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Technical Paper

Effects of Fuel Injection Pressure in an Optically-Accessed DISI Engine with Side-Mounted Fuel Injector

2001-05-07
2001-01-1975
This paper presents the results of an experimental study into the effects of fuel injection pressure on mixture formation within an optically accessed direct-injection spark-ignition (DISI) engine. Comparison is made between the spray characteristics and in-cylinder fuel distributions due to supply rail pressures of 50 bar and 100 bar subject to part-warm, part-load homogeneous charge operating conditions. A constant fuel mass, corresponding to stoichiometric tune, was maintained for both supply pressures. The injected sprays and their subsequent liquid-phase fuel distributions were visualized using the 2-D laser Mie-scattering technique. The experimental injector (nominally a hollow-cone pressure-swirl design) was seen to produce a dense filled spray structure for both injection pressures under investigation. In both cases, the leading edge velocities of the main spray suggest the direct impingement of liquid fuel on the cylinder walls.
Technical Paper

Fiber Optic Sensor for Crank Angle Resolved Measurements of Burned Gas Residual Fraction in the Cylinder of an SI Engine

2001-05-07
2001-01-1921
A fiber optic infrared spectroscopic sensor was developed to measure the crank angle resolved residual fraction of burned gas retained in the cylinder of a four-stroke SI engine. The sensor detected the attenuation of infrared radiation in the 4.3 μm infrared vibrational-rotational absorption band of CO2. The residual fraction remaining in the cylinder is proportional to the CO2 concentration. The sensor was tested in a single-cylinder CFR spark ignition engine fired on propane at a speed of 700 rpm. The sensor was located in one of two spark plug holes of the CFR engine. A pressure-transducer-type spark plug was used to record the cylinder pressure and initiate the spark. The temporal resolution of the measurements was 540 μs (equivalent to 2.3 crank angle degrees) and the spatial resolution was 6 mm. Measurements were made during the intake and compression stroke for several intake manifold pressures. The compression ratio of the engine was varied from 6.3 to 9.5.
Technical Paper

Air Charge Estimation in Camless Engines

2001-03-05
2001-01-0581
An electromechanically driven valve train offers unprecedented flexibility to optimize engine operation for each speed load point individually. One of the main benefits is the increased fuel economy resulting from unthrottled operation. The absence of a restriction at the entrance of the intake manifold leads to wave propagation in the intake system and makes a direct measurement of air flow with a hot wire air meter unreliable. To deliver the right amount of fuel for a desired air-fuel ratio, we therefore need an open loop estimate of the air flow based on measureable or commanded signals or quantities. This paper investigates various expressions for air charge in camless engines based on quasi-static assumptions for heat transfer and pressure.
Technical Paper

Event-Based Mean-Value Modeling of DI Diesel Engines for Controller Design

2001-03-05
2001-01-1242
Models often use time rather than strokes (crank-angle) as the independent variable to describe engine dynamics despite the fact that the dynamics of an internal combustion engine are intrinsically linked to the combustion events. In this paper, two models are developed in parallel in which not only the independent variable is changed but the notion of mass flows as well: flows are in [g/s] for the time-based model and in [g/st] for the event-based model. Both models are of the same computational complexity and show the same accuracy in validation. The investigation of the model properties shows that variations in the flow-related parameters are reduced by a factor of two to five for the event-based model. However, those of the crankshaft dynamics are increased. It is concluded that the model should be chosen in context of the control system to be designed.
Technical Paper

Quantification of Friction Component Engagement Controllability

2001-03-05
2001-01-1156
Conventional automatic transmissions (AT) use wet friction components, such as plate clutches and band brakes to engage gears or change speed ratios during vehicle operation. The quality of engagements and ratio changes depends greatly on the frictional characteristics of the friction components, which are typically evaluated with industry standard SAE #2 test machines. These inertia absorption-type dynamometer test stands energize a friction component with prescribed level of apply force and load of inertia flywheels rotating at a specified speed until the friction elements are brought to a stop. During the slip, apply force, engagement torque, and rotating speed are digitally recorded for visual evaluation of dynamic engagement behavior. The shape of the dynamic torque curve during the engagement is known to affect AT shift quality. When many curves are generated, it becomes intractable to quantify torque curve shape differences.
Technical Paper

