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Technical Paper

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

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

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

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

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

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

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

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

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

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

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

Emission Tests of Diesel Fuel with NOx Reduction Additives

In this paper results are given from single-cylinder, steady-state engine tests using the Texaco Diesel Additive (TDA) as an in-fuel emission reducing agent. The data include NOx, total unburned hydrocarbons, indicated specific fuel consumption, and heat release analysis for one engine speed (1500 RPM) with two different loads (Φ ≈ 0.3, IMEP = 0.654 MPa and Φ ≈ 0.5, IMEP = 1.006 MPa) using the baseline fuel and fuels with one percent and five percent additive by weight. The emissions were measured in the exhaust stream of a modified TACOM-LABECO single cylinder engine. This engine is a 114 mm x 114 mm (4.5″ x 4.5″) open chamber low swirl design with a 110.5 MPa (16,000 psi) peak pressure Bosch injector. The injector has 8 holes, each of 0.2 mm diameter. The intake air was slightly boosted (approximately 171 kPa (25 psia)) and slightly heated (333 K (140 °F)). In previous research on this engine the emissions, including soot, were well documented.
Technical Paper

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

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

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

Comparison of Unburned Fuel and Aldehyde Emissions from a Methanol-Fueled Stratified Charge and Homogeneous Charge Engine

This paper presents the results of an experimental program in which a Texaco L-163S engine was fueled with methanol and operated in its traditional stratified charge mode and then modified to run as a homogeneous charge spark ignited engine. The primary data taken were the aldehyde and unburned fuel emissions (UBF). These data were taken using a continuous time-averaging sampling probe at the exhaust tank and at the exhaust port and with a rotary time-resolving sampling valve located at the exhaust port. The data are for two loads, 138.1 kPa (20 psi) and 207.1 kPa (30 psi) BMEP and three speeds, 1000, 1400 and 1800 rpm. The data indicate that for both the stratified charge and the homogeneous charge modes of operation formaldehyde was the only aldehyde detected in the exhaust and it primarily originated in the cylinder.
Technical Paper

Effects of Oxygen Enhancement on the Emissions from a DI Diesel via Manipulation of Fuels and Combustion Chamber Gas Composition

Oxygen enhancement in a direct injection (DI) diesel engine was studied to investigate the potential for particulate matter and NOx emissions control. The local oxygen concentration within the fuel plume was modified by oxygen enrichment of the intake air and by oxygenating the base fuel with 20% methyl t-butyl ether (MTBE). The study collected overall engine performance and engine-out emissions data as well as in-cylinder two-color measurements at 25% and 75% loads over a range of injection timings. The study found oxygen enhancement, whether it be from intake air enrichment or via oxygenated fuels, reduces particulate matter, the effectiveness depending on the local concentration of oxygen in the fuel plume. Since NOx emissions depend strongly on the temperature and oxygen concentration throughout the bulk cylinder gas, the global thermal and dilution effects from oxygen enrichment were greater than that from operation on oxygenated fuel.
Technical Paper

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

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

Detailed Diesel Exhaust Particulate Characterization and DPF Regeneration Behavior Measurements for Two Different Regeneration Systems

Three distinct types of diesel particulate matter (PM) are generated in selected engine operating conditions of a single-cylinder heavy-duty diesel engine. The three types of PM are trapped using typical Cordierite diesel particulate filters (DPF) with different washcoat formulations and a commercial Silicon-Carbide DPF. Two systems, an external electric furnace and an in-situ burner, were used for regeneration. Furnace regeneration experiments allow the collected PM to be classified into two categories depending on oxidation mechanism: PM that is affected by the catalyst and PM that is oxidized by a purely thermal mechanism. The two PM categories prove to contribute differently to pressure drop and transient filtration efficiency during in-situ regeneration.
Technical Paper

Detailed Diesel Exhaust Particulate Characterization and Real-Time DPF Filtration Efficiency Measurements During PM Filling Process

An experimental study was performed to investigate diesel particulate filter (DPF) performance during filtration with the use of real-time measurement equipment. Three operating conditions of a single-cylinder 2.3-liter D.I. heavy-duty diesel engine were selected to generate distinct types of diesel particulate matter (PM) in terms of chemical composition, concentration, and size distribution. Four substrates, with a range of geometric and physical parameters, were studied to observe the effect on filtration characteristics. Real-time filtration performance indicators such as pressure drop and filtration efficiency were investigated using real-time PM size distribution and a mass analyzer. Types of filtration efficiency included: mass-based, number-based, and fractional (based on particle diameter). In addition, time integrated measurements were taken with a Rupprecht & Patashnick Tapered Element Oscillating Microbalance (TEOM), Teflon and quartz filters.
Technical Paper

