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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

Velocity Measurements in the Wall Boundary Layer of a Spark-Ignited Research Engine

1987-11-01
872105
Laser Doppler velocimetry has been used to measure velocity and turbulence intensity profiles in the wall boundary layer of a spark-ignited homogeneous-charge research engine. By using a toroidal contoured engine head it was possible to bring the laser probe volume to within 60 μm of the wall. Two different levels of engine swirl were used to vary the flow Reynolds number. For the high swirl case under motored operation the boundary layer thickness was less than 200 μm, and the turbulence intensity increased as the wall was approached. With low swirl the 700-1000 μm thick boundary layer had a velocity profile that was nearly laminar in shape, and there was no increase in turbulence intensity near the wall. When the engine was fired the boundary layer thickness increased for both levels of swirl.
Technical Paper

Thermodynamic Benefits of Opposed-Piston Two-Stroke Engines

2011-09-13
2011-01-2216
A detailed thermodynamic analysis was performed to demonstrate the fundamental efficiency advantage of an opposed-piston two-stroke engine over a standard four-stroke engine. Three engine configurations were considered: a baseline six-cylinder four-stroke engine, a hypothetical three-cylinder opposed-piston four-stroke engine, and a three-cylinder opposed-piston two-stroke engine. The bore and stroke per piston were held constant for all engine configurations to minimize any potential differences in friction. The closed-cycle performance of the engine configurations were compared using a custom analysis tool that allowed the sources of thermal efficiency differences to be identified and quantified.
Technical Paper

The Prediction of Auto Ignition in a Spark-Ignited Engine

1984-10-01
841337
A constant volume combustion simulation has been used to compute the ignition delays of pure fuels and binary fuel mixtures in air. Minima in the ignition delays were predicted by a comprehensive chemical kinetic mechanism for binary fuel mixtures with methane. A model has been developed to predict the occurrence of autoignition in a spark ignited engine. Experimental pressure data from a CFR engine were used in the model to simulate the temperature-pressure history of the end gas and to determine the time when autoignition occurred. Comprehensive chemical kinetic mechanisms were used to predict the reactions in the end gas. Methanol, methane, ethane, ethylene, propane and n-butane were used as fuels. The initial temperatures in the model were adjusted to give agreement between predicted and observed autoignition. Engine data for methane-ethane mixtures indicated a problem with the kinetic mechanism.
Technical Paper

The Effects of Oxygenate and Gasoline-Diesel Fuel Blends on Diesel Engine Emissions

2000-03-06
2000-01-1173
A study was performed in which the effects on the regulated emissions from a commercial small DI diesel engine were measured for different refinery-derived fuel blends. Seven different fuel blends were tested, of which two were deemed to merit more detailed evaluation. To investigate the effects of fuel properties on the combustion processes with these fuel blends, two-color pyrometry was used via optically accessible cylinderheads. Additional data were obtained with one of the fuel blends with a heavy-duty DI diesel engine. California diesel fuel was used as a baseline. The fuel blends were made by mixing the components typically found in gasoline, such as methyl tertiary-butyl ether (MTBE) and whole fluid catalytic cracking gasoline (WH-FCC). The mixing was performed on a volume basis. Cetane improver (CI) was added to maintain the same cetane number (CN) of the fuel blends as that of the baseline fuel.
Technical Paper

The Effects of Intake Charge Preheating in a Gasoline-Fueled HCCI Engine

2005-10-24
2005-01-3742
Experiments were performed on a homogeneously fueled compression ignition gasoline-type engine with a high degree of intake charge preheating. It was observed that fuels that contained lower end and/or non-branched hydrocarbons (gasoline and an 87 octane primary reference fuel (PRF) blend) exhibited sensitivity to thermal conditions in the surge tanks upstream of the intake valves. The window of intake charge temperatures, measured near the intake valve, that provided acceptable combustion was shifted to lower values when the upstream surge tank gas temperatures were elevated. The same behavior, however, was not observed while using isooctane as a fuel. Gas chromatograph mass spectrometer analysis of the intake charge revealed that oxygenated species were present with PRF 87, and the abundance of the oxygenated species appeared to increase with increasing surge tank gas temperatures. No significant oxygenated species were detected when running with isooctane.
Technical Paper

The Effect of Split Injection on Soot and NOx Production in an Engine-Fed Combustion Chamber

