Search Results

Fatigue behaviors of aluminum 5754-O spot friction welds made by a concave tool in lap-shear specimens are investigated based on experimental observations and a fatigue life estimation model. Optical micrographs of the welds before and after failure under quasi-static and cyclic loading conditions are examined. The micrographs indicate that the failure modes of the 5754 spot friction welds under quasi-static and cyclic loading conditions are quite different. The dominant kinked fatigue cracks for the final failures of the welds under cyclic loading conditions are identified. Based on the experimental observations of the paths of the dominant kinked fatigue cracks, a fatigue life estimation model based on the stress intensity factor solutions for finite kinked cracks is adopted to estimate the fatigue lives of the welds.

A potential correlation between OH* chemiluminescence and exhaust NO concentration is investigated to pursue a simple diagnostic technique for measurements of NO cycle-to-cycle fluctuations. Previous investigations of NO formation in a direct-injection gasoline engine have indicated that there may be a correlation between the concentration of NO and OH* chemiluminescence. Shortcomings of this work, namely phase-locked measurements, were overcome in the present study by using highspeed imaging capability to obtain chemiluminescence within the entire engine cycle and from entire engine cylinder volume. Cycle-resolved NO exhaust gas detection were performed synchronously with the chemiluminescence measurements on an optical spark-ignited engine with spray-guided direct-injection. A quartz cylinder liner, head and piston windows provide optical access for a highspeed CMOS camera and image intensifier to capture OH* images.

Near-term energy policy for ground transportation is likely to have a strong focus on both gains in efficiency as well as the use of alternate fuels; as both can reduce crude oil dependence and carbon loading on the environment. Stratified-charge spark-ignition direct-injection (SIDI) engines are capable of achieving significant gains in efficiency. In addition, these engines are likely to be run on alternative fuels. Specifically, lower alcohols such as ethanol and iso-butanol, which can be produced from renewable sources. SIDI engines, particularly the spray-guided variant, tend to be very sensitive to mixture preparation since fuel injection and ignition occur within a short time of each other. This close spacing is necessary to form a flammable mixture near the spark plug while maintaining an overall lean state in the combustion chamber. As a result, the physical properties of the fuel have a large effect on this process.

This paper analyzes and compares reactor and engine behavior of a diesel oxidation catalyst (DOC) in the presence of conventional diesel exhaust and low temperature premixed compression ignition (PCI) diesel exhaust. Surrogate exhaust mixtures of n-undecane (C11H24), ethene (C2H4), CO, O2, H2O, NO and N2 are defined for conventional and PCI combustion and used in the gas flow reactor tests. Both engine and reactor tests use a DOC containing platinum, palladium and a hydrocarbon storage component (zeolite). On both the engine and reactor, the composition of PCI exhaust increases light-off temperature relative to conventional combustion. However, while nominal conditions are similar, the catalyst behaves differently on the two experimental setups. The engine DOC shows higher initial apparent HC conversion efficiencies because the engine exhaust contains a higher fraction of trappable (i.e., high boiling point) HC.

The feature of offered algorithm is that it allows, without record and analysis of the display diagram, to estimate a running cycle of a diesel engine parameters which characterize ecological and economic performances. The mathematical model described in report allows to determine connection of coefficient of filling, pressure and temperature of air boost, factor of excess of air with effectiveness ratio of combustion and contents of soot in exhaust gas and to take into account this connection at a choice initial data for control fuel feed or for elaboration of diesel engine dynamic model. The algorithm incorporated, for example, in the microcontroller of an electronic fuel feed controller allows analyzing the sensors data and theoretically determine of smoke amount in the exhaust gases for chosen cycle of fuel feed. The restriction of smoke is possible by criterion dD/dGT, where D - contents of soot in exhaust gas and GT - fuel cycle submission under the program-adaptive schema.

A fatigue crack growth model is adopted in this paper to investigate the fatigue lives of resistance spot welds in square-cup and lap-shear specimens of dual phase, low carbon and high strength steels under cyclic loading conditions. The fatigue crack growth model is based on the global stress intensity factor solutions for main cracks, the local stress intensity factor solutions for kinked cracks as functions of the kink length, the experimentally determined kink angles, and the Paris law for kinked crack propagation. The predicted fatigue lives based on the fatigue crack growth model are then compared with the experimental data. The results indicate that the fatigue life predictions based on the fatigue crack growth model are in agreement with or lower than the experimental results.