Modeling Iso-octane HCCI Using CFD with Multi-Zone Detailed Chemistry; Comparison to Detailed Speciation Data Over a Range of Lean Equivalence Ratios

Multi-zone CFD simulations with detailed kinetics were used to model iso-octane HCCI experiments performed on a single-cylinder research engine. The modeling goals were to validate the method (multi-zone combustion modeling) and the reaction mechanism (LLNL 857 species iso-octane) by comparing model results to detailed exhaust speciation data, which was obtained with gas chromatography. The model is compared to experiments run at 1200 RPM and 1.35 bar boost pressure over an equivalence ratio range from 0.08 to 0.28. Fuel was introduced far upstream to ensure fuel and air homogeneity prior to entering the 13.8:1 compression ratio, shallow-bowl combustion chamber of this 4-stroke engine. The CFD grid incorporated a very detailed representation of the crevices, including the top-land ring crevice and head-gasket crevice. The ring crevice is resolved all the way into the ring pocket volume. The detailed grid was required to capture regions where emission species are formed and retained.
Technical Paper

A Numerical Study to Control Combustion Duration of Hydrogen-Fueled HCCI by Using Multi-Zone Chemical Kinetics Simulation

An engine cycle simulation code with detailed chemical kinetics has been developed to study Homogeneous Charge Compression Ignition (HCCI) combustion with hydrogen as the fuel. In order to attain adequate combustion duration, resulting from the self-accelerating nature of the chemical reaction, fuel and temperature inhomogeneities have been brought to the calculation by considering the combustion chamber to have various temperature and fuel distributions. Calculations have been done under various conditions including both perfectly homogeneous and inhomogeneous cases, changing the degree of inhomogeneity. The results show that intake gas temperature is more dominant on ignition timing of HCCI than equivalence ratio and that there is a possibility to control HCCI by introducing appropriate temperature inhomogeneity to in-cylinder mixture.
Technical Paper

Investigation of MicroFlow Machining Effects on Diesel Injector Spray Characteristics

An investigation of the effect of microflow machining on the spray characteristics of diesel injectors was undertaken. A collection of four VCO injector tips were tested prior to and after an abrasive flow process using a high viscosity media. The injector nozzles were tested on a spray fixture. Rate of injection measurements and high-speed digital images were used for the quantification of the air entrainment rate. Comparisons of the spray characteristics and A/F ratios were made for conditions of before and after the abrasive flow process. Results showed a significant decrease in the injection-to-injection variability and improvement of the spray symmetry. A link between the quantity of air entrained and potential differences in spray plume internal chemical composition and temperature is proposed via equilibrium calculations.
Technical Paper

A New Approach to System Level Soot Modeling

A procedure has been developed to build system level predictive models that incorporate physical laws as well as information derived from experimental data. In particular a soot model was developed, trained and tested using experimental data. It was seen that the model could fit available experimental data given sufficient training time. Future accuracy on data points not encountered during training was estimated and seen to be good. The approach relies on the physical phenomena predicted by an existing system level phenomenological soot model coupled with ‘weights’ which use experimental data to adjust the predicted physical sub-model parameters to fit the data. This approach has developed from attempts at incorporating physical phenomena into neural networks for predicting emissions. Model training uses neural network training concepts.
Technical Paper

Determination of Diesel Injector Nozzle Characteristics Using Two-Color Optical Pyrometry

An investigation of several diesel injector nozzles that produced different engine emissions performance was performed. The nozzle styles used were two VCO type nozzles that were manufactured using two different techniques, and two mini-sac nozzles that provided comparison. Fired experiments were conducted on a Detroit Diesel Series 50 engine. Optical access was obtained by substituting a sapphire window for one exhaust valve. Under high speed, high load, retarded injection timing conditions, it was discovered that each nozzle produced different specific soot and NOx emissions. High-speed film images were obtained. It was discovered that the temperature and KL factor results from the 2-color optical pyrometry showed significant differences between the nozzles. The authors propose the possibility that differences in air entrainment, caused by potential differences in CD due to surface finish, may contribute to the variance in emissions performance.