Daimler Truck (United States)

Presentation d'une methode numerique par volume fini pour la resolution des equations de Navier-Stokes bidimensionnelles, incompressibles, et stationnaires, en coordonnees generales curvilignes. Application de la methode aux ecoulements turbulents sur des profils avec et sans separation au bord de sortie posterieur. Comparaison des calculs avec des donnees experimentales

Stability characteristics of a single-phase free convection loop are presented. In the experiments, water was placed inside a toroidal glass loop oriented in a vertical plane. The lower half of the loop was heated and the upper half was cooled. At low heat-transfer rates and also a t high heat-transfer rates the free convection flow was observed to be steady. For the intermediate range, however, the flow was found to be highly oscillatory. Stability predictions are also developed. The comparison between theory and experiment yields favourable agreement. Observations of unstable behaviour have been reported previously for single-phase fluids in the vicinity of the thermodynamic critical point. In these situations it has been assumed that the unusual behaviour of the fluid properties in the near-critical region necessarily constitutes the underlying cause of such instabilities. In contrast t o this view, analyses by Keller (1966) and Welander (1967) indicate that instabilities can occur for ordinary fluids as well. Results of the present study confirm this contention, since instabilities were clearly observed for water at atmospheric pressure and moderate temperatures.

Three airfoil data sets were selected for use in evaluating currently available analytical models for predicting airfoil surface heat transfer distributions in a 2-D flow field. Two additional airfoils, representative of highly loaded, low solidity airfoils currently being designed, were selected for cascade testing at simulated engine conditions. Some 2-D analytical methods were examined and a version of the STAN5 boundary layer code was chosen for modification. The final form of the method utilized a time dependent, transonic inviscid cascade code coupled to a modified version of the STAN5 boundary layer code featuring zero order turbulence modeling. The boundary layer code is structured to accommodate a full spectrum of empirical correlations addressing the coupled influences of pressure gradient, airfoil curvature, and free-stream turbulence on airfoil surface heat transfer distribution and boundary layer transitional behavior. Comparison of pedictions made with the model to the data base indicates a significant improvement in predictive capability.

An analysis of existing data on low Reynolds number flows strongly suggests that the conclusion of Simpson (1970) concerning the variation of von Kármás constant κ with Reynolds number is not correct. This implies that Coles’ (1962) assumption of the validity of the logarithmic velocity profile at low Reynolds numbers is correct and, moreover, that the inference drawn by Coles and later authors regarding the presence of viscous effects in the outer layer is valid. The analysis shows that these viscous effects are not present in duct flows, so that they are presumably associated with the presence of a turbulent-irrotational interface; it is argued that the ‘viscous superlayer’ can affect a large part of the outer layer at low Reynolds numbers. The data analysis incidentally shows that the viscous sublayer is more strongly affected by shear-stress gradients or transverse wall curvature than is the rest of the inner layer.

<div class="htmlview paragraph">The use of small-hole diesel injector tips and high injection pressures was investigated as a countermeasure to the increased particulate matter (PM) emissions formed when using exhaust gas recirculation (EGR) in diesel engines. This study examined the use of injector tip hole sizes down to about 0.09-mm (0.0035 in.), and injection pressures to 300 MPa (3000 bar, or 43,500 psi). The first phase of these studies was conducted in a high-temperature, high-pressure combustion bomb, with supporting calculations using a unit injector model, a jet-mixing model, and a diesel jet evaporation model.</div> <div class="htmlview paragraph">The second phase was conducted in a commercial diesel engine of 12.7-liter displacement designed to meet U.S. 1998 emissions levels. Engine tests were conducted with a baseline cam and a faster rise-rate cam, and three different hole tip sizes. The cams consisted of a baseline cam and a cam of similar design, but with a 12 percent faster rise rate. Injector hole tip sizes included the baseline tips, with hole sizes roughly 8 × 0.18-mm, and smaller hole tips of 8 × 0.170-mm and 8 × 0.131-mm.</div> <div class="htmlview paragraph">Dramatic reductions in soot were observed in both the combustion bomb and the engine with increases in injection pressure and reductions in hole size.</div>

Labyrinth air seal static and dynamic performance was evaluated using solid, abradable, and honeycomb lands with standard and advanced seal designs. The effects on leakage of land surface roughness, abradable land porosity, rub grooves in abradable lands, and honeycomb land cell size and depth were studied using a standard labyrinth seal. The effects of rotation on the optimum seal knife pitch were also investigated. Selected geometric and aerodynamic parameters for an advanced seal design were evaluated to derive an optimized performance configuration. The rotational energy requirements were also measured to determine the inherent friction and pumping energy absorbed by the various seal knife and land configurations tested in order to properly assess the net seal system performance level. Results indicate that: (1) seal leakage can be significantly affected with honeycomb or abradable lands; (2) rotational energy absorption does not vary significantly with the use of a solid-smooth, an abradable, or a honeycomb land; and (3) optimization of an advanced lab seal design produced a configuration that had leakage 25% below a conventional stepped seal.

