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High Load HCCI Operation Using Different Valving Strategies in a Naturally-Aspirated Gasoline HCCI Engine

2012-02-16
This session focuses on kinetically controlled combustion. Experimental and simulation studies pertaining to various means of controlling combustion are welcome. Examples are research studies dealing with temperature and composition distribution inside the cylinder and their impact on heat release process. Studies clarifying the role of fuel physical and chemical properties in autoignition are also welcome. Presenter Hanho Yun, General Motors Company
Technical Paper

Conditional Analysis of Enhanced Combustion Luminosity Imaging in a Spray-Guided Gasoline Engine with High Residual Fraction

2011-04-12
2011-01-1281
High-speed (12 kHz) imaging of combustion luminosity (enhanced by using a sodium fuel additive) has been analyzed and compared to crank angle resolved heat release rates and mass fraction burn profiles in a spray-guided spark-ignited direct-injection (SG-SIDI) optical single-cylinder engine. The addition of a sodium-containing additive to gasoline greatly increases the combustion luminosity, which allows unintensified high-speed (12 kHz) imaging of early partially premixed flame kernel growth and overall flame propagation with excellent signal-to-noise ratio for hundreds of consecutive engine cycles. Ignition and early flame kernel growth are known to be key to understanding and eliminating poor burn cycles in SG-SIDI engines.
Technical Paper

The Influence of DISI Engine Operating Parameters on Particle Number Emissions

2011-04-12
2011-01-0143
The future EURO 6 emission standard will limit the particle number and mass for gasoline engines. The proposed limit for particle mass is 4.5 mg/km. For particle number there is not yet a limit defined but a wide range of proposals are under discussion (6E11 - 8E12 Particles/km) The particle emissions on a homogeneous SIDI engine are mainly caused by insufficient mixture preparation. A combustion improvement could be achieved by a careful recalibration as well as a hardware optimization that mainly avoids wall impingement and substoichiometric zones in the combustion chamber. The analyses of current SIDI vehicles show significant PN emission peaks during cold start and transient operation on a NEDC cycle. To give a better understanding of cause and effect of the particle formation at steady state results so as transient load steps were performed at an engine dynamometer.
Technical Paper

An Analysis for Floating Bearings in a Turbocharger

2011-04-12
2011-01-0375
A comprehensive analysis has been performed for floating bearings applied in a turbocharger. It is found that Couette power loss for a full-floating bearing (the floating ring rotates) decreases with increasing inner and outer clearances, while its Poiseuille power loss increases with increasing inner and outer film clearances. In comparison with a semi-floating bearing (the floating ring does not rotate), a full-floating bearing can reduce both Couette and Poiseuille power losses. However, floating bearing is found to have a smaller minimum film thickness for a given dynamic loading from rotor-dynamics. The total power loss reduction for typical full-floating bearings ranges from 13% to 27%, which matches well with some published experimental data. In general, the speed ratio increases with increasing outer film clearance, while it decreases with increasing inner film clearance because of shear stresses on the outer and inner film.
Technical Paper

Individual Cylinder Air-Fuel Ratio Control Part I: L3 and V6 Engine Applications

2011-04-12
2011-01-0695
A frequency-domain approach to balancing of air-fuel ratio (A/F) in a multi-cylinder engine is described. The technique utilizes information from a single Wide-Range Air-Fuel ratio (WRAF) or a single switching (production) O₂ sensor installed in the exhaust manifold of an internal combustion engine to eliminate the imbalances. At the core of the proposed approach is the development of a simple novel method for the characterization of A/F imbalances among the cylinders. The proposed approach provides a direct objective metric for the characterization of the degree of A/F imbalances for diagnostic purposes as well as a methodology for the control of A/F imbalances among various cylinders. The fundamental computational requirement is based on the calculation of a Discrete Fourier Transform (DFT) of the A/F signal as measured by a WRAF or a switching O₂ sensor.
Technical Paper

Evaluation and Design of Injector Hole Patterns Using CFD with a Fuel Tracer Diagnostic for Gasoline Direct Injection (GDI) Engines

2011-04-12
2011-01-0840
A CFD code is enhanced with a fuel tracer diagnostic to track the liquid and vapor fuel mass separately from individual spray plumes of a multi-hole injector and the wall film. The approach works by solving a set of additional scalar transport equations for fuel vapor generated from individual nozzle hole and the wall film. The diagnostic tool is first validated against experiments from a 4-valve, wall-guided spark-ignition direct-injection (SIDI) engine. A CFD analysis is carried out to understand the experimentally observed trade-offs in combustion stability and smoke emissions between a 70degree hollow-cone swirl injector and a 40 degree, 5-hole, circular-type multi-hole injector at a lean, stratified idle operating condition. Engine tests show that the multi-hole injector results in lower COV of IMEP than the hollow-cone swirl injector at the expense of significantly higher smoke emissions.
Technical Paper