The spark process has previously been shown to heavily influence ignition stability, particularly in direct-injected gasoline engines. Despite this influence, few studies have addressed spark behavior in direct-injected engines. This study examines the role of environmental factors on the behavior of the spark. Through measurement of the spark duration, by way of the ignition current trace, several observations are made on the influence of external factors on the behavior of the spark. Changing the level of nitrogen in the cylinder (to simulate EGR), the level of wetting and velocity imparted by the spray, the ignition dwell time and the orientation of the ground strap, observations are made as to which conditions are likely to produce unfavorable (shorter) spark durations. Through collection of a statistically significant number of sample spark lengths under each condition, histograms have been assembled and compared under each case.

Ignition stability was studied in an optical spray guided spark ignition direct injection engine. The impact of intake air dilution with nitrogen, spark plug orientation, ignition system dwell time, and fuel injector targeting was addressed. Crank angle resolved fuel distributions were measured with a high-speed planar laser-induced fluorescence technique for hundreds of consecutive cycles. IMEP, COV of IMEP, burn rates and spark energy delivered to the gas were examined and used in conjunction with the imaging data to identify potential reasons for misfires.

Fatigue failures of spot friction welds in lap-shear specimens of aluminum 6111-T4 sheets under cyclic loading conditions are investigated in this paper. The paths of fatigue cracks near the spot friction welds are first discussed. A fatigue crack growth model based on the Paris law for crack propagation and the global and local stress intensity factors for kinked cracks is then adopted to predict the fatigue lives of these spot friction welds. The global stress intensity factors and the local stress intensity factors based on the recent published works for resistance spot welds in lap-shear specimens are used to estimate the local stress intensity factors for kinked cracks with experimentally determined kink angles. The results indicate that the fatigue life predictions based on the Paris law and the local stress intensity factors as functions of the kink length agree well with the experimental results.

The effects of image size on perceived distance have been of concern for convex rearview mirrors as well as camera-based rear vision systems. We suggest that the importance of image size is limited to cases-such as current rearview mirrors-in which the field of view is small. With larger, richer fields of view it is likely that other distance cues will dominate image size, thereby substantially diminishing the concern that distortions of size will result in distortions of distance perception. We report results from an experiment performed in a driving simulator, with static simulated rearward images, in which subjects were asked to make judgments about the distance to a rearward vehicle. The images showed a field of view substantially wider than provided by any of the individual rearview mirrors in current systems. The field of view was 38 degrees wide and was presented on displays that were either 16.7 or 8.5 degrees wide, thus minifying images by factors of 0.44 or 0.22.

A combination of imaging techniques for investigations of highly transient processes and cyclic variations in internal combustion engines is presented. The single high-speed camera setup uses a CMOS camera combined with a two-stage image-intensifier and two excimer lasers. Fuel mixing, ignition and combustion were monitored via planar laser induced fluorescence imaging of toluene as a tracer that was added to iso-octane in combination with the simultaneous recording of light emission from the spark plasma and OH* chemiluminescence of the developing flame. Image frame rates of 12 kHz for hundreds of cycles were achieved. Application to misfire events in a spray-guided gasoline direct-injection engine is described to illustrate the merits of the technique.

The spatial and temporal formation of nitric oxide in an optical engine operated with iso-octane fuel under spray-guided direct-injection conditions was studied with a combination of laser-induced fluorescence imaging, UV-chemiluminescence, and cycle resolved NO exhaust gas analysis. NO formation during early and late (homogeneous vs. stratified) injection conditions were compared. Strong spatial preferences and cyclic variations in the NO formation were observed depending on engine operating conditions. While engine-out NO levels are substantially lower for stratified engine operation, cyclic variations of NO formation are substantially higher than for homogeneous, stoichiometric operation.

A four-valve-pentroof, direct-injection, optical engine fueled with n-heptane has been operated at four different steady-state HCCI operating conditions including 10% and 65% residuals, both at low and high swirl conditions. Both, planar toluene LIF and volume chemiluminescence show large scale inhomogeneity in the ensemble averaged images. The interpretation of the toluene-tracer LIF signals (when premixed with the fresh-air charge) as a marker for reaction homogeneity is discussed. A binarization scheme and a statistical analysis of the LIF images were applied to the per-cycle planar-LIF images revealing inhomogeneities both from cycle-to-cycle and within the regions of individual cycles that track with the average heat release rate. Comparison of these two homogeneity metrics between the four operating conditions reveals weak but discernable differences.

