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The identification of the dominant noise sources in diesel engines and the assessment of their contribution to far-field noise is a process that can involve both fired and motored testing. In the present work, the cross-spectral densities of signals from cylinder pressure transducers, accelerometers mounted on the engine surface, and microphones (in the near and far fields), were used to identify dominant noise sources and estimate the transfer paths from the various “inputs” (i.e., the cylinder pressures, the accelerometers and the near field microphones) to the far field microphones. The method is based on singular value decomposition of the input cross-spectral matrix to relate the input measurements to independent virtual sources. The frequencies at which a particular input is strongly affected by an independent source are highlighted, and with knowledge of transducer locations, inferences can be drawn as to possible noise source mechanisms.

The structural excitation by turbulent flow pressure fluctuations continues to be an important part of vehicle NVH analysis and design. Much of the analytical work on turbulent flow has been limited to flow over smooth, flat surfaces. Measurements and CFD analyses show a significantly different pressure spectrum for flows over an obstruction. The coupling of the turbulent pressure excitation to the structural vibration and transmitted sound depends on the spatial matching between the source and response fields. This paper develops an analytical model for the spatial correlation of turbulent flow pressure fluctuations downstream of an obstruction. Such a model is useful in the early design stage of a vehicle and is compatible with SEA models of the fluid structure interaction.

Experimental measurements of tire tread band vibration have provided direct evidence that higher order structural-acoustic modes exist in tires, not just the well-known fundamental acoustical mode. These modes display both circumferential and radial pressure variations within the tire's air cavity. The theory governing these modes has thus been investigated. A brief recapitulation of the previously-presented coupled structural-acoustical model based on a tensioned string approach will be given, and then an improved tire-acoustical model with a ring-like shape will be introduced. In the latter model, the effects of flexural and circumferential stiffness are considered. This improved model accounts for propagating in-plane vibration in addition to the essentially structure-borne flexural wave and the essentially airborne longitudinal wave accounted for in the previous model. The longitudinal structure-borne wave “cuts on” at the tire's circumferential ring frequency.

Component sound quality is an important factor in the design of competitive diesel engines. One component noise that causes complaints is the gear rattle that originates in the front-of-engine gear train which drives the fuel pump and other accessories. The rattle is caused by repeated tooth impacts resulting from fluctuations in differential torsional acceleration of the driving gears. These impacts generate a broadband, impulsive noise that is often perceived as annoying. In most previous work, the overall sound quality of diesel engines has been considered without specifically focusing on predicting the perception of gear rattle. Gear rattle level has been quantified based on angular acceleration measurements, but those measurements can be difficult to perform. Here, the emphasis was on developing a metric based on subjective testing of the perception of gear rattle.

This paper is part of a larger body of experimental and computational work devoted to studying the role of close-coupled post injections on soot reduction in a heavy-duty optical engine. It is a continuation of an earlier computational paper. The goals of the current work are to develop new CFD analysis tools and methods and apply them to gain a more in depth understanding of the different in-cylinder environments into which fuel from main- and post-injections are injected and to study how the in-cylinder flow, thermal and chemical fields are transformed between start of injection timings. The engine represented in this computational study is a single-cylinder, direct-injection, heavy-duty, low-swirl engine with optical components. It is based on the Cummins N14, has a cylindrical shaped piston bowl and an eight-hole injector that are both centered on the cylinder axis. The fuel used was n-heptane and the engine operating condition was light load at 1200 RPM.

An experiment has been developed to investigate the ignition characteristics of ultra-lean premixed H2/air mixtures by a supersonic hot jet. The hot jet is generated by combustion of a stoichiometric mixture in a small prechamber. The apparatus adopted a dual-chamber design in which a small-volume (1% of the main chamber by volume) prechamber was installed within a large-volume main chamber. A small orifice (nozzle) connects the two chambers. Spark initiated combustion inside the prechamber causes a pressure rise and pushes the gases though the nozzle, resulting in a hot jet that would ignite the lean mixture in the main chamber. Simultaneous high-speed Schlieren photography and OH* Chemiluminescence were applied to visualize the jet penetration and the ignition processes inside the main chamber. Hot Wire Pyrometry (HWP) was used to measure temperature distribution of the transient hot jet.

