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Technical Paper

Turbocharger Matching for a 4-Cylinder Gasoline HCCI Engine Using a 1D Engine Simulation

2010-10-25
2010-01-2143
Naturally aspirated HCCI operation is typically limited to medium load operation (∼ 5 bar net IMEP) by excessive pressure rise rate. Boosting can provide the means to extend the HCCI range to higher loads. Recently, it has been shown that HCCI can achieve loads of up to 16.3 bar of gross IMEP by boosting the intake pressure to more than 3 bar, using externally driven compressors. However, investigating HCCI performance over the entire speed-load range with real turbocharger systems still remains an open topic for research. A 1 - D simulation of a 4 - cylinder 2.0 liter engine model operated in HCCI mode was used to match it with off-the-shelf turbocharger systems. The engine and turbocharger system was simulated to identify maximum load limits over a range of engine speeds. Low exhaust enthalpy due to the low temperatures that are characteristic of HCCI combustion caused increased back-pressure and high pumping losses and demanded the use of a small and more efficient turbocharger.
Journal Article

Comparison of Different Boosting Strategies for Homogeneous Charge Compression Ignition Engines - A Modeling Study

2010-04-12
2010-01-0571
Boosted Homogeneous Charge Compression Ignition (HCCI) has been modeled and has demonstrated the potential to extend the engine's upper load limit. A commercially available engine simulation software (GT-PowerÖ) coupled to the University of Michigan HCCI combustion and heat transfer correlations was used to model a 4-cylinder boosted HCCI engine with three different boosting configurations: turbocharging, supercharging and series turbocharging. The scope of this study is to identify the best boosting approach in order to extend the HCCI engine's operating range. The results of this study are consistent with the literature: Boosting helps increase the HCCI upper load limit, but matching of turbochargers is a problem. In addition, the low exhaust gas enthalpy resulting from HCCI combustion leads to high pressures in the exhaust manifold increasing pumping work. The series turbocharging strategy appears to provide the largest load range extension.
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

Comparison of Diesel Oxidation Catalyst Performance on an Engine and a Gas Flow Reactor

2007-04-16
2007-01-0231
This paper analyzes and compares reactor and engine behavior of a diesel oxidation catalyst (DOC) in the presence of conventional diesel exhaust and low temperature premixed compression ignition (PCI) diesel exhaust. Surrogate exhaust mixtures of n-undecane (C11H24), ethene (C2H4), CO, O2, H2O, NO and N2 are defined for conventional and PCI combustion and used in the gas flow reactor tests. Both engine and reactor tests use a DOC containing platinum, palladium and a hydrocarbon storage component (zeolite). On both the engine and reactor, the composition of PCI exhaust increases light-off temperature relative to conventional combustion. However, while nominal conditions are similar, the catalyst behaves differently on the two experimental setups. The engine DOC shows higher initial apparent HC conversion efficiencies because the engine exhaust contains a higher fraction of trappable (i.e., high boiling point) HC.
Technical Paper

Speciated Hydrocarbon Emissions from an Automotive Diesel Engine and DOC Utilizing Conventional and PCI Combustion

2006-04-03
2006-01-0201
Premixed compression ignition low-temperature diesel combustion (PCI) can simultaneously reduce particulate matter (PM) and oxides of nitrogen (NOx). Carbon monoxide (CO) and total hydrocarbon (THC) emissions increase relative to conventional diesel combustion, however, which may necessitate the use of a diesel oxidation catalyst (DOC). For a better understanding of conventional and PCI combustion, and the operation of a platinum-based production DOC, engine-out and DOC-out exhaust hydrocarbons are speciated using gas chromatography. As combustion mode is changed from lean conventional to lean PCI to rich PCI, engine-out CO and THC emissions increase significantly. The relative contributions of individual species also change; increasing methane/THC, acetylene/THC and CO/THC ratios indicate a richer combustion zone and a reduction in engine-out hydrocarbon incremental reactivity.
Technical Paper

Characterizing Light-Off Behavior and Species-Resolved Conversion Efficiencies During In-Situ Diesel Oxidation Catalyst Degreening

2006-04-03
2006-01-0209
Degreening is crucial in obtaining a stable catalyst prior to assessing its performance characteristics. This paper characterizes the light-off behavior and conversion efficiency of a Diesel Oxidation Catalyst (DOC) during the degreening process. A platinum DOC is degreened for 16 hours in the presence of actual diesel engine exhaust at 650°C and 10% water (H2O) concentration. The DOC's activity for carbon monoxide (CO) and for total hydrocarbons (THC) conversion is checked at 0, 1, 2, 3, 4, 6, 8, 10, 12, and 16 hours of degreening. Pre-and post-catalyst hydrocarbon species are analyzed via gas chromatography at 0, 4, 8, and 16 hours of degreening. It is found that both light-off temperature and species-resolved conversion efficiencies change rapidly during the first 8 hours of degreening and then stabilize to a large degree. T50, the temperature where the catalyst is 50% active towards a particular species, increases by 14°C for CO and by 11°C for THC through the degreening process.
Technical Paper

