO2) mixtures. Experiments were conducted over a temperature range of 650K-900K at 20bar and 10 bar compressed conditions for equivalence ratios (Φ =) 0.6, 0.8, 1.0 and 1.3. CO2 dilution by mass was introduced at 0%, 15% and 30% levels with the O2:N2 mole ratio fixed at 1:3.76 emulating the exhaust gas recirculation (EGR) substitution in spark ignition (SI) engines. In this study the direct test chamber (DTC) approach is used for introducing iso-octane directly into the RCM test chamber via a direct injector. The results using this approach are compared with other RCM data available in the literature at undiluted Φ = 1.0 and 20 bar compressed pressure and show good agreement.
Technical Paper

An Experimental Study on the Factors Affecting Ethanol Ignition Delay Times in a Rapid Compression Machine

2019-04-02
2019-01-0576
Ignition delay, using a rapid compression machine (RCM), is defined as the time period between the end of compression and the maximum rate of pressure rise due to combustion, at a given compressed condition of temperature and pressure. The same compressed conditions can be reached by a variety of combinations of compression ratio, initial temperature, initial pressure, diluent gas composition, etc. It has been assumed that the value of ignition delay, for a given fuel and at a given set of compressed conditions, would be the same, irrespective of the variety of the above-mentioned combinations that were used to achieve the compressed conditions. In this study, a range of initial conditions and compression ratios are studied to determine their effect on ignition delay time and to show how ignition delay time can differ even at the same compressed conditions.
Technical Paper

POD-Based Analysis of In-Cylinder Flow Data from Molecular Tagging Velocimetry in a Spark-Ignition Engine

2018-09-10
2018-01-1770
The fluid motion inside the engine cylinder is transient, three-dimensional and highly turbulent. It is also well known that cycle-to-cycle flow variations have a considerable influence on cycle-to-cycle combustion variations. Laser-based diagnostic techniques, for example, particle image velocimetry (PIV) or molecular tagging velocimetry, can be used to measure two or three components of the velocity field simultaneously at multiple locations over a plane. The use of proper orthogonal decomposition (POD) allows quantification of cycle-to-cycle flow variations, as demonstrated using PIV data [1]. In the present work, POD is used to explore the cycle-to-cycle flow variations utilizing molecular tagging velocimetry data. The instantaneous velocity fields were obtained over a swirl measurement plane when engine was operated at 1500 rpm and 2500 rpm.
Technical Paper

Performance Assessment of a Single Jet, Dual Diverging Jets, and Dual Converging Jets in an Auxiliary Fueled Turbulent Jet Ignition System

2018-04-03
2018-01-1135
An auxiliary fueled prechamber ignition system can be used in an IC engine environment to provide lean limit extension with minimal cyclic variability and low emissions. Geometry and distribution of the prechamber orifices form an important criterion for performance of these systems since they are responsible for transferring and distributing the ignition energy into the main chamber charge. Combustion performance of nozzles with a single jet, dual diverging jets and dual converging jets for a methane fueled prechamber ignition system is evaluated and compared in a rapid compression machine (RCM). Upon entering the main chamber, the dual diverging jets penetrate the main chamber in opposite directions creating two jet tips, while the dual converging jets, after exiting the orifices, converge into a single location within the main chamber. Both these configurations minimize jet-wall impingement compared to the single jet.
Technical Paper

Characterization of Crankcase Pressure Variation during the Engine Cycle of an Internal Combustion Engine

2017-03-28
2017-01-1088
High frequency variations in crankcase pressure have been observed in Inline-four cylinder (I4) engines and an understanding of the causes, frequency and magnitude of these variations is helpful in the design and effective operation of various engine systems. This paper shows through a review and explanation of the physics related to engine operation followed by comparison to measured vehicle data, the relationship between crankcase volume throughout the engine cycle and the observed pressure fluctuations. It is demonstrated that for a known or proposed engine design, through knowledge of the key engine design parameters, the frequency and amplitude of the cyclic variation in crankcase pressure can be predicted and thus utilized in the design of other engine systems.
Technical Paper

