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Technical Paper

Characterizing the In Vehicle Performance of Expandable Sealants Used As Acoustic Baffles

1999-05-17
1999-01-1687
Chemically and heat reactive, expandable sealants are used as “acoustical baffles” in the automotive industry. These acoustic baffles are used to impede noise, water and dust propagation inside of structural components and body cavities. Use of these sealant materials has grown significantly as the demands to improve vehicle acoustic performance has increased. Various test methods have been developed to quantify the performance of these materials through direct comparison of material samples. These investigations use standardized testing procedures to characterize the acoustic performance of a material sample on the basis of controlled laboratory test conditions. This paper presents a step in the progression of evaluating acoustic baffle performance in the vehicle. Standard experimental techniques are used to investigate the influence of the baffles on the vehicle acoustic performance.
Technical Paper

Effect of High Squish Combustion Chamber on Simultaneous Reduction of NOx and Particulate from a Direct-Injection Diesel Engine

1999-05-03
1999-01-1502
In this study it is tried to reduce NOx and particulate emissions simultaneously in a direct injection diesel engine based on the concept of two-stage combustion. At initial combustion stage, NOx emission is reduced with fuel rich combustion. At diffusion combustion stage, particulate emission is reduced with high turbulence combustion. The high squish combustion chamber with reduced throat diameter is used to realize two-stage combustion. This combustion chamber is designed to produce strong squish that causes high turbulence. When throat diameter of the high squish combustion chamber is reduced to some extent, simultaneous reduction of NOx and particulate emissions is achieved with less deterioration of fuel consumption at retarded injection timing. Further reduction of NOx emission is realized by reducing the cavity volume of the high squish combustion chamber. Analysis by endoscopic high speed photography and CFD calculation describes the experimental results.
Technical Paper

Activities of the Federal Aviation Administration’s Aviation Weather Research Program

1999-04-20
1999-01-1578
Weather is a major cause of aircraft accidents and incidents and the single largest contributor to air traffic system delays. Through improvements in the knowledge of current weather conditions and reliable forecasts, the Federal Aviation Administration (FAA) can improve aviation safety, increase system capacity, and enhance flight planning and fuel efficiency. The FAA has established an Aviation Weather Research (AWR) program to address specific requirements for weather support to aviation by providing the capability to generate more accurate and accessible weather observations, warnings, and forecasts and also by increasing the scientific understanding of atmospheric processes that spawn aviation weather hazards. The goal of AWR is to provide meteorological research that leads to the satisfaction of specific aviation weather requirements.
Technical Paper

AQUAZOLE™: An Original Emulsified Water-Diesel Fuel for Heavy-Duty Applications

2000-06-19
2000-01-1861
1 Since 1997 the ELF group has been working on a new fuel designed in priority for use with urban services (buses, lorries). Basically, it is a diesel/water emulsion stabilised by a series of new additives. A lot of testing programmes on engine and vehicles test benches was carried out. They have clearly shown that with this new fuel there is a reduction of nitrogen oxide emissions by up to 30% and black smoke by up to 80%, without any technological modifications being necessary as against EN 590 diesel fuel marketed normally. The water content is, however, the cause of a certain loss in engine performances. Nevertheless, hydrocarbon consumption is reduced by up to 4%. The use of an oxidation catalyst is compatible with a water-diesel emulsified fuel and results in larger emission benefits. Furthermore, a 50 ppm sulphur emulsion with a continuously regenerating particle filter give a particle reduction of 90%.
Technical Paper

Multi-Dimensional Modeling of Ignition, Combustion and Nitric Oxide Formation in Direct Injection Natural Gas Engines

2000-06-19
2000-01-1839
The heat release and pollutant formation processes in a direct injection natural gas engine are studied by coupling detailed chemistry with a multi-dimensional reactive flow code. A detailed kinetic mechanism consisting of 22 species and 104 elementary reactions is chosen by comparing ignition delay predictions with measurements in a combustion bomb. The ignition model is then coupled with a turbulent combustion model and extended Zeldovich kinetics to simulate heat release and nitric oxide production in a direct injection engine. Parametric studies are conducted to investigate the effect of engine operating conditions which include speed, load, injection timing and level of boost. It is shown that use of detailed chemistry is extremely important to predict the correct ignition delay period as engine operating conditions change. Use of both time and crank angle as the independent variable reveals interesting details of the heat release process as a function of engine speed.
Technical Paper

