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Technical Paper

Control of a Multi-Cylinder HCCI Engine During Transient Operation by Modulating Residual Gas Fraction to Compensate for Wall Temperature Effects

2007-04-16
2007-01-0204
The thermal conditions of an engine structure, in particular the wall temperatures, have been shown to have a great effect on the HCCI engine combustion timing and burn rates through wall heat transfer, especially during transient operations. This study addresses the effects of thermal inertia on combustion in an HCCI engine. In this study, the control of combustion timing in an HCCI engine is achieved by modulating the residual gas fraction (RGF) while considering the wall temperatures. A multi-cylinder engine simulation with detailed geometry is carried out using a 1-D system model (GT-Power®) that is linked with Simulink®. The model includes a finite element wall temperature solver and is enhanced with original HCCI combustion and heat transfer models. Initially, the required residual gas fraction for optimal BSFC is determined for steady-state operation. The model is then used to derive a map of the sensitivity of optimal residual gas fraction to wall temperature excursions.
Technical Paper

Experimental and Simulated Results Detailing the Sensitivity of Natural Gas HCCI Engines to Fuel Composition

2001-09-24
2001-01-3609
Natural gas quality, in terms of the volume fraction of higher hydrocarbons, strongly affects the auto-ignition characteristics of the air-fuel mixture, the engine performance and its controllability. The influence of natural gas composition on engine operation has been investigated both experimentally and through chemical kinetic based cycle simulation. A range of two component gas mixtures has been tested with methane as the base fuel. The equivalence ratio (0.3), the compression ratio (19.8), and the engine speed (1000 rpm) were held constant in order to isolate the impact of fuel autoignition chemistry. For each fuel mixture, the start of combustion was phased near top dead center (TDC) and then the inlet mixture temperature was reduced. These experimental results have been utilized as a source of data for the validation of a chemical kinetic based full-cycle simulation.
Technical Paper

Extinction Measurements of In-Cylinder Soot Deposition in a Heavy-Duty DI Diesel Engine

2001-03-05
2001-01-1296
The combustion process in diesel engines deposits soot on the in-cylinder surfaces. Previous works have suggested that these soot deposits eventually break off during cylinder blow-down and the exhaust stroke and contribute significantly to exhaust soot emissions. In order to better understand this potential pathway to soot emissions, the authors recently investigated combusting fuel-jet/wall interactions in a diesel engine. This work, published as a companion paper, showed how soot escaped from the combusting fuel jet and was brought in close proximity to the wall so that it could become a deposit. The current study extends this earlier work with laser-extinction measurements of the soot-deposition rate in the same single-cylinder, heavy-duty DI diesel engine. Measurements were made by passing the beam of a CW-diode laser through a window in the piston bowl rim that was in-line with one of the fuel jets.
Technical Paper

Diffusion-Flame / Wall Interactions in a Heavy-Duty DI Diesel Engine

2001-03-05
2001-01-1295
Over the past decade, laser diagnostics have improved our understanding of many aspects of diesel combustion. However, interactions between the combusting fuel jet and the piston-bowl wall are not well understood. In heavy-duty diesel engines, with typical fuels, these interactions occur with the combusting vapor-phase region of the jet, which consists of a central region containing soot and other products of rich-premixed combustion, surrounded by a diffusion flame. Since previous work has shown that the OH radical is a good marker of the diffusion flame, planar laser-induced fluorescence (PLIF) imaging of OH was applied to an investigation of the diffusion flame during wall interaction. In addition, simultaneous OH PLIF and planar laser-induced incandescence (PLII) soot imaging was applied to investigate the likelihood for soot deposition on the bowl wall.
Technical Paper

Fuel Stratification for Low-Load HCCI Combustion: Performance & Fuel-PLIF Measurements

2007-10-29
2007-01-4130
Fuel stratification has been investigated as a means of improving the low-load combustion efficiency in an HCCI engine. Several stratification techniques were examined: different GDI injectors, increased swirl, and changes in injection pressure, to determine which parameters are effective for improving the combustion efficiency while maintaining NOx emissions below U.S. 2010 limits. Performance and emission measurements were obtained in an all-metal engine. Corresponding fuel distribution measurements were made with fuel PLIF imaging in a matching optically accessible engine. The fuel used was iso-octane, which is a good surrogate for gasoline. For an idle fueling rate (ϕ = 0.12), combustion efficiency was improved substantially, from 64% to 89% at the NOx limit, using delayed fuel injection with a hollow-cone injector at an injection pressure of 120 bar.
Technical Paper