CFD Modeling and Experimental Analysis of a Homogeneously Charged Turbulent Jet Ignition System in a Rapid Compression Machine

2017-03-28
2017-01-0557
Three dimensional numerical simulation of the transient turbulent jet and ignition processes of a premixed methane-air mixture of a turbulent jet ignition (TJI) system is performed using Converge computational software. The prechamber initiated combustion enhancement technique that is utilized in a TJI system enables low temperature combustion by increasing the flame propagation rate and therefore decreasing the burn duration. Two important components of the TJI system are the prechamber where the spark plug and injectors are located and the nozzle which connects the prechamber to the main chamber. In order to model the turbulent jet of the TJI system, RANS k-ε and LES turbulent models and the SAGE chemistry solver with a reduced mechanism for methane are used.
Journal Article

Optical Engine Operation to Attain Piston Temperatures Representative of Metal Engine Conditions

2017-03-28
2017-01-0619
Piston temperature plays a major role in determining details of fuel spray vaporization, fuel film deposition and the resulting combustion in direct-injection engines. Due to different heat transfer properties that occur in optical and all-metal engines, it becomes an inevitable requirement to verify the piston temperatures in both engine configurations before carrying out optical engine studies. A novel Spot Infrared-based Temperature (SIR-T) technique was developed to measure the piston window temperature in an optical engine. Chromium spots of 200 nm thickness were vacuum-arc deposited at different locations on a sapphire window. An infrared (IR) camera was used to record the intensity of radiation emitted by the deposited spots. From a set of calibration experiments, a relation was established between the IR camera measurements of these spots and the surface temperature measured by a thermocouple.
Technical Paper

A Computational Study of the Effects of Spark Location on the Performance of a Turbulent Jet Ignition System

2016-04-05
2016-01-0608
In this purely computational study, fluid dynamic simulations with active combustion are performed for a Turbulent Jet Ignition (TJI) system installed in a rapid compression machine. The simulations compare the effects that the location of the TJI system’s spark ignition source inside the TJI’s prechamber have on the combustion within the system through the use of four simulations, which are all identically setup with the same initial and boundary conditions except for the location of their respective ignition sources. The four ignition sources are located along the centerline of the axisymmetric prechamber and at varied distances from the orifice exit of the prechamber. Comparison of the simulations demonstrate that the locations furthest from the orifice produce better main chamber ignition as reflected in shorter 0-10% mass fraction burn times. Meanwhile all three of the test cases that were not closest to the orifice all produced similar 10-90% mass fraction burn times.
Technical Paper

CFD Modeling of an Auxiliary Fueled Turbulent Jet Ignition System in a Rapid Compression Machine

2016-04-05
2016-01-0599
Three-dimensional numerical simulation of the turbulent jet ignition combustion process of a premixed methane-air mixture in a Rapid Compression Machine (RCM) was performed using the Converge computational software. Turbulent jet ignition is a prechamber initiated combustion system that can replace the spark plug in a spark ignition engine. The prechamber is a small volume chamber where an injector and spark plug are located and is connected to the main combustion chamber via one or multiple small orifices. Turbulent jet ignition is capable of enabling low temperature combustion, through either lean or dilute combustion. A RANS model, which included a k-ε turbulence model to solve the mean flow and the SAGE chemistry solver with a reduced methane mechanism to solve the chemistry, was used to model the turbulent jet ignition system.
Technical Paper

Analysis of Variations in Fuel Spray, Combustion, and Soot Production in an Optical Diesel Engine Operating Under High Simulated Exhaust Gas Recirculation Operating Conditions