<div class="htmlview paragraph">Minimizing fuel consumption is emerging as the next major challenge for engine control and calibration, even as the requirements of complying with ever lower transient emissions regulations cannot be underestimated. Meeting these difficult and apparently conflicting emissions and efficiency goals is becoming increasingly onerous as engine and aftertreatment control complexity increases. Conventional engine calibration techniques are by nature time-intensive, ad-hoc and repetitive, resulting in low productivity of test facilities and engineering effort. Steady state engine mapping methods, such as design of experiments, do little to ensure transient emissions compliance or fuel consumption optimization.</div> <div class="htmlview paragraph">A new model-based Rapid Transient Calibration system has been developed, tested and validated using a 2007 production-specification Detroit Diesel Series 60 heavy-duty diesel engine. This system has demonstrated a significant reduction in the time required to calibrate compared to conventional calibration methods by moving an appreciable proportion of the engineering effort from the physical transient dynamometer test cell to the virtual, computational desktop environment, thus offering significant reductions in product development costs and schedules. Significant improvements in actual fuel consumption were shown at the same or lower overall integrated emissions levels in real-world validation testing, proving that this new process offers considerable advantages over conventional calibration methods.</div> <div class="htmlview paragraph">This paper details the first complete beginning-to-end validation of this rapid transient calibration optimization process. The calibration process commences with a limited data collection campaign in a transient emissions test cell and is then transferred to the computational environment where high-fidelity dynamically predictive engine emissions and performance models are created.</div> <div class="htmlview paragraph">The engine calibration is then optimized off-line using these transient models in conjunction with a set of optimization and constraint functions. To prove the accuracy of the method, a number of engine calibration data sets, each optimized for a different emissions target, are then validated on the engine back in the transient emissions test cell.</div>

<div class="htmlview paragraph">The Common-rail injection system has allowed achieving a more flexible fuel injection control in DI-diesel engines by permitting a free mapping of the start of injection, injection pressure, rate of injection. All these benefits have been gained by installing this device in combustion chambers born to work with the conventional distributor and in-line-pump injection systems. Their design was aimed to improve air-fuel mixing and therefore they were characterized by the adoption of high-swirl ports and re-entrant bowls. Experiments have shown that the high injection velocities induced by common rail systems determine an enhancement of the air fuel mixing. By contrast, they cause a strong wall impingement too. The present paper aims to exploit a new configuration of the combustion chamber more suited to CR injection systems and characterized by low-swirl ports and larger bowl diameter in order to reduce the wall impingement. The goal is to achieve a higher air flow rate during induction as well as to reduce the fuel vapor wall impingement without compromising air-fuel mixing efficiency. This new combustion chamber configuration has been tested numerically and its performances have been compared to those of a H.S.D.I four valve diesel engine conventional combustion chamber. The analysis has been carried out by using a customized version of the CFD code KIVA3. Experimental results of the conventional combustion chamber have been used to validate the numerical models. The influence of the injection system configuration (i.e, hole numbers, inclination of the spray axis with respect cylinder head) on pressure cycle and NO<sub>x</sub> and soot engine-out emissions has been analyzed too. Computational results seem to indicate that the new combustion system concept may provide relevant benefits with respect to engine-out emissions without reducing engine performance.</div>

<div class="htmlview paragraph">The products of diesel combustion, including hydrocarbons, nitric oxide, carbon monoxide, and exhaust smoke are being controlled by current and future emission standards of federal and state governments. Fuel injection parameters, including tip design, injection timing, rate of injection, and the number and size of tip orifices were investigated with the unit injector, used in Detroit Diesel engines, for influence on these emissions. Results are presented to show control of hydrocarbon emissions by injector tip design. Reduction in nitric oxide emissions by changing injection parameters is limited by increased exhaust smoke and carbon monoxide and losses in fuel economy. Emission levels with the standard injector and an experimental injector, combining several injection parameter revisions, are compared with the 1973 California emission standards for diesel engines.</div>

