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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.
Technical Paper

Turbulence Intensity Calculation from Cylinder Pressure Data in a High Degree of Freedom Spark-Ignition Engine

2010-04-12
2010-01-0175
The number of control actuators available on spark-ignition engines is rapidly increasing to meet demand for improved fuel economy and reduced exhaust emissions. The added complexity greatly complicates control strategy development because there can be a wide range of potential actuator settings at each engine operating condition, and map-based actuator calibration becomes challenging as the number of control degrees of freedom expand significantly. Many engine actuators, such as variable valve actuation and flow control valves, directly influence in-cylinder combustion through changes in gas exchange, mixture preparation, and charge motion. The addition of these types of actuators makes it difficult to predict the influences of individual actuator positioning on in-cylinder combustion without substantial experimental complexity.
Technical Paper

Development and Use of a Computer Simulation of the Turbocompounded Diesel System for Engine Performance and Component Heat Transfer Studies

1986-03-01
860329
A computer simulation of the turbocharged turbocompounded direct-injection diesel engine system has been developed in order to study the performance characteristics of the total system as major design parameters and materials are varied. Quasi-steady flow models of the compressor, turbines, manifolds, intercooler, and ducting are coupled with a multi-cylinder reciprocator diesel model where each cylinder undergoes the same thermodynamic cycle. Appropriate thermal loading models relate the heat flow through critical system components to material properties and design details. This paper describes the basic system models and their calibration and validation against available experimental engine test data. The use of the model is illustrated by predicting the performance gains and the component design trade-offs associated with a partially insulated engine achieving a 40 percent reduction in heat loss over a baseline cooled engine.
Technical Paper

Catalysts for Methanol Vehicles

1987-11-01
872052
A Methanol catalyst test program has been conducted in two phases. The purpose of Phase I was to determine whether a base metal or lightly-loaded noble metal catalyst could reduce Methanol engine exhaust emissions with an efficiency comparable to conventional gasoline engine catalytic converters. The goal of Phase II was the reduction of aldehyde and unburned fuel emissions to very low levels by the use of noble metal catalysts with catalyst loadings higher than those in Phase I. Catalysts tested in Phase I were evaluated as three-way converters as well as under simulated oxidation catalyst conditions. Phase II catalysts were tested as three-way converters only. For Phase I, the most consistently efficient catalysts over the range of pollutants measured were platinum/rhodium configurations. None of the catalysts tested in Phase I were able to meet a NOx level of 1 gram per mile when operated in the oxidation mode.
Technical Paper

Cylinder Pressure Reconstruction and its Application to Heat Transfer Analysis

2004-03-08
2004-01-0922
In this paper, a new method for cylinder pressure reconstruction is proposed based on the concept of a dimensionless pressure curve in the frequency domain. It is shown that cylinder pressure profiles, acquired over a wide range of engine speeds and loads, exhibit similarity. Hence, cylinder pressure traces collapse into a set of dimensionless curves within a narrow range after normalization in the frequency domain. The dimensionless pressure traces can be described by a curve-fit family, which can be used for reconstructing pressure diagrams back into the time domain at any desired condition. The accuracy associated with this method is analyzed and its application to engine heat transfer analysis is demonstrated.
Technical Paper

Quantification of Thermal Shock in a Piezoelectric Pressure Transducer

2005-05-11
2005-01-2092
One of the major problems limiting the accuracy of piezoelectric transducers for cylinder pressure measurements in an internal-combustion (IC) engine is the thermal shock. Thermal shock is generated from the temperature variation during the cycle. This temperature variation results in contraction and expansion of the diaphragm and consequently changes the force acting on the quartz in the pressure transducer. An empirical equation for compensation of the thermal shock error was derived from consideration of the diaphragm thermal deformation and actual pressure data. The deformation and the resulting pressure difference due to thermal shock are mainly a function of the change in surface temperature and the equation includes two model constants. In order to calibrate these two constants, the pressure inside the cylinder of a diesel engine was measured simultaneously using two types of pressure transducers, in addition to instantaneous wall temperature measurement.
Technical Paper

Modeling of Diesel Combustion and NO Emissions Based on a Modified Eddy Dissipation Concept

