Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3631. Adviser: Dimitrios C. Kyritsis. Includes bibliographical references (leaves 144-149) Available on microfilm from Pro Quest Information and Learning.

This thesis investigates the principle of integration of vehicle dynamics control systems by proposing a novel control architecture to integrate the brake-based electronic stability control (ESC), active front steering (AFS), normal suspension force control (NFC) and variable torque distribution (VTD). A nonlinear 14 degree of freedom passive vehicle dynamics model was developed in Matlab/Simulink and validated against commercially available vehicle dynamics software CarSim. Dynamics of the four active vehicle control systems were developed. Fuzzy logic and PID control strategies were employed considering their robustness and effectiveness in controlling nonlinear systems. Effectiveness of active systems in extending the vehicle operating range against the passive ones was investigated. From the research, it was observed that AFS is effective in improving the stability at lower lateral acceleration (latac) region with less interference to the longitudinal vehicle dynamics. But its ability diminishes at higher latac regions due to tyre lateral force saturation. Both ESC and VTD are found to be effective in stabilising the vehicle over the entire operating region. But the intrusive nature of ESC promotes VTD as a preferred stability control mechanism at the medium latac range. But ESC stands out in improving stability at limits where safety is of paramount importance. NFC is observed to improve the ability to generate the tyre forces across the entire operating range. Based on this analysis, a novel rule based integrated chassis control (ICC) strategy is proposed. It uses a latac based stability criterion to assign the authority to control the stability and ensures the smooth transition of the control authority amongst the three systems, AFS, VTD and ESC respectively. The ICC also optimises the utilisation of NFC to improve the vehicle handling performance further, across the entire operating regions. The results of the simulation are found to prove that the integrated control strategy improves vehicle stability across the entire vehicle operating region.

<p>This thesis describes a custom algorithm developed to optimize a simple planetary gear set. The optimization minimizes volume for one simple planetary gear set using American Gear Manufacturers Association stress equations, custom design constraints, and material constraints. Through predetermined reactions to adjustments, component features and planetary variables are modified systematically to obtain the target solution. This thesis demonstrates that the defined approach is an effective means of balancing all three components of a simple planetary gear set, thus resulting in a solution that has been optimized for volume. </p>

<p> Personal transportation has a large and increasing impact on people, society, and the environment globally. Computational energy-use simulation is becoming a key tool for automotive research and development in designing efficient, sustainable, and consumer acceptable personal transportation systems. Historically, research in personal transportation system design has not been held to the same standards as other scientific fields in that classical experimental design concepts have not been followed in practice. Instead, transportation researchers have built their analyses around available automotive simulation tools, but conventional automotive simulation tools are not well-equipped to answer system-level questions regarding transportation system design, environmental impacts, and policy analysis. </p><p> The proposed work in this dissertation aims to provide a means for applying more relevant simulation and analysis tools to these system-level research questions. First, I describe the objectives and requirements of vehicle energy-use simulation and design research, and the tools that have been used to execute this research. Next this dissertation develops a toolset for constructing system-level design studies with structured investigations and defensible hypothesis testing. The roles of experimental design, optimization, concept of operations, decision support, and uncertainty are defined for the application of automotive energy simulation and system design studies. </p><p> The results of this work are a suite of computational design and analysis tools that can serve to hold automotive research to the same standard as other scientific fields while providing the tools necessary to complete defensible and objective design studies.</p>