The quasi-static crush behavior of aluminum 5052-H38 honeycomb specimens under non-proportional compression dominant combined loads is investigated by experiments. Compression dominant combined loads and pure compressive loads were applied in different sequences to induce non-proportional combined loads. The experimental results show that the normal crush and shear strengths in combined loading regions and the normal crush strengths in pure compressive loading regions of the non-proportional combined loads are quite consistent with the existing phenomenological yield criterion based on the experimental normal crush and shear strengths under proportional combined loads. The experimental results indicate that the sequence of loading paths for the non-proportional combined loads does not affect the crush strengths of honeycomb specimens.

For applications of planar laser induced fluorescence (PLIF) to measure the fuel or equivalence ratio distributions in internal combustion (IC) engines it is typically assumed that the addition of a fluorescence tracer to a base fuel does not alter the combustion performance. We have investigated the impact on combustion performance through the addition of various amounts of 3-pentanone or toluene to iso-octane fuel. Correlations between equivalence ratio for a range of fuel/tracer mixtures and engine parameters, like peak pressure, location of peak pressure, indicated mean effective pressure (IMEP), and peak burn rate are discussed for data obtained in a spark-ignition direct-injection (SIDI) gasoline engine operated with near homogeneous charge. For typical tracer concentrations the impact on combustion performance is mostly negligible.

This paper reports the development of a model of diesel combustion and NO emissions, based on a modified eddy dissipation concept (EDC), and its implementation into the KIVA-3V multidimensional simulation. The EDC model allows for more realistic representation of the thin sub-grid scale reaction zone as well as the small-scale molecular mixing processes. Realistic chemical kinetic mechanisms for n-heptane combustion and NOx formation processes are fully incorporated. A model based on the normalized fuel mass fraction is implemented to transition between ignition and combustion. The modeling approach has been validated by comparison with experimental data for a range of operating conditions. Predicted cylinder pressure and heat release rates agree well with measurements. The predictions for NO concentration show a consistent trend with experiments. Overall, the results demonstrate the improved capability of the model for predictions of the combustion process.

Effects of impact velocity on the crush behavior of aluminum 5052-H38 honeycomb specimens are investigated by experiments. An impact test machine using pressurized nitrogen was designed to perform dynamic crush tests. A test fixture was designed such that inclined loads can be applied to honeycomb specimens in dynamic crush tests. The results of dynamic crush tests indicate that the effects of impact velocity on the normal and inclined crush strengths are significant. The trends of the inclined crush strengths for specimens with different in-plane orientation angles as functions of impact velocity are very similar to that of the normal crush strength. Experimental results show similar progressive folding mechanisms for honeycomb specimens under pure compressive and inclined loads. Under inclined loads, the inclined stacking patterns were observed. The inclined stacking patterns are due to the asymmetric locations of the horizontal plastic hinge lines.

Quantitative LIF measurements of liquid fuel films on the piston of direct-injected gasoline engines are difficult to achieve because generally these films are thin and the signal strength is low. Additionally, interference from scattered laser light or background signal can be substantial. The selection of a suitable fluorescence tracer and excitation wavelength plays an important role in the success of such measurements. We have investigated the possibility of using toluene as a tracer for fuel film measurements and compare it to the use of 3-pentanone. The fuel film dynamics in a motored engine at different engine speeds, temperatures and in-cylinder swirl levels is characterized and discussed.

The link between manufacturing process and product performance is studied in order to construct analytical, quantifiable criteria for the introduction of new engine technologies and processes. Cost associated with a new process must be balanced against increases in engine performance and thus demand for the particular vehicle. In this work, the effect of the Abrasive Flow Machining (AFM) technique on surface roughness is characterized through measurements of specimens, and a predictive engine simulation is used to quantify performance gains due to the new surface finish. Subsequently, economic cost-benefit analysis is used to evaluate manufacturing decisions based on their impact on firm's profitability. A demonstration study examines the use of AFM for finishing the inner surfaces of intake manifolds for two engines, one installed in a compact car and the other in an SUV.

Resonant frequencies of a resonant bending system with notched crankshaft sections are obtained experimentally and numerically in order to investigate the effect of notch depth on the drop of the resonant frequency of the system. Notches with the depths ranging from 1 to 5 mm, machined by an EDM (Electrical-Discharging Machining) system, were introduced in crankshaft sections at the fillet between the main crank pin and crank cheek. The resonant frequencies of the resonant bending system with the crankshaft sections with various notch depths were first obtained from the experiments. Three-dimensional finite element models of the resonant bending system with the crankshafts sections with various notch depths are then generated. The resonant frequencies based on the finite element computations are in good agreement with those based on the experimental results.