Analysis of Port Injection Systems for SI Engines P M V Subbarao Professor Mechanical Engineering Department Methods & Means to Control Premixed Combustion…..

Initial Remarks Ever increasing rate in the production of fuel injection vehicles lead to decrease in release of the pollutions in nature. This triggered: Numerous researches in optimizing the fuel injection system. Recognition of the fuel behavior. Analysis of the process of preparation of mixtures in the inlet port of fuel injection vehicles using MPFI system. Current SI engines generate homogenous mixture of air and fuel in the cylinder to complete combustion. The most prevalent belief at present is; possible fuel should be evaporated in the ports and mixed with the inlet air, and the less possible fuel as a liquid layer should be formed at the port and the cylinder walls.

Essential Knowledge Systems : MPFI Recognition of the structure and spray pattern. The time and condition with which the fuel should be sprayed in the port. Selection of suitable parameters of the spray: Atomization specification Spay pattern Appropriate angles

Identification of Angles After injection, the droplets flow takes place in the intake port Orientation Angle of Injector Orientation Angle of Valve Orientation Angle of intake port Spray Angle

YAMAHA MOTOR TECHNICAL REVIEW Shoichi Kato, Takanori Hayashida, Minoru Iida A/F : 14.5, Coolant Temp. 80℃ MEP 380 kPa,

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The System Reliability

Selection of Injection Timing & Durations

Analysis of Mixture And Wall Film Behavior The injection system configuration, injection timing and coolant temperature exert an influence on combustion stability and duration. Change of injection affects; mixture formation in the intake port, wall film location and amount, size and number of droplets, and finally mixture distribution in the combustion chamber.

Film images at t=10 ms after start of injection for three impingement angles

Splashed particle clouds at t=10 ms after start of injection for three impingement angles

Air –Fuel Interactions in the Manifold As the droplet group moves in the air stream, it decelerates or accelerates depending on operating conditions. At the same time, the droplets vaporization is initiated. As the droplets move to the end of the pipe, some of the unvaporized droplets are assumed to impinge on the intake port wall bend to form a droplet deposition film. Because of the heat transfer from the wall and from the air stream, the liquid film continuously vaporizes.

Two Way Air –Fuel Interactions in the Manifold The processes described above influence the state of the gas, i.e., the gas stream may be retarded, speeded up, cooled and enriched with fuel-vapor components. The changes in the gas-phase properties in turn influence the dynamics and vaporization of droplets, which are subsequently injected. A comprehensive understanding is essential to develop an efficient and safe Port Injection System.

Physics of Wall Impingement The wall impingement process is defined is classsified as four regimes: The regime transition criteria are determined based on the Reynolds number and Weber number of the incident droplet and the surface condition: splash is the most important and also the most complex. It is commonly observed in engine ports.

Splash Splash results in the rebounding of many smaller secondary droplets from the impinging location. The size and velocities of the secondary droplets are statistically distributed. The splash threshold Hcr  : non-dimensional surface roughness = (roughness height/incident droplet diameter),  : non-dimensional film thickness =(film thickness/incident droplet diameter)

Instantaneous Rate of Fuel Evaporation in Port In PFI gasoline engines, it a large portion of the spray impinges on the walls of the port or the intake valves. Such wall wetting phenomena are found to be major contributors for high unburned hydrocarbon emissions. Instantaneous rate of fuel evaporation in a port is the sum of evaporation rate of fuel droplets and evaporation rate of fuel films