2016-04-05
2016-01-0727
In-cylinder visualization experiments were completed using an International VT275-based optical DI Diesel engine operating under high simulated exhaust gas recirculation combustion conditions. Experiments were run at four load conditions to examine variations in fuel spray, combustion, and soot production. Mass fraction burned analyses of pressure data were used to investigate the combustion processes of the various operating conditions. An infrared camera was used to visualize fuel spray events and exothermic combustion gases. A visible, high-speed camera was used to image natural luminosity produced by soot. The recorded images were post-processed to analyze the fuel spray, the projected exothermic areas produced by combustion, as well as soot production of different load conditions. Probability maps of combustion and fuel spray occurrence in the cylinder are presented for insight into the combustion processes of the different conditions.
Journal Article

Experimental Studies of a Liquid Propane Auxiliary Fueled Turbulent Jet Igniter in a Rapid Compression Machine

2016-04-05
2016-01-0708
Lean combustion is a promising combustion technology that has the potential to improve engine efficiency while decreasing emissions. One reason why lean combustion has not been more widely implemented is that as the air-fuel ratio increases, the resulting flame propagation speed becomes slower and combustion becomes unstable. Turbulent jet ignition is a pre-chamber ignition enhancement concept that facilitates ultra-lean combustion by using a hot combusting jet as a distributed ignition source. The jet penetration allows for shorter flame travel distances, which decreases the overall burn duration and improves stability. By using a rich mixture in the pre-chamber, the pre-chamber mixture is easily ignitable and the transport of chemically active radical species and unburned fuel into the main-chamber charge improves ignition quality.
Technical Paper

Computational Study of a Turbulent Jet Ignition System for Lean Burn Operation in a Rapid Compression Machine

2015-04-14
2015-01-0396
Fully three-dimensional computational fluid dynamic simulations with detailed chemistry of a single-orifice turbulent jet ignition device installed in a rapid compression machine are presented. The simulations were performed using the computational fluid dynamics software CONVERGE and its RANS turbulence models. Simulations of propane fueled combustion are compared to data collected in the optically accessible rapid compression machine that the model's geometry is based on to establish the validity and limitations of the simulations and to compare the behavior of the different air-fuel ratios that are used in the simulations.
Technical Paper

Modeling of Piston Ring-Cylinder Bore-Piston Groove Contact

2015-04-14
2015-01-1724
A three-dimensional piston ring model has been developed using finite element method with eight-node hexahedral elements. The model predicts the piston ring conformability with the cylinder wall as well as the separation gap between the interfaces if existing in the radial direction. In addition to the radial interaction between the ring front face and the cylinder wall, the model also predicts the contact between the ring and groove sides in the axial direction. This means, the ring axial lift, ring twist, contact forces with the groove sides along the circumferential direction are all calculated simultaneously with the radial conformability prediction. The ring/groove side contact can be found for scraper ring at static condition, which is widely used as the second compression ring in a ring pack. Thermal load is believed having significant influence on the ring pack performance.
Journal Article

Combustion Visualization, Performance, and CFD Modeling of a Pre-Chamber Turbulent Jet Ignition System in a Rapid Compression Machine

2015-04-14
2015-01-0779
Turbulent jet ignition is a pre-chamber ignition enhancement method that produces a distributed ignition source through the use of a chemically active turbulent jet which can replace the spark plug in a conventional spark ignition engine. In this paper combustion visualization and characterization was performed for the combustion of a premixed propane/air mixture initiated by a pre-chamber turbulent jet ignition system with no auxiliary fuel injection, in a rapid compression machine. Three different single orifice nozzles with orifice diameters of 1.5 mm, 2 mm, and 3 mm were tested for the turbulent jet igniter pre-chamber over a range of air to fuel ratios. The performance of the turbulent jet ignition system based on nozzle orifice diameter was characterized by considering both the 0-10 % and the 10-90 % burn durations of the pressure rise due to combustion.
Technical Paper

Establishment of a Database by Conducting Intake Manifold and In-Cylinder Flow Measurements inside an Internal Combustion Engine Assembly