<div class="htmlview paragraph">Exhaust hydrocarbons and odor were reduced in Detroit Diesel Series “71” engines by revising the fuel injector tip design. Five injector tips were investigated which had different volumes of uncontrolled fuel below the injector valve. Results are presented to show that exhaust hydrocarbons and odor can be substantially reduced by minimizing the uncontrolled volume of fuel in the injector tip. The hydrocarbon emissions are attributed to uncontrolled fuel being pushed from the tip by expansion of the fuel at elevated temperatures. This conclusion is supported by test results with fuels having different 10% distillation temperatures.</div>

<div class="htmlview paragraph">A new injector has been designed for sequential injection of high-pressure natural gas and a quantity of liquid diesel fuel directly into diesel engine cylinders late in the compression stroke. Injected a few degrees before the natural gas, the pilot liquid fuel auto-ignites and serves, as it burns, to ignite the gaseous fuel which enters the chamber as an underexpanded sonic jet generating high local turbulence. Tests on a single-cylinder two-stroke engine with full electronic control have demonstrated the capability of this fueling method to nearly match conventional diesel engine efficiency over a wide range of load and substantially reduce the emissions of oxides of nitrogen (NO<sub>x</sub>), particulate mater (PM) and carbon dioxide (CO<sub>2</sub>).</div>

In order to complement associated experimental studies, the development of a theoretical approach to the evaluation of gas turbine combustors is extremely attractive. For this purpose a computer program is needed which starts from hypotheses about the fundamental processes and predicts the distributions of velocity, concentrations, and temperature. A new primitive pressure-velocity variable, finite-difference computer code has been developed to allow the computation of inert and reacting turbulent swirling flows in an axisymmetric combustor. The method and program involve a staggered grid system for axial and radial velocities, and a line relaxation technique for efficient solution of the equations. Turbulence simulation is by way of a two-equation k-e model combustion via a simple one-step chemical reaction model based on Arrhenius and eddy-breakup concepts for diffusion or premixed situations. Computational results show the interesting effects of combustor design parameters (such as: degree of swirl, existence of a recirculation zone amplifier, i.e., trip, and effect of laterally induced secondary air supply) on subsequent flowfield development and combustor performance. Available experimental data provide confirmatory comparisons.

<div class="htmlview paragraph">A multi-objective genetic algorithm methodology was applied to a heavy-duty diesel engine at three different operating conditions of interest. Separate optimizations were performed over various fuel injection nozzle parameters, piston bowl geometries and swirl ratios (SR). Different beginning of injection (BOI) timings were considered in all optimizations. The objective of the optimizations was to find the best possible fuel economy, NOx, and soot emissions tradeoffs.</div> <div class="htmlview paragraph">The input parameter ranges were determined using design of experiment methodology. A non-dominated sorting genetic algorithm II (NSGA II) was used for the optimization. For the optimization of piston bowl geometry, an automated grid generator was used for efficient mesh generation with variable geometry parameters. The KIVA3V release 2 code with improved ERC sub-models was used. The characteristic time combustion (CTC) model was employed to improve computational efficiency. Six individual optimizations were performed, with two of them performed for each of the three operating conditions (full load, mid-load, and low-load). The first set of three optimized BOI, spray angle, hole size, and the number of holes with fixed piston geometry. The second set optimized BOI, piston geometry, and swirl ratio with fixed fuel injector nozzle design. The optimizations were subject to design constraints including peak cylinder pressure and the temperature at exhaust valve opening. The sensitivity of engine performance to the design parameters of interest was evaluated using a response surface analysis method. The results show that significant reductions in engine-out emissions and fuel consumption can be achieved.</div>

