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Technical Paper

The Effect of Intake Air Temperature, Compression Ratio and Coolant Temperature on the Start of Heat Release in an HCCI (Homogeneous Charge Compression Ignition) Engine

2001-12-01
2001-01-1880
In this paper, effect of intake air temperature, coolant temperature, and compression ratio on start of heat release (SOHR) in HCCI engines is investigated. The operational range with HCCI operation was determined experimentally using a CFR (Cooperative Fuels Research) engine with n-butane as the fuel. In-cylinder pressure was processed to evaluate SOHR. The effect of intake air and coolant temperature on SOHR increases as engine speed increases. In order to gain more insight into the combustion phenomena, SOHR was calculated using the theory of Livengood-Wu and compared with the experimental data. Dependence of SOHR on the equivalence ratio shows good correspondence between experiment and calculation. On the contrary, dependence on the intake air temperature and compression ratio shows poorer correspondence with predictions, especially under low engine speed. We interpret this as an indication of the importance of the active intermediate species that remain in the combustion chamber.
Technical Paper

Comparison of Numerical Results and Experimental Data on Emission Production Processes in a Diesel Engine

2001-03-05
2001-01-0656
Simulations of DI Diesel engine combustion have been performed using a modified KIVA-II package with a recently developed phenomenological soot model. The phenomenological soot model includes generic description of fuel pyrolysis, soot particle inception, coagulation, and surface growth and oxidation. The computational results are compared with experimental data from a Cummins N14 single cylinder test engine. Results of the simulations show acceptable agreement with experimental data in terms of cylinder pressure, rate of heat release, and engine-out NOx and soot emissions for a range of fuel injection timings considered. The numerical results are also post-processed to obtain time-resolved soot radiation intensity and compared with the experimental data analyzed using two-color optical pyrometry. The temperature magnitude and KL trends show favorable agreement.
Technical Paper

Modeling the Effects of EGR and Injection Pressure on Emissions in a High-Speed Direct-Injection Diesel Engine

2001-03-05
2001-01-1004
Experimental data is used in conjunction with multi-dimensional modeling in a modified version of the KIVA-3V code to characterize the emissions behavior of a high-speed, direct-injection diesel engine. Injection pressure and EGR are varied across a range of typical small-bore diesel operating conditions and the resulting soot-NOx tradeoff is analyzed. Good agreement is obtained between experimental and modeling trends; the HSDI engine shows increasing soot and decreasing NOx with higher EGR and lower injection pressure. The model also indicates that most of the NOx is formed in the region where the bulk of the initial heat release first takes place, both for zero and high EGR cases. The mechanism of NOx reduction with high EGR is shown to be primarily through a decrease in thermal NOx formation rate.
Technical Paper

Effect of Injection Timing on Detailed Chemical Composition and Particulate Size Distributions of Diesel Exhaust

2003-05-19
2003-01-1794
An experimental study was carried out to investigate the effects of fuel injection timing on detailed chemical composition and size distributions of diesel particulate matter (PM) and regulated gaseous emissions in a modern heavy-duty D.I. diesel engine. These measurements were made for two different diesel fuels: No. 2 diesel (Fuel A) and ultra low sulfur diesel (Fuel B). A single-cylinder 2.3-liter D.I. diesel engine equipped with an electronically controlled unit injection system was used in the experiments. PM measurements were made with an enhanced full-dilution tunnel system at the Engine Research Center (ERC) of the University of Wisconsin-Madison (UW-Madison) [1, 2]. The engine was run under 2 selected modes (25% and 75% loads at 1200 rpm) of the California Air Resources Board (CARB) 8-mode test cycle.
Technical Paper

Effect of Fuel Composition on Combustion and Detailed Chemical/Physical Characteristics of Diesel Exhaust

2003-05-19
2003-01-1899
An experimental study was performed to investigate the effect of fuel composition on combustion, gaseous emissions, and detailed chemical composition and size distributions of diesel particulate matter (PM) in a modern heavy-duty diesel engine with the use of the enhanced full-dilution tunnel system of the Engine Research Center (ERC) of the UW-Madison. Detailed description of this system can be found in our previous reports [1,2]. The experiments were carried out on a single-cylinder 2.3-liter D.I. diesel engine equipped with an electronically controlled unit injection system. The operating conditions of the engine followed the California Air Resources Board (CARB) 8-mode test cycle. The fuels used in the current study include baseline No. 2 diesel (Fuel A: sulfur content = 352 ppm), ultra low sulfur diesel (Fuel B: sulfur content = 14 ppm), and Fisher-Tropsch (F-T) diesel (sulfur content = 0 ppm).
Technical Paper

