In-Cylinder Fuel Drop Size and Wall Impingement Measurements

A significant fraction of hydrocarbon (HC) emissions occurs during the cold-start phase of an engine's operating cycle. Fuel drop sizes in the cylinder and impingement of fuel on the cylinder wall are two factors which can affect the HC emissions during this period. Therefore, measurements of in-cylinder drop sizes and wall fuel impingement were made on a steady flow bench at flow rates and manifold vacuum conditions which simulated desired engine operating conditions. Experimental variables included three injector types, two cylinder head geometries, three valve lifts, and two simulated engine speeds.

Injector performance was assessed prior to the flow bench studies. Fuel injector performance was found to affect in-cylinder drop size and wall fuel impingement. The dual-jet injector produced two liquid streams which were not atomized into drops at a distance of 10 cm (a typical injector to valve distance) from the injector tip. The pintle and air-assist injectors produced finer sprays with line-of-sight Sauter Mean Diameters (SMD's) of 119 μm and 39 μm, respectively. SMD's in the cylinder ranged from 15 to 140 μm for the dual-jet injector and from 15 to 70 μm for the pintle injector. With the air assist injector, which produced the smallest line-of sight SMD, the SMD's in the cylinder ranged from 5 to 20 μm and cylinder wall impingement was only a third to half as much as impingement with the pintle or dual-jet injector.