This paper describes a novel design and verification process for analytical methods used in the development of advanced combustion strategies in internal combustion engines (ICE). The objective was to improve brake thermal efficiency (BTE) as part of the US Department of Energy SuperTruck program. The tools and methods herein discussed consider spray formation and injection schedule along with piston bowl design to optimize combustion efficiency, air utilization, heat transfer, emission, and BTE. The methodology uses a suite of tools to optimize engine performance, including 1D engine simulation, high-fidelity CFD, and lab-scale fluid mechanic experiments. First, a wide range of engine operating conditions are analyzed using 1-D engine simulations in GT Power to thoroughly define a baseline for the chosen advanced engine concept; secondly, an optimization and down-select step is completed where further improvements in engine geometries and spray configurations are considered.

One way to develop an understanding of soot formation and oxidation processes that occur during direct injection and combustion in an internal combustion engine is to image the natural luminosity from soot over time. Imaging is possible when there is optical access to the combustion chamber. After the images are acquired, the next challenge is to properly interpret the luminous distributions that have been captured on the images. A major focus of this paper is to provide guidance on interpretation of experimental images of soot luminosity by explaining how radiation from soot is predicted to change as it is transmitted through the combustion chamber and to the imaging. The interpretations are only limited by the scope of the models that have been developed for this purpose. The end-goal of imaging radiation from soot is to estimate the amount of soot that is present.

Excessive vibration and poor controllability occur in many mobile fluid power applications, with negative consequences as concerns operators' health and comfort as well as machine safety and productivity. This paper addresses the problem of reducing oscillations in fluid power machines presenting a novel control technique of general applicability. Strong nonlinearities of hydraulic systems and the unpredictable operating conditions of the specific application (e.g. uneven ground, varying loads, etc.) are the main challenges to the development of satisfactory general vibration damping methods. The state of the art methods are typically designed as a function of the specific application, and in many cases they introduce energy dissipation and/or system slowdown. This paper contributes to this research by introducing an energy efficient active damping method based on feedback signals from pressure sensors mounted on the flow control valve block.

Helmholtz resonator has been used in industry for a long time to reduce the noise from exhaust system in vehicle or machinery. Numerous investigations have been done in the past to study the effect of a Helmholtz resonator connected to a pipeline. A general procedure for the analysis of curved or flat, thin two dimensional gas cavities such as thin compressor or engine manifolds or so-called thin shell type muffler elements, which can efficiently utilize the limited space of hermetically sealed compressors or small engine compartments, has been developed by the authors, as long as the thickness of the cavities is substantially small compared to the shortest wavelength of interest. However, to the authors' knowledge, a Helmholtz resonator attached to a rectangular thin muffler element, which is similar to a refrigeration compressor muffler, has not been analyzed.

An experimental apparatus and a numerical model have been designed and developed to examine the lubrication condition and frictional losses at the piston and cylinder interface. The experimental apparatus utilizes components from a single cylinder, ten horsepower engine in a novel suspended liner arrangement. The test rig has been specifically designed to reduce the number of operating variables while utilizing actual components and geometry. A mixed lubrication model for the complete ring-pack and piston skirt was developed to correlate with experimental measurements and provide further insight into the sources of frictional losses. The results demonstrate the effects of speed and viscosity on the overall friction losses at the piston and cylinder liner interface. Comparisons between the experimental and analytical results show good agreement.

Legislation world-wide has made it necessary to find ways to control the level of engine emissions and reduce the damage to our environment. Increasing restrictions have made the elimination of zinc dithiophosphates from crankcase oils and increasing the effectiveness of catalytic converters viable options. Lead and phosphorus containing compounds in the exhaust are known catalyst poisons that shorten the life of current automotive catalysts. Unleaded fuel has successfully resulted in a reduction of harmful emissions due to the fuel. Current government and industry research is actively pursuing replacement of phosphorus additives with phosphorus free additives. Several phosphorus-free oils were developed and are evaluated in bench tests in this study. Test comparisons with phosphorus- containing oils demonstrated satisfactory oxidation stability and wear performance of the phosphorus free oils.

The objective of this work is to demonstrate the influence of line length concerning noise source generation using a coupled pump-motor-line model predicting superimposed pulsations of a hydrostatic transmission. This transmission model predicts superimposed flow pulsations throughout the connecting lines as well as oscillating forces dependant on system pressure variances; such oscillations are the primary sources of noise in hydrostatic transmissions which are known as FBN and SBN (Fluid Borne Noise and Structure Borne Noise), respectively. This study is a part of novel research where the prediction of superimposed noise sources considering interrelating dynamics of the pump/motor and connecting lines is accomplished and can potentially be used to develop noise source reduction strategies. An investigation considering the influence of line length demonstrates the potential to further reduce noise source generation in hydrostatic transmissions.

