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Journal Article

Use of Low-Pressure Direct-Injection for Reactivity Controlled Compression Ignition (RCCI) Light-Duty Engine Operation

Reactivity-controlled compression ignition (RCCI) has been shown to be capable of providing improved engine efficiencies coupled with the benefit of low emissions via in-cylinder fuel blending. Much of the previous body of work has studied the benefits of RCCI operation using high injection pressures (e.g., 500 bar or greater) with common rail injection (CRI) hardware. However, low-pressure fueling technology is capable of providing significant cost savings. Due to the broad market adoption of gasoline direct injection (GDI) fueling systems, a market-type prototype GDI injector was selected for this study. Single-cylinder light-duty engine experiments were undertaken to examine the performance and emissions characteristics of the RCCI combustion strategy with low-pressure GDI technology and compared against high injection pressure RCCI operation. Gasoline and diesel were used as the low-reactivity and high-reactivity fuels, respectively.
Technical Paper

The Influence of Boost Pressure on Emissions and Fuel Consumption of a Heavy-Duty Single-Cylinder D.I. Diesel Engine

An electronically controlled Caterpillar single-cylinder oil test engine (SCOTE) was used to study diesel combustion. The SCOTE retains the port, combustion chamber, and injection geometry of the production six cylinder, 373 kW (500 hp) 3406E heavy-duty truck engine. The engine was equipped with an electronic unit injector and an electronically controlled common rail injector that is capable of multiple injections. An emissions investigation was carried out using a six-mode cycle simulation of the EPA Federal Transient Test Procedure. The results show that the SCOTE meets current EPA mandated emissions levels, despite the higher internal friction imposed by the single-cylinder configuration. NOx versus particulate trade-off curves were generated over a range of injection timings for each mode and results of heat release calculations were examined, giving insight into combustion phenomena in current “state of the art” heavy-duty diesel engines.
Technical Paper

The Effects of Split Injection and Swirl on a HSDI Diesel Engine Equipped with a Common Rail Injection System

To overcome the trade-off between NOx and particulate emissions for future diesel vehicles and engines it is necessary to seek methods to lower pollutant emissions. The desired simultaneous improvement in fuel efficiency for future DI (Direct Injection) diesels is also a difficult challenge due to the combustion modifications that will be required to meet the exhaust emission mandates. This study demonstrates the emission reduction capability of split injections, EGR (Exhaust Gas Recirculation), and other parameters on a High Speed Direct Injection (HSDI) diesel engine equipped with a common rail injection system using an RSM (Response Surface Method) optimization method. The optimizations were conducted at 1757 rev/min, 45% load. Six factors were considered for the optimization, namely the EGR rate, SOI (Start of Injection), intake boost pressure, and injection pressure, the percentage of fuel in the first injection, and the dwell between injections.
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

The Effects of Mixture Stratification on Combustion in a Constant-Volume Combustion Vessel

The role of mixture stratification on combustion rate has been investigated in a constant volume combustion vessel in which mixtures of different equivalence ratios can be added in a spatially and temporally controlled fashion. The experiments were performed in a regime of low fluid motion to avoid the complicating effects of turbulence generated by the injection of different masses of fluid. Different mixture combinations were investigated while maintaining a constant overall equivalence ratio and initial pressure. The results indicate that the highest combustion rate for an overall lean mixture is obtained when all of the fuel is contained in a stoichiometric mixture in the vicinity of the ignition source. This is the result of the high burning velocity of these mixtures, and the complete oxidation which releases the full chemical energy.
Technical Paper

The Effect of Swirl Ratio and Fuel Injection Parameters on CO Emission and Fuel Conversion Efficiency for High-Dilution, Low-Temperature Combustion in an Automotive Diesel Engine

Engine-out CO emission and fuel conversion efficiency were measured in a highly-dilute, low-temperature diesel combustion regime over a swirl ratio range of 1.44-7.12 and a wide range of injection timing. At fixed injection timing, an optimal swirl ratio for minimum CO emission and fuel consumption was found. At fixed swirl ratio, CO emission and fuel consumption generally decreased as injection timing was advanced. Moreover, a sudden decrease in CO emission was observed at early injection timings. Multi-dimensional numerical simulations, pressure-based measurements of ignition delay and apparent heat release, estimates of peak flame temperature, imaging of natural combustion luminosity and spray/wall interactions, and Laser Doppler Velocimeter (LDV) measurements of in-cylinder turbulence levels are employed to clarify the sources of the observed behavior.
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

The Development of the University of Wisconsin's Parallel Hybrid-Electric Aluminum Intensive Vehicle