<p> Under pressure from rising fuel costs, emissions constraints, and new government regulations on medium- and heavy-duty vehicles, hybrid technologies for these classes of vehicles are becoming more prevalent. A variety of technologies have been proposed to meet these requirements including power-assist hybrid electric and hybrid hydraulic systems. Although there has been great discussion about the benefits surrounding each of the technologies individually, no direct comparisons are available on the basis of economics and fuel economy. This study focuses on comparing these power-assist technologies on these bases as well as determines the ability of these technologies to fulfill the newly adopted fuel economy regulations. </p><p> In order to accomplish this goal, three computational models of vehicle dynamics, thermal behavior and fuel economy were created and validated to simulate the conventional vehicle and hydraulic and electric hybrids. These models were simulated over the Heavy-Duty Urban Dynamometer Driving Schedule, the HTUF Class 4 Parcel Delivery Cycle, and the Orange County Bus cycle. These drive cycles were chosen on their ability to characterize the variety of operating conditions observed in medium- and heavy-duty vehicles. Using these models, cross technology comparisons were constructed comparing commercially available systems, systems with a fixed mass, and systems with a fixed incremental cost. </p><p> The results of the commercially available systems showed that the Azure Dynamics HEV provided greater fuel economy improvement than the Lightning Hybrids HHV for drive cycle kinetic intensities less than 3.19 miles^-1. Although this system showed a cost of fuel savings over the HHV, it was seen that the incremental cost of the HEV exceeded the cost of fuel savings over the HHV. The fixed mass comparison case, which compared vehicles with equal cargo carrying utility, showed similar results to that of the commercially available case. Although the increase in incremental cost for the varying HEV systems designed for the fixed mass case correlated to an improvement in fuel savings, the cost associated with the systems surpassed the savings seen. Lastly, the fixed cost case provided results which were also similar to the commercially available case. Due to the fixed system cost, it was seen that for these systems, the fuel economy benefits and associated cost showed the greatest benefits for the HEV. </p><p> This study concluded that given the evaluation, the HEV was the only power-assist hybrid technology which could fulfill the regulated fuel economy improvement of 15%. Although the HEV was the only technology which could fulfill the requirements, the HHV showed an improvement upwards of 7% greater than the HEV for the Orange County Bus Drive Cycle.</p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4777. Adviser: Chia-Fon F. Lee. Includes bibliographical references (leaves 434-447) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4792. Adviser: Chia-Fon Lee. Includes bibliographical references (leaves 196-205) Available on microfilm from Pro Quest Information and Learning.

<p> Natural gas/diesel dual fuel engines offer a path towards meeting current and future emissions standards with lower fuel cost. However, numerous technical challenges remain that require a greater understanding of the in-cylinder combustion physics. For example, due to the high compression ratio of diesel engines, substitution of natural gas for diesel fuel at high load is often limited by engine knock and pre-ignition. Additionally, increasing the natural gas percentage in a dual fuel engine often results in decreasing maximum load. These problems limit the substitution percentage of natural gas in high compression ratio diesel engines and therefore reduce the fuel cost savings. Furthermore, when operating at part load dual fuel engines can suffer from excessive emissions of unburned natural gas. Computational fluid dynamics (CFD) is a multi-dimensional modeling tool that can provide new information about the in-cylinder combustion processes causing these issues. </p><p> In this work a multi-dimensional CFD model has been developed for dual fuel natural gas/diesel combustion and validated across a wide range of engine loads, natural gas substitution percentages, and natural gas compositions. The model utilizes reduced chemical kinetics and a RANS based turbulence model. A new reduced chemical kinetic mechanism consisting of 141 species and 709 reactions was generated from multiple detailed mechanisms, and has been validated against ignition delay, laminar flame speed, diesel spray experiments, and dual fuel engine experiments using two different natural gas compositions. Engine experiments were conducted using a GM 1.9 liter turbocharged 4-cylinder common rail diesel engine, which was modified to accommodate port injection of natural gas and propane. A combination of experiments and simulations were used to explore the performance limitations of the light duty dual fuel engine including natural gas substitution percentage limits due to fast combustion or engine knock, pre-ignition, emissions, and maximum load. In particular, comparisons between detailed computations and experimental engine data resulted in an explanation of combustion phenomena leading to engine knock in dual fuel engines. </p><p> In addition to conventional dual fuel operation, a low temperature combustion strategy known as reactivity controlled compression ignition (RCCI) was explored using experiments and computations. RCCI uses early diesel injection to create a reactivity gradient leading to staged auto-ignition from the highest reactivity region to the lowest. Natural gas/diesel RCCI has proven to yield high efficiency and low emissions at moderate load, but has not been realized at the high loads possible in conventional diesel engines. Previous attempts to model natural gas/diesel RCCI using a RANS based turbulence model and a single component diesel fuel surrogate have shown much larger combustion rates than seen in experimental heat release rate profiles, because the reactivity gradient of real diesel fuel is not well captured. To obtain better agreement with experiments, a reduced dual fuel mechanism was constructed using a two component diesel surrogate. A sensitivity study was then performed on various model parameters resulting in improved agreement with experimental pressure and heat release rate.</p>