Quasi-Dimensional Computer Simulation of the Turbocharged Spark-Ignition Engine and its Use for 2- and 4-Valve Engine Matching Studies

1991-02-01
910075
A quasi-dimensional computer simulation of the turbocharged spark-ignition engine has been developed in order to study system performance as various design parameters and operating conditions are varied. The simulation is of the “filling and emptying” type. Quasi-steady flow models of the compressor, intercooler, manifolds, turbine, wastegate, and ducting are coupled with a multi-cylinder engine model where each cylinder undergoes the same thermodynamic cycle. A turbulent entrainment model of the combustion process is used, thus allowing for studies of the effects of various combustion chamber shapes and turbulence parameters on cylinder pressure, temperature, NOx emissions and overall engine performance. Valve open areas are determined either based on user supplied valve lift data or using polydyne-generated cam profiles which allow for variable valve timing studies.
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

Pressure Reactive Piston Technology Investigation and Development for Spark Ignition Engines

2005-04-11
2005-01-1648
Variable Compression Ratio (VCR) technology has long been recognized as a method of improving Spark Ignition (SI) engine fuel economy. The Pressure Reactive Piston (PRP) assembly features a two-piece piston, with a piston crown and separate piston skirt which enclose a spring set between them. The unique feature is that the upper piston reacts to the cylinder pressure, accommodating rapid engine load changes passively. This mechanism effectively limits the peak pressures at high loads without an additional control device, while allowing the engine to operate at high compression ratio during low load conditions. Dynamometer engine testing showed that Brake Specific Fuel Consumption (BSFC) improvement of the PRP over the conventional piston ranged from 8 to 18 % up to 70% load. Knock free full load operation was also achieved. The PRP equipped engine combustion is characterized by reverse motion of the piston crown near top dead center and higher thermal efficiency.
Technical Paper

New Heat Transfer Correlation for an HCCI Engine Derived from Measurements of Instantaneous Surface Heat Flux

2004-10-25
2004-01-2996
An experimental study has been carried out to provide qualitative and quantitative insight into gas to wall heat transfer in a gasoline fueled Homogeneous Charge Compression Ignition (HCCI) engine. Fast response thermocouples are embedded in the piston top and cylinder head surface to measure instantaneous wall temperature and heat flux. Heat flux measurements obtained at multiple locations show small spatial variations, thus confirming relative uniformity of in-cylinder conditions in a HCCI engine operating with premixed charge. Consequently, the spatially-averaged heat flux represents well the global heat transfer from the gas to the combustion chamber walls in the premixed HCCI engine, as confirmed through the gross heat release analysis. Heat flux measurements were used for assessing several existing heat transfer correlations. One of the most popular models, the Woschni expression, was shown to be inadequate for the HCCI engine.
Technical Paper

A Prototype Thin-Film Thermocouple for Transient Heat Transfer Measurements in Ceramic-Coated Combustion Chambers

1990-02-01
900691
A prototype chromel-alumel overlapping thin-film thermocouple (TFTC) has been developed for transient heat transfer measurements in ceramic-coated combustion chambers. The TFTC has been evaluated using various metallurgical techniques such as scanning electron microscopy, energy dispersive x-ray detection, and Auger electron spectroscopy. The sensor was calibrated against a standard thermocouple in ice, boiling water, and a furnace at 1000°C. The microstructural and chemical analysis of the thin-films showed the alumel film composition was very similar to the bulk material, while the chromel film varied slightly. An initial set of ceramic plug surface temperatures was taken while motoring and firing the engine at 1900 rpm to verify thermocouple operation. The data shows a 613 K mean temperature and a 55 K swing for the ceramic surface compared with a 493 K mean temperature and a 20 K swing for the metal surface at the same location.
Technical Paper

Thin Thermal Barrier Coatings for Engines

1989-02-01
890143
Contrary to the thick thermal barrier coating approach used in adiabatic diesel engines, the authors have investigated the merits of thin coatings. Transient heat transfer analysis indicates that the temperature swings experienced at combustion chamber surfaces depend primarily on material thermophysical properties, i.e., conductivity, density, and specific heat. Thus, cyclic temperature swings should be alike whether thick or thin (less than 0.25 mm) coatings are applied, Furthermore, thin coatings would lead to lower mean component temperatures and would be easier to apply than thick coatings. The thinly-coated engine concept offers several advantages including improved volumetric efficiency, lower cylinder liner wall temperatures, improved piston-liner tribological behavior, and improved erosion-corrosion resistance and thus greater component durability.
Technical Paper