Zero-Dimensional Soot Modeling

2003-03-03
2003-01-1070
A zero-dimension model of spray development and particulate emissions for direct-injection combustion was developed. The model describes the major characteristics of the injection plume including: spray angle, liquid penetration, lift-off length, and temperatures of regions within the spray. The model also predicts particulate mass output over a span of combustion cycles, as well as a particulate mass-history over a single combustion event. The model was developed by applying established conceptual models for direct injection combustion to numerical relations, to develop a mathematical description of events. The model was developed in a Matlab Simulink environment to promote modularity and ease of use.
Technical Paper

An Experimental Assessment of Turbulence Production, Reynolds Stress and Length Scale (Dissipation) Modeling in a Swirl-Supported DI Diesel Engine

2003-03-03
2003-01-1072
Simultaneous measurements of the radial and the tangential components of velocity are obtained in a high-speed, direct-injection diesel engine typical of automotive applications. Results are presented for engine operation with fuel injection, but without combustion, for three different swirl ratios and four injection pressures. With the mean and fluctuating velocities, the r-θ plane shear stress and the mean flow gradients are obtained. Longitudinal and transverse length scales are also estimated via Taylor's hypothesis. The flow is shown to be sufficiently homogeneous and stationary to obtain meaningful length scale estimates. Concurrently, the flow and injection processes are simulated with KIVA-3V employing a RNG k-ε turbulence model. The measured turbulent kinetic energy k, r-θ plane mean strain rates ( 〈Srθ〉, 〈Srr〉, and 〈Sθθ〉 ), deviatoric turbulent stresses , and the r-θ plane turbulence production terms are compared directly to the simulated results.
Technical Paper

Exploring the Limits of Improving DI Diesel Emissions By Increasing In-Cylinder Mixing

1998-10-19
982677
In the current investigation, the authors identified conditions under which increased in-cylinder turbulence can be used to improve diesel emissions. Two separate regimes of engine operation were identified; one in which combustion was constrained by mixing and one in which it was not. These regimes were dubbed under-mixed and over-mixed, respectively. It was found that increasing mixing in the former regime had a profound effect on soot emission. Fuel injection characteristics were found to be extremely important in determining the point at which mixing became inadequate. In addition, the ratio of the fuel injection momentum flux relative to that of the gas injection was found to be important in determining how increasing mixing would effect soot emissions.
Technical Paper

Characterization of the Mixing of Fresh Charge with Combustion Residuals Using Laser Raman Scattering with Broadband Detection

1998-05-04
981428
Spontaneous Raman scattering with broadband signal collection is used to simultaneously measure the mole fractions of CO2, H2O, N2, O2, and fuel (C3H8) in a spark-ignition engine operating at low load. Both cycle-averaged and single-shot, cycle-resolved measurements of the mixing between residual and fresh charge are made from the beginning of the intake stroke to TDC compression. The measurements are made at twelve locations simultaneously with sub-millimeter spatial precision, which is sufficient to resolve the characteristic scales of inhomogeneity in most cases. Analysis of the spatial covariance functions provides a measure of the noise contribution to the measured mole fractions and, in certain instances, allows the determination of whether the measured composition fluctuations are associated with spatial inhomogeneities or with cyclic variations in overall charge composition.
Technical Paper

Modeling of Soot Formation During DI Diesel Combustion Using a Multi-Step Phenomenological Model

1998-10-19
982463
Predictive models of soot formation during Diesel combustion are of great practical interest, particularly in light of newly proposed strict regulations on particulate emissions. A modified version of the phenomenological model of soot formation developed previously has been implemented in KIVA-II CFD code. The model includes major generic processes involved in soot formation during combustion, i.e., formation of soot precursors, formation of surface growth species, soot particle nucleation, coagulation, surface growth and oxidation. The formulation of the model within the KIVA-II is fully coupled with the mass and energy balances in the system. The model performance has been tested by comparison with the results of optical in-cylinder soot measurements in a single cylinder Cummins NH Diesel engine. The predicted soot volume fraction, number density and particle size agree reasonably well with the experimental data.
Technical Paper