2004-03-08
2004-01-0107
This paper reports the development of a model of diesel combustion and NO emissions, based on a modified eddy dissipation concept (EDC), and its implementation into the KIVA-3V multidimensional simulation. The EDC model allows for more realistic representation of the thin sub-grid scale reaction zone as well as the small-scale molecular mixing processes. Realistic chemical kinetic mechanisms for n-heptane combustion and NOx formation processes are fully incorporated. A model based on the normalized fuel mass fraction is implemented to transition between ignition and combustion. The modeling approach has been validated by comparison with experimental data for a range of operating conditions. Predicted cylinder pressure and heat release rates agree well with measurements. The predictions for NO concentration show a consistent trend with experiments. Overall, the results demonstrate the improved capability of the model for predictions of the combustion process.
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

Design Optimization of the Piston Compounded Adiabatic Diesel Engine Through Computer Simulation

1993-03-01
930986
This paper describes the concept and a practical implementation of piston-compounding. First, a detailed computer simulation of the piston-compounded engine is used to shed light into the thermodynamic events associated with the operation of this engine, and to predict the performance and fuel economy of the entire system. Starting from a baseline design, the simulation is used to investigate changes in system performance as critical parameters are varied. The latter include auxiliary cylinder and interconnecting manifold volumes for a given main cylinder volume, auxiliary cylinder valve timings in relation to main cylinder timings, and degree of heat loss to the coolant. Optimum designs for either highest power density or highest thermal efficiency (54%) are thus recommended. It is concluded that a piston-compounded adiabatic engine concept is a promising future powerplant.
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

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

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

Measurements and Predictions of Steady-State and Transient Stress Distributions in a Diesel Engine Cylinder Head

1999-03-01
1999-01-0973
A combined experimental and analytical approach was followed in this work to study stress distributions and causes of failure in diesel cylinder heads under steady-state and transient operation. Experimental studies were conducted first to measure temperatures, heat fluxes and stresses under a series of steady-state operating conditions. Furthermore, by placing high temperature strain gages within the thermal penetration depth of the cylinder head, the effect of thermal shock loading under rapid transients was studied. A comparison of our steady-state and transient measurements suggests that the steady-state temperature gradients and the level of temperatures are the primary causes of thermal fatigue in cast-iron cylinder heads. Subsequently, a finite element analysis was conducted to predict the detailed steady-state temperature and stress distributions within the cylinder head. A comparison of the predicted steady-state temperatures and stresses compared well with our measurements.
Technical Paper

An Early-Design Methodology for Predicting Transient Fuel Economy and Catalyst-Out Exhaust Emissions

1997-05-19
971838
An early-design methodology for predicting both expected fuel economy and catalyst-out CO, HC and NOx concentrations during arbitrarily-defined transient cycles is presented. The methodology is based on utilizing a vehicle-powertrain model with embedded maps of fully warmed up engine-out performance and emissions, and appropriate temperature-dependent correction factors to account for not fully warmed up conditions during transients. Similarly, engine-out emissions are converted to catalyst-out emissions using conversion efficiencies based on the catalyst brick temperature. A crucial element of the methodology is hence the ability to predict heat flows and component temperatures in the engine and the exhaust system during transients, consistent with the data available during concept definition and early design phases.
Journal Article

Evaluation of Diesel Oxidation Catalyst Conversion of Hydrocarbons and Particulate Matter from Premixed Low Temperature Combustion of Biodiesel

2011-04-12
2011-01-1186
Premixed low temperature combustion (LTC) in diesel engines simultaneously reduces soot and NOx at the expense of increased hydrocarbon (HC) and CO emissions. The use of biodiesel in the LTC regime has been shown to produce lower HC emissions than petroleum diesel; however, unburned methyl esters from biodiesel are more susceptible to particulate matter (PM) formation following atmospheric dilution due to their low volatility. In this study, the efficacy of a production-type diesel oxidation catalyst (DOC) for the conversion of light hydrocarbons species and heavier, semi-volatile species like those in unburned fuel is examined. Experimental data were taken from a high speed direct-injection diesel engine operating in a mid-load, late injection partially premixed LTC mode on ultra-low sulfur diesel (ULSD) and neat soy-based biodiesel (B100). Gaseous emissions were recorded using a conventional suite of analyzers and individual light HCs were measured using an FT-IR analyzer.
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.
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