A four vane subsonic cascade was used to investigate how free stream turbulence influences pressure surface heat transfer. A simulated combustor turbulence generator was built to generate high level (13 percent) large scale (Lu approximately 44 percent inlet span) turbulence. The mock combustor was also moved upstream to generate a moderate level (8.3 percent) of turbulence for comparison to smaller scale grid generated turbulence (7.8 percent). The high level combustor turbulence caused an average pressure surface heat transfer augmentation of 56 percent above the low turbulence baseline. The smaller scale grid turbulence produced the next greatest effect on heat transfer and demonstrated the importance of scale on heat transfer augmentation. In general, the heat transfer scaling parameter U(sub infinity) TU(sub infinity) LU(sub infinity)(exp -1/3) was found to hold for the turbulence. Heat transfer augmentation was also found to scale approximately on Re(sub ex)(exp 1/3) at constant turbulence conditions. Some evidence of turbulence intensification in terms of elevated dissipation rates was found along the pressure surface outside the boundary layer. However, based on the level of dissipation and the resulting heat transfer augmentation, the amplification of turbulence has only a moderate effect on pressure surface heat transfer. The flow field turbulence does drive turbulent production within the boundary layer which in turn causes the high levels of heat transfer augmentation. Unlike heat transfer, the flow field straining was found to have a significant effect on turbulence isotropy. On examination of the one dimensional spectra for u' and v', the effect to isotropy was largely limited to lower wavenumber spectra. The higher wavenumber spectra showed little or no change. The high level large scale turbulence was found to have a strong influence on wake development. The free stream turbulence significantly enhanced mixing resulting in broader and shallower wakes than the baseline case. High levels of flow field turbulence were found to correlate with a significant increase in total pressure loss in the core of the flow. Documenting the wake growth and characteristics provides boundary conditions for the downstream rotor.

<div class="htmlview paragraph">Engine hardware modifications, fuel and lube oil properties, electronic controls, and aftertreatment devices may all play a role in meeting future heavy-duty diesel engine emission standards. Detroit Diesel Corporation (DDC) is actively involved in evaluating the contributions of these technologies to reduce emissions as well as evaluating the impact on initial and life cycle system cost, fuel consumption, reliability and durability. This paper focuses on the potential of low emission diesel fuels to contribute to lower engine-out emissions.</div> <div class="htmlview paragraph">DDC has been testing low emission diesel fuels with low sulfur and aromatics and higher cetane number, synthetic diesel fuels, and today's fuels with various additives. Other industry programs have generated similar data. These results have led us to the conclusion that a significant contribution can be made by tailoring future diesel fuels to produce low emissions. While more work needs to be done to identify what a low emission diesel fuel specification should be, this paper is intended to stimulate more interest in this subject and encourage engine manufacturers and fuel suppliers to work together to define an acceptable future fuel.</div>

Measurement of the capacitance formed between the piston ring and a probe mounted in the cylinder liner provides an accurate means of determining the oil film thickness provided that the region between the ring and probe is flooded with oil and the dielectric constant of the oil is known. All aspects of the design, construction, installation of capacitance probes, and analysis of the resulting measurements are reviewed in this paper. Biases introduced due to the fringing of the electric field, curvature of the ring face profile, roughness of the ring profile, and the tilt angle of the ring face are analyzed, and correction algorithms are proposed. Errors associated with the proposed algorithms are gauged through comparisons to finite difference solutions. Shielding the sensing electrode is found to eliminate fringing effects and also stray capacitance which can affect the signal. A rectangular probe design with a high aspect ratio is suggested as an optimum. The small axis of the probe provides high spatial resolution, while the longer length, which is in the circumferential direction, provides a sufficient surface area to ensure sufficient signal strength. A design procedure which allows for the sizing of probe dimensions for a given level of allowable error and capacitance measuring circuitry is developed.

<div class="htmlview paragraph">This oil category was driven by two new cooled exhaust gas recirculation (EGR) engine tests operating with 15% EGR, with used oil soot levels at the end of the test ranging from 6 to 9%. These tests are the Mack T-10 and Cummins M11 EGR, which address ring, cylinder liner, bearing, and valve train wear; filter plugging, and sludge. In addition to these two new EGR tests, there is a Caterpillar single-cylinder test without EGR which measures piston deposits and oil consumption control using an articulated piston. This test is called the Caterpillar 1R and is included in the existing Global DHD-1 specification.</div> <div class="htmlview paragraph">In total, the API CI-4 category includes eight fired-engine tests and seven bench tests covering all the engine oil parameters. The new bench tests include a seal compatibility test for fresh oils and a low temperature pumpability test for used oils containing 5% soot.</div> <div class="htmlview paragraph">This paper provides a review of the all the tests, matrix results, and limits for this new oil category. This work was completed by the ASTM Heavy Duty Engine Oil Classification Panel (HDEOCP) in October 2001, at a cost of $5.71 million (6.28 million Euro). This was followed by a successful ASTM D.02.B ballot in December 2001. API-licensed products designated API CI-4 will become available in August 2002.</div> <div class="htmlview paragraph">API CI-4 oils are pivotal components in maintaining diesel engine durability using cooled EGR. API CI-4 is a higher quality oil than the previous diesel oil categories, so it will provide engine protection for both existing and new EGR engines.</div>