Effects of Fuel Volatility, Load, and Speed on HC Emissions Due to Piston Wetting

2001-05-07
2001-01-2024
Piston wetting can be isolated from the other sources of HC emissions from DISI engines by operating the engine predominantly on a gaseous fuel and using an injector probe to impact a small amount of liquid fuel on the piston top. This results in a marked increase in HC emissions. In a previous study, we used a variety of pure liquid hydrocarbon fuels to examine the influence of fuel volatility and structure on the HC emissions due to piston wetting. It was shown that the HC emissions correspond to the Leidenfrost effect: fuels with very low boiling points yield high HCs and those with a boiling point near or above the piston temperature produce much lower HCs. All of these prior tests of fuel effects were performed at a single operating condition: the Ford World Wide Mapping Point (WWMP). In the present study, the effects of load and engine speed are examined.
Technical Paper

Flame Temperature Correlation of Emissions from Diesels Operated on Alternative Fuels

2001-05-07
2001-01-2014
Work by Plee, Ahmad, and coworkers in the 1980s [1, 2, 3, 4 and 5] showed that for changes in intake air state, Diesel NOx, soot, soluble organic fraction, and HC emissions could be correlated using the stoichiometric flame temperature calculated at SOC or peak pressure conditions. In the present work, similar flame temperature correlations are obtained for emissions from three test engines; a 1.2L high speed direct injection (HSDI) Diesel, a 2.4L HSDI Diesel, and a 2.34 L single cylinder direct injection (DI) Diesel engine, the first of which was tested using four alternative fuels. Use of the flame temperature correlations presented may reduce the number of engine tests required to evaluate the effects of EGR on emissions of NOx, particulate, and HC, even when alternative fuels are used.
Technical Paper

Modeling of HCCI Combustion and Emissions Using Detailed Chemistry

2001-03-05
2001-01-1029
To help guide the design of homogeneous charge compression ignition (HCCI) engines, single and multi-zone models of the concept are developed by coupling the first law of thermodynamics with detailed chemistry of hydrocarbon fuel oxidation and NOx formation. These models are used in parametric studies to determine the effect of heat loss, crevice volume, temperature stratification, fuel-air equivalence ratio, engine speed, and boosting on HCCI engine operation. In the single-zone model, the cylinder is assumed to be adiabatic and its contents homogeneous. Start of combustion and bottom dead center temperatures required for ignition to occur at top dead center are reported for methane, n-heptane, isooctane, and a mixture of 87% isooctane and 13% n-heptane by volume (simulated gasoline) for a variety of operating conditions.
Technical Paper

Powerplant Block-Crank Dynamic Interaction and Radiated Noise Prediction

2003-05-05
2003-01-1735
This paper discusses flexible, multi-body, coupled dynamic simulation of a crankshaft system acting upon a power plant structure that includes an engine block, cylinder heads, oil pan, crank train (i.e., crankshaft, connecting rods, bearings etc.) and transmission. The simulation is conducted using AVL/EXCITE [1]. Engine loads are first predicted, and then used to compute radiated noise from the engine assembly. Radiated noise level is computed by sweeping the excitation frequency through a range associated with the normal operating RPM of the engine. The results of the radiated noise computation are plotted on a “3D” Campbell plot diagram. The effects of different crankshaft materials is evaluated by imposing steel and cast iron material properties on the analysis model. A design of experiment (DOE) study is also performed to investigate the effects of main and rod bearing clearance, damper, and flexplate design on overall engine radiated sound power.
Technical Paper

PIV Characterization of a 4-valve Engine with a Camshaft Profile Switching (CPS) system