In Cylinder Augmented Mixing Through Controlled Gaseous Jet Injection

1995-10-01
952358
An investigation was performed on a direct injection diesel engine equipped with a gaseous injector to determine the effects of augmented mixing on emission characteristics. The gaseous injector introduced a jet of gas of particular composition in the cylinder during the latter portion of diesel combustion. This injector was controlled to inject the gas at specific engine timings and at various injection pressures. Engine experiments were done on a LABECO/TACOM single cylinder, direct injected, 1.2 liter, four stroke diesel engine. This engine was operated at 1500 rpm at an equivalence ratio of 0.5 with simulated turbocharging. The fuel injection timing was changed for some cases to accommodate the gaseous injection. Exhaust particulate emissions were measured with a mini-dilution tunnel. All other emissions data were measured on a REGA 7000 Real-Time Exhaust Gas Analyzer Fourier Transform Infrared (FT-IR) system.
Technical Paper

In-Cylinder Gas Velocity Measurements Comparing Crankcase and Blower Scavenging in a Fired Two-Stroke Cycle Engine

1994-03-01
940401
The in-cylinder flow field of a Schnürle (loop) scavenged two-stroke engine has been examined under conditions simulating both blower and crankcase driven scavenging. Measurements of the radial component of velocity were obtained along the cylinder centerline during fired operation at delivery ratios of 0.4, 0.6, and 0.8. Both mean velocity profiles and root mean square velocity fluctuations near top center show a strong dependence on the scavenging method. Complementary in-cylinder pressure measurements indicate that combustion performance is better under blower driven scavenging for the engine geometry studied. IN THE PAST TEN YEARS the engine research and development community has demonstrated a renewed interest in two-stroke engine technology. Many manufacturers have new engine designs operating on test stands and in prototype vehicles being road tested.
Technical Paper

Cycle-by-Cycle Variations in Combustion and Mixture Concentration in the Vicinity of Spark Plug Gap

1995-02-01
950814
The correlations between IMEP and pressures at referenced crank angles have different trends for different equivalence ratios. A fiber optic spark plug was used to detect the initial flame development which was then used to analyze the combustion cyclic variation. Rayleigh scattering measurements were applied to detect the air-fuel mixture fluctuations in the vicinity of spark plug gap for both homogeneous and inhomogeneous mixture preparations in a spark ignition engine. The variation in mixture concentration in the vicinity of spark plug gap was not confirmed as a major contributor to cycle-by-cycle variation in combustion for any of the homogeneous mixture cases or for the stoichiometric and lean mixtures of port injection. However, a leaner mixture((ϕ=0.80) of port injection did correlate with the cyclic variation in combustion.
Technical Paper

Quantitative In-Cylinder Fluid Composition Measurements Using Broadband Spontaneous Raman Scattering

1996-02-01
960828
A measurement technique is described which permits quantitative, multi-point, in-cylinder fluid composition measurements in an internal combustion engine. The technique is based on spontaneous Raman scattering with broadband signal collection, and provides simultaneous determination of the mole fractions of H2O, CO2, N2, O2, and fuel (C3H8). Calibration and data reduction procedures which largely eliminate interference between the signals from the various species are discussed. Mean mole fractions obtained in an optical access engine from the beginning of the intake stroke to the end of the compression stroke are reported. The mean mole fractions of the individual species are used to obtain independent estimates of the mean mole fraction of burnt residual gases, which, in turn, are used to evaluate the accuracy and consistency of the data. An over-prediction of the CO2 mole fraction in hot exhaust gases is found to be the most significant shortcoming of the technique.
Technical Paper

Optical Measurements of Soot Particle Size, Number Density, and Temperature in a Direct Injection Diesel Engine as a Function of Speed and Load