An Investigation in Measuring Crank Angle Resolved In-Cylinder Engine Friction Using Instantaneous IMEP Method

2007-10-29
2007-01-3989
This paper describes the measurement of in-cylinder engine friction using the instantaneous IMEP method. This method has been applied to measure in-cylinder friction force in a modern, low friction design production spark ignited engine. An improved mechanical telemetry system has been developed to implement this method. The telemetry system continues to provide excellent data even after 50+ hours of operation at speeds as high as 2000 rpm. Investigated in this study were the primary sources of error associated with this technique. Also presented are the steps taken to minimize the effects of these errors. The refined technique has been subsequently used to obtain piston assembly friction data for both motoring and a limited number of firing cases. The effects of design parameters and operating conditions were investigated.
Technical Paper

An Approach for Modeling the Effects of Gas Exchange Processes on HCCI Combustion and Its Application in Evaluating Variable Valve Timing Control Strategies

2002-10-21
2002-01-2829
The present study introduces a modeling approach for investigating the effects of valve events and gas exchange processes in the framework of a full-cycle HCCI engine simulation. A multi-dimensional fluid mechanics code, KIVA-3V, is used to simulate exhaust, intake and compression up to a transition point, before which chemical reactions become important. The results are then used to initialize the zones of a multi-zone, thermo-kinetic code, which computes the combustion event and part of the expansion. After the description and the validation of the model against experimental data, the application of the method is illustrated in the context of variable valve actuation. It has been shown that early exhaust valve closing, accompanied by late intake valve opening, has the potential to provide effective control of HCCI combustion.
Technical Paper

Effects of Fuel Parameters and Diffusion Flame Lift-Off on Soot Formation in a Heavy-Duty DI Diesel Engine

2002-03-04
2002-01-0889
To better understand the factors affecting soot formation in diesel engines, in-cylinder soot and diffusion flame lift-off were measured in a heavy-duty, direct-injection diesel engine. Measurements were obtained at two operating conditions using two commercial diesel fuels and a range of oxygenated paraffinic fuel blends. A line-of-sight laser extinction diagnostic was improved and employed to measure the relative soot concentration within the jet (“jet-soot”) and the rates of soot-wall deposition on the piston bowl-rim. An OH chemiluminescence imaging technique was developed to determine the location of the diffusion flame and to measure the lift-off lengths of the diffusion flame to estimate the amount of oxygen entrainment in the diesel jets. Both the jet-soot and the rate of soot-wall deposition were found to decrease with increasing fuel oxygen-to-carbon ratio (O/C) over a wide range of O/C.
Technical Paper

A Computational Study of the Effects of Low Fuel Loading and EGR on Heat Release Rates and Combustion Limits in HCCI Engines

2002-03-04
2002-01-1309
Two fundamental aspects of HCCI engine combustion have been investigated using a single-zone model with time-varying compression and the full chemical-kinetic mechanisms for iso-octane, a representative liquid-phase fuel. This approach allows effects of the kinetics and thermodynamics to be isolated and evaluated in a well-characterized manner, providing an understanding of the selected fundamental processes. The computations were made using the CHEMKIN-III kinetic-rate code for an 1800 rpm operating condition. The study consists of two parts. First, low-load HCCI operation was investigated to determine the role of bulk-gas reactions as a source for HC and CO emissions. The computations show that as fueling is reduced to equivalence ratios of 0.15 and lower (very light load and idle), the bulk-gas reactions do not go to completion, leading to inefficient combustion and high emissions of HC and CO.
Technical Paper

Overview of Techniques for Measuring Friction Using Bench Tests and Fired Engines

2000-06-19
2000-01-1780
This paper presents an overview of techniques for measuring friction using bench tests and fired engines. The test methods discussed have been developed to provide efficient, yet realistic, assessments of new component designs, materials, and lubricants for in-cylinder and overall engine applications. A Cameron-Plint Friction and Wear Tester was modified to permit ring-in-piston-groove movement by the test specimen, and used to evaluate a number of cylinder bore coatings for friction and wear performance. In a second study, it was used to evaluate the energy conserving characteristics of several engine lubricant formulations. Results were consistent with engine and vehicle testing, and were correlated with measured fuel economy performance. The Instantaneous IMEP Method for measuring in-cylinder frictional forces was extended to higher engine speeds and to modern, low-friction engine designs.
Technical Paper

An Investigation of Thermal Stratification in HCCI Engines Using Chemiluminescence Imaging