2003-05-19
2003-01-1803
Particle Image Velocimetry (PIV) measurements were performed on a single cylinder optically accesible version of a 3.0L 4-valve engine using a Camshaft Profile Switching (CPS) system. The flow field was investigated at two engine speeds (750 and 1500 rpm), two manifold pressures (75 and 90 kPa) and two intake cam centerlines (maximum lift at 95° and 115° aTDCi respectively). Images were taken in the swirl plane at 10 mm and 40 mm below the deck with the piston at 300° aTDC of intake (60° bTDC compression) and BDC respectively. In the tumble plane, images were taken in a plane bisecting the intake valves with the piston at BDC and 300° aTDC. The results showed that the swirl ratio was slightly lower for this system compared with a SCV system (swirl control valve in the intake port) under the same operating conditions. The swirl and tumble ratios generated were not constant over the range of engine speeds and manifold pressures (MAP) but instead increased with engine speed and MAP.
Technical Paper

Evaluation of Idle Combustion Stability Using Flywheel Acceleration

2003-05-05
2003-01-1673
Vehicle idle quality has become an increasing quality concern for car manufacturers because of its impact on customer satisfaction. To get better fuel economy the overall trend is to reduce idle speed at both drive and neutral idles. This typically has adverse impact on vehicle idle quality. Lowering the idle rpm generally degrades the engine combustion stability and also makes the engine driving forces more likely to align with vehicle sensitivities (Powertrain rigid body modes, body modes, etc.). To better understand the contribution to the idle quality from different factors and carry out well-planned improvement measures, a quick and easy way to assess engine combustion stability is required.
Technical Paper

Up-Front Prediction of the Effects of Cylinder Head Design on Combustion Rates in SI Engines

1998-02-23
981049
Accurate prediction of engine combustion characteristics, especially burn rates, can eliminate a number of hardware iterations, thus resulting in a significant reduction in design and developmental time and cost. An analytical methodology has been developed which allows the determination of part-load MBT spark timing to within 2 crank-angle degrees. The design methodology employs the in-house-developed steady-state quasi-dimensional engine simulation model (GESIM), coupled with full-field measurement of the in-cylinder fluid motion at bottom dead center (BDC) in the computer-controlled water analog system (AquaDyne). The in-cylinder flow-field measurements are obtained using 3-D Particle Tracking Velocimetry (3-D PTV), also developed in-house. In this methodology, the in-cylinder flow measurement data are used to calibrate both the tumble and swirl models in GESIM.
Technical Paper

Stratified-Charge Engine Fuel Economy and Emission Characteristics

1998-10-19
982704
Data from two engines with distinct stratified-charge combustion systems are presented. One uses an air-forced injection system with a bowl-in-piston combustion chamber. The other is a liquid-only, high-pressure injection system which uses fluid dynamics coupled with a shaped piston to achieve stratification. The fuel economy and emission characteristics were very similar despite significant hardware differences. The contributions of indicated thermal efficiency, mechanical friction, and pumping work to fuel economy are investigated to elucidate where the efficiency gains exist and in which categories further improvements are possible. Emissions patterns and combustion phasing characteristics of stratified-charge combustion are also discussed.
Technical Paper

Piston Ring / Cylinder Bore Friction Under Flooded and Starved Lubrication Using Fresh and Aged Engine Oils

1998-10-19
982659
The friction reducing capability of engine oils in the piston ring/cylinder bore contact was investigated under fully-flooded and starved lubrication conditions at 100° C using a laboratory piston ring/cylinder bore friction rig. The rig is designed to acquire instantaneous transient measurements of applied loads and friction forces at the ring/bore interface in reciprocating motion over a 50.8 mm stroke. The effects of increasing load and speed on the friction coefficient have been compared with new and used engine oils of different viscosity that were formulated with and without friction modifying additives. Test results with fully formulated engine oils containing molybdenum dithiocarbamate (MoDTC) show that friction is always lower than that obtained with non-friction modified oils but in regions of persistent starvation the coefficient of friction can increase significantly, approaching levels equivalent to fully-flooded non-friction modified formulations.
Technical Paper

Cranktrain Design for Ford's HEV DI Diesel Engine

1998-08-11
981915
This paper focuses on the cranktrain design for Ford's HEV DI Diesel Engine called the DIATA. The design started with the piston pin. The minimum piston pin diameter for the lowest reciprocation weight was achieved by tapering the small end of the connecting rod. Geometry constraints sized the connecting rod's big end diameter, oil film analyses determined the width, and an FEA verified the design. Next, the crankshaft mains were sized to reach an acceptable factor of safety, bending and torsional stiffness, and oil films. Finally, the flywheel was sized to be the minimum weight to reduce transmission gear rattle to an acceptable level.
Technical Paper

