Development of Finer Spray Atomization for Fuel Injectors of Gasoline Engines Tetsuharu MATSUO Yukio SAWADA Yukio TOMIITA This report describes the technology of Fuel Injectors a critical part of the Electronic Fuel Injection system of gasoline engines. DENSO has developed finer spray atomization for fuel injectors using multiple-hole nozzles. Research was focused on the development of the internal fuel flow and the upper face of the nozzle. The developed injector has contributed to the reduction of gas emissions. Key words : Gasoline engine, Fuel system, Engine component, Spray, Fuel Injector, Atomization, Nozzle Table 1 Transition of injector development A type ( 86-) B type ( 89-) C type ( 96-) ( 97-) ( 99-) UC ( 2-) Figure Weight (g) 12 Nozzle shape spray direction Atomization SMD ( µ m) Pintle 1-Jet 2 79 42 34 1 hole 4 holes 4 holes 4 holes (Air assist) 12 holes (Straight nozzle) 12 holes (Taper nozzle)
Delivery pipe Fuel pulsation damper Pressure regulator Injector Itake manifold Fuel pump module Fuel filter Fuel pump Fuel tank ECU Fig. 1 Electronic Fuel Injection system for gasoline engine Injector Pressure regulator Surge tank Fuel Air assist piping Intake manifold Fig. 3 Air assist system Throttle body Air control valve Electrical signal Electrical connector Spring Needle Core Nozzle Spray injection Filter Connector Solenoid coil <Detail of nozzle> Fig. 2 Configuration of the injector
Conventional valve Flat needle valve Analysis conditions Apprication code: Star-CD Model: to liquid injection Injection pressure: 3kPa Analysis results (flow cectors) Configuration needle Valve seat Nozzle plate A A A A A-A enlargement A-A enlargement Fig. 4 Analysis results of the flow at the nozzle upper face (Comparison of spherical needle and flat tip nozzle) Conventional valve Nozzle holes column 4-.26 φ View Flat tip valve Nozzle holes 4-.26 φ View Brake-up flow Fig. Actual condition at the nozzle hole and spray pattern
Needle r e w q Nozzle Nozzle plate t Break-up spray Continuous flow Valve sheet Arrange. Flow analysis Spray pattern A-A Unequal pitches Aspect ratio=1.3 Turbulent energy =.61m 2 /s 2 SMD A-A Equal pitches Aspect ratio=1. Turbulent energy =.7m 2 /s 2 1 µ m SMD 9 µ m Fig. 6 Analysis results of the flow at the nozzle upper face and spray patterns (Comparison of unequal pitches and equal pitches) Fig. 7 Mechanism of spray atomization Scale (mm) Splay pattern at below of nozzle Static flow rate: 21cm 3 /min@gasoline2kpa Injection pressure: 3kPa Fuel: n-heptane 1 Droplet size measuring Large droplet 2 1 bulk film Minute droplet Fig. 8 Break-up pattern of the spray injected from a single hole 2 1 1 2 3 1 2 3 Droplet diameter ( µ m) Droplet diameter ( µ m)
Straight nozzle Nozzle diameter Fuel flow Nozzle angle Fig. 1 Shape of straight nozzle and taper nozzle Scale (mm) Straight nozzle bulk Taper nozzle Nozzle diameter Fuel flow Nozzle angle Taper nozzle film Taper angle Static flow rate : 21cm 3 /min @gasoline2kpa Injection pressure : 3kPa Fuel: n-heptane Flow of nozzle wall Inlet of nozzle hole Air Center of nozzle hole Outlet of nozzle hole 1 and air at the inlet of nozzle hole Lateral flow and air at the center of nozzle hole Air and air at the outlet of nozzle hole bulk film Droplet size measuring Area rario (%) 1 1 1 2 3 1 2 3 Droplet diameter ( µ m) Droplet diameter ( µ m) Large droplet reduced Fig. 11 Break-up pattern of the spray injected from a single hole (Comparison of straight nozzle and taper nozzle) Area rario (%) film Fig. 9 Analysis results of fuel flow in nozzle
Development injector Conventional injector mm mm Development spray SMD µ m Conventional spray SMD6 µ m 1.mm 1.mm Fig. 12 Spray pattern of injector using 12 holes nozzle 2 1 2 1 2 1 2 2 1 2 Large droplet reduced µ m µ m Droplet diameter (SMD) ( µ m) 16 14 12 1 8 6 4 2 Nozzle diameter φ.13 φ.16 φ.2 φ.22 2 3 4 6 7 8 9 1 Fuel pressure (kpa) <Nozzle specification> Shape: Taper nozzle Hole number: 12 <Measuring condition> Measuring method: Laser diffraction Fuel: n-heptane Fuel pressure: 3kPa Fuel temperature: 2 C Pulse period: Hz Pulse width: 4.2ms Measuring point: mm below Fig. 13 Influence of fuel pressure and nozzle diameter on droplet diameter
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