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This paper describes the transient spray characteristics of a high pressure, single fluid injector, intended for use in a direct-injection spark-ignited (DISI) engine. The injector was a single hole, pintle type injector and was electronically controlled. A variety of measurement diagnostics, including full-field imaging and line-of-sight diffraction based particle sizing were employed for spray characterization. Transient patternator measurements were also performed to obtain temporally resolved average mass flux distributions. Particle size and obscuration measurements were performed at three locations in the spray and at three injection pressures: 3.45 MPa (500 psi), 4.83 Mpa (700 psi), and 6.21 MPa (900 psi). Results of the spray imaging experiments indicated that the spray shapes varied with time after the start of injection and contained a leading mass, or slug along the center line of the spray.

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.

A study was performed that takes into account both turbulence and chemical kinetic effects in the numerical simulation of diesel engine combustion in order to better understand the importance of their respective roles at changing operating conditions. An approach was developed which combines the simplicity and low computational and storage requests of the laminar-and-turbulent characteristic-time model with a detailed combustion chemistry model based on well-known simplified mechanisms. Assuming appropriate simplifications such as steady state or equilibrium for most of the radicals and intermediate species, the kinetics of hydrocarbons can be described by means of three overall steps. This approach was integrated in the KIVA-II code. The concept was validated and applied to a single-cylinder, heavy-duty engine. The simulation covers a wide range of operating conditions.

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.

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.

Combustion simulations utilizing the characteristic time combustion model have been performed for four DI diesel engines ranging in size from heavy-duty to large-bore designs. It has been found that the pre-factor to the turbulent characteristic time acts as a scaling parameter between the engines. This phenomenon is explained in terms of the non-equilibrium behavior of the turbulent time and length scales, as is encountered in the rapidly distorting, spray-induced flows of DI diesel engines. In fact, the equilibrium assumption between turbulence production and dissipation, which forms the basis for the employed k-ε-type turbulence models, does not hold in these situations. For such flows, the real turbulent dissipation time scale is locally proportional to the turbulent characteristic time scale which is determined by a typical eddy turnover time.

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.

A correction for the turbulence dissipation, based on non-equilibrium turbulence considerations from rapid distortion theory, has been derived and implemented in combination with the RNG k - ε model in a KIVA-based code. This model correction has been tested and compared with the standard RNG k - ε model for the compression and the combustion phase of two heavy duty DI diesel engines. The turbulence behavior in the compression phase shows clear improvements over the standard RNG k - ε model computations. In particular, the macro length scale is consistent with the corresponding time scale and with the turbulent kinetic energy over the entire compression phase. The combustion computations have been performed with the characteristic time combustion model. With this dissipation correction no additional adjustments of the turbulent characteristic time model constant were necessary in order to match experimental cylinder pressures and heat release rates of the two engines.

A numerical study of air-fuel mixing in a direct-injection spark-ignition engine was carried out. In this paper, the numerical models are described and grid generation methods to represent a realistic port-valve-chamber geometry is discussed. To model a vaporizing hollow-cone spray resulting from an automotive pressure-swirl injector, a newly developed sheet spray atomization model was used to compute the processes of disintegration of the liquid sheet and breakup of the subsequent drops. Computations were performed of a particular 4-valve pent-roof engine configuration in which the intake process and an early fuel injection scheme were considered. After an analysis of the intake-generated flow structures in this engine configuration, the spray behavior and the spatial and temporal evolution of fuel liquid and vapor phases are characterized.

Multidimensional computations were carried out to simulate the in-cylinder fuel/air mixing process of a direct-injection spark-ignition engine using a modified version of the KIVA-3 code. A hollow cone spray was modeled using a Lagrangian stochastic approach with an empirical initial atomization treatment which is based on experimental data. Improved Spalding-type evaporation and drag models were used to calculate drop vaporization and drop dynamic drag. Spray/wall impingement hydrodynamics was accounted for by using a phenomenological model. Intake flows were computed using a simple approach in which a prescribed velocity profile is specified at the two intake valve openings. This allowed three intake flow patterns, namely, swirl, tumble and non-tumble, to be considered. It was shown that fuel vaporization was completed at the end of compression stroke with early injection timing under the chosen engine operating conditions.

Control of the flow of thermal energy in an air-cooled engine is important to the overall performance of the engine because of potential effects on engine performance, durability, design, and emissions. A methodology is being developed for the assessment of thermal flows in air-cooled engines, which includes the use of cycle simulation and in-cylinder heat flux measurements. The mechanism for the combination of cycle simulation, the measurement of in-cylinder heat flux and wall temperatures, and comparison of predicted and measured heat flux in the methodology is presented. The methodology consists of both simulation and experimental phases. To begin, a one-dimensional gas dynamics code (WAVE) has been used in conjunction with a detailed in-cylinder flow and combustion model (IRIS) in order to simulate engine operation in a variety of operating conditions. The methods used to apply the model to the air-cooled engine case are described in detail.