A Comparison of Time-Averaged Piston Temperatures and Surface Heat Flux Between a Direct-Fuel Injected and Carbureted Two-Stroke Engine

1998-02-23
980763
Time-averaged temperatures at critical locations on the piston of a direct-fuel injected, two-stroke, 388 cm3, research engine were measured using an infrared telemetry device. The piston temperatures were compared to data [7] of a carbureted version of the two-stroke engine, that was operated at comparable conditions. All temperatures were obtained at wide open throttle, and varying engine speeds (2000-4500 rpm, at 500 rpm intervals). The temperatures were measured in a configuration that allowed for axial heat flux to be determined through the piston. The heat flux was compared to carbureted data [8] obtained using measured piston temperatures as boundary conditions for a computer model, and solving for the heat flux. The direct-fuel-injected piston temperatures and heat fluxes were significantly higher than the carbureted piston. On the exhaust side of the piston, the direct-fuel injected piston temperatures ranged from 33-73 °C higher than the conventional carbureted piston.
Technical Paper

The Volume Acoustic Modes of Spark-Ignited Internal Combustion Chambers

1998-02-23
980893
Acoustic standing waves are excited in internal combustion chambers by both normal combustion and autoignition. The energy in these acoustic modes can be transmitted through the engine block and radiated as high-frequency engine noise. Using finite-element models of two different (four-valve and two-valve) production engine combustion chambers, the mode shapes and relative frequencies of the in-cylinder volume acoustic modes are calculated as a function of crank angle. The model is validated by comparison to spectrograms of experimental time-sampled waveforms (from flush-mounted cylinder pressure sensors and accelerometers) from these two typical production spark-ignited engines.
Technical Paper

Modeling and Analysis of Powertrain Torsional Response

1998-02-23
980276
An analytical model is developed to describe the torsional responses of the powertrain system. The model is used to analyze system equilibrium, free vibration, forced and self-excited vibrations. The equations of motion are linearized about the equilibrium to determine natural frequencies and mode shapes of the torsional modes. The forced responses of the system are investigated by including the excitations of gas combustion forces and inertia torques induced by the reciprocating motions of the piston and connecting rod. The self-excited vibration induced by negative damping behavior of clutch torque capacity is studied. For an example rear-wheel drive powertrain considered, the free vibration analyses show the natural frequencies and the associated mode shapes. The forced and the self-excited vibrations for the transmission gearset and the driveline components are examined. Experimental measurements from a test powertrain are used to confirm the theoretical predictions.
Technical Paper

Novel CFD Techniques For In-Cylinder Flows On Tetrahedral Grids

1998-02-01
980138
An innovative approach for computing in-cylinder flowfields on tetrahedral grids is developed and demonstrated. The primary focus of the preliminary work presented in this paper is the development of an efficient mesh motion scheme for realistic engine geometries. An automated cell layering technique has been devised which embeds/deletes layers of tetrahedral cells as the cylinder flow domain expands/shrinks. The ability to compute in-cylinder flows using this new “multi-zone” concept is demonstrated for a twin-valve gasoline engine.
Technical Paper

Cranktrain Component Conceptual Design and Weight Optimization

1998-02-23
980566
Powertrain Engineering Tool (PET) [1, 2, 3], developed at Ford Powertrain and Vehicle Research Laboratory, is a powertrain computer model that allows rapid development of preliminary powertrain component geometry, and evaluation of engine performance and friction. Based on specified design objectives such as engine torque, power and geometric constraints, PET calculates the powertrain component geometry by employing its integrated design rules and a non-linear SQP-based (Sequential Quadratic Programming) geometry optimizer. PET also generates parametric solid models of powertrain systems based on its integrated dynamic component assembly schemes and solid modeling database. The cranktrain system consists of high-speed moving and rotating components. Complex dynamic analysis is typically required to achieve optimum cranktrain component design. This paper discusses development of a systematic approach in the calculation of optimal cranktrain component geometry.
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