The effects of in-cylinder and injection pressures on the formation and autoignition of diesel sprays at realistic automotive in-cylinder conditions was investigated. A two-stroke diesel Proteus engine has been modified to allow optical access for visualisation of in-cylinder combustion processes. Various optical techniques were used to investigate the combustion processes. These include high-speed video recording of the liquid phase, high-speed schlieren video recording of the vapour phase and laser-induced incandescence for soot imaging. The spray cone angle and penetration with time data extracted from photographic and high-speed video studies are presented. The effects of droplet evaporation, breakup and air entrainment at the initial stage of spray penetration were studied theoretically using three models. It was found that the predictions of the model combining bag breakup and air entrainment are in good agreement with the experimental measurements. Spray autoignition was investigated using video, in-cylinder pressure, and schlieren recordings. Pseudo three-dimensional visualisation of the autoignition was achieved by simultaneous use of two high-speed video cameras at right angles to each other. The effects of elevated injection and in-cylinder pressures on the ignition delay and ignition sites have been investigated. Laser-induced incandescence was performed to obtain maps of soot concentration for a range of engine conditions. The influence of in-cylinder and injection pressures on soot formation sites and relative soot concentration has been studied. The work has been mainly focused on the specificities of soot formation under extreme in-cylinder conditions.

The results of a comparative analysis of liquid and gas phase models for fuel droplets heating and evaporation, suitable for implementation into computational fluid dynamics (CFD) codes, are presented. Among liquid phase models, the analysis is focused on the model based on the assumption that the liquid thermal conductivity is infinitely large, and the so called effective thermal conductivity model. Seven gas phase models are compared. These are six semi-theoretical models, based on various assumptions, and a model based solely on the approximation to experimental data. It is pointed out that the gas phase model, taking into account the finite thickness of the thermal boundary layer around the droplet, predicts the evaporation time closest to the one based on the approximation to experimental data. The values of the absorption coefficients of gasoline fuel (BP Pump Grade 95 RON ULG), 2,2,4-trimethylpentane (CH3)2CHCH2C(CH3)3 (iso-octane) and 3-pentanone CH3CH2COCH2(CH3)3 have been measured experimentally in the range of wavelengths between 0.2 μm and 4 μm. The values of the average absorption efficiency factor for all fuels have been approximated by a power function aRdb, where Rd is the droplet radius. a and b in turn have been approximated by piecewise quadratic functions of the radiation temperature, with the coefficients calculated separately in the ranges 2 - 5 μm, 5 - 50 μm, 50 - 100 μm and 100 - 200 μm for all fuels. This new approximation is shown to be more accurate compared with the case when a and b are approximated by quadratic functions or fourth power polynomials of the radiation temperature, with the coefficients calculated in the full range of 2 - 200 μm. Results of experimental studies of heating and evaporation of monodisperse ethanol and acetone droplets in two regimes are compared with the results of modelling. It is pointed out that for relatively small droplets the experimentally measured droplet temperatures are close to the predicted average droplet temperatures, while for larger droplets the experimentally measured droplet temperatures are close to the temperatures predicted at the centre of droplets. All the developed models have been implemented into the KIVA-2 CFD code and validated against available in-house experimental data referring to spray penetration and ignition delay in Diesel engines.