This paper describes the numerical modeling of the hydraulic circuit of a self-moving boom lift. Boom lifts consist of several hydraulic actuators, each of them performs a specific movement. Hydraulic systems for lifting applications must ensure consistent performance no matter what the load and how many users are in operation at the same time. Common solutions comprise a fixed or a variable displacement pump with load-sensing control strategy. Instead, the hydraulic circuit studied in this paper includes a fixed displacement pump and an innovative (patented) proportional valve assembly. Each proportional valve (one for each user) permits a flow regulation for all typical load conditions and movement simultaneously. The study of the hydraulic system required a detailed modeling of some components such as: the overcenter valves, for the control of the assistive loads; the proportional valve, which keeps a constant flow independently of pressure drop across itself.

Noise Vibration Harshness (NVH) is one of the key factors in selecting and designing Automotive A/C systems. This paper will deal with the analysis of pressure pulsation in the suction manifold of a multi-cylinder compressor. Numerical simulation methods have been developed to model and simulate the compression cycle, valve dynamics and mass flow rate into the compressor cylinder. The model was also enhanced to include pressure fluctuations due to the interactions between multiple cylinders in the suction manifold. The analytical results from the simulation program compared favorably with the experimental results. The validation and confirmation of the simulation model was successfully accomplished thus yielding a very valuable tool that could be used during the design stage.

Experimental modal analysis (EMA) provides many parameters that are required in numerical modeling of dynamic and vibratory behavior of structures. This paper discusses EMA on an exhaust system of an off-road car. The exhaust structure is tested under three boundary conditions: free-free, supported with two elastomeric mounts, and mounted to the car. The free-free modal parameters are compared to finite element results. The two-mount tests are done with the mounts fixed to a rigid and heavy frame. The rigidity of the frame is verified experimentally. The on-car test is done with realistic boundary conditions, where the exhaust structure is fixed to the engine manifold as well as the two elastomeric mounts. The two-mount and the on-car tests result in highly complex mode shapes.

Modern pulse-turbocharged systems produce a turbine operating environment that is dominated by unsteady flow. Effective utilization of the unsteady exhaust gas energy content at the turbine inlet is critical to achieving optimum system efficiency. This work presents predictions for turbocharger unsteady performance from a model based on the Euler equations with source terms (EEST). This approach allows the time-accurate performance of the turbine to be determined, allowing comparisons of actual energy utilization and that estimated from steady flow performance maps.

The damping effect that is observed when a fibrous acoustical treatment is applied to a thin metal panel typical of automotive structures has been modeled by using three independent techniques. In the first two methods the fibrous treatment was modeled by using the limp frame formulation proposed by Bolton et al., while the third method makes use of a general poro-elastic model based on the Biot theory. All three methods have been found to provide consistent predictions that are in excellent agreement with one another. An examination of the numerical results shows that the structural damping effect results primarily from the suppression of the nearfield acoustical motion within the fibrous treatment, that motion being closely coupled with the vibration of the base panel. The observed damping effect is similar in magnitude to that provided by constrained layer dampers having the same mass per unit area as the fibrous layer.

Electric machinery is typically based upon the interaction of magnetic fields and current to produce electromagnetic force or torque. However, force and torque can also be produced through the use of electric fields. The purpose of this investigation is to briefly analyze the use of a switched capacitance electric field based machine to see if it may have aerospace applications for use as either propulsion motor for unmanned aerospace vehicle (UAV) or lightweight flywheel applications for aerospace applications. It is shown that although its use as a hub propulsion motor is not feasible, it may be a candidate for use in a power flywheel energy storage system.

A mathematical model of a gas-charged mono-tube racing damper is presented. The model includes bleed orifice, piston leakage, and shim stack flows. It also includes models of the floating piston and the stiffness characteristics of the shim stacks. The model is validated with experimental tests on an Ohlins WCJ 22/6 damper and shown to be accurate. The model is exercised to show the effects of tuning on damper performance. The important results of the exercise are 1) the pressure variation on the compression side of the piston is insignificant relative to that on the rebound side because of the gas charge, 2) valve shim stiffness can be successfully modeled using stacked thin circular plates, 3) bleed orifice settings dominate the low speed regime, and 4) shim stack stiffness dominates the high speed regime.