For competition in the 1998 FutureCar Challenge (FCC98), the University of Wisconsin - Madison FutureCar Team has designed and built a lightweight, charge sustaining, parallel hybrid electric vehicle by modifying a 1994 Mercury Sable Aluminum Intensive Vehicle (AIV), nicknamed the Aluminum Cow. The Wisconsin team is striving for a combined, FTP cycle gasoline-equivalent fuel economy of 21.3 km/L (50 mpg) and Ultra Low Emissions Vehicle (ULEV) federal emissions levels while maintaining the full passenger/cargo room, appearance, and feel of a full-size car. To reach these goals, Wisconsin has concentrated on reducing the overall vehicle weight. In addition to customizing the drivetrain, the team has developed a vehicle control strategy that both aims to achieve these goals and also allows for the completion of a reliable hybrid in a short period of time.
Technical Paper

Temperature Effects on Fuel Sprays from a Multi-Hole Nozzle Injector

A study of fuel spray characteristics for diesel fuel from a multi-hole nozzle injector was performed yielding tip penetration length and spray cone angle for each of the spray plumes from a six hole injector. The main feature of the system used was that analysis of all the fuel plumes could occur at one time, as all the plumes were imaged on the same piece of film. Spray behavior was examined for two injection pressures (72 MPa and 122 MPa) and for ambient temperatures up to 523 K (250°C). The results in this paper show how the spray plumes behave as they leave each of the six holes of the injector. The characteristics of each hole differs during injection. The variations of spray cone angle and tip penetration length between holes are small, but significant. These variations in tip penetration and cone angle changed as the temperature of the chamber changed, but the overall characteristics of the spray plumes changed only slightly for the temperatures used in this paper.
Technical Paper

Spectral Characteristics of Turbulent Flow in a Scale Model of a Diesel Fuel Injector Nozzle

An experimental investigation of the spectral characteristics of turbulent flow in a scale model of a high pressure diesel fuel injector nozzle hole has been conducted. Instantaneous velocity measurements were made in a 50X transparent model of one hole of an injector nozzle using an Aerometrics Phase/Doppler Particle Analyzer (PDPA) in the velocity mode. Turbulence spectra were calculated from the velocity data using the Lomb-Scargle method. Injector hole length to diameter ratio (L/D) values of 1.3, 2.4, 4.9, and 7.7 and inlet radius to diameter ratio (R/D) values of approximately 0 and 0.3 were investigated. Results were obtained for a steady flow average Reynolds number of 10,500, which is analogous to a fuel injection velocity of 320 m/s and a sac pressure of approximately 67 MPa (10,000 psi). Turbulence time frequency spectra were obtained for significant locations in each geometry, in order to determine how geometry affects the development of the turbulent spectra.
Technical Paper

Simplified Engine Combustion Diagnostics Using “Synthetic” Variables

This paper presents a diagnostics methodology that has applications to internal combustion engines as well as other dynamic devices. Included is an overview of the theoretical foundation of the approach, discussions on its application to internal combustion engine diagnostics, and experimental engine data showing the application of this methodology. Also included are the recent developments addressing issues of the effect of motoring compression and expansion work on crankshaft speed fluctuations and the resulting torque estimation. The methodology consists of a hard-wired nonlinear to linear transformation of engine variables that allow all subsequent diagnostics and control calculations to use linear mathematics, which significantly simplifies the size and complexity of the engine control and diagnostics strategy and code.
Technical Paper

Regenerative Testing of Hydraulic Pump/Motor Systems

Regenerative testing methods can be used to allow the testing of hydraulic pumps and motors at significantly higher power and flow levels than that of the power supply used. This method can also increase the accuracy of system efficiency measurements. The increase in accuracy is realized because only the power added to compensate for the system losses needs to be measured with great accuracy. Typically, for the operation points of interest this will be a much smaller quantity than the overall power of the system. Knowing that the error in flow measurements is a function of the quantity measured, the benefit of measuring the losses becomes clear. An additional, distinct advantage of regenerative testing is that no dynamometer or load is needed. This results in a much simpler test setup. This paper documents the development of such a test program at the University of Wisconsin-Madison.
Technical Paper

Reducing Particulate and NOx Emissions by Using Multiple Injections in a Heavy Duty D.I. Diesel Engine

An experimental study has been completed which evaluated the effectiveness of using double, triple and rate shaped injections to simultaneously reduce particulate and NOx emissions. The experiments were done using a single cylinder version of a Caterpillar 3406 heavy duty D.I. diesel engine. The fuel system used was a common rail, electronically controlled injector that allowed flexibility in both the number and duration of injections per cycle. Injection timing was varied for each injection scheme to evaluate the particulate vs. NOx tradeoff and fuel consumption. Tests were done at 1600 rpm using engine load conditions of 25% and 75% of maximum torque. The results indicate that a double injection with a significantly long delay between injections reduced particulate by as much as a factor of three over a single injection at 75% load with no increase in NOx. Double injections with a smaller dwell gave less improvement in particulate and NOx at 75% load.
Technical Paper