2006-04-03
2006-01-1518
Chemiluminescence imaging has been applied to investigate the naturally occurring charge stratification in an HCCI engine. This stratification slows the pressure-rise rate (PRR) during combustion, making it critical to the high-load operating limit of these engines. Experiments were conducted in a single-cylinder HCCI engine modified with windows in the combustion chamber for optical access. Using this engine, chemiluminescence images were obtained from three different view angles. These included both single-shot images with intensified CCD cameras and high-speed (20kHz) sequences with an intensified CMOS video camera. The engine was fueled with iso-octane, which has been shown to be a reasonable surrogate for gasoline and exhibits only single-stage ignition at these naturally aspirated conditions. The chemiluminescence images show that the HCCI combustion is not homogeneous but has a strong turbulent structure even when the fuel and air are fully premixed prior to intake.
Technical Paper

Development and Validation of a Comprehensive CFD Model of Diesel Spray Atomization Accounting for High Weber Numbers

2006-04-03
2006-01-1546
Modern diesel engines operate under injection pressures varying from 30 to 200 MPa and employ combinations of very early and conventional injection timings to achieve partially homogeneous mixtures. The variety of injection and cylinder pressures results in droplet atomization under a wide range of Weber numbers. The high injection velocities lead to fast jet disintegration and secondary droplet atomization under shear and catastrophic breakup mechanisms. The primary atomization of the liquid jet is modeled considering the effects of both infinitesimal wave growth on the jet surface and jet turbulence. Modeling of the secondary atomization is based on a combination of a drop fragmentation analysis and a boundary layer stripping mechanism of the resulting fragments for high Weber numbers. The drop fragmentation process is predicted from instability considerations on the surface of the liquid drop.
Technical Paper

Characterizing the Effect of Combustion Chamber Deposits on a Gasoline HCCI Engine

2006-10-16
2006-01-3277
Homogenous Charge Compression Ignition (HCCI) engines offer a good potential for achieving high fuel efficiency while virtually eliminating NOx and soot emissions from the exhaust. However, realizing the full fuel economy potential at the vehicle level depends on the size of the HCCI operating range. The usable HCCI range is determined by the knock limit on the upper end and the misfire limit at the lower end. Previously proven high sensitivity of the HCCI process to thermal conditions leads to a hypothesis that combustion chamber deposits (CCD) could directly affect HCCI combustion, and that insight about this effect can be helpful in expanding the low-load limit. A combustion chamber conditioning process was carried out in a single-cylinder gasoline-fueled engine with exhaust re-breathing to study CCD formation rates and their effect on combustion. Burn rates accelerated significantly over the forty hours of running under typical HCCI operating conditions.
Technical Paper

Simultaneous Reduction of NOX and Soot in a Heavy-Duty Diesel Engine by Instantaneous Mixing of Fuel and Water

2007-04-16
2007-01-0125
Meeting diesel engine emission standards for heavy-duty vehicles can be achieved by simultaneous injection of fuel and water. An injection system for instantaneous mixing of fuel and water in the combustion chamber has been developed by injecting water in a mixing passage located in the periphery of the fuel spray. The fuel spray is then entrained by water and hot air before it burns. The experimental work was carried out on a Rapid Compression Machine and on a Komatsu direct-injection heavy-duty diesel engine with a high pressure common rail fuel injection system. It was also supported by Computational Fluid Dynamics simulations of the injection and combustion processes in order to evaluate the effect of water vapor distribution on cylinder temperature and NOX formation. It has been concluded that when the water injection is appropriately timed, the combustion speed is slower and the cylinder temperature lower than in conventional diesel combustion.
Technical Paper

Spatial Analysis of Emissions Sources for HCCI Combustion at Low Loads Using a Multi-Zone Model

2004-06-08
2004-01-1910
We have conducted a detailed numerical analysis of HCCI engine operation at low loads to investigate the sources of HC and CO emissions and the associated combustion inefficiencies. Engine performance and emissions are evaluated as fueling is reduced from typical HCCI conditions, with an equivalence ratio ϕ = 0.26 to very low loads (ϕ = 0.04). Calculations are conducted using a segregated multi-zone methodology and a detailed chemical kinetic mechanism for iso-octane with 859 chemical species. The computational results agree very well with recent experimental results. Pressure traces, heat release rates, burn duration, combustion efficiency and emissions of hydrocarbon, oxygenated hydrocarbon, and carbon monoxide are generally well predicted for the whole range of equivalence ratios. The computational model also shows where the pollutants originate within the combustion chamber, thereby explaining the changes in the HC and CO emissions as a function of equivalence ratio.
Technical Paper

