Fuel Spray Characteristics Of Different Types Of Injectors Through Visualization

The increase in fuel injection pressure is one of the most effective means of improving fuel atomization and engine’s combustion efficiency. The use of bio-ethanol and bio-butanol in gasoline engines not only decreases the consumption of fossil fuel, but also reduces the emissions from gasoline engines. The structure of injectors, fuel injection pressure and the physical properties of the fuel are all the important factors affecting the spray characteristics and fuel injection rate and thus engine performances. Hence, the spray characteristics of a multi-hole injector fuelled with gasoline, diesel, gasoline-diesel blends containing different volume fraction gasoline at the pressure higher than 50 MPa and that of an outward-opening gasoline piezoelectric injector fuelled with gasoline, ethanol and n-butanol were investigated through different optical approaches in a constant volume chamber. The transient injection rates in the latter cases were measured. The main conclusions are drawn as following:For the multi-hole injector, the spray cone angle is slightly affected by the increase in fuel injection pressure while it is significantly increased with back pressure. Furthermore, the spray cone angle slightly increases with increasing volume fraction of gasoline in the gasoline-diesel blends. With the increase of fuel injection pressure, the penetration of spray sharply increases first and then its growth rate decreases. However, it decreases significantly with back pressure. For the gasoline-diesel blends, the penetration of the spray decreases little with the volume fraction of gasoline in the blends. But the differences of the penetration between different fuels increase with back pressure. The volume of spray increases with fuel injection pressure but it significantly reduces with back pressure at the same time after start of injection. At low back pressure, the volume of spray increases with the volume fraction of gasoline in the blends. But at high back pressure, it is the lowest in the case of pure diesel.The hollow conical spray of an outward-opening gasoline piezoelectric injector is composed of numerously tiny jets. With the increase of back pressure, the gap between the two adjacent jets decreases. In the meantime, the penetration and projected area of the spray sharply reduce. Furthermore, the decline in spray penetration is larger in horizontal direction than in vertical direction. However, the spray cone angel is nearly unchanged with time regardless of the magnitude of back pressure and fuel types. The spray penetration in vertical direction for n-butanol is longer than that for gasoline and ethanol.With the increase of injection pressure, the injection rate of outward-opening injector rises and cavitation number decreases. The higher the input voltage to drive the injector is, the greater the needle lift and the larger the injection rate is. The amount of the injected fuel during one injection pulse width under a certain injection pressure approximately linearly grows with the injector driving voltage. For gasoline, ethanol and n-butanol, the injection rate of gasoline is the largest while that of n-butanol is the least at the same injection conditions.