Progress in Diesel Engine Intake Flow and Combustion Modeling

The three-dimensional computer code, KIVA, is being modified to include state-of-the-art submodels for diesel engine flow and combustion. Improved and/or new submodels which have already been implemented are: wall heat transfer with unsteadiness and compressibility, laminar-turbulent characteristic time combustion with unburned HC and Zeldo'vich NOx, and spray/wall impingement with rebounding and sliding drops. Progress on the implementation of improved spray drop drag and drop breakup models, the formulation and testing of a multistep kinetics ignition model and preliminary soot modeling results are described. In addition, the use of a block structured version of KIVA to model the intake flow process is described. A grid generation scheme has been developed for modeling realistic (complex) engine geometries, and initial computations have been made of intake flow in the manifold and combustion chamber of a two-intake-valve engine.
Journal Article

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

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.
Technical Paper

PIV Measurements of In-Cylinder Flow in a Four-Stroke Utility Engine and Correlation with Steady Flow Results

Large-scale flows in internal combustion engines directly affect combustion duration and emissions production. These benefits are significant given increasingly stringent emissions and fuel economy requirements. Recent efforts by engine manufacturers to improve in-cylinder flows have focused on the design of specially shaped intake ports. Utility engine manufacturers are limited to simple intake port geometries to reduce the complexity of casting and cost of manufacturing. These constraints create unique flow physics in the engine cylinder in comparison to automotive engines. An experimental study of intake-generated flows was conducted in a four-stroke spark-ignition utility engine. Steady flow and in-cylinder flow measurements were made using three simple intake port geometries at three port orientations. Steady flow measurements were performed to characterize the swirl and tumble-generating capability of the intake ports.
Technical Paper

Optimizing the University of Wisconsin's Parallel Hybrid-Electric Aluminum Intensive Vehicle

The University of Wisconsin - Madison FutureCar Team has designed and built a lightweight, charge sustaining, parallel hybrid-electric vehicle for entry into the 1999 FutureCar Challenge. The base vehicle is a 1994 Mercury Sable Aluminum Intensive Vehicle (AIV), nicknamed the “Aluminum Cow,” weighing 1275 kg. The vehicle utilizes a high efficiency, Ford 1.8 liter, turbo-charged, direct-injection compression ignition engine. The goal is to achieve a combined FTP cycle fuel economy of 23.9 km/L (56 mpg) with California ULEV emissions levels while maintaining the full passenger/cargo room, appearance, and feel of a full-size car. Strategies to reduce the overall vehicle weight are discussed in detail. Dynamometer and experimental testing is used to verify performance gains.
Technical Paper

Optimization of an Asynchronous Fuel Injection System in Diesel Engines by Means of a Micro-Genetic Algorithm and an Adaptive Gradient Method

Optimal fuel injection strategies are obtained with a micro-genetic algorithm and an adaptive gradient method for a nonroad, medium-speed DI diesel engine equipped with a multi-orifice, asynchronous fuel injection system. The gradient optimization utilizes a fast-converging backtracking algorithm and an adaptive cost function which is based on the penalty method, where the penalty coefficient is increased after every line search. The micro-genetic algorithm uses parameter combinations of the best two individuals in each generation until a local convergence is achieved, and then generates a random population to continue the global search. The optimizations have been performed for a two pulse fuel injection strategy where the optimization parameters are the injection timings and the nozzle orifice diameters.
Technical Paper

Optimization of a Large Diesel Engine via Spin Spray Combustion*

A numerical simulation and optimization study was conducted for a medium speed direct injection diesel engine. The engine's operating characteristics were first matched to available experimental data to test the validity of the numerical model. The KIVA-3V ERC CFD code was then modified to allow independent spray events from two rows of nozzle holes. The angular alignment, nozzle hole size, and injection pressure of each set of nozzle holes were optimized using a micro-genetic algorithm. The design fitness criteria were based on a multi-variable merit function with inputs of emissions of soot, NOx, unburned hydrocarbons, and fuel consumption targets. Penalties to the merit function value were used to limit the maximum in-cylinder pressure and the burned gas temperature at exhaust valve opening. The optimization produced a 28.4% decrease in NOx and a 40% decrease in soot from the baseline case, while giving a 3.1% improvement in fuel economy.
Technical Paper

Optimization of Heavy-Duty Diesel Engine Operating Parameters Using A Response Surface Method

A study of statistical optimization of engine operating parameters was conducted. The objective of the study was to develop a strategy to efficiently optimize operating parameters of diesel engines with multiple injection and EGR capabilities. Previous studies have indicated that multiple injections with EGR can provide substantial simultaneous reductions in emissions of particulate and NOx from heavy-duty diesel engines, but careful optimization of the operating parameters is necessary in order to receive the full benefit of these combustion control techniques. The goal of the present study was to optimize the control parameters to reduce emissions and brake specific fuel consumption. An instrumented single-cylinder heavy-duty diesel engine was used with a prototype mechanically actuated (cam driven) fuel injection system.