Radiation Heat Transfer

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View Factor Orientation (or View factor or shape factor) plays an important role in radiation heat transfer. View factor is defined as, "fraction of radiation leaving surface 'i' and strike 'j' ". Summation Rule (View Factor) If there is are similar surfaces 'i' and 'j' , then: Blackbody Radiation Exchange Radiation Exchange between Opaque, Diffuse, Gray surfaces in an Enclosure 1. Opaque 2. Surfaces 3. Two surface enclosure Radiation Shield It is used to protect surfaces from radiation act like a reflective surface. References: Material from Class Lectures + Book named Fundamentals of Heat and Mass Transfer by Theodore L. Bergman + My knowledge.  Photoshoped pics  are developed.  Some pics and GIF from Google.   Videos from YouTube ( Engineering Sights ).

Mechanical Injection System

Mechanical Injection System:

  • Used to inject fuel into the combustion chamber.
  • Fuel speed > air speed at delivery point to atomize fuel.
  • Amount of fuel delivered into the air stream going into the engine is controlled by pump which forces the fuel under pressure.
A device used to initiate and control the combustion process is called Mechanical Injection System.

Functional Requirements of Injection System:

  • Metering of Fuel: Used to control fuel to meet speed and load requirements of the engine.
  • Injection Timing: Have proper injection timing to obtain max. power, fuel economy and proper burning. It is done by Camshaft or Push rod (Rocker Arm) Mechanism.
  • Proper Control of Injection Rate: To get desired heat release pattern during combustion.
  • Proper Atomization of Fuel: Proper making of droplets to make best Air/Fuel mixture.
  • Proper Spray Pattern: Distribution of droplets to ensure rapid mixing of fuel & air.
  • Uniform Distribution of Fuel: If distribution of fuel is not uniform throughout the combustion chamber, combustion is improper.

Classification Of Injection Systems:

There are two types of injection systems which are described as follows:

 1. Air Injection System:

Injection system in which fuel is forced into the cylinder by means of compressed air is called Air Injection System.
  • Having good mixing of Air-Fuel mixture, Higher MEP, can utilize high viscosity fuel.
  • The requirement of bulky multistage air compressor making air injection system obsolete.

2. Solid Injection System or Airless Mechanical Injection System:

Injection system in which liquid fuel is directly injected into the combustion chamber without compressed air is called Solid Injection System.
There are 4 types of Solid injection system which we are going to discuss.

A. Individual Pump & Nozzle System:

  • Each cylinder is provided with one pump and injector are placed near to the cylinder (separate or cluster).
  • Fuel is controlled by Plunger Effective Stroke.

B. Unit Injector System:

  • It consist of housing containing HP pump and injector is provided on each cylinder.
  • Fuel is brought up to the injector by a low pressure (LP) pump.
  • Rocker arm is connected with plunger and thus injects the fuel into the cylinder.
  • Fuel is controlled by plunger effective stroke.

C. Common Rail System:

  • Hp pump supplies high pressure fuel to the header.
  • Header forces the fuel into the injector.
  • Rocker arm & push rod valve allows the fuel to enter the proper cylinder through nozzle.
  • Fuel is controlled by the length of Push Rod Stroke.

D. Distributor System:

  • Single pump is used to pressurized & meters fuel.
  • Rotating distributor distributes fuel to each cylinder at proper time.
  • Number of injection strokes per cycle for the pump is equal to the number of cylinders.
  • Since it has only one metering element in each pump, a uniform distribution is automatically ensured.
  • Cost efficient less than 2/3rd for individual pump system.

Components Of Mechanical Injection System:

  1. Fuel Tank  ↔  contains fuel.
  2. Fuel Feed Pump  ↔  to supply fuel from the main fuel tank to the injection system.
  3. Injection Pump  ↔  to meter and pressurize the fuel.
  4. Governors  ↔  to ensure that the amount of fuel injected with respect to the variation in load.
  5. Injector  ↔  take fuel from the pump and distribute it into the combustion chamber by atomization into fine droplets.
  6. Fuel Filters  ↔  prevent dust and abrasive particles from entering the pump and injector, minimizing wear & tear of components.

Fuel Feed Pump:

  • Spring loaded plunger type pump.
  • Plunger is actuated through a push rod from the camshaft.
  • At minimum lift position of cam, rod moves down creates suction pressure, fuel comes into the pump.
  • When cam is at maximum lift position, rod moves up and compress fuel, inlet valve close and open outlet valve.

Injection Pump:

It is used to deliver metered fuel under high pressure of about 120-200 bars. There are two types of injection pumps which are discussed ahead:

a. Jerk Type Pumps:

  • Reciprocating plunger inside a barrel driven by camshaft.
  • Fuel is always available at intake.
  • Axial movement (rotation) of plunger by camshaft (due to rack).
  • When plunger is below intake opening, fuel get into barrel. As plunger rises, it closes intake port and fuel will flow out from the output port.
  • As plunger rotates output port closes, it pressurized fuel and fuel will pass through the injection port. That's the beginning of injection called Plunger Effective Stroke
  • As plunger rotates, output port uncovers and injection stops.
  • Axial distance traversed between the time intake port is closed off and the time intake port is uncovered is called Plunger Effective Stroke.

b. Distributor Type Pump:

  • Pump has only one single pumping element and fuel is distributed to each cylinder by means of a rotor.
  • Rotor is provided by two holes. One for inlet and the other for outlet.
  • Inlet port is connected to pump and outlet port is connected to injectors through delivery fuel lines.
  • When rotor coincides with inlet port, fuel comes in and plunger moves away from each other.
  • Fuel is pressurized by moving plunger towards each other.
  • When rotor coincides with outlet port, fuel is delivered to the injectors.

 Injection Pump Governors:

When speed is increased or decreased, the A/F mixture should change. If speed is high (rich A/F mix), if speed is low (Lean A/F mix). If speed is suddenly increased or decreased A/F ratio cannot reduce with same proportion producing high emissions.
There are two types of Governors:

a. Mechanical Governors:

  • When speed exceeds limit, centrifugal weights moves apart, causes lever to raise sleeves and operate the control lever in downward direction. 
  • This actuates the control rack connected to fuel injection pump in direction which reduces the fuel. Lesser fuel causes the engine speed to decrease.

b. Pneumatic Governors:

  • Amount of vacuum applied to diaphragm is controlled by accelerator pedal through the position of butterfly valve in venturi unit.
  • Diaphragm is connected to a fuel pump control rack.
  • Position of accelerator pedal also determines the position of the pump control rack and hence the amount of fuel injected.

   Fuel Injector Assembly:

  • When fuel comes from injection pump, it exerts forces against the spring to open nozzle valve, fuel is sprayed into the combustion chamber.
  • Atomization of fuel is done by passing fuel in combustion chamber through nozzle under high pressure.
  • When fuel gets injected, pressure is released which closes the nozzle valve.
  • For lubrication, fuel is leak off through the clearance between nozzle valve and it's guide.
  • The spring tension (valve opening pressure) is controlled by adjusting screw on the top.
Fuel injector assembly consists of following parts:
  1. A needle valve
  2. A compression spring
  3. A nozzle
  4. An injector body

Nozzle:

Part of injector assembly by which fuel is sprayed into the combustion chamber is called a Nozzle.

Functions of Nozzle:

  1. Atomization of Fuel  ↣  To obtain proper mixing of fuel and air in C/C.
  2. Distribution of Fuel  ↣  Distribution of fuel increases with the increase in injection pