An investigation has been made to determine the effects of the degree of fuel atomization on exhaust emissions, fuel consumption, lean limit, MBT spark timing, and cyclic variations in peak cylinder pressure. A single-cylinder engine was used to isolate the effects of atomization on combustion from the additional effects of maldistribution that would be present in a multicylinder engine.
Three degrees of gasoline atomization were investigated, along with the case of a well-mixed charge of gaseous propane. The degrees of atomization investigated varied from “Good” (10-20 μm droplets) to “Bad” (400-700 μm droplets) to “Wall-Wetted” (400-700 μm droplets deposited on the intake-port walls).
Results from this investigation show that the degree of atomization can have considerable effect on exhaust emissions, but little effect on fuel consumption. Generally, as atomization deteriorated, hydrocarbon emissions increased; nitric oxide and carbon monoxide emissions increased for certain air-fuel ratio ranges; MBT (Minimum for Best Torque) spark advance decreased; lean limit was extended; and cyclic variations in peak cylinder pressure decreased.
It was hypothesized that the case of Good atomization resulted in an essentially homogeneous charge of vaporized gasoline and air at the time of ignition, while the cases of Bad and Wall-Wetted atomization resulted in in-homogeneous charges; that is, some form of stratification of the fuel-air mixture existed. All of the results are discussed in light of this hypothesis and are shown to be consistent with it.