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There is an increasing interest in transient thermal simulations of automotive brake systems. This paper presents a high-fidelity CFD tool for modeling complete braking cycles including both the deceleration and acceleration phases. During braking, this model applies the frictional heat at the interface on the contacting rotor and pad surfaces. Based on the conductive heat fluxes within the surrounding parts, the solver divides the frictional heat into energy fluxes entering the solid volumes of the rotor and the pad. The convective heat transfer between the surfaces of solid parts and the cooling airflow is simulated through conjugate heat transfer, and the discrete ordinates model captures the radiative heat exchange between solid surfaces. It is found that modeling the rotor rotation using the sliding mesh approach provides more realistic results than those obtained with the Multiple Reference Frames method.

The ozone forming potential (OFP) and specific reactivity (SR) of tailpipe exhaust are among the factors that determine the environmental impact of a motor vehicle. OFP and SR measurements require a lengthy determination of about 190 non-methane hydrocarbon species. A rapid gas chromatography (GC) instrument has been constructed to separate both the light (C2 - C4) and the midrange (C5 - C12) hydrocarbons in less than 10 minutes. The limit of detection is about 0.002 parts per million carbon (ppmC). Thirty exhaust samples from natural gas vehicles (NGV's) were analyzed to compare the rapid GC method with the standard GC method, which required 40-minute analyses on two different instruments. In general, evaluation of the commercial prototype from Separation Systems, Inc., indicates that a high speed, high resolution gas chromatograph can meet the need for fast, efficient exhaust hydrocarbon speciation.

Aqua-ammonia absorption refrigeration cycle and R-134a Vapor jet-ejector refrigeration cycle for automotive air-conditioning were studied and analyzed. Thermally activated refrigeration cycles would utilize combustion engine exhaust gas or engine coolant to supply heat to the generator. For the absorption system, the thermodynamic cycle was analyzed and pressures, temperatures, concentrations, enthalpies, and mass flow rates at every point were computed based on input parameters simulate practical operating conditions of vehicles. Then, heat addition to the generator, heat removal rates from absorber, condenser, and rectifying unit, and total rejection heat transfer area were all calculated. For the jet-ejector system, the optimum ejector vapor mass ratio based on similar input parameters was found by solving diffuser's conservation equations of continuity, momentum, energy, and flow through primary ejector nozzle simultaneously.

A global thermal model of a vehicle powertrain is used to quantify how different engine design and powertrain calibration strategies influence the performance of a vehicle heating system. Each strategy is evaluated on its ability to improve the warm-up and heat rejection characteristics of a small-displacement, spark-ignition engine while minimizing any adverse effect on fuel consumption or emissions. An energy audit analysis shows that the two strategies having the greatest impact on heating system performance are advancing the spark and forcing the transmission to operate in a lower gear. Changes in head mass, exhaust port diameter, and coolant flow rate influence the coolant warm-up rate but have relatively little effect on steady state heat transfer at the heater core.

Air flow around the front brake assembly was computed using STAR-CD version 2.300, a commercial Computational Fluid Dynamics (CFD) code in order to explore the possibility of using this technique as a design tool. The primary objective in a brake corner assembly design is to maximize air cooling of the brake rotor. It is a very challenging task that requires experiments that are both expensive and time consuming in order to evaluate and optimize the various design possibilities. In this study, it is demonstrated that the design procedure can be shortened and made less expensive and be accurate using flow simulations. Accordingly, the air flow around the front brake assembly was computed for three different designs and for three different car speeds. A computational mesh was built using PROSTAR, the STAR-CD pre and post-processor. The three-dimensional mesh had almost 900,000 cells. All geometrical components were modelled.

Component operating temperatures affect both the reliability and performance of automotive alternators. It is desirable to keep the rectifier bridge and regulator temperatures below 175 C because of the semiconductors contained in this area. At temperatures greater than this, expected lifespans have been observed to decay exponentially [1]. The air flow field surrounding an alternator and component temperature fields were investigated with Computational Fluid Dynamics (CFD) simulations. The objectives of the simulations were to examine the velocity field for the flow passage and the temperature fields for the components. Design proposals have been made to improve the air flow and to reduce the operating temperature. An initial investigation was performed by setting an alternator in a test configuration and applying the appropriate heat generation for each component. The high temperatures in the alternator components occurred in the stator and the rectifier.

