Effects of fuel atomization on cold starting of a 4 stroke cycle spark ignition engine

Effects of fuel atomization on cold starting of a 4 stroke cycle spark ignition engine were investigated experimentally. Two kinds of ultrasonic fuel injectors using a micro nozzle array (MNA injectors) were applied, whose nozzle diameter d = 4 and 6 μm, respectively. A conventional port fuel injector (PFI injector) was also used for comparison. The Sauter mean diameters (SMDs) of the sprays were 15μm (MNA, d = 4 μm). 23 μm (MNA, d=6μm), and 59μm (PFI), respectively. An air cooled, single cylinder, 4 stroke cycle, spark ignition engine was used. The first ignition cycles and the cumulative fuel amount were investigated at a wide range of the air fuel ratio. For the MNA injector (d = 4 μm), the first ignition cycle became much earlier when compared with the PFI injector. The cumulative fuel amount during cold starting reduced by about 30%. It is shown that, by use of the MNA injector, the unburned hydrocarbon emissions during cold starting could be reduced.