Aqueous Ethanol Fueled Catalytic Ignition Engine

1999-09-28
1999-01-3267
The goal of this research is to determine the feasibility of a catalytic compression-ignition engine running on aqueous ethanol fuel. A naturally aspirated, three-cylinder, direct-injection diesel engine manufactured by Yanmar has been modified to operate as a homogeneous-charge, compression-ignition engine. This involved removing the fuel injectors, replacing them with catalytic elements located inside a small pre-chamber, and installing a pulse width modulated fuel injection system. The fuel is 35% water and 65% ethanol by volume. The catalytic igniters allow the engine to operate continuously at various load levels corresponding to a broad range of air/fuel ratios. To adjust ignition timing and monitor in-cylinder combustion, the engine has been instrumented with a piezoelectric pressure transducer and a crankshaft encoder. Pressure traces are quite repeatable from cycle to cycle and resemble combustion patterns in typical Otto cycle engines.
Technical Paper

A Study of Exhaust Emission Control for Direct Fuel Injection Two-stroke Engine

1999-09-28
1999-01-3287
An attempt to reduce the HC emission of a two-stroke engine was carried out. A simple homogeneous charge combustion created with a Direct Fuel Injection (DFI) system was applied to a Personal Water Craft (PWC) engine. 1/4 HC emission of the base carbureted engine was obtained in International Council of Marine Industry Association (ICOMIA) driving mode due to the exclusion of fuel short-circuiting. Then stratified charge combustion was introduced. A numerical simulation of air and spray motion was performed and mixture formation was optimized. The low load misfiring was completely overcome and finally, less than 1/8 HC emission was achieved.
Technical Paper

NOx Reactivity Studies of Prototype Catalysts for a Plasma–Catalyst Aftertreatment System

1999-10-25
1999-01-3685
The reactivity of NOx over two prototype catalysts has been measured in a new bench reactor for characterizing plasma–catalyst systems that allows for in–situ post–analysis of any species which may have adsorbed on the catalyst. In these initial studies without a plasma, NO2 was used to mimic the NOx output of a plasma reactor in a blended feedstream that mimics diesel exhaust. The baseline performance of the catalysts was measured as a function of temperature, hydrocarbon concentration, hydrocarbon type, and water content, usually at a space velocity of 29,000 h–1. Performance was assessed in terms of the percent conversion of the incoming NO2 to desirable non–NOx N–containing species. For the better of the two catalysts the conversion without water present peaked in the 30–40% range between 125°C and 175°C using a propene/propane mixture of hydrocarbons in a 10:1 C1:N ratio. Experiments with NO as the NOx component yielded very poor activities.
Technical Paper

Correlation Between the Measured Flame Surface Density and Turbulence Parameters in Turbulent Premixed Flames

2000-03-06
2000-01-1383
Recent findings on the characteristics of flame surface density are introduced for turbulent premixed combustion in typical operating conditions of SI engines. The maximum flame surface density tends to show linear dependence on the K -factor defined as a function of the integral length scale and . The flame surface density shows an asymmetric profile in the space with the peak location correlated in terms of the dimensionless parameter, NB, which represents the degree of gradient or counter-gradient diffusion by turbulence. The effects of the K -factor and NB are discussed in the wrinkled flamelet and corrugated flamelet regime respectively. The flame surface density increases at a higher ambient pressure due to decrease in the laminar flame speed and the length scales of flame wrinkling. Comments are made on the turbulent stretch and turbulent flux terms in the Σ -equation in modeling combustion of an SI engine.
Technical Paper

INVESTIGATION ON COMBUSTION BEHAVIOR OF EXTREMELY LEAN MIXTURES IN A CLOSED BOMB LIKE A GASOLINE ENGINE

2000-01-15
2000-01-1423
From the viewpoint of energy saving and air pollution prevention which are needed for development of internal combustion engines, experiments have been carried out to elucidate the true combustion bahavior of extremely lean mixtures in a closed bomb by using the microgravity techniques. Microgravity conditions established in a falling assembly enables the flame propagation and the measurement in lean-limit states. The oscillatory nature of flame propgation appeared in very lean mixtures of propane-air may be explained in term of Lewis number which is less than unity. Turbulence is shown to be ineffective in enhanching the burning velocities and indeed may cause extinction in very lean mixtures.
Technical Paper