The Influence of Biodiesel Fuel Quality on Modern Diesel Vehicle Performance

2012-04-16
2012-01-0858
Vehicle manufacturers have developed new vehicle and diesel engine technologies compatible with B6-B20 biodiesel blends meeting ASTM D7467, “Standard Specification for Diesel Fuel Oil, Biodiesel Blend (B6 to B20).” However, recent U.S. market place fuel surveys have shown that many retail biodiesel samples are out of specification. A vehicle designed to use biodiesel blends is likely to encounter occasional use of poor quality biodiesel fuel; and therefore understanding the effects of bad marketplace biodiesel fuels on engine and fuel system performance is critical to develop durable automotive technologies. The results presented herein are from vehicle evaluation studies with both on-specification and off-specification bio-based fuels. These studies focused on the performance of fuel injection equipment, engine, engine oil, emissions and emissions system durability.
Technical Paper

Model-Based Analysis and Optimization of Turbocharged Diesel Engines with a Variable Geometry Compressor and Turbine System

2012-04-16
2012-01-0716
In the last few years, the application of downsizing and turbocharging to internal combustion engines has considerably increased due to the proven potential of this technology to increase engine efficiency. Variable geometry turbines have been largely adopted to optimize the exhaust energy recovery over a large operating range. Two-stage turbocharger systems have also been studied as a solution to improve engine low-end torque and efficiency, with the first units currently available on the market. However, the compressor technology is today still based on fixed geometry machines, which are sized to efficiently operate at the maximum air flow and therefore lead to poor efficiency values at low air flow conditions. Furthermore, the surge limits prevents the full capabilities of VGT systems to increase the boosting at low engine speed.
Technical Paper

Optimal Use of Boosting Configurations and Valve Strategies for High Load HCCI - A Modeling Study

2012-04-16
2012-01-1101
This study investigates a novel approach towards boosted HCCI operation, which makes use of all engine system components in order to maximize overall efficiency. Four-cylinder boosted HCCI engines have been modeled employing valve strategies and turbomachines that enable high load operation with significant efficiency benefits. A commercially available engine simulation software, coupled to the University of Michigan HCCI combustion and heat transfer correlations, was used to model the HCCI engines with three different boosting configurations: turbocharging, variable geometry turbocharging and combined supercharging with turbocharging. The valve strategy features switching from low-lift Negative Valve Overlap (NVO) to high-lift Positive Valve Overlap (PVO) at medium loads. The new operating approach indicates that heating of the charge from external compression is more efficient than heating by residual gas retention strategies.
Journal Article

An Analysis of Floating Piston Pin

2011-04-12
2011-01-1407
Presented in the paper is a comprehensive analysis for floating piston pin. It is more challenging because it is a special type of journal bearing where the rotation of the journal is coupled with the friction between the journal and the bearing. In this analysis, the multi-degree freedom mass-conserving mixed-EHD equations are solved to determine the coupled pin rotation and friction. Other bearing characteristics, such as minimum film thickness, pin secondary motions in both connecting-rod small-end bearing and piston pin-boss bearing, power loss etc are also determined. The mechanism for floating pin to have better scuffing resistance is discovered. The theoretical and numerical model is implemented in the GM internal software FLARE (Friction and Lubrication Analysis for Reciprocating Engines).
Journal Article

Study of the Motion of Floating Piston Pin against Pin Bore

2013-04-08
2013-01-1215
One of the major problems that the automotive industry faces is reducing friction to increase efficiency. Researchers have shown that 30% of the fuel energy was consumed to overcome the friction forces between the moving parts of any automobile, Holmberg et al. [1]. The interface of the piston pin and pin bore is one of the areas that generate high friction under severe working conditions of high temperature and lack of lubrication. In this research, experimental investigation and theoretical simulation have been carried out to analyze the motion of the floating pin against pin bore. In the experimental study, the focus was on analyzing the floating pin motion by using a bench test rig to simulate the floating pin motion in an internal combustion engine. A motion data acquisition system was developed to capture and record the pin motion. Thousands of images were recorded and later analyzed by a code written by MATLAB.
Journal Article

Numerical Investigation of Buoyancy-Driven Flow in a Simplified Underhood with Open Enclosure

2013-04-08
2013-01-0842
Numerical results are presented for simulating buoyancy driven flow in a simplified full-scale underhood with open enclosure in automobile. The flow condition is set up in such a way that it mimics the underhood soak condition, when the vehicle is parked in a windbreak with power shut-down after enduring high thermal loads due to performing a sequence of operating conditions, such as highway driving and trailer-grade loads in a hot ambient environment. The experimental underhood geometry, although simplified, consists of the essential components in a typical automobile underhood undergoing the buoyancy-driven flow condition. It includes an open enclosure which has openings to the surrounding environment from the ground and through the top hood gap, an engine block and two exhaust cylinders mounted along the sides of the engine block. The calculated temperature and velocity were compared with the measured data at different locations near and away from the hot exhaust plumes.
Journal Article

Design of Engine-Out Virtual NOx Sensor Using Neural Networks and Dynamic System Identification