An experimental investigation of turbulent flow patterns in a scale model of a high pressure diesel fuel injector nozzle has been conducted. Instantaneous velocity measurements were made in a 50X transparent model of one hole of the injector nozzle using an Aerometrics Phase Doppler Particle Analyzer (PDPA) in the velocity mode. 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. Two steady flow average Reynolds numbers (10,500 and 13,300), analogous to fuel injection velocities and sac pressures of approximately 320 and 405 m/s and 67 and 107 MPa (10,000 and 16,000 psi), were investigated. The axial progression of mean and root mean square (rms) axial velocities was obtained for both sharp and rounded inlet conditions and varying L/D. The discharge coefficient was also calculated for each geometry.

The impingement of liquid fuels on surfaces in IC engines affects performance and emissions. To better understand liquid/solid interactions, the impact of single droplets on a healed surface was experimentally examined. The droplet impingement was photographed with a high speed cine camera to obtain a history of the hydrodynamics of the impingement process. Images obtained from the cine photography were inspected to determine hydrodynamic regimes: wetting, transition, and non-wetting, associated with the specific impingement conditions (droplet size, velocity, surface temperature, and ambient pressure). Images from selected impingement conditions were further analyzed to quantify the atomization resulting from the impingement.

The ability to make fully resolved turbulent scalar field measurements has been demonstrated in an internal combustion engine using one-dimensional fluorobenzene fluorescence measurements. Data were acquired during the intake stroke in a motored engine that had been modified such that each intake valve was fed independently, and one of the two intake streams was seeded with the fluorescent tracer. The scalar energy spectra displayed a significant inertial subrange that had a −5/3 wavenumber power dependence. The scalar dissipation spectra were found to extend in the high-wavenumber regime, to where the magnitude was more than two decades below the peak value, which indicates that for all practical purposes the measurements faithfully represent all of the scalar dissipation in the flow.

High-resolution planar laser-induced fluorescence (PLIF) measurements were performed on the scalar field in an optical engine. The measurements were of sufficient resolution to fully resolve all of the length scales of the flow field through the full cycle. The scalar dissipation spectrum was calculated, and by fitting the results to a model turbulent spectrum the Batchelor scale of the turbulent flow was estimated. The scalar inhomogeneity was introduced by a low-momentum gas jet injection. A consistent trend was observed in all data; the Batchelor scale showed a minimum value at top dead center (TDC) and was nearly symmetric about TDC. Increasing the engine speed resulted in a decrease of the Batchelor scale, and the presence of a shroud on the intake valve, which increased the turbulence intensity, also reduced the Batchelor scale. The effect of the shrouded valve was less significant compared to the effect of engine speed.

Transient operation of automobile engines is known to contribute significantly to regulated exhaust emissions, and is also an area of drivability concerns. Furthermore, many on-board diagnostic algorithms do not perform well during transient operation and are often temporarily disabled to avoid problems. The inability to quickly and repeatedly test engines during transient conditions in a laboratory setting limits researchers and development engineers ability to produce more effective and robust algorithms to lower vehicle emissions. To meet this need, members of the Powertrain Control Research Laboratory (PCRL) at the University of Wisconsin-Madison have developed a high-bandwidth, hydrostatic dynamometer system that will enable researchers to explore transient characteristics of engines and powertrains in the laboratory.

Forage harvesting, processing and handling equipment research is currently underway which will improve commodity quality, produce “value -added” products from forages, reduce energy and labor requirements of the equipment and improve forage marketability. Technologies are described which could increase forage quality and value by removing it from the field sooner after it is mowed to minimize the risk of weather damage. Mechanisms and management strategies for reducing the labor and energy required for field processing and for improving the marketability of forages are also described.

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.

Fundamental simulations in a quiescent cell under adiabatic conditions were made to understand the effect of temperature, equivalence ratio and the components of the recirculated exhaust gas, viz., CO2 and H2O, on the combustion of n-Heptane. Simulations were made in single phase in which evaporated n-Heptane was uniformly distributed in the domain. Computations were made for two different temperatures and four different EGR levels. CO2 or H2O or N2was used as EGR. It was found that the initiation of the main combustion process was primarily determined by two competing factors, i.e., the amount of initial OH concentration in the domain and the specific heat of the mixture. Further, initial OH concentration can be controlled by the manipulating the ambient temperature in the domain, and the specific heat capacity of the mixture via the mixture composition. In addition to these, the pre combustion and the subsequent post combustion can also be controlled via the equivalence ratio.

Combustion under stratified operating conditions in a direct-injection spark-ignition engine was investigated using simultaneous planar laser-induced fluorescence imaging of the fuel distribution (via 3-pentanone doped into the fuel) and the combustion products (via OH, which occurs naturally). The simultaneous images allow direct determination of the flame front location under highly stratified conditions where the flame, or product, location is not uniquely identified by the absence of fuel. The 3-pentanone images were quantified, and an edge detection algorithm was developed and applied to the OH data to identify the flame front position. The result was the compilation of local flame-front equivalence ratio probability density functions (PDFs) for engine operating conditions at 600 and 1200 rpm and engine loads varying from equivalence ratios of 0.89 to 0.32 with an unthrottled intake. Homogeneous conditions were used to verify the integrity of the method.