Design of Port Injection Systems P M V Subbarao Professor Mechanical Engineering Department Collection of Models to Predict Multi-physics of Spray …...
Electrical Input to Control Injector Operation Once in two Revolutions Full Open Accelerator Idling Cold Starting Injection Pulse An injector is essentially a gate valve for fuel delivery. Increasing fuel pressure can allow to cram more fuel into the intake port for a given injector pulse width.
Actuation of EFI
Flow Characteristics of EFI Port Injector 1.7 gms/s Throttle Body Injector 7.0 gms/s
Injection Pulse The length of time an injector is open and squirting fuel is called the "pulse width," and it is measured in milliseconds (ms). At a given rpm, an injector can only be held open for so long before it needs to be held open again for the next engine revolution -- this is called its "duty cycle."
Selection of Injector Driving Pulse Duration Considering a specific injection end time, the fuel should be injected in the port later with increasing injection pressure has below results: 1. Increasing vaporization rate in case of relative velocity increase of fuel injection. 2. Reduction in droplets means diameter and increase of droplets surface contact that makes much vaporization rate. 3. Increasing the spray cone angle that provides wither spray angle and much fuel wetted surface in the intake port. 4. Reducing the in hand time for fuel vaporization in the port and cylinder because of thinner injection pulse width.
Fuel Droplet Dynamics : Prediction of Trajectory
Measurement of Mean diameter distribution of droplets 300 kPa & 25 C 100 mm downstream
Frequency diagram of droplets mean diameter Distribution D is the droplet diameter and N is the normalized number distribution. Rosin & Rammler Distribution
Evaluation of Model Constants Model constants are evaluated by applying following physical and statistical constraints : (i)The sum of all probabilities must be unity: (ii) the mass flow of sprayed liquid must be equal to the mass of all droplets produced per unit time: where n is the total number of droplets produced per unit time and m L is the liquid mass flux.
Momentum & Energy Constraint The total kinetic power of sprayed liquid must be equal to the sum of kinetic power of all droplets produced per unit time and rate work done against surface tension. The total momentum rate of sprayed liquid must be equal to the sum of momentum rates of all droplets produced per unit time and drag force on liquid sheet.
Distribution of droplets Distribution of Droplet Velocity:
Representative Mean Diameter Introducing the definition of SMD: where d nozz is the nozzle diameter, μ f, μ g are the fuel and gas dynamic viscosity, respectively, Re the Reynolds number and We the Weber number. German scientist J. Sauter : 1920 Empirical Formula for SMD: