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Technical Paper

A Study of Flow Characteristics on the Diesel-Gasoline Dual-Fuel Combustion by 3-D CFD

2019-09-09
2019-24-0117
Various advanced combustion concepts, which can achieve higher thermal efficiency and emissions reduction, have been suggested as the emissions regulation gets stricter. Dual-fuel combustion that operates by using different fuels having both premixed and non-premixed combustion characteristics is one of the viable alternatives. In dual-fuel combustion, it is critical to understand air-fuel mixture distribution as it determines the ignition spot and following combustion phase. The fuel distribution in the engine is affected by various factors, such as chamber geometry, injection strategy or in-cylinder flow motion. Furthermore, among them, in-cylinder motion, usually described in terms of swirl or tumble motion, is mostly affected by in-cylinder port geometry. In this paper, 3-dimensional Computational Fluid Dynamics (CFD) was used to investigate the effect of in-cylinder flow motion in dual-fuel combustion. Two head and port geometries were used in the simulations.
Technical Paper

New Index for Diagnosis of Abnormal Combustion Using a Crankshaft Position Sensor in a Diesel Engine

2019-04-02
2019-01-0720
Most research of internal combustion engine focuses on improving the fuel economy and reducing exhaust emissions to satisfy regulations and marketability. Engine combustion is a key factor in determining engine performance. Generally, engine operating parameters are optimized for the best performance and less exhaust emissions. However, abnormal combustion results in engine conditions that are far from an optimized operation. Abnormal combustion, including a misfire, can happen for a variety of reasons, such as superannuated vehicles, extreme changes in the driving environment, etc. Abnormal combustion causes serious deterioration of not only noise, vibration and harshness (NVH), but also the fuel economy and exhaust emission. NVH stands for unwanted noise, vibration and harshness from the vehicle. The misfiring especially deteriorates vehicle comfortability. Abnormal combustion at one cylinder breaks the exciting force balance between cylinders and causes unexpected vibration.
Technical Paper

Numerical Analysis on the Effect of Piston Bowl Geometry in Gasoline-Diesel Dual-Fuel Combustion

2019-04-02
2019-01-1164
As emissions regulations become stricter, a variety of advanced combustion concepts that can reduce emissions with a higher thermal efficiency have been suggested. Dual-fuel combustion is one of the alternatives that has both premixed and non-premixed combustion characteristics. Knowing the effects of the mixture formation in dual-fuel combustion is important because it determines the ignition location and the following combustion phase. Hence, a thorough investigation on the related factors, such as the engine hardware or fuel spray, is required. Meanwhile, Computational Fluid Dynamics (CFD) is a good technique to visualize the in-cylinder phenomena and enables quantitative investigations into the detailed combustion characteristics. In this paper, a 3-dimensional CFD simulation was used to investigate the effects of the mixture formation in dual-fuel combustion. The combustion model consists of two parts.
Technical Paper

A Quasi-Dimensional Model for Prediction of In-Cylinder Turbulence and Tumble Flow in a Spark-Ignited Engine

2018-04-03
2018-01-0852
Improving fuel efficiency and emission characteristics are significant issues in engine research. Because the engine has complex systems and various operating parameters, the experimental research is limited by cost and time. One-dimensional (1D) simulation has attracted the attention of researchers because of its effectiveness and relatively high accuracy. In a 1D simulation, the applied model must be accurate for the reliability of the simulation results. Because in-cylinder turbulence mainly determines the combustion characteristics, and mean flow velocity affects the in-cylinder heat transfer and efficiency in a spark-ignited (SI) engine, a number of sophisticated models have been developed to predict in-cylinder turbulence and mean flow velocity. In particular, tumble is a significant factor of in-cylinder turbulence in SI engine.
Technical Paper

Impact of Grid Density on the LES Analysis of Flow CCV: Application to the TCC-III Engine under Motored Conditions

2018-04-03
2018-01-0203
Large-eddy simulation (LES) applications for internal combustion engine (ICE) flows are constantly growing due to the increase of computing resources and the availability of suitable CFD codes, methods and practices. The LES superior capability for modeling spatial and temporal evolution of turbulent flow structures with reference to RANS makes it a promising tool for describing, and possibly motivating, ICE cycle-to-cycle variability (CCV) and cycle-resolved events such as knock and misfire. Despite the growing interest towards LES in the academic community, applications to ICE flows are still limited. One of the reasons for such discrepancy is the uncertainty in the estimation of the LES computational cost. This in turn is mainly dependent on grid density, the CFD domain extent, the time step size and the overall number of cycles to be run. Grid density is directly linked to the possibility of reducing modeling assumptions for sub-grid scales.
Technical Paper

Investigation of Sub-Grid Model Effect on the Accuracy of In-Cylinder LES of the TCC Engine under Motored Conditions

2017-09-04
2017-24-0040
The increasing interest in the application of Large Eddy Simulation (LES) to Internal Combustion Engines (hereafter ICEs) flows is motivated by its capability to capture spatial and temporal evolution of turbulent flow structures. Furthermore, LES is universally recognized as capable of simulating highly unsteady and random phenomena driving cycle-to-cycle variability (CCV) and cycle-resolved events such as knock and misfire. Several quality criteria were proposed in the recent past to estimate LES uncertainty: however, definitive conclusions on LES quality criteria for ICEs are still far to be found. This paper describes the application of LES quality criteria to the TCC-III single-cylinder optical engine from University of Michigan and GM Global R&D; the analyses are carried out under motored condition.
Technical Paper

Study of LES Quality Criteria in a Motored Internal Combustion Engine

2017-03-28
2017-01-0549
In recent years, Large-Eddy Simulation (LES) is spotlighted as an engineering tool and severe research efforts are carried out on its applicability to Internal Combustion Engines (ICEs). However, there is a general lack of definitive conclusions on LES quality criteria for ICE. This paper focuses on the application of LES quality criteria to ICE and to their correlation, in order to draw a solid background on future LES quality assessments for ICE. In this paper, TCC-III single-cylinder optical engine from University of Michigan is investigated and the analysis is conducted under motored condition. LES quality is mainly affected by grid size and type, sub-grid scale (SGS) model, numeric schemes. In this study, the same grid size and type are used in order to focus on the effect on LES quality of SGS models and blending factors of numeric scheme only.
Technical Paper

A Study on the Refinement of Turbulence Intensity Prediction for the Estimation of In-Cylinder Pressure in a Spark-Ignited Engine

2017-03-28
2017-01-0525
The role of 1D simulation tool is growing as the engine system is becoming more complex with the adoption of a variety of new technologies. For the reliability of the 1D simulation results, it is necessary to improve the accuracy and applicability of the combustion model implemented in the 1D simulation tool. Since the combustion process in SI engine is mainly determined by the turbulence, many models have been concentrating on the prediction of the evolution of in-cylinder turbulence intensity. In this study, two turbulence models which can resemble the turbulence intensity close to that of 3D CFD tool were utilized. The first model is dedicated to predicting the evolution of turbulence intensity during intake and compression strokes so that the turbulence intensity at the spark timing can be estimated properly. The second model is responsible for predicting the turbulence intensity of burned and unburned zone during the combustion process.
Technical Paper

Virtual NOx sensor for Transient Operation in Light-Duty Diesel Engine

2016-04-05
2016-01-0561
Currently, diesel engine-out exhaust NOx emission level prediction is a major challenge for complying with the stricter emission legislation and for control purpose of the after-treatment system. Most of the NOx prediction research is based on the Zeldovich thermal mechanism, which is reasonable from the physical point of view and for its simplicity. Nevertheless, there are some predictable range limitations, such as low temperature with high EGR rate operating conditions or high temperature with low EGR rates. In the present paper, 3 additional considerations, pilot burned gas mixing before the main injection; major NO formation area; concentration correction, were applied to the previously developed real-time NO estimation model based on in-cylinder pressure and data available from ECU. The model improvement was verified on a 1.6 liter EURO5 diesel engine in both steady and transient operation.
Technical Paper

Development of a Vehicle System Model for the First Medium- and Heavy-Duty Commercial Vehicle Fuel Efficiency Standards in Korea

2015-09-29
2015-01-2774
To properly respond to demands to reduce national energy consumption and meet greenhouse gas emission targets based on environment policy, the Ministry of Trade, Industry, and Energy of Korea formed a research consortium consisting of government agencies and academic and research institutions to establish the first fuel efficiency standards for medium- and heavy-duty (MHD) commercial vehicles. The standards are expected to be introduced in 2017 as Phase 1 of the plan and will regulate trucks with a gross vehicle weight in excess of 3.5 tons and buses with a carrying capacity of more than 16 persons. Most MHD commercial vehicles are custom-made and manufactured in diversified small-quantity batch production systems for commercial or public use, resulting in difficulties in utilizing mandatory vehicle tests for fuel efficiency evaluations.
Technical Paper

Numerical Study on the Multiple Injection Strategy in Diesel Engines using a Modified 2-D Flamelet Model

2015-09-06
2015-24-2406
The flamelet model is a widely used combustion model that demonstrates a good prediction of non-premixed combustion. In this model, the chemical time scales are considered to be smaller compared to those of the turbulence, which allows the heat and mass transfer equation to be decoupled from the flow equation. However, the model's dependency on the mixture fraction limits the combustion analysis to a single injection. To overcome this limitation, a two dimensional flamelet model, which uses two mixture fraction variables, was introduced to represent the non-premixed combustion of multiple injections. However, the model's computational time drastically increased due to the expansion of the solution domain. Thus, a modified 2-D flamelet model was introduced to reduce the computational time of the two dimensional flamelet model.
Technical Paper

Study on the Correlation between the Heat Release Rate and Vibrations from a Diesel Engine Block

2015-04-14
2015-01-1673
In this study, a correlation between the maximum heat release rate and vibrations from a diesel engine block was derived, and a methodology to determine the maximum heat release rate is presented. To investigate and analyze the correlation, an engine test and an actual road vehicle test were performed using a 1.6-L diesel engine. By varying the engine speed, load and main injection timing, the vibration signals from the engine block were measured and analyzed using a continuous wavelet transform (CWT). The results show that the maximum heat release rate has a strong correlation with the magnitude of the vibrations. A specific bandwidth, the vibration signals between 0.3∼1.5 kHz, was affected by the variation in the heat release rate. The vibrations excited by combustion lasted over 50 CAD; however, the signals during the period of 35 CAD after the start of injection had a dominant effect on the maximum heat release rate.
Technical Paper

Study on the Application of the Waste Heat Recovery System to Heavy-Duty Series Hybrid Electric Vehicles

2013-04-08
2013-01-1455
A waste heat recovery system is applied to a heavy-duty series hybrid electric vehicle. The engine in a series hybrid electric vehicle can operate at steady state for most of the time because the engine and drivetrain are decoupled, providing the waste heat recovery system with a steady state heat source. Thus, it is possible to optimize the waste heat recovery system design while maximizing the amount of useful energy converted in the system. To realize such a waste heat recovery system, the Rankine steam cycle is selected for the bottoming cycle. The heat exchanger is implemented as a quasi-1D simulation model to calculate the accurate quantity of recovered energy and to determine the working fluid state. The optimal geometric characteristics of the heat exchanger and the efficiency are considered according to the working fluid. The Rankine steam cycle model is constructed, and the output power is calculated.
Journal Article

Fuel Economy Research on Series-Type HEV Intracity Buses with Different Traction Motor Capacity Combinations

2012-04-16
2012-01-1035
Research on HEV (hybrid electric vehicle) intracity buses has become a topic of interest because the well-known service routes of intracity buses and the frequent stop/go pattern make the energy management of the vehicle straightforward. Thus, the energy flow and the energy management of the intracity bus have been studied extensively in order to improve fuel economy. However, the HEV buses that have been studied previously were equipped with a single traction motor or with dual motors with the same capacity for the convenience of the equipment without considering the motoring or generating efficiency of the traction motor. Therefore, the energy flow from the engine/generator unit to the traction motor that has been optimized by many kinds of energy distribution strategies could not be transferred to the wheels in the most efficient manner. This paper investigates this aspect of the energy flow.
Journal Article

The Measurement of Penetration Length of Diesel Spray by Using Background Oriented Schlieren Technique

2011-04-12
2011-01-0684
The measurement of spray penetration length is one of crucial tasks for understanding the characteristics of diesel spray and combustion. For this reason, many researchers have devised various measurement techniques, including Mie scattering, schlieren photography, and laser induced exciplex fluorescence (LIEF). However, the requirements of expensive lasers, complicated optics, delicate setups, and tracers that affect fuel characteristics have been disadvantages of previous techniques. In this study, the background-oriented schlieren (BOS) technique is employed to measure the vapor penetration length of diesel spray for the first time. The BOS technique has a number of benefits over the previous techniques because of its quantitative, non-intrusive nature which does not require lasers, mirrors, optical filters, or fuel tracers.
Technical Paper

Laminar Flame Speed Characteristics and Combustion Simulation of Synthetic Gas Fueled SI Engine

2008-04-14
2008-01-0965
As the real-time supplying of hydrogen-rich gas becomes possible by the advances in the on-board fuel reforming technologies, utilizations of synthetic gas in IC engines are actively studied. However, due to the lack of fundamental studies on the combustion characteristics of synthetic gas, there is no precedent for the simulation of combustion process in synthetic gas fueled SI engine. In this study, the laminar flame speeds of synthetic gas and its mixture with iso-octane were calculated under extensive initial conditions of 3,575 points derived by combinations of temperature, pressure, fraction of lower heating value of synthetic gas and air-excess ratio variations.
Technical Paper

Modeling of Combustion Process of Multiple Injection in HSDI Diesel Engines using Modified Two-Dimensional Flamelet

2007-09-16
2007-24-0042
Ignition delay of the second injection of HSDI diesel engines is generally much shorter than that of the first injection because of the interaction between the radicals generated during the combustion process and the mixed gas of the second injection. Although previous Diesel combustion models could not explain this reaction, Hasse and Peters described the mass and heat transfer of the second injection and estimated the ignition delay of the second injection using two-dimensional flamelet equations. But a simulation of the two-dimensional flamelet equations requires enormous computational time. Thus, to analyze the combustion phenomena of the multiple injection mode in HSDI diesel engines effectively, the two-dimensional flamelet combustion model was modified in this study. To reduce the calculation time, two-dimensional flamelet equations were only applied near the stoichiometric region.
Technical Paper

Modeling of Unburned Hydrocarbon Oxidation in Engine Conditions using Modified One-step Reaction Model

2007-08-05
2007-01-3536
Modeling of unburned hydrocarbon oxidation in an SI engine was performed in engine condition using modified one-step oxidation model. The new one-step equation was developed by modifying the Arrhenius reaction rate coefficients of the conventional one-step model. The modified model was well matched with the results of detailed chemical reaction mechanism in terms of 90 % oxidation time of the fuel. In this modification, the effect of pressure and intermediate species in the burnt gas on the oxidation rate investigated and included in developed one-step model. The effect of pressure was also investigated and included as an additional multiplying factor in the reaction equation. To simulate the oxidation process of piston crevice hydrocarbons, a computational mesh was constructed with fine mesh density at the piston crevice region and the number of cell layers in cylinder was controlled according to the motion of piston.
Technical Paper

Hydraulic Simulation and Experimental Analysis of Needle Response and Controlled Injection Rate Shape Characteristics in a Piezo-driven Diesel Injector

2006-04-03
2006-01-1119
The More precise control of the multiple-injection is required in common-rail injection system of direct injection diesel engine to meet the low NOx emission and optimal PM filter system. The main parameter for obtaining the multiple-injections is the mechanism controlling the injector needle energizing and movement. In this study, a piezo-driven diesel injector, as a new method driven by piezoelectric energy, has been applied with a purpose to develop the analysis model of the piezo actuator to predict the dynamics characteristics of the hydraulic component (injector) by using the AMESim code and to evaluate the effect of this control capability on spray formation processes. Aimed at simulating the hydraulic behavior of the piezo-driven injector, the circuit model has been developed and verified by comparison with the experimental results.
Technical Paper

Premixed Combustion Modeling in an SI Engine Considering the Burned Gas Composition

2005-05-11
2005-01-2108
Conventional combustion models are suitable for predicting flame propagation for a wrinkled flamelet configuration. But they cannot predict the burned gas composition. This causes the overestimation of burned gas temperature and pressure. A modified method of combustion simulation was established to calculate the chemical composition and to investigate their ultimate fate in the burned gas region. In this work, the secondary products of combustion process, like CO and H2, were considered as well as the primary products like CO2 and H2O. A 3-dimensional CFD program was used to simulate the turbulent combustion and a zero dimensional equilibrium code was used to predict the chemical composition of burned gas. With this simple connection, more reasonable temperature and pressure approaching the real phenomena were predicted without additional time costs.
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