Integrated Vehicle Dynamics

Presently, components of the vehicle act independently of one another to control various aspects of the vehicle's dynamics. In this research, the dynamics of a moving vehicle are controlled by coordinating and integrating the various subsystems of the chassis. Wheel torque, steering forces, and suspension forces are combined in a synergistic approach to achieve levels of vehicle performance and safety that are superior to previous approaches. Extensive use of modern control techniques is made to determine the optimal combination of forces.

The controllable flow of energy into and out of a vehicle suspension is studied in two phases: active control and semiactive control. Active control means being able to remove and/or add energy to the suspension from an external power source. Performance comparisons between active suspensions and passive suspensions, capable of only constant energy removal rates, demonstrate the benefits of the active systems. Semiactive control means being able to control the rate of energy removal but not being able to add energy to the system. Both approaches are investigated using theory, simulation, and experiment.

A single-cylinder, four-valve, extended piston, spark-ignition engine is used to study the effects of in-cylinder flow patterns on combustion and heat loss. Shrouded inlet values are used to vary turbulence levels, while five independent cooling systems can control component operating temperatures. Fast-response thermocouples are used to measure instantaneous temperatures and heat transfer rates at various locations inside the combustion chamber. The program will examine the local heat transfer rates at incipient knock conditions on both this piston and combustion chamber.

Atomization of liquid jets is of primary importance for many industrial applications. Models for prediction of instability and disintegration of liquid sheet jets and round jets are being developed. Aerodynamic instability that occurs at a disturbed two-phase interface is studied by using perturbation analysis. Detailed numerical simulation of the unstable waves on the two-phase interface is conducted to extend the analytical model well into the nonlinear breakup regime. The resulting models for both sheet jets and round jets will be incorporated into a multidimensional code for computations of internal combustion engines.

The fuel flow inside the intake port can be characterized in three phases: gaseous, dispersed droplet, and continuous liquid film. Computer simulations are conducted using a multidimensional code with spray and wall-film submodels to study the interaction among the three phases, intake valves and walls. The simulations are validated against data from previous measurements in a steady flow bench for testing port injection systems. The validated computational tool can be used to provide insight into the reduction of cold start emission from port-injection engines.

Knowledge of the instantaneous vapor and liquid fuel distributions is important to the improvement of direct-injection engines. A fluorobenzene/DEMA exciplex system is developed for concentration measurements of lower boiling fuel, such as hexane and gasoline. Particular attention is paid to linearity and spatial nonuniformity of the intensified camera, gain calibration and modulation transfer function of the signal collection system, fluorescence saturation, the selection of filters and of the concentrations of the two dopants to reject Mie scattering and reduce crosstalk while enhancing the vapor signal. This system is capable of yielding qualitative liquid and quantitative vapor instantaneous spatial distributions.

Natural gas is an attractive alternative fuel for diesel engines because of the potential for achieving high thermal efficiencies and power densities, reduced fuel costs, and reduced particulate emissions. A single cylinder engine has been modified to provide optical access to the cylinder for measurements of fuel/air mixing, flame propagation, and NO formation using laser-induced fluorescence. In-cylinder measurements of temperatures and fuel-air ratios will be performed using coherent anti-Stokes Raman scattering. Modeling of the natural gas injection, mixing, ignition, and combustion will be conducted using a modified version of the KIVA 3 code.

The preparation of fuel and air mixtures during cold start conditions for port injection systems is being inves tigated. Because cold start emissions of unburned hydrocarbons are strongly influenced by the presence of liquid fuel in the combustion chamber, this study seeks to develop an improved understanding of the fuel preparation process as it relates to cold start atomization and mixing. Laser diagnostics are being used to study liquid atomization, vaporization, and mixing with air in the intake port and cylinder as a function of engine variables including valve lift, air flow, manifold geometry, and fuel injector type.

Fuel atomization and vaporization processes can strongly influence cold start hydrocarbon emissions, drivability, and idle stability. The goal of this research is to determine the effects of fuel properties on the mixture preparation in port-injected reciprocating engines. Laser diagnostic techniques are used to characterize droplet size distributions and fuel vapor concentrations for different fuels.

Use of compressed natural gas is attractive for large-displacement, heavy-duty engines because of emission standards and availability. Mixing of natural gas with air and the distribution of the gas-air mixture to the cylinders is important to avoid cylinder-to-cylinder variations. The velocity and concentration distributions of the gas-air mixture are being measured throughout the intake system to determine the contribution of individual components on engine performance and exhaust emissions. Improved intake system components could then be designed to minimize undesirable cycle-to-cycle variations.