A variety of diagnostic techniques useful for the study of cold start phenomena are presented. Although the tools are demonstrated in a port fuel-injected engine, they are also suitable for direct-injection gasoline engines.
A very useful technique, seemingly forgotten in the literature (and applicable to diesel engines as well), is the use of a short focal-length lens inside a Bowditch piston to expand the field-of-view. Rather than being limited by the clear aperture of the window in the piston, this technique permits the entire combustion chamber and the top section of the cylinder liner to be seen. Results using this technique are presented for the imaging of pool fires and laser-induced fluorescence of fuel films.
Two other simple, but overlooked, measurement techniques are described: 1) The cylinder pressure at the time of ignition, or the peak pressure in the absence of ignition, is shown to be a useful measure of the vapor-phase fuel concentration; 2) Thermocouple measurement of the exhaust gas temperature, while too slow-responding to provide an accurate, absolute temperature, does provide a useful relative temperature that is shown to correlate with unburned hydrocarbon emissions.
Finally, measurements of flame luminosity at wavelengths characteristic of pool fires were found to increase with increased hydrocarbon emissions only for an ensemble of cold start cycles; on an individual cycle basis, no correlation was found.