Designers of engines have always looked for ways to improve the power to weight ratio of mobile internal combustion engines. This was especially true in aircraft engine design and engines for various forms of racing. Today designers are looking for ways to make everything from cars to road tractors to farm tractors lighter and thereby more efficient. In addition, in many cases these vehicles only need the maximum power that an engine can produce for a small amount of time. What is needed is a small, lightweight engine with the ability to produce a large amount of power for a short duration. The work here describes one possible method for constructing just such a type of engine. By adding a combustion chamber in the exhaust flow between the engine exhaust valve and the turbine inlet on a turbocharged diesel engine, it should be possible to increase the turbine temperature. This will in turn allow the turbine to deliver more power to the compressor and create a higher inlet pressure and allow the engine to create more power. This paper describes both a computer simulation and an engine with this combustion chamber installed. There were however, problems with both the simulation as well as the test engine. While no quantitative data was obtained from the test engine, some valuable observations were made. The computer simulation yielded results and from these results and observations made while testing the engine with the combustion chamber installed it was determined that this design shows promise of creating an engine with higher specific power. / Master of Science

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The trend in passenger vehicle internal combustion (IC) engines is to produce smaller, more fuel-efficient engines with power outputs comparable to those of large displacement engines. One way to accomplish this goal is through using turbochargers (TCs) supported on semi-floating ring bearings (SFRBs). The thesis presents progress on the nonlinear modeling of rotor-bearing systems (RBSs) by including engine-induced TC housing excitations. Test data collected from an engine-mounted TC unit operating to a top speed of 160 krpm (engine speed = 3,600 rpm) validates the nonlinear predictions of shaft motion. Engine-induced housing excitations are input into the nonlinear time transient rotor model as Fourier coefficients (and corresponding phase angles) derived from measured TC center housing accelerations. Analysis of recorded housing accelerations shows the IC engine induces TC motions with a broad range of subsynchronous frequencies, rich in engine (e) superharmonics. In particular, 2e and 4e vibration frequencies contribute greatly to housing motion. Most importantly, the analysis reveals TC center and compressor housings do not vibrate as a rigid body. Eigenvalue analysis of the TC system evidences four damped natural frequencies within the TC operating speed range. However, only the highest damped natural frequency (first elastic mode, f = 2,025 Hz, ξ = 0.14) is lightly-damped (critical speed = 150 krpm). Predicted linear and nonlinear imbalance response amplitudes increase with TC shaft speed, with linear predictions agreeing with test data at high shaft speeds. The differences between predictions and test data are attributed to an inaccurate knowledge of the actual TC rotor imbalance distribution. For the nonlinear analysis, predicted shaft motions not accounting for housing accelerations show the TC is stable (i.e. no subsynchronous whirl) at all but the lowest shaft speeds (<70 krpm). However, predicted shaft motions accounting for housing accelerations, as well as the test data, reveal TC motions rich in subsynchronous activity. Clearly, engine-induced housing accelerations have a significant impact on TC shaft motions. Predicted total shaft motions show good agreement with test data. Predicted nonlinear subsynchronous amplitudes as well as peak shaft amplitudes also agree well with test data. However, nonlinear predictions only show TC shaft vibrations attributed to engine order frequencies below 6e, whereas test data evidences TC vibrations are due to order frequencies greater than 6e. Overall, nonlinear predictions and test data illustrate the importance of accounting for engine-induced housing vibrations in the design and operation of TC systems. The good agreement between predictions and test data serve to validate the rotor model. The tools developed will aid a TC manufacturer in reducing development time and expenditures.

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One of the common failure modes of the diesel engine turbochargers is high-cycle fatigue of the turbine-wheel blades. Mistuning of the blades due to the casting process is believed to contribute to this failure mode. A laser vibrometer is used to characterize mistuning for a population of turbine wheels through the analysis of the blade-response to piezo-speaker induced noise. The turbine-wheel design under investigation is radial and is typically used in 6-12L diesel engine applications. FRFs and resonance frequencies are reviewed and summarized. The study includes test results for a paddle wheel that represents a perfectly tuned system and acts as a reference. A discrete mass-spring model is developed for the paddle wheel and the model suitability is tested against measured data. Density randomization is applied to model mistuning in the turbine wheels. Frequency mistuning and relative amplitude modelling for blade modes is found in good agreement with the data, however the mass-spring model over-predicts amplitude-amplification factors for a population of radial-turbine wheels, especially with regard to hub-dominant modes. A continuous twisted-blade model is developed in Matlab using finite-element techniques. Experimental data is shown to have good agreement with the twisted-blade model. Whitehead’s maximum amplitude-amplification prediction using RMS value for a tuned amplitude value is calculated, and the turbine-wheel response is found to fit within the theoretical limit. Different mistuning patterns are studied using the twisted-blade model. Maximum and minimum response patterns are identified and recommended.

