An optical sensor for measuring fuel film dynamics in a port-fuel-injected engine

Past research on fuel film dynamics has provided models of mass transport mechanisms in intake ports of port-fuel-injected engines, yet to date no validated method of measuring fuel film has been presented. This research attempts to fill this gap with design and development of a method of measuring port wall wetting in production, port-fuel-injected engines. The dissertation describes two iterations of refinement and engine testing of an accurate film measuring system. Each iteration includes design, manufacture, and installation of multiple optical sensors flush in the engine's intake port.;Optical measurement and flush mounting were used to minimize intrusion into fuel film behavior. Optical fibers carry light from lasers to port-mounted sensors where transmitting components in each sensor guide light into the fuel film so that it is internally reflected by the fuel-air interface. Receiving components of each sensor guide the reflected light to other optical fibers. Reflected light is sent to photodetectors and conditioning electronics, physically isolated from the running engine. Intensity of light varies with varying film thicknesses; intensity variation is converted into a voltage; and a calibration curve converts the voltage to a depth. Measurements are taken in an operating engine, unaltered except for installation of film sensors, an in-cylinder pressure transducer, and a universal exhaust oxygen sensor, installed in a test facility. Engine operation is controlled by the factory engine control computer. The engine is operated at various steady-state and transient conditions, and dynamic film depths measured are compared to film models and measured engine data.;Results show the sensors are capable of measuring dynamic changes in fuel films in operating engines. Dynamic fuel film signals were correlated with intake port events, such as injector firing, on a cycle-by-cycle basis. Fuel film was found to vary, both in magnitude of film and in the manner intake events effect measurements, with changes in engine operating conditions. Thus, this research appears to have developed a viable technique for measuring fuel films in an operating engine, and the measurements it provides may be used to validate film dynamics models and further understanding of relationships between fuel films and engine performance.