Optimizing Gaseous Fuel-Air Mixing in Direct Injection Engines Using an RNG Based k-ε Model

1998-02-23
980135
Direct injection of natural gas under high pressure conditions has emerged as a promising option for improving engine fuel economy and emissions. However, since the gaseous injection technology is new, limited experience exists as to the optimum configuration of the injection system and associated combustion chamber design. The present study uses KIVA-3 based, multidimensional modeling to improve the understanding and assist the optimization of the gaseous injection process. Compared to standard k-ε models, a Renormalization Group Theory (RNG) based k-ε model [1] has been found to be in better agreement with experiments in predicting gaseous penetration histories for both free and confined jet configurations. Hence, this validated RNG model is adopted here to perform computations in realistic engine geometries.
Book

Homogeneous Charge Compression Ignition (HCCI) Engines

2003-03-03
The homogeneous charge, compression-ignition (HCCI) combustion process has the potential to significantly reduce NOx and particulate emissions, while achieving high thermal efficiency and the capability of operating with a wide variety of fuels. This makes the HCCI engine an attractive technology that can ostensibly provide diesel-like fuel efficiency and very low emissions, which may allow emissions compliance to occur without relying on lean aftertreatment systems.
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

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

Bridging the Gap between HCCI and SI: Spark-Assisted Compression Ignition

2011-04-12
2011-01-1179
Homogeneous charge compression ignition (HCCI) has received much attention in recent years due to its ability to reduce both fuel consumption and NO emissions compared to normal spark-ignited (SI) combustion. However, due to the limited operating range of HCCI, production feasible engines will need to employ a combination of combustion strategies, such as stoichiometric SI combustion at high loads and leaner burn spark-assisted compression ignition (SACI) and HCCI at intermediate and low loads. The goal of this study was to extend the high load limit of HCCI into the SACI region while maintaining a stoichiometric equivalence ratio. Experiments were conducted on a single-cylinder research engine with fully flexible valve actuation. In-cylinder pressure rise rates and combustion stability were controlled using cooled external EGR, spark assist, and negative valve overlap. Several engine loads within the SACI regime were investigated.
Technical Paper

Analysis of Load and Speed Transitions in an HCCI Engine Using 1-D Cycle Simulation and Thermal Networks

2006-04-03
2006-01-1087
Exhaust gas rebreathing is considered to be a practical enabler that could be used in HCCI production engines. Recent experimental work at the University of Michigan demonstrates that the combustion characteristics of an HCCI engine using large amounts of hot residual gas by rebreathing are very sensitive to engine thermal conditions. This computational study addresses HCCI engine operation with rebreathing, with emphasis on the effects of engine thermal conditions during transient periods. A 1-D cycle simulation with thermal networks is carried out under load and speed transitions. A knock integral auto-ignition model, a modified Woschni heat transfer model for HCCI engines and empirical correlations to define burn rate and combustion efficiency are incorporated into the engine cycle simulation model. The simulation results show very different engine behavior during the thermal transient periods compared with steady state.
Technical Paper

Thermal Characterization of Combustion Chamber Deposits on the HCCI Engine Piston and Cylinder Head Using Instantaneous Temperature Measurements

2009-04-20
2009-01-0668
Extending the operating range of the gasoline HCCI engine is essential for achieving desired fuel economy improvements at the vehicle level, and it requires deep understanding of the thermal conditions in the cylinder. Combustion chamber deposits (CCD) have been previously shown to have direct impact on near-wall phenomena and burn rates in the HCCI engine. Hence, the objectives of this work are to characterize thermal properties of deposits in a gasoline HCCI engine and provide foundation for understanding the nature of their impact on autoignition and combustion. The investigation was performed using a single-cylinder engine with re-induction of exhaust instrumented with fast-response thermocouples on the piston top and the cylinder head surface. The measured instantaneous temperature profiles changed as the deposits grew on top of the hot-junctions.
Technical Paper

The Effects of Spray, Mixing, and Combustion Model Parameters on KIVA-II Predictions

1991-09-01
911785
The combustion process in a diesel engine was simulated using KIVA-II, a multi-dimensional computer code. The original combustion model in KIVA-II is based on chemical kinetics, and thus fails to capture the effects of turbulence on combustion. A mixing-controlled, eddy break-up combustion model was implemented into the code. Realistic diesel fuel data were also compiled. Subsequently, the sensitivity of the code to a number of parameters related to fuel injection, mixing, and combustion was studied. Spray injection parameters were found to have a strong influence on the model's predictions. Higher injection velocity and shorter injection duration result in a higher combustion rate and peak pressure and temperature. The droplet size specified at injection significantly affects the rate of spray penetration and evaporation, and thus the combustion rate. Contrary to expectation, the level of turbulence at the beginning of the calculation did not affect fuel burning rate.
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