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Technical Paper

Characteristics of Vaporizing Continuous Multi-Component Fuel Sprays in a Port Fuel Injection Gasoline Engine

2001-03-05
2001-01-1231
Vaporization models for continuous multi-component liquid sprays and liquid wall films are presented using a continuous thermodynamics formulation. The models were implemented in the KIVA3V-Release 2.0 code. The models are first applied to clarify the characteristics of vaporizing continuous multi-component liquid wall films and liquid drops, and then applied to numerically analyze a practical continuous multi-component fuel - gasoline behavior in a 4-valve port fuel injection (PFI) gasoline engine under warm conditions. Corresponding computations with single-component fuels are also performed and presented for comparison purposes. As compared to the results of its single-component counterpart, the vaporizing continuous multi-component fuel drop displays a larger vaporization rate initially and a smaller vaporization rate as it becomes more and more dominated by heavy species.
Technical Paper

Multi-Dimensional Modeling of Mixing and Combustion of a Two-Stroke Direct-Injection Spark Ignition Engine

2001-03-05
2001-01-1228
Multi-Dimensional modeling was carried out for a Mercury Marine two-stroke DISI engine. Recently developed spray, ignition, and combustion models were applied to medium load cases with an air-fuel ratio of 30:1. Three injection timings, 271, 291 and 306 ATDC were selected to investigate the effects of the injection timing on mixture formation, ignition and combustion. The results indicate that at this particular load condition, earlier injection timing allows more fuel to evaporate. However, because the fuel penetrates further toward the piston, a leaner mixture is created near the spark plug; thus, a slower ignition process with a weaker ignition kernel was found for the SOI 271 ATDC case. The measured and computed combustion results such as average in-cylinder pressure and NOx are in good agreements. The later injection case produces lower NOx emission and higher CO emission; this is due to poor mixing and is in agreement with experimental measurements.
Technical Paper

Development of an Ignition and Combustion Model for Spark-Ignition Engines

2000-10-16
2000-01-2809
A new ignition and combustion model has been developed and tested for use in premixed spark-ignition engines. The ignition model is referred to as the Discrete Particle Ignition Kernel (DPIK) model, and it uses Lagrangian markers to track the flame-front growth. The model includes the effects of electrode heat transfer on the early flame kernel growth process, and it is used in conjunction with a characteristic-time-scale combustion model once the ignition kernel has grown to a size where the effects of turbulence on the flame must be considered. A new term which accounts for the effect of air-fuel ratio, was added to the combustion model for modeling combustion in very lean and very rich mixtures. The flame kernel size predicted by the DPIK model was compared with measurements of Maly and Vogel. Furthermore, predictions of the electrode heat transfer were compared with data of Kravchik and Heywood. In both comparisons the model predictions were in good agreement with the experiments.
Technical Paper

Modeling the Effect of Split Injections on DISI Engine Performance

2001-03-05
2001-01-0965
A spray model for pressure-swirl atomizers that is based on a linearized instability analysis of liquid sheets has been combined with an ignition and combustion model for stratified charge spark ignition engines. The ignition model has been advanced, such that the presence of dual spark plugs can now be accounted for. Independent validation of the spray model is achieved by investigating a pressure-swirl injector inside a pressure bomb containing air at ambient temperature. In a second step, the complete model is used to estimate the performance of a small marine DISI Two-Stroke engine operating in stratified charge mode. Simulation results and experimental data are compared for several different injection timings and the agreement is generally good such that there is confidence in the predictive quality of the combustion model. Finally the model is applied in a conceptual study to investigate possible benefits of split injections.
Technical Paper

Application of Micro-Genetic Algorithms for the Optimization of Injection Strategies in a Heavy-Duty Diesel Engine

2005-04-11
2005-01-0219
In this paper, optimized single and double injection schemes were found using multi-dimensional engine simulation software (KIVA-3V) and a micro-genetic algorithm for a heavy duty diesel engine. The engine operating condition considered was at 1737 rev/min and 57 % load. The engine simulation code was validated using an engine equipped with a hydraulic-electronically controlled unit injector (HEUI) system. Five important parameters were used for the optimization - boost pressure, EGR rate, start-of-injection timing, fraction of fuel in the first pulse and dwell angle between first and second pulses. The optimum results for the single injection scheme showed significant improvements for the soot and NOx emissions. The start of injection timing was found to be very early, which suggests HCCI-like combustion. Optimized soot and NOx emissions were reduced to 0.005 g/kW-hr and 1.33 g/kW-hr, respectively, for the single injection scheme.
Technical Paper

Improving Diesel Engine Performance Using Low and High Pressure Split Injections for Single Heat Release and Two-Stage Combustion

2010-04-12
2010-01-0340
This study explores an Adaptive Injection Strategy (AIS) that employs multiple injections at both low and high pressures to reduce spray-wall impingement, control combustion phasing, and limit pressure rise rates in a Premixed Compression Ignition (PCI) engine. Previous computational studies have shown that reducing the injection pressure of early injections can prevent spray-wall impingement caused by long liquid penetration lengths. This research focuses on understanding the performance and emissions benefits of low and high pressure split injections through experimental parametric sweeps of a 0.48 L single-cylinder test engine operating at 2000 rev/min and 5.5 bar nominal IMEP. This study examines the effects of 2nd injection pressure, EGR, swirl ratio, and 1st and 2nd injection timing, for both single heat release and two-peak high temperature heat release cases. In order to investigate the AIS concept experimentally, a Variable Injection Pressure (VIP) system was developed.
Technical Paper

Efficient Simulation of Diesel Engine Combustion Using Realistic Chemical Kinetics in CFD

2010-04-12
2010-01-0178
Detailed knowledge of hydrocarbon fuel combustion chemistry has grown tremendously in recent years. However, the gap between detailed chemistry and computational fluid dynamics (CFD) remains, because of the high cost of solving detailed chemistry in a large number of computational cells. This paper presents the results of applying a suite of techniques aimed at closing this gap. The techniques include use of a surrogate blend optimizer and a guided mechanism reduction methodology, as well as advanced methods for efficiently and accurately coupling the pre-reduced kinetic models with the multidimensional transport equations. The advanced methods include dynamic adaptive chemistry (DAC) and dynamic cell clustering (DCC) algorithms.
Technical Paper

Engine Development Using Multi-dimensional CFD and Computer Optimization

2010-04-12
2010-01-0360
The present work proposes a methodology for diesel engine development using multi-dimensional CFD and computer optimization. A multi-objective genetic algorithm coupled with the KIVA3V Release 2 code was used to optimize a high speed direct injection (HSDI) diesel engine for passenger car applications. The simulations were conducted using high-throughput computing with the CONDOR system. An automated grid generator was used for efficient mesh generation with 11 variable piston bowl geometry parameters. The first step in the procedure was to search for an optimal nozzle and piston bowl design. In this case, spray targeting, swirl ratio, and piston bowl shape were optimized separately for two full-load cases using simpler efficient combustion models (the characteristic time scale model and the shell ignition model). The optimal designs from the two optimizations were then validated using a combustion model with detailed chemistry (KIVA-CHEMKIN model and ERC n-heptane mechanism).
Technical Paper

Heavy-Duty Diesel Combustion Optimization Using Multi-Objective Genetic Algorithm and Multi-Dimensional Modeling

2009-04-20
2009-01-0716
A multi-objective genetic algorithm methodology was applied to a heavy-duty diesel engine at three different operating conditions of interest. Separate optimizations were performed over various fuel injection nozzle parameters, piston bowl geometries and swirl ratios (SR). Different beginning of injection (BOI) timings were considered in all optimizations. The objective of the optimizations was to find the best possible fuel economy, NOx, and soot emissions tradeoffs. The input parameter ranges were determined using design of experiment methodology. A non-dominated sorting genetic algorithm II (NSGA II) was used for the optimization. For the optimization of piston bowl geometry, an automated grid generator was used for efficient mesh generation with variable geometry parameters. The KIVA3V release 2 code with improved ERC sub-models was used. The characteristic time combustion (CTC) model was employed to improve computational efficiency.
Technical Paper

CFD Optimization of DI Diesel Engine Performance and Emissions Using Variable Intake Valve Actuation with Boost Pressure, EGR and Multiple Injections

2002-03-04
2002-01-0959
A computational optimization study was performed for a direct-injection diesel engine using a recently developed 1-D-KIVA3v-GA (1-Dimensional-KIVA3v-Genetic Algorithm) computer code. The code performs a full engine cycle simulation within the framework of a genetic algorithm (GA) code. Design fitness is determined using a 1-D (one-dimensional) gas dynamics code for the simulation of the gas exchange process, coupled with the KIVA3v code for three-dimensional simulations of spray, combustion and emissions formation. The 1-D-KIVA3v-GA methodology was used to simultaneously investigate the effect of eight engine input parameters on emissions and performance for four cases, which include cases at 2500 RPM and 1000 RPM, with both simulated at high-load and low-load conditions.
Technical Paper

Optimization of a Large Diesel Engine via Spin Spray Combustion*

2005-04-11
2005-01-0916
A numerical simulation and optimization study was conducted for a medium speed direct injection diesel engine. The engine's operating characteristics were first matched to available experimental data to test the validity of the numerical model. The KIVA-3V ERC CFD code was then modified to allow independent spray events from two rows of nozzle holes. The angular alignment, nozzle hole size, and injection pressure of each set of nozzle holes were optimized using a micro-genetic algorithm. The design fitness criteria were based on a multi-variable merit function with inputs of emissions of soot, NOx, unburned hydrocarbons, and fuel consumption targets. Penalties to the merit function value were used to limit the maximum in-cylinder pressure and the burned gas temperature at exhaust valve opening. The optimization produced a 28.4% decrease in NOx and a 40% decrease in soot from the baseline case, while giving a 3.1% improvement in fuel economy.
Technical Paper

Stoichiometric Combustion in a HSDI Diesel Engine to Allow Use of a Three-way Exhaust Catalyst

2006-04-03
2006-01-1148
The objectives of this study were 1) to evaluate the characteristics of rich diesel combustion near the stoichiometric operating condition, 2) to explore the possibility of stoichiometric operation of a diesel engine in order to allow use of a three-way exhaust after-treatment catalyst, and 3) to achieve practical operation ranges with acceptable fuel economy impacts. Boost pressure, EGR rate, intake air temperature, fuel mass injected, and injection timing variations were investigated to evaluate diesel stoichiometric combustion characteristics in a single-cylinder high-speed direct injection (HSDI) diesel engine. Stoichiometric operation in the Premixed Charge Compression Ignition (PCCI) combustion regime and standard diesel combustion were examined to investigate the characteristics of rich combustion. The results indicate that diesel stoichiometric operation can be achieved with minor fuel economy and soot impact.
Technical Paper

Use of a Pressure Reactive Piston to Control Diesel PCCI Operation - A Modeling Study

2006-04-03
2006-01-0921
The heavy-duty diesel engine industry is required to meet stringent emission standards. There is also the demand for more fuel efficient engines by the customer. In a previous study on an engine with variable intake valve closure timing, the authors found that an early single injection and accompanying premixed charge compression ignition (PCCI) combustion provides advantages in emissions and fuel economy; however, unacceptably high peak pressures and rates of pressure-rise impose a severe operating constraint. The use of a Pressure Reactive Piston assembly (PRP) as a means to limit peak pressures is explored in the present work. The concept is applied to a heavy-duty diesel engine and genetic algorithms (GA) are used in conjunction with the multi-dimensional engine simulation code KIVA-3V to provide an optimized set of operating variables.
Technical Paper

An Evaluation of Common Rail, Hydraulically Intensified Diesel Fuel Injection System Concepts and Rate Shapes

1998-08-11
981930
Hydraulically intensified medium pressure common rail (MPCR) electronic fuel injection systems are an attractive concept for heavy-duty diesel engine applications. They offer excellent packaging flexibility and thorough engine management system integration. Two different concepts were evaluated in this study. They are different in how the pressure generation and injection events are related. One used a direct principle, where the high-pressure generation and injection events occur simultaneously producing a near square injection rate profile. Another concept was based on an indirect principle, where potential energy (pressure) is first stored inside a hydraulic accumulator, and then released during injection, as a subsequent event. A falling rate shape is typically produced in this case. A unit pump, where the hydraulic intensifier is separated from the injector by a high-pressure line, and a unit injector design are considered for both concepts.
Technical Paper

Simultaneous Reduction of Engine Emissions and Fuel Consumption Using Genetic Algorithms and Multi-Dimensional Spray and Combustion Modeling

2000-06-19
2000-01-1890
A computational optimization study is performed for a heavy-duty direct-injection diesel engine using the recently developed KIVA-GA computer code. KIVA-GA performs full cycle engine simulations within the framework of a Genetic Algorithm (GA) global optimization code. Design fitness is determined using a one-dimensional gas -dynamics code for calculation of the gas exchange process, and a three-dimensional CFD code based on KIVA-3V for spray, combustion and emissions formation. The performance of the present Genetic Algorithm is demonstrated using a test problem with a multi-modal analytic function in which the optimum is known a priori. The KIVA-GA methodology is next used to simultaneously investigate the effects of six engine input parameters on emissions and performance for a high speed, medium load operating point for which baseline experimental validation data is available.
Technical Paper

Modeling Fuel System Performance and Its Effect on Spray Characteristics

2000-03-06
2000-01-1253
Fuel Injection System (FIS) research on injection pressure, timing control, and rate shaping, and studies on the modeling of injector nozzle flows and their effect on fuel spray characteristics are usually conducted separately. Only recently has the fuel injection and spraying process been studied as a complete system, i.e., including both the high-pressure fuel delivery and its effect on the nozzle flow characteristics, including nozzle cavitation. A methodology for coupling the fuel injection system and its effect on spray characteristics is presented here. The method is applied to an example case of a conventional pump-line-nozzle system. Mathematical models for characterizing the flows from the pump to the nozzle are formulated and solved using the Method of Characteristics and finite difference techniques. The nozzle internal flow is modeled using zero-dimensional flow models, in which the nozzle cavitation and its effect on the nozzle exit flow are accounted for.
Technical Paper

Effects of Injection Timing on Air-Fuel Mixing in a Direct-Injection Spark-Ignition Engine

1997-02-24
970625
Multidimensional modeling is used to study air-fuel mixing in a direct-injection spark-ignition engine. Emphasis is placed on the effects of the start of fuel injection on gas/spray interactions, wall wetting, fuel vaporization rate and air-fuel ratio distributions in this paper. It was found that the in-cylinder gas/spray interactions vary with fuel injection timing which directly impacts spray characteristics such as tip penetration and spray/wall impingement and air-fuel mixing. It was also found that, compared with a non-spray case, the mixture temperature at the end of the compression stroke decreases substantially in spray cases due to in-cylinder fuel vaporization. The computed trapped-mass and total heat-gain from the cylinder walls during the induction and compression processes were also shown to be increased in spray cases.
Technical Paper

CFD Study of Soot Reduction Mechanisms of Post-Injection in Spray Combustion

2015-04-14
2015-01-0794
The application of close-coupled post injections in diesel engines has been proven to be an effective in-cylinder strategy for soot reduction, without much fuel efficiency penalty. But due to the complexity of in-cylinder combustion, the soot reduction mechanism of post-injections is difficult to explain. Accordingly, a simulation study using a three dimensional computational fluid dynamics (CFD) model, coupled with the SpeedChem chemistry solver and a semi-detailed soot model, was carried out to investigate post-injection in a constant volume combustion chamber, which is more simple and controllable with respect to the boundary conditions than an engine. A 2-D axisymmetric mesh of radius 2 cm and height 5 cm was used to model the spray. Post-injection durations and initial oxygen concentrations were swept to study the efficacy of post-injection under different combustion conditions.
Journal Article

Study of High Speed Gasoline Direct Injection Compression Ignition (GDICI) Engine Operation in the LTC Regime

2011-04-12
2011-01-1182
An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections.
Journal Article

Optimization of a HSDI Diesel Engine for Passenger Cars Using a Multi-Objective Genetic Algorithm and Multi-Dimensional Modeling

2009-04-20
2009-01-0715
A multi-objective genetic algorithm coupled with the KIVA3V release 2 code was used to optimize the piston bowl geometry, spray targeting, and swirl ratio levels of a high speed direct injected (HSDI) diesel engine for passenger cars. Three modes, which represent full-, mid-, and low-loads, were optimized separately. A non-dominated sorting genetic algorithm II (NSGA II) was used for the optimization. High throughput computing was conducted using the CONDOR software. An automated grid generator was used for efficient mesh generation with variable geometry parameters, including open and reentrant bowl designs. A series of new spray models featuring reduced mesh dependency were also integrated into the code. A characteristic-time combustion (CTC) model was used for the initial optimization for time savings. Model validation was performed by comparison with experiments for the baseline engine at full-, mid-, and low-load operating conditions.
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