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Simple devices have been shown to be capable of tailoring the flow field around a vehicle and reducing aerodynamic drag. An experimental and computational investigation of a drag reduction device for bluff bodies in ground proximity has been conducted. The main goal of the research is to gain a better understanding of the drag reduction mechanisms in bluff-body square-back geometries. In principle, the device modifies the flow field behind the test model by disturbing the shear layer. As a consequence, the closure of the wake is altered and reductions in aerodynamic drag of more than 20 percent are observed. We report unsteady base pressure, hot-wire velocity fluctuations and Particle Image Velocimetry (PIV) measurements of the near wake of the two models (baseline and the modified models). In addition, the flows around the two configurations are simulated using the Reynolds Averaged Navier-Stokes (RANS) equations in conjunction with the V2F turbulence model.

A two phase, global combustion model has been developed for quiescent chamber, direct injection diesel engines. The first stage of the model is essentially a spark ignition engine flame spread model which has been adapted to account for fuel injection effects. During this stage of the combustion process, ignition and subsequent flame spread/heat release are confined to a mixing layer which has formed on the injected jet periphery during the ignition delay period. Fuel consumption rate is dictated by mixing layer dynamics, laminar flame speed, large scale turbulence intensity, and local jet penetration rate. The second stage of the model is also a time scale approach which is explicitly controlled by the global mixing rate. Fuel-air preparation occurs on a large-scale level throughout this phase of the combustion process with each mixed fuel parcel eventually burning at a characteristic time scale as dictated by the global mixing rate.

A series of inflator tank tests was carried out to determine the amount of transient heat losses to the tank wall during these tests. The time history data of tank wall temperature, and tank interior gas temperature and pressure, were measured. The tank wall temperature data were analyzed using an inverse heat conduction method to generate the transient heat loss fluxes from the tank gas to the tank wall. The validity of the results are discussed along with the physical reasoning and experimental observations. This is the first part of an effort in a research project to develop a comprehensive heat transfer model to predict the transient heat losses to the tank wall during the inflator tank test.

Thermal distortions of friction disks caused by frictional heating modify pressure distribution on friction surfaces. Pressure distribution, in turn, determines distribution of generated frictional heat. These interdependencies create a complex thermoelastic system that, under some conditions, may become unstable and may lead to severe pressure concentrations with very high local temperature and stress. The phenomenon is responsible for many common thermal failure modes of friction elements and is known as frictionally excited thermoelastic instability (TEI). In the paper, one of the cases of TEI is investigated theoretically and experimentally. The study involves a two-disk structure with one fiction disk and one matching steel disk that have one friction interface. An unsteady heat conduction problem and an elastic contact problem are modeled as axisymmetric ones and are solved using the finite element method.

A detailed chemical kinetic mechanism, consisting of 22 species and 104 elementary reactions, has been used in conjunction with the multi-dimensional reactive flow code KIVA-3 to study autoignition of natural gas injected under compression ignition conditions. Calculations for three different blends of natural gas are performed on a three-dimensional computational grid by modeling both the injection and ignition processes. Ignition delay predictions at pressures and temperatures typical of top-dead-center conditions in compression ignition engines compare well with the measurements of Naber et al. [1] in a combustion bomb. Two different criteria, based on pressure rise and mass of fuel burned, are used to detect the onset of ignition. Parametric studies are conducted to show the effect of additives like ethane and hydrogen peroxide in increasing the fuel consumption rate.

The evaluation of the performance of a particular inflator for the design of the entire airbag system is typically carried out by examining the pressure pattern in a standard tank test. This study assesses the adequacy of the tank test as a true measure of the likely performance of the actual inflator-airbag system. Theoretical arguments, numerical experiments, and physical experiments show that the time rate of pressure change may be an appropriate measure to evaluate performance of a specific type of inflator, particularly if variations in the inflator design maintain the same working gas components. However, when evaluating and comparing the dynamic behavior between different types of inflators, the time rate of pressure change provides useful but incomplete information.

A program to explore the effects of natural and additive-derived cetane on various aspects of diesel performance and combustion has been carried out. Procedures have been developed to measure diesel engine fuel consumption and power to a high degree of precision. These methods have been used to measure fuel consumption and power in three heavy-duty direct-injection diesel engines. The fuel matrix consisted of three commercial fuels of cetane number (CN) of 40-42, the same fuels raised to CN 48-50 with a cetane improver additive, and three commercial fuels of base CN 47-50. The engines came from three different U.S. manufacturers and were of three different model years and emissions configurations. Both fuel economy and power were found to be significantly higher for the cetane-improved fuels than for the naturally high cetane fuels. These performance advantages derive mainly from the higher volumetric heat content inherent to the cetane-improved fuels.

An experimental heat release rate analysis was conducted on a six cylinder, 12.7 liter Detroit Diesel Series 60 turbocharged engine operating under steady state conditions. The overall chemical, or gross, rate of heat release and the net apparent rate of heat release were determined from experimental measurements. The gross, time averaged, heat release rate was determined by two separate concepts/methods using exhaust gas concentration measurements from the Nicolet Rega 7000 Real Time Exhaust Gas Analyzer and the measured exhaust gas flow rate. The net apparent rate of heat release was determined from the in-cylinder pressure measurements for each of the six cylinders, averaged over 80 cycles. These pressure measurements were obtained using a VXI based Tektronix data acquisition system and LabVIEW software. A computer algorithm then computed the net apparent rate of heat release from the averaged in-cylinder pressure measurements.

Engine performance under transients is greatly affected by the fuel behavior in the induction systems. To better understand the fuel behavior, a computer model has been developed to study the one-dimensional coupled heat and mass transfer processes occurring during the transient evaporation of liquid fuel from a heated surface into stagnant air. The energy and mass diffusion equations are solved simultaneously to yield the transient temperatures and species concentrations using a modified finite difference technique. The numerical technique is capable of solving the coupled equations while simultaneously tracking the movement of the evaporation interface. Evaporation results are presented for various initial film thicknesses representing typical puddle thicknesses for multi-point fuel injection systems using heptane, octane, and nonane pure hydrocarbon fuels.

Testing for vehicle emissions and fuel economy certification occurs primarily on chassis dynamometers in a laboratory setting and therefore the actual road conditions, such as forces due to tire rolling resistance and internal friction, must be simulated. Test track coastdown procedures measure vehicle road load forces and produce an equation which relates these forces to velocity. The recent inclusion of onboard anemometry has allowed the coastdown procedure to account for varying wind effects; however, the new anemometer based mechanical loss coefficients do not take into account ambient weather conditions. The two purposes of this study are (1) to determine the new tire rolling resistance temperature correction coefficient that should be used when test ambient temperature is different from the standard reference value of 68°F, and (2) to investigate the effects of auxiliary measurements, such as other ambient conditions and vehicle settings, on this correction coefficient.

As the federal regulations of on-road engine exhaust emissions become more and more stringent, the exhaust emissions of small utility engines are now under close study and are becoming subject to federal regulations. This paper reports the on-going research on emissions and test procedures for small utility engines at the University of Michigan. A group of small utility engines, selected by the National Fuels and Emissions Laboratory of the U.S. Environmental Protection Agency (EPA), were tested at various air/fuel ratios under steady state and transient operation. Mass rate of emissions of carbon monoxide (CO), carbon dioxide (CO2), total hydrocarbons (HC) and oxides of nitrogen (NOx) were measured using dilute sampling. The lean operation limit of some engines was studied to find a compromise among emissions, engine power, and engine life. Experimental research was also undertaken to study emission control techniques; such as catalytic conversion, air injection, and fuel injection.

Cost reduction, quality improvement, and regulatory compliance are well-recognized competitive issues. Companies must excel along each of these fronts while operating in an environment of rapid and multi-faceted change, limited financial and human capital, and increasing product development time pressure. In addition, consumers are demanding automobiles that provide greater performance, function, and comfort while emitting lower emissions, consuming fewer gallons of gasoline, injuring fewer humans, and requiring fewer dollars to build and purchase. A solution to these seemingly conflicting objectives is to take a systems view of the product and industry. This paper explores the material decision process so that manufacturers, component suppliers, and material providers may better understand the interlocking web of compromises that shape the pursuit of value-added alternatives and avoidance of unprofitable compromises.

A cylindrical combustion bomb with dynamic charging system and electro-hydraulic sampling valve is used to study the effects of turbulence on hydrocarbon (HC) emissions from a quench layer and from artificial crevices. The turbulence level is varied by changing the delay time between induction of combustible charge and ignition. Propane-air mixtures were studied over an initial pressure range of 150 to 500 kPa and equivalence ratios of 0.7 to 1.4. Sampling valve experiments show that quench-layer fuel hydrocarbons are extensively oxidized within 5 ms of flame arrival under laminar conditions and that turbulence further reduces the already low level. Upper limit estimates of the residual wall layer HC concentration show that residual quench layer hydrocarbons are only a small fraction of the exhaust HC emission.

Rolling resistance measurements were made on a sample of twenty-four retreaded and four new truck tires spanning a variety of constructions, tread patterns and tread depths. Examination of the results showed some relationship between three construction features and the resulting rolling resistance values. These are (a) Radial or bias carcass construction, (b) Tread pattern, and (c) Tread depth. The latter two characteristics can over-ride radial or bias construction effects. The effect of tread compound could not be analyzed in this limited test program. Good quality retreaded truck tires can exhibit comparable rolling resistance with new truck tires.

A method has been developed for calculating the internal temperature distribution in an aircraft tire while free rolling under load. The method uses an approximate stress analysis of each point in the tire as it rolls through the contact patch, and from this stress change the mechanical work done on each volume element may be obtained and converted into a heat release rate through a knowledge of material characteristics. The tire cross-section is then considered as a body with internal heat generation, and the diffusion equation is solved numerically with appropriate boundary conditions at the wheel and runway surface. Comparisons with buried thermocouples in actual aircraft tires shows good agreement.

Secondary injection in a diesel engine is defined as the introduction of additional fuel into the combustion chamber after the end of the main injection. It is usually caused by residual pressure waves in the high-pressure pipe line connecting the pump and injector. When these waves exceed the injector opening pressure, secondary injection occurs. Tests revealed that the U.S. Army TACOM single-cylinder engine used in this investigation, fitted with an American Bosch injection system, had secondary injection within the normal engine operating region. The pump spill ports and delivery valve were redesigned to eliminate secondary injection, in accordance with previously reported work. Comparative tests of both the conventional and modified injection systems were run on the same engine, and the effects of secondary injection on engine power, economy, and exhaust emissions were determined.

After-injection is the introduction of additional fuel to the combustion chamber after the end of the main injection. It is a persistent diesel fuel injection problem which usually results in reduced engine power and economy and increased emissions. After-injection is caused by uncontrolled pressure transients at the injector after the opening of the pump spill port. These pressure transients are related to the wave propagation phenomena in the high-pressure pipeline connecting the pump and injector. Use of experimental trial-and-error methods in attempts to control this phenomenon has met with limited success. The analytical control method described in another paper is used to determine design means by which after-injection may be controlled. Further investigation and evaluation of two design changes which release the injection system excess elastic energy in a controlled manner are considered herein. One design change is the addition of a control valve in the pump delivery chamber.

A theoretical digital simulation of a conventional diesel fuel injection system has been developed. The influence of such factors as wave propagation phenomena, pipe friction, and cavitation are included. The computer results are compared with transient pressures as measured on an actual fuel injection system operated on a test bench. The comparisons show the accuracy and validity of this simulation scheme. Special attention is given to some of the important factors that affect the accuracy of the simulation model. These include the effect of pressure on the fuel bulk modulus and wave speed, the pipe line residual pressure, and the coefficient of discharge of important orifices.

Strain gage instrumented transducers were used to measure the cord loads at a number of locations in several different automotive tires loaded against both flat and cylindrical road wheel surfaces. The two basic types of cord load fluctuation encountered in all automobile tires have been identified from these measurements, and the most severe location for cord load fluctuations has been closely bracketed. By these measurements, it has been possible to show that for each tire definite relations exist between the cord loads induced while running on a cylindrical drum and while running on a flat surface. The maximum cord load fluctuations in a tire are the same for the NBS roadwheel and flat surface when the tire is loaded against the roadwheel with a load of between 85 and 90% of that used on the flat surface.

Based on a review of existing theoretical and empirical knowledge of the mechanics of pneumatic tires and tire/vehicle systems, a requirement is defined for experimental data relating the shear forces developed at the tire-road interface to the kinematic variables of influence. Test equipment to satisfy this requirement consists of two complementary pieces of apparatus: a laboratory facility which is a modified version of the B. F. Goodrich flat-bed tester, and a mobile device which consists of a three-component (Fx, Fy, Mz) strain-gage dynamometer mounted on a heavy duty highway tractor. The latter provides a capability for testing at speeds up to 70 mph, normal loads up to 2000 lb, tire sideslip angles up to 18 deg, and steady state or programmed variations in longitudinal tire slip from fully locked (100% slip) to 30% overdriven (-30% slip). Representative samples of tire mechanics data obtained using the new equipment are presented and discussed.