The transcritical vaporization of a fuel drop placed in supercritical ambient is reported. A detailed model based on the numerical solution of the time-dependent conservation equations for both liquid and gas phase is employed. The equations are solved using an arbitrary Lagrangian-Eulerian procedure, which allows a dynamically adaptive mesh to analyze interfacial time-history effects, and a comprehensive thermodynamic model that accounts for the variation of thermotransport properties and the gas-phase nonidealities in the transcritical regime. The transcritical vaporization behavior is shown to be characterized by two parameters. One is the minimum pressure ( P min ) required for the drop surface to reach the critical mixing state, and the other is the time ratio parameter ( t r ), which is the ratio of the time to attain critical mixing state to the drop lifetime. For pressures below P min , the droplet undergoes subcritical vaporization ( t r =1), characterized by a distinct liquid-gas interface whose regression rate is determined by the gas-phase mass diffusivity and the difference between fuel vapor concentrations at the surface and in the ambient. For pressures above P min , the droplet undergoes transcritical vaporization, i.e., it attains the critical mixing state sometime during its lifetime. The instant at which the critical mixing state is reached determines t r . The subsequent surface regression or "supercritical vaporization" rate is given by the inward velocity of the critical surface, which is determined by the gas-phase thermal diffusivity and the difference between critical mixing temperature and liquid temperature in the droplet interior. While both the subcritical and supercritical vaporization rates are enhanced as the pressure is increased, the latter is consistently higher than the former. The effects of ambient temperature and initial drop size on P min and t r are quantified. The parameter P min shows a strong dependence on ambient temperature ( T ∞ ), decreasing rapidly as T ∞ increases, but a weak dependence on drop size. The parameter t r is strongly sensitive to ambient temperature, pressure, and droplet size. It decreases as ambient temperature and pressure are increased, and as drop size is decreased.

<div class="htmlview paragraph">The aggressive reduction of future diesel engine NO<sub>x</sub> emission limits forces the heavy- and light-duty diesel engine manufacturers to develop means to comply with stringent legislation. As a result, different exhaust emission control technologies applicable to NO<sub>x</sub> have been the subject of many investigations. One of these systems is the NO<sub>x</sub> adsorber catalyst, which has shown high NO<sub>x</sub> conversion rates during previous investigations with acceptable fuel consumption penalties. In addition, the NO<sub>x</sub> adsorber catalyst does not require a secondary on-board reductant.</div> <div class="htmlview paragraph">However, the NO<sub>x</sub> adsorber catalyst also represents the most sulfur sensitive emissions control device currently under investigation for advanced NO<sub>x</sub> control. To remove the sulfur introduced into the system through the diesel fuel and stored on the catalyst sites during operation, specific regeneration strategies and boundary conditions were investigated and developed. To achieve the required exhaust temperature under slightly rich conditions, a pre-catalyst may be required. Under constant engine operating conditions, the duration of the desulfurization process was varied to determine the required desulfurization period. In addition, the catalysts were aged and periodically desulfurized to determine the influence of multiple desulfurization events on long-term catalyst performance.</div> <div class="htmlview paragraph">The test results show that using a pre-catalyst, the NO<sub>x</sub> conversion capability of a NO<sub>x</sub> adsorber catalyst can be restored even after multiple desulfurizations. However, a decline in conversion efficiency can be observed over time. In anticipation of future catalyst improvements, it can be concluded, that the adsorber catalyst is a promising technology for future vehicle applications.</div>

A spur gear efficiency prediction method previously developed by the authors was extended to include power loss of planetary gearsets. A friction coefficient model was developed for MIL-L-7808 oil based on disc machine data. This combined with the recent capability of predicting losses in spur gears of nonstandard proportions allows the calculation of power loss for complete aircraft gearboxes that utilize spur gears. The method was applied to the T56/501 turboprop gearbox and compared with measured test data. Bearing losses were calculated with large scale computer programs. Breakdowns of the gearbox losses point out areas for possible improvement.