Optimization of Natural Gas Combustion in Spark-Ignited Engines Through Manipulation of Intake-Flow Configuration

2000-06-19
2000-01-1948
An investigation was performed to try to quantify the relative importance of large-scale mixing and turbulence in a multi-valve spark-ignited automotive engine converted to use natural gas fuel. The role of mixing was examined by comparing single-point versus multi-point combustion performance at several operating conditions. The fuel-air mixture passed through a static mixer prior to entering the intake manifold in the single point case. This configuration was assumed to produce a well-mixed charge entering the combustion chamber. The fuel was delivered just upstream of the intake port in the multi-point configuration. The charge was assumed to be stratified in this case. The results showed a significant degradation in combustion stability and maximum power but little difference in ignition delay and fully-developed burn duration using multi-point injection. The relative role of turbulence was examined by altering the intake-flow configuration to create three levels of inlet swirl.
Technical Paper

Do Turbulent Premixed Flame Fronts in Spark-Ignition Engines Behave Like Passive Surfaces?

2000-06-19
2000-01-1942
A widely held belief in the combustion community is that the chemical and hydrodynamic structure of a stretched laminar premixed flame can be preserved in a turbulent flow field over a range of conditions collectively known as the flamelet regime, and the homogeneous charge spark-ignition engine combustion falls within the domain of this regime. The major assumption in the laminar flamelet concept as applied to the turbulent premixed flames is that the flame front behaves as a constant-property passive scalar surface, and an increase in the wrinkled flame surface area with increasing turbulence intensity is the dominant mechanism for the observed flame velocity enhancement. The two approaches that have been recently used for estimating a measure of the wrinkled flame surface area in spark-ignition engines and other premixed flames are the flame surface density concept and fractal geometry.
Technical Paper

A Research in the Cause of Simultaneous Reduction of NOx • SFC on HONDA CVCC SI Engine

2000-06-19
2000-01-1938
(1) Through the accumulation of many researches during 1974∼94 done by the authors [8∼12,15], as like temperature measurement or the calculation of it by normal flame propagation model, it was clarified the difficulty of explanation for the captioned theme shown in the title by the conventional past concept. (2) To conquer these issued problems a new hypothesis in which the burned gas jet from pre-chamber has mixed with premixed gas in the main-chamber and acted as same as internal EGR was proposed. (3) The calculated result of this hypothesis coincided qualitatively and quantitatively with the measured flame temperature and others that the appropriateness of this was verified. (4) The result of the state in combustion at A/F=18 has been in 7% of low oxygen concentration, 2350°K of high temperature and strong turbulent condition. (5) This paper suggests a new guideline for the target to lower NOx, lower fuel consumption by low oxygen, high temperature and strong turbulent combustion.
Technical Paper

Turbulent Premixed Flames Under Lean Conditions Studied with Ion Current Measurement in a Homogeneous Charge Spark-Ignition Engine

2000-06-19
2000-01-1940
The structures of the turbulent premixed flame in the engine cylinder under lean burn conditions were investigated using ion probe method. The flow fields were measured with an LDA for two tumble ratios and two compression ratios. And ion-current signal was analyzed to discuss the interaction between the turbulence and the flame structure. The effects of turbulence and equivalence ratio on the characteristic values of the turbulent flame, that is to say number of ion-current peaks, thickness of flame front and thickness of burning zone of the flamelet, were investigated. In normal combustion, the structure of the turbulent flame front is almost the same as the laminar flame. In the lean limit, the flamelet is broken and stretched and then the structure may change.
Technical Paper

Quasi-Dimensional and CFD Modelling of Turbulent and Chemical Flame Enhancement in an Ultra Lean Burn S.I. Engine

2000-03-06
2000-01-1263
HAJI, or Hydrogen Assisted Jet Ignition, is an ignition system which uses a hot gaseous jet to initiate and stabilise combustion. HAJI allows a dramatic reduction of cyclic variability, and an extension of the lean limit of the engine to lambda 5. Improvements in cyclic variability lead to increased power output, reduced noise, wear on components and emissions. The ability to operate ultra lean gives 25% improvements in efficiency and extremely low emissions, particularly of NOx. Combustion analysis based on the fractal dimensions of the propagating flame fronts, obtained from optical flame data, support the hypothesis of enhancement of flame speeds through the presence of active chemical species. However, the relative contributions of turbulence and active species to the mechanisms of combustion enhancement realised with HAJI are not well defined. HAJI ignition has also been simulated with a comprehensive three dimensional combustion code, KIVA3.
Technical Paper