An Investigation of the Relationship Between Measured Intake Temperature, BDC Temperature, and Combustion Phasing for Premixed and DI HCCI Engines

2004-06-08
2004-01-1900
Combustion phasing is one important issue that must be addressed for HCCI operation. The intake temperature can be adjusted to achieve ignition at the desired crank angle. However, heat-transfer during induction will make the effective intake temperature different from the temperature measured in the runner. Also, depending on the engine speed and port configuration, dynamic flow effects cause various degrees of charge heating. Additionally, residuals from the previous cycle can have significant influence on the charge temperature at the beginning of the compression stroke. Finally, direct injection of fuel will influence the charge temperature since heat is needed for vaporization. This study investigates these effects in a systematic manner with a combination of experiment and cycle simulation using WAVE from Ricardo.
Technical Paper

Analysis of Premixed Charge Compression Ignition Combustion With a Sequential Fluid Mechanics-Multizone Chemical Kinetics Model

2005-04-11
2005-01-0115
We have developed a methodology for analysis of Premixed Charge Compression Ignition (PCCI) engines that applies to conditions in which there is some stratification in the air-fuel distribution inside the cylinder at the time of combustion. The analysis methodology consists of two stages: first, a fluid mechanics code is used to determine temperature and equivalence ratio distributions as a function of crank angle, assuming motored conditions. The distribution information is then used for grouping the mass in the cylinder into a two-dimensional (temperature-equivalence ratio) array of zones. The zone information is then handed on to a detailed chemical kinetics model that calculates combustion, emissions and engine efficiency information. The methodology applies to situations where chemistry and fluid mechanics are weakly linked.
Technical Paper

Modeling Iso-octane HCCI Using CFD with Multi-Zone Detailed Chemistry; Comparison to Detailed Speciation Data Over a Range of Lean Equivalence Ratios

2008-04-14
2008-01-0047
Multi-zone CFD simulations with detailed kinetics were used to model iso-octane HCCI experiments performed on a single-cylinder research engine. The modeling goals were to validate the method (multi-zone combustion modeling) and the reaction mechanism (LLNL 857 species iso-octane) by comparing model results to detailed exhaust speciation data, which was obtained with gas chromatography. The model is compared to experiments run at 1200 RPM and 1.35 bar boost pressure over an equivalence ratio range from 0.08 to 0.28. Fuel was introduced far upstream to ensure fuel and air homogeneity prior to entering the 13.8:1 compression ratio, shallow-bowl combustion chamber of this 4-stroke engine. The CFD grid incorporated a very detailed representation of the crevices, including the top-land ring crevice and head-gasket crevice. The ring crevice is resolved all the way into the ring pocket volume. The detailed grid was required to capture regions where emission species are formed and retained.
Technical Paper

Development of a Two-Zone HCCI Combustion Model Accounting for Boundary Layer Effects

2001-03-05
2001-01-1028
The Homogeneous Charge Compression Ignition (HCCI) combustion concept is currently under widespread investigation due to its potential to increase thermal efficiency while greatly decreasing harmful exhaust pollutants. Simulation tools have been developed to explore the implications of initial mixture thermodynamic state on engine performance and emissions. In most cases these modeling efforts have coupled a detailed fuel chemistry mechanism with empirical descriptions of the in-cylinder heat transfer processes. The primary objective of this paper is to present a fundamentally based boundary layer heat transfer model. The two-zone combustion model couples an adiabatic core zone with a boundary layer heat transfer model. The model predicts film coefficient, with approximately the same universal shape and magnitudes as an existing global model.
Technical Paper

Numerical Modeling and Experimental Investigations of EGR Cooler Fouling in a Diesel Engine

2009-04-20
2009-01-1506
EGR coolers are mainly used on diesel engines to reduce intake charge temperature and thus reduce emissions of NOx and PM. Soot and hydrocarbon deposition in the EGR cooler reduces heat transfer efficiency of the cooler and increases emissions and pressure drop across the cooler. They may also be acidic and corrosive. Fouling has been always treated as an approximate factor in heat exchanger designs and it has not been modeled in detail. The aim of this paper is to look into fouling formation in an EGR cooler of a diesel engine. A 1-D model is developed to predict and calculate EGR cooler fouling amount and distribution across a concentric tube heat exchanger with a constant wall temperature. The model is compared to an experiment that is designed for correlation of the model. Effectiveness, mass deposition, and pressure drop are the parameters that have been compared. The results of the model are in a good agreement with the experimental data.
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