2013-04-08
2013-01-0565
An experimental study has been conducted to quantify the velocity and pressure inside an idealized intake manifold of a motored internal combustion engine assembly. The aim of this work is to provide the real-time boundary conditions for more accurate multi-dimensional numerical simulations of complex in-cylinder flows in an internal combustion engine as well as the resultant in-cylinder flow patterns. The geometry of the intake manifold is simplified for this purpose. A hot-wire anemometer and a piezoresistive absolute pressure transducer are used to measure the velocity and pressure, respectively, over a plane inside the circular section of the intake manifold. In addition, pressure measurements are performed over an elliptical section near the intake port. Phase-averaged velocity and pressure profiles are then calculated from the instantaneous measurements. Experiments were performed at 900 and 1200 rpm engine speeds with wide open throttle.
Technical Paper

Large Eddy Simulation of Evaporating Spray with a Stochastic Breakup Model

2013-04-08
2013-01-1101
Large Eddy Simulations of atomization and evaporation of liquid fuel sprays in diesel engine conditions are performed with stochastic breakup and non-equilibrium droplet heat and mass transfer models. The size and number density of the droplets generated by the breakup model are assumed to be governed by a Fokker-Planck equation, describing the evolution of the PDF of droplet radii. The fragmentation intensity spectrum is considered to be Gaussian and the scale of Lagrangian relative velocity fluctuations is included in the breakup frequency calculations. The aerodynamic interactions of droplets in the dense part of the spray are modeled by correcting the relative velocity of droplets in the wake of other droplets. The stochastic breakup model is employed together with the wake interaction model for simulations of non-evaporating and evaporating sprays in various gas temperature and pressure conditions.
Journal Article

Visualization of Propane and Natural Gas Spark Ignition and Turbulent Jet Ignition Combustion

2012-10-23
2012-32-0002
This study focuses on the combustion visualization of spark ignition combustion in an optical single cylinder engine using natural gas and propane at several air to fuel ratios and speed-load operating points. Propane and natural gas fuels were compared as they are the most promising gaseous alternative fuels for reciprocating powertrains, with both fuels beginning to find wide market penetration on the fleet level across many regions of the world. Additionally, when compared to gasoline, these gaseous fuels are affordable, have high knock resistance and relatively low carbon content and they do not suffer from the complex re-fueling and storage problems associated with hydrogen.
Technical Paper

In-cylinder Combustion Visualization of a Direct-injection Spark-ignition Engine with Different Operating Conditions and Fuels

2012-09-10
2012-01-1644
A direct-injection and spark-ignition single-cylinder engine with optical access to the cylinder was used for the combustion visualization study. Gasoline and ethanol-gasoline blended fuels were used in this investigation. Experiments were conducted to investigate the effects of fuel injection pressure, injection timing and the number of injections on the in-cylinder combustion process. Two types of direct fuel injectors were used; (i) high-pressure production injector with fuel pressures of 5 and 10 MPa, and (ii) low-pressure production-intent injector with fuel pressure of 3 MPa. Experiments were performed at 1500 rpm engine speed with partial load. In-cylinder pressure signals were recorded for the combustion analyses and synchronized with the high-speed combustion imaging recording. Visualization results show that the flame growth is faster with the increment of fuel injection pressure.
Technical Paper

Optical Diagnostic Combustion Comparisons of Pump Diesel with Bio-Derived Diesel Blends in an Optical DI Diesel Engine

2012-04-16
2012-01-0868
Combustion studies were completed using an International VT275-based, optical DI Diesel engine fueled with Diesel fuel, a Canola-derived FAMES biodiesel, as well as with a blend of the Canola-derived biodiesel and a cetane-reducing, oxygenated fuel, Di-Butyl Succinate. Three engine operating conditions were tested to examine the combustion of the fuels across a range of loads and combustion schemes. Pressure data and instantaneous images were recorded using a high-speed visible imaging, infrared imaging, and high-speed OH imaging techniques. The recorded images were post processed to analyze different metrics, such as projected areas of in-cylinder soot, OH, and combustion volumes. A substantially reduced in-cylinder area of soot formation is observed for the Canola-DBS blended fuel with a slight reduction from the pure FAMES biodiesel compared to pump Diesel fuel.
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