Water Carryover Characteristics From Evaporator Coils During Transitional Airflows

2000-03-06
2000-01-1268
In this paper, the results from an experimental investigation to determine the water carryover characteristics from the evaporator coil during transitional airflows is presented. The tests were conducted at the following transitional operating conditions: blower speed low to medium; and blower speed low to high. For both of these tests the system operated at low blower speed for an extended period of operation before switching to either medium or high speeds. A laminate (plate type) evaporator with louvered fins with hydrophilic coating was used for this investigation. Tests were also conducted with a screen at the downstream face of the core to prevent water carryover. This test was conducted for the worst case scenario, i.e., when the blower speed was increased to high from an extended period of operation at low speed.
Technical Paper

Effect of Desiccant on the Stability of Automotive Air Conditioning Systems

2000-03-06
2000-01-0983
Desiccant materials are commonly used in the automotive industry to reduce the level of moisture in vehicle air conditioning systems. The primary purpose for removing moisture from these systems is to avoid corrosion of metals, compatibility problems with polymeric materials, and possible freeze-up associated with free water. In nonpolar R-12/mineral oil systems with low solubility for water, moisture levels are usually controlled to 25 ppm or less. However, R-134a and PAG are highly polar and have good solubility for moisture, thus presenting reduced risk of free water in the air-conditioning systems. This paper addresses the questions of whether desiccants are required in air conditioning systems using R- 134a/PAG, and if required, what is the optimum quantity of desiccant for system stability and long-term system reliability Tests were conducted in the laboratory (accelerated sealed tube aging according to ASHRAE standard 97- 1989) as well as in the field (vehicle fleet tests).
Technical Paper

Use of Multizone Combustion Models to Analyze and Predict the Effect of Cyclic Variations on SI Engines

2000-03-06
2000-01-0961
In this paper, a parameter to quantify the cyclic variability in first stages of combustion is presented, as an evolution of the parameter proposed by Hill and Kapil. This parameter relates the mean time necessary for the initial flame to reach the periphery of a turbulence eddy structure moving from the flame kernel position. This parameter is used in combination with quasi-dimensional models in order to predict and analyze small-scale turbulence contribution to cyclic variations. The cyclic dispersion parameter could be introduced in the predictive models as a delay in the combustion beginning. The parameter is compared with the experimental standard deviations in mass burned fraction at spark time obtained from others researchers works and own experimental data. A satisfying agreement between predictions and measurements is achieved.
Technical Paper

Effect of Inhomogeneities in the End Gas Temperature Field on the Autoignition in SI Engines

2000-03-06
2000-01-0954
This paper reports an one–dimensional modeling procedure of the hot spot autoignition with a detailed chemistry and multi–species transport in the end gas in an SI engine. The governing equations for continuity of mass, momentum, energy and species for an one–dimensional, unsteady, compressible, laminar, reacting flow and thermal fields are discretized and solved by a fully implicit method. A chemical kinetic mechanism is used for the primary reference fuels n–heptane and iso–octane. This mechanism contains 510 chemical reactions and 75 species. The change of the cylinder pressure is calculated from both flame propagation and piston movement. The turbulent velocity of the propagating flame is modeled by the Wiebe function. Adiabatic conditions, calculated by minimizing Gibb's free energy at each time step, are assumed behind the flame front in the burned gas.
Technical Paper

Assessment of CFD Methods for Large Diesel Engines Equipped with a Common Rail Injection System

2000-03-06
2000-01-0948
A KIVA-based CFD tool has been utilized to simulate the effect of a Common-Rail injection system applied to a large, uniflow-scavenged, two-stroke diesel engine. In particular, predictions for variations of injection pressure and injection duration have been validated with experimental data. The computational models have been evaluated according to their predictive capabilities of the combustion behavior reflected by the pressure and heat release rate history and the effects on nitric oxide formation and wall temperature trends. In general, the predicted trends are in good agreement with the experimental observations, thus demonstrating the potential of CFD as a design tool for the development of large diesel engines equipped with Common-Rail injection. Existing deficiencies are identified and can be explained in terms of model limitations, specifically with respect to the description of turbulence and combustion chemistry.
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