Rotordynamic instability is present in most or all automotive turbochargers. High subsynchronous amplitudes can cause a variety of problems in areas such as mechanical failures, emissions regulations and rotor design. Self-excited vibrations from sources of damping can lock in at lateral natural frequencies causing dangerously high vibration levels. The resulting high-amplitude conical and bending modes can be reduced in order to achieve a more robust system. This research focuses on the relationship between synchronous and subsynchronous amplitude levels. It is theorized that an increase in unbalance could cause a reduction in subsynchronous vibration amplitudes. Through the use of a custom turbocharger, a series of unbalances were applied to both the turbine and compressor wheels and the resulting amplitudes were recorded off a modified compressor nut. The resulting data were reduced and are presented at the end of this paper. / Master of Science

Automotive turbochargers experience self-excited instabilities through the majority of their operating speed range. The results of these instabilities can cause damage to the bearings, shafts, and housing walls. Preventing this damage while maintaining or increasing performance characteristics is a huge concern to industry due to the time and money needed to replace vital components. The aim of this research is to determine which characteristics of the bearings have the greatest influence on the damped natural frequencies. It was believed that axial groove bearings could offer an acceptable alternative to the floating ring bearings currently found in automotive turbochargers. DyRoBeS rotor dynamics software was used to determine analytically damped natural frequencies for floating ring bearings, and also for six, eight, and ten axial groove fixed geometry bearings, under different speed and loading conditions. The resulting data were compared to experimental test results from an on-engine turbocharger test stand and presented in this report. / Master of Science

This research investigates the effects of an electric turbocharger in a hybrid electric powertrain. First generic vehicle models are created and run to understand the overall powertrain requirements of torque, power and energy of a performance consumer vehicle. Then a low fidelity baseline model of a conventional vehicle is created in Simulink to serve as a baseline measure. To analyze an electric turbocharger system a high-fidelity model in AMESIM of a 4 cylinder turbocharged engine was modified. This engine model was analyzed using virtual dynamometer tests and a simplified look-up table based controller was developed for the electric motor within the electric turbocharger. Next this engine model was inserted within three different types of hybrid powertrain architectures models in AMESIM. Each hybrid powertrain required a unique supervisory controller which was developed using Stateflow in Simulink. These controller algorithms were imported into AMESIM and the model was simulated over standard drive cycles. Since a very wide variation of electrification level exists within hybrid powertrains the supervisory controllers are calibrated for charge-sustaining simulations. This allows for impartial comparisons across the hybrid architectures. Lastly a track drive cycle was developed to understand electric turbocharger effects under high performance loading conditions / Thesis / Master of Applied Science (MASc) / Turbochargers on internal combustion engines can utilize a portion of waste exhaust energy to pump more air into the cylinder leading to greater power and efficiency. A modern high performance 4-cylinder turbocharged engine is capable of replacing a V6 engine of much higher cylinder displacement. However turbocharged engines suffer from ‘turbo lag’ when the engine cannot immediately produce power. An electric turbocharger can virtually eliminate this ‘turbo lag’ as well as generate electricity from excess energy the turbocharger does not use. Electric turbochargers have been development by researchers and various automotive manufacturers. However the potential effects of such a system within the framework of a hybrid electric powertrain in a consumer vehicle has not been quantified. The objective of this research is to use high fidelity models to investigate the effects of an electric turbocharger system within a hybrid powertrain.

Rotors in fluid-film bearing supported turbomachinery are known to develop elliptical orbits as a result of rotor-bearing interactions, mass unbalance within the rotor, gravitational bending of the shaft and external excitation. In synchronous whirl, where the speed at which the shaft travels about the orbit is equal to the rotational speed of the rotor, temperature gradients may develop across the journal as a result of viscous shear in the bearing's lubricant film. This thermal gradient leads to bending of the shaft in a phenomenon known as The Morton Effect. Such thermally induced bending causes further growth of the elliptical orbit resulting in further bending leading to excessive vibration levels and premature bearing failure. This analysis examines the development of the Morton Effect in medium-speed turbochargers typical to shipboard propulsion engines and the effect that bearing clearance has on thermal stability. Floating ring and tilting pad journal bearings are considered with a single stage, overhung centrifugal compressor and an overhung axial turbine. Results indicate a correlation between bearing clearance and thermal stability in the rotor-bearing system. A model for the aerodynamic force generated as a result of interaction between air exiting a centrifugal compressor and the compressor's annulus in a turbocharger is then developed and applied to the rotor-bearing systems. Results suggest little correlation between this aerodynamic force and the development of the Morton Effect. / Master of Science