A proportional sampler for vehicle feedgas and tailpipe emissions has been developed that extracts a small, constant fraction of the total exhaust flow during rapid transient changes in engine speed. Heated sampling lines are used to extract samples either before or after the catalytic converter. Instantaneous exhaust mass flow is measured by subtracting the CVS dilution air volume from the total CVS volume. This parameter is used to maintain a constant dilution ratio and proportional sample. The exhaust sample is diluted with high-purity air or nitrogen and is delivered into Tedlar sample bags. These transient test cycle weighted feedgas samples can be collected for subsequent analysis of hydrocarbons and oxygenated hydrocarbon species. This “mini-diluter” offers significant advantages over the conventional CVS system. The concentration of the samples are higher than those collected from the current CVS system because the dilution ratio can be optimized depending on the fuel.

Analytical procedures for the speciation of hydrocarbons and oxygenates (ethers, aldehydes, ketones and alcohols) in vehicle evaporative and tailpipe exhaust emissions have been improved for Phase II studies of the Auto/Oil Air Quality Improvement Research Program (AQIRP). One gas chromatograph (GC) was used for measurement of C1-C4 species and a second GC for C4-C12 species. Detection limits for this technique are 0.005 ppm C or 0.1 mg/mile exhaust emission level at a chromatographic signal-to-noise ratio of 3/1, a ten-fold improvement over the Phase I technique. The Phase I library was modified to include additional species for a total of 154 species. A 23-component gas standard was used to establish a calibration scale for automated computer identification of species. This method identifies 95±3% of the total hydrocarbon mass measured by GC for a typical exhaust sample. Solid adsorbent cartridges or impingers were used to collect aldehydes and ketones.

A running loss test procedure has been developed which integrates a point-source collection method to measure fuel evaporative running loss from vehicles during their operation on the chassis dynamometer. The point-source method is part of a complete running loss test procedure which employs the combination of site-specific collection devices on the vehicle, and a sampling pump with sampling lines. Fugitive fuel vapor is drawn into these collectors which have been matched to characteristics of the vehicle and the test cell. The composite vapor sample is routed to a collection bag through an adaptation of the ordinary constant volume dilution system typically used for vehicle exhaust gas sampling. Analysis of the contents of such bags provides an accurate measure of the mass and species of running loss collected during each of three LA-4* driving cycles. Other running loss sampling methods were considered by the Auto-Oil Air Quality Improvement Research Program (AQIRP or Program).

Diesel exhaust gas dilution and odor intensity were measured in the immediate vicinity of a transit bus equipped with a rear-mounted horizontal exhaust pipe, a rear-mounted vertical exhaust pipe, and a roof-top diffusion system. Exhaust dilution ratios were measured indoors during vehicle idle operation, using propane added to the exhaust gas as a tracer. Exhaust odor intensities were measured also indoors during vehicle idle operation by a human panel, using a threshold odor measurement technique. On the average, the dilution of the exhaust gas around the bus with the vertical exhaust pipe was about eight times greater than it was with the horizontal pipe. Odor intensity, as measured by the threshold response distance, was about 35% less with the vertical pipe than with the horizontal pipe. The roof-top diffuser was not as effective as the vertical exhaust pipe in increasing exhaust gas dilution or in reducing exhaust odor intensity.

TECHNIQUES, based on panel estimates, were developed for evaluating the odor and irritation intensities of undiluted diesel-engine exhaust gases or of various dilutions of these gases in air. Along with the estimates, chemical analyses were made to determine the concentrations of total aldehydes, formaldehyde, and oxides of nitrogen. Statistically significant correlations were found between odor or irritation intensity estimates and the analytical data, but these correlations were too weak to permit accurate prediction of odor or irritation from chemical analyses. Effects of some engine variables on diesel odor were studied. Possible means of reducing diesel odor are discussed.