1993-10-01
932655
This research focused on the effects of split injection on combustion in a diesel environment. It was done in a specially designed engine-fed combustion chamber (swirl ratio of 5) with full field optical access through a quartz window. The simulated engine combustion chamber used a special backwards spraying injector (105°). The electronically controlled injector could control the size and position of it's, two injections. Both injections were through the same nozzle and it produced very rapid injections (1.5 ms) with a maximum injection pressure of 130 MPa. Experimental data included: rate of injection, injector pressure, combustion chamber dumping (NO & NOx concentrations), flame temperature, KL factor (soot concentration) combustion pressure, and rate of pressure rise. Injection rates indicate that the UCORS injection system creates very rapid injections with the ability to produce controllable split injections.
Technical Paper

The Effect of Split Injection on Fuel Distribution in an Engine-Fed Combustion Chamber

1993-03-01
930864
This research focused on the effects of split injection on fuel spray behavior in a diesel environment. It was done in a special designed engine-fed combustion chamber (swirl ratio of 5) with full field optical access through a quartz window. The simulated engine combustion chamber used a special backwards spraying injector (105°). The electronically controlled injector could control the size and position of it's two injections. Both injections were through the same nozzle and it produced very rapid injections (1.5 ms) with a maximum injection pressure of 130 MPa. Experimental data included: rate of injection, injector pressure, spray plume images, tip penetration, liquid and vapor fuel distributions, combustion pressure, and rate of pressure rise. From 105° forward scatter images, tip penetration was observed to be very rapid and reached a plateau at 25 mm.
Technical Paper

The Effect of Mixing Intensity and Degree of Premix on Soot Formation in a Backmixed Combustor

1983-09-12
831295
To date there is no universal agreement as to the interaction between fuel type, fuel-air mixture preparation and combustion chamber flow characteristics and their effect on soot formation. A propane fueled modified conical back-mixed steady flow reactor was built in which the fuel and air could be mixed together in varying degrees and reacted in at different mixing intensities. The onset of soot and soot loading were determined qualitatively by a photomultiplier focused on the volume inside the reactor. Increasing the degree of premix from a diffusion flame to a distribution of Φmax/Φavg = 5.0 resulted in increases of 3 to 17 percent of the soot-onset equivalence ratio and decreases in soot loading down to zero. Changes in the mixing intensity from 32.5 sec−1 to 75.7 sec−1 resulted in a change in the soot-onset equivalence ratio from 1.26 to 1.52. Soot loading was found to depend on both the mixing intensity, β, and the average number of mixes per mean residence time, β/α.
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
ABSTRUCT 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.
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

Study on Characteristics of Gasoline Fueled HCCI Using Negative Valve Overlap

2006-11-13
2006-32-0047
Gasoline fueled Homogeneous Charge Compression Ignition (HCCI) combustion with internal exhaust gas re-circulation using Negative Valve Overlap (NOL) was investigated by means of calculation and experiment in order to apply this technology to practical use with sufficient operating range and with acceptable emission and fuel consumption. In this paper we discuss the basic characteristics of NOL-HCCI with emphasis on the influence of intake valve timing on load range, residual gas fraction and induction air flow rate. Emission and fuel consumption under various operation conditions are also discussed. A water-cooled 250cc single cylinder engine with a direct injection system was used for this study. Three sets of valve timing were selected to investigate the effect of intake valve opening duration. Experimental results demonstrated that an engine speed of approximately 2000rpm yields an NMEP (Net Mean Effective Pressure) range from 200kPa to 400kPa.
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

Sources of UHC Emissions from a Light-Duty Diesel Engine Operating in a Partially Premixed Combustion Regime

2009-04-20
2009-01-1446
Sources of unburned hydrocarbon (UHC) emissions are examined for a highly dilute (10% oxygen concentration), moderately boosted (1.5 bar), low load (3.0 bar IMEP) operating condition in a single-cylinder, light-duty, optically accessible diesel engine undergoing partially-premixed low-temperature combustion (LTC). The evolution of the in-cylinder spatial distribution of UHC is observed throughout the combustion event through measurement of liquid fuel distributions via elastic light scattering, vapor and liquid fuel distributions via laser-induced fluorescence, and velocity fields via particle image velocimetry (PIV). The measurements are complemented by and contrasted with the predictions of multi-dimensional simulations employing a realistic, though reduced, chemical mechanism to describe the combustion process.
Technical Paper

Sources and Tradeoffs for Transient NO and UHC Emissions with Low Temperature Diesel Combustion

