Factors in charge preparation and their effect on performance and emissions from a direct injection spark ignition engine
The effects of flow field and Start Of Injection (SOI) timing were investigated to determine their effect on mixture preparation in a direct injection spark ignition engine. The flow field and SOI timing were varied in order to produce changes in the location and amount of surface wetting and to vary the extent of in-cylinder mixing. The equivalence ratio at the spark plug was measured using a fiber optic probe developed at The University of Texas at Austin. The flow field and SOI timing were shown to have an effect on both the equivalence ratio history and the equivalence ratio at ignition, as well as the cyclic variation in its value. A separate technique, also developed at The University of Texas at Austin, used IR absorption to measure the time resolved hydrocarbon (HC) emissions in the exhaust port. The location of the in-cylinder surface wetting had a strong influence on the level of HC emissions from the engine. Engine performance was influenced by both the amount of mixing and surface wetting. Liquid fuel effects in the cylinder were investigated using schlieren imaging and Mie scattering to visualize both the in-cylinder evaporation of fuel films and particulate matter formation respectively. In-cylinder evaporation was found to be a slow process and dependent on the difference between the fuel boiling point and the piston surface temperature. The in-cylinder formation of particulates was found to be dependent on the in-cylinder flow field and showed high cycle-to-cycle fluctuations.