1994-03-01
940270
In-cylinder measurements of soot particle size, number density, and temperature have been made using optical measurements in a direct injection diesel engine. The measurements were made at one location approximately 5 mm long and 1.5 mm wide above the bowl near the head. Two optical techniques were used simultaneously involving light scattering, extinction and radiation. An optical probe was designed and mounted in a modified exhaust valve which introduced a beam of light into the cylinder and collected the scattered and radiating light from the soot. The resulting measurements were semi-quantitative, giving an absolute uncertainty on the order of ± 50% which was attributed mainly to the uncertainty of the optical properties of the soot and the heterogeneous nature of the soot cloud. Measurements at three speeds and three overall equivalence ratios were made.
Technical Paper

Modeling the Effect of Engine Speed on the Combustion Process and Emissions in a DI Diesel Engine

1996-10-01
962056
Previous studies have shown that air motion affects the combustion process and therefore also the emissions in a DI diesel engine. Experimental studies indicate that higher engine speeds enhance the turbulence and this improves air and fuel mixing. However, there are few studies that address fundamental combustion related factors and possible limitations associated with very high speed engine operation. In this study, operation over a large range of engine speeds was simulated by using a multi-dimensional computer code to study the effect of speed on emissions, engine power, engine and exhaust temperatures. The results indicate that at higher engine speeds fuel is consumed in a much shorter time period by the enhanced air and fuel mixing. The shorter combustion duration provides much less available time for soot and NOx formations. In addition, the enhanced air/fuel mixing decreases soot and NOx by reducing the extent of the fuel rich regions.
Technical Paper

The Effect of Fuel Aromatic Structure and Content on Direct Injection Diesel Engine Particulates

1992-02-01
920110
A single cylinder, Cummins NH, direct-injection, diesel engine has been operated in order to evaluate the effects of aromatic content and aromatic structure on diesel engine particulates. Results from three fuels are shown. The first fuel, a low sulfur Chevron diesel fuel was used as a base fuel for comparison. The other fuels consisted of the base fuel and 10% by volume of 1-2-3-4 tetrahydronaphthalene (tetralin) a single-ring aromatic and naphthalene, a double-ring aromatic. The fuels were chosen to vary aromatic content and structure while minimizing differences in boiling points and cetane number. Measurements included exhaust particulates using a mini-dilution tunnel, exhaust emissions including THC, CO2, NO/NOx, O2, injection timing, two-color radiation, soluble organic fraction, and cylinder pressure. Particulate measurements were found to be sensitive to temperature and flow conditions in the mini-dilution tunnel and exhaust system.
Technical Paper

Data from a Variable Rate Shape High Pressure Injection System Operating in an Engine Fed Constant Volume Combustion Chamber

1990-10-01
902082
In current systems, for a given nozzle and injection pressure (pump speed), the shape of the injection rate is fixed and the injection timing is the only variable the engine designer can vary. For this non-interactive injection system, changing the injector nozzle (number and diameter of holes) will proportionately change the injection shape. New injection systems in which the rate of injection is a controlled variable are being developed. Results from one such injector, called the UCORS (Universal Combustion Optimization and Rate Shaping), are reported in this paper. The system can dynamically control its injection rate shape by controlling the position and size of a pilot injection relative to the main injection. Data and analysis from an out-of-engine and combustion chamber study of the UCORS injection system are presented.
Technical Paper

Computations of a Two-Stroke Engine Cylinder and Port Scavenging Flows

1991-02-01
910672
A modification of the computational fluid dynamics code KIVA-II is presented that allows computations to be made in complex engine geometries. An example application is given in which three versions of KIVA-II are run simultaneously. Each version considers a separate block of the computational domain, and the blocks exchange boundary condition information with each other at their common interfaces. The use of separate blocks permits the connectedness of the overall computational domain to change with time. The scavenging flow in the cylinder, transfer pipes (ports), and exhaust pipe of a ported two-stroke engine with a moving piston was modeled in this way. Results are presented for three engine designs that differ only in the angle of their boost ports. The calculated flow fields and the resulting fuel distributions are shown to be markedly different with the different geometries.
Technical Paper

A Comparison of the Bosch and Zuech Rate of Injection Meters

1991-02-01
910724
This paper will discuss the fundamentals of the Bosch rate of injection meter which has been the standard measurement tool for the last 25 years and a newly developed tool which uses the Zuech constant volume technique. A fundamental and experimental comparison is presented. Using a high pressure accumulator type injector, each of the injection systems produced almost identical injection rate shapes. The integrated values of these traces (injection quantity) were within a few percent of the physically measured quantities.
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