2011-04-12
2011-01-1356
High bandwidth transient data from a multi-cylinder diesel engine operating in a low temperature combustion regime was analyzed to identify and characterize the transient response behaviors primarily responsible for transient emissions of NO and UHC. Numerous different speed and load transients as well as different combustion modes and control strategies were studied to determine how these parameters affect transient performance. Limitations in the transient response of the air system were found to be the largest contributor to transient emissions, although the mechanism by which these limitations affect performance can vary greatly depending on conditions. Analysis of the data shows that transient emissions for low temperature combustion strategies are highly dependent on cycle-to-cycle changes in intake charge conditions. No fundamental difference was observed between the transient processes controlling speed and load changes.
Technical Paper

Soot Structure in a Conventional Non-Premixed Diesel Flame

2006-04-03
2006-01-0196
An analysis of the soot formation and oxidation process in a conventional direct-injection (DI) diesel flame was conducted using numerical simulations. An improved multi-step phenomenological soot model that includes particle inception, particle coagulation, surface growth and oxidation was used to describe the soot formation and oxidation process. The soot model has been implemented into the KIVA-3V code. Other model Improvements include a piston-ring crevice model, a KH/RT spray breakup model, a droplet wall impingement model, a wall-temperature heat transfer model, and the RNG k-ε turbulence model. The Shell model was used to simulate the ignition process, and a laminar-and-turbulent characteristic time combustion model was used for the post-ignition combustion process. Experimental data from a heavy-duty, Cummins N14, research DI diesel engine operated with conventional injection under low-load conditions were selected as a benchmark.
Technical Paper

Sensitivity Analysis of a Diesel Exhaust System Thermal Model

2004-03-08
2004-01-1131
A modeling study has been conducted in order to characterize the heat transfer in an automotive diesel exhaust system. The exhaust system model, focusing on 2 exhaust pipes, has been created using a transient 1-D engine flow network simulation program. Model results are in excellent agreement with experimental data gathered before commencement of the modeling study. Predicted pipe exit stream temperatures are generally within one percent of experimental values. Sensitivity analysis of the model was the major focus of this study. Four separate variables were chosen for the sensitivity analysis. These being the external convective heat transfer coefficient, external emissivity, mass flow rate of exhaust gases, and amplitude of incoming pressure fluctuations. These variables were independently studied to determine their contribution to changes in exhaust gas stream temperature and system heat flux. There are two primary benefits obtained from conducting this analysis.
Technical Paper

Predictions of Autoignition in a Spark-Ignition Engine Using Chemical Kinetics

1986-03-01
860322
A model developed to predict outoignition is used with data from a premixed charge, spark-ignition engine. A detailed chemical kinetics mechanism is used to predict the reactions which occur in the end-gas and lead to autoignition. Experimental pressure data from a CFR engine are used in the model to determine end-gas temperatures. The initial temperature at the time of spark must be increased above the bulk temperature for the predicted time of outoignition to agree with the observed time. A method for estimating the initial temperature based on an adiabotic compression from the time of intake valve closing is presented. The predictions of the model are examined over a range of engine speeds and fuel-air equivalence ratios. The magnitude by which the initial temperature must be increased above the bulk temperature decreases with increasing engine speed. This magnitude follows a trend which can be related to a heat transfer correlation.
Journal Article

Pathline Analysis of Full-cycle Four-stroke HCCI Engine Combustion Using CFD and Multi-Zone Modeling

2008-04-14
2008-01-0048
This paper investigates flow and combustion in a full-cycle simulation of a four-stroke, three-valve HCCI engine by visualizing the flow with pathlines. Pathlines trace massless particles in a transient flow field. In addition to visualization, pathlines are used here to trace the history, or evolution, of flow fields and species. In this study evolution is followed from the intake port through combustion. Pathline analysis follows packets of intake charge in time and space from induction through combustion. The local scalar fields traversed by the individual packets in terms of velocity magnitude, turbulence, species concentration and temperatures are extracted from the simulation results. The results show how the intake event establishes local chemical and thermal environments in-cylinder and how the species respond (chemically react) to the local field.
Journal Article

Particulate Matter Sampling and Volatile Organic Compound Removal for Characterization of Spark Ignited Direct Injection Engine Emissions

2011-08-30
2011-01-2100
More stringent emissions regulations are continually being proposed to mitigate adverse human health and environmental impacts of internal combustion engines. With that in mind, it has been proposed that vehicular particulate matter (PM) emissions should be regulated based on particle number in addition to particle mass. One aspect of this project is to study different sample handling methods for number-based aerosol measurements, specifically, two different methods for removing volatile organic compounds (VOCs). One method is a thermodenuder (TD) and the other is an evaporative chamber/diluter (EvCh). These sample-handling methods have been implemented in an engine test cell with a spark-ignited direct injection (SIDI) engine. The engine was designed for stoichiometric, homogeneous combustion.
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