2011-04-12
2011-01-0694
Fuel economy improvement and stringent emission regulations worldwide require advanced air charging and combustion technologies, such as low temperature combustion, PCCI or HCCI combustion. Furthermore, NOx aftertreatment systems, like Selective Catalyst Reduction (SCR) or lean NOx trap (LNT), are needed to reduce vehicle tailpipe emissions. The information on engine-out NOx emissions is essential for engine combustion optimization, for engine and aftertreatment system development, especially for those involving combustion optimization, system integration, control strategies, and for on-board diagnosis (OBD). A physical NOx sensor involves additional cost and requires on-board diagnostic algorithms to monitor the performance of the NOx sensor.
Journal Article

Development of the Combustion System for General Motors' High-Efficiency Range Extender Ecotec Small Gas Engine

2015-04-14
2015-01-1272
General Motors has developed an all-new Ecotec 1.5 L range extender engine for use in the 2016 next generation Voltec propulsion system. This engine is part of a new Ecotec family of small displacement gasoline engines introduced in the 2015 model year. Major enhancements over the range extender engine in the current generation Voltec propulsion system include the adoption of direct injection (DI), cooled external exhaust gas recirculation (EGR), and a high 12.5:1 geometric compression ratio (CR). Additional enhancements include the adoption of high-authority phasers on both the intake and exhaust camshafts, and an integrated exhaust manifold (IEM). The combination of DI with cooled EGR has enabled significant thermal efficiency gains over the 1.4 L range extender engine in the current generation Voltec propulsion system at high engine loads.
Journal Article

Engine Diagnostics Using Acoustic Emissions Sensors

2016-04-05
2016-01-0639
Engine acoustics measured by microphones near the engine have been used in controlled laboratory settings for combustion feedback and even combustion phasing control, but the use of these techniques in a vehicle where many other noise sources exist is problematic. In this study, surface-mounted acoustic emissions sensors are embedded in the block of a 2.0L turbocharged GDI engine, and the signal is analyzed to identify useful feedback features. The use of acoustic emissions sensors, which have a very high frequency response and are commonly used for detecting material failures for health monitoring, including detecting gear pitting and ring scuffing on test stands, enables detection of acoustics both within the range of human hearing and in the ultrasonic spectrum. The high-speed acoustic time-domain data are synchronized with the crank-angle-domain combustion data to investigate the acoustic emissions response caused by various engine events.
Journal Article

Experimental and Numerical Investigations of Close-Coupled Pilot Injections to Reduce Combustion Noise in a Small-Bore Diesel Engine

2015-04-14
2015-01-0796
A pilot-main injection strategy is investigated for a part-load operating point in a single cylinder optical Diesel engine. As the energizing dwell between the pilot and main injections decreases below 200 μs, combustion noise reaches a minimum and a reduction of 3 dB is possible. This decrease in combustion noise is achieved without increased pollutant emissions. Injection schedules employed in the engine are analyzed with an injection analyzer to provide injection rates for each dwell tested. Two distinct injection events are observed even at the shortest dwell tested; rate shaping of the main injection occurs as the dwell is adjusted. High-speed elastic scattering imaging of liquid fuel is performed in the engine to examine initial liquid penetration rates.
Journal Article

Determination of Used Crankcase Oil Condition by Capillary Electrophoresis Analysis of Extracted Organic Acids

2009-11-02
2009-01-2689
Organic acid degradation products and other anions in engine oil were speciated by capillary electrophoresis (CE) and liquid chromatography-mass spectrometry (LCMS) with electrospray ionization. The sample preparation procedure involved selectively extracting the acids and other water soluble salts into 0.05M aqueous potassium hydroxide. Samples of engine-aged mineral oil and synthetic engine oil contained formic acid, acetic acid, and complex mixtures of fatty acid degradation products. CE analysis of formic acid, acetic acid and selected fatty acids is proposed as a new chemical analysis method for evaluating the condition of engine oil and for studying the effects of high temperature-high load (HTHL) oxidation. Because the overall pattern of CE peaks in the electropherogram changes with oil age or condition, CE-fingerprint (i.e., pattern recognition) techniques may also be useful for evaluating an aged oil's condition or remaining service life.
Journal Article

Fundamental Approach to Investigate Pre-Ignition in Boosted SI Engines

2011-04-12
2011-01-0340
A comprehensive experimental and theoretical approach was undertaken to understand the phenomenon of pre-ignition and to assess parameters to improve or even eliminate it completely. Oil mixing with fuel was identified as the leading theory of self ignition of the fuel. End of compression temperature has to meet a minimum level for pre-ignition to take place. In this work a comprehensive list of parameters were identified that have a direct and crucial role in the onset of pre-ignition including liner wetting, injection targeting, stratification, mixture motion and oil formulation. Many secondary effects were identified including ring dynamics, ring tension, spark plug electrode temperature and coolant temperature. CFD has been extensively used to understand test results including wall film, A/F ratio distribution and temperature at the end of compression when looked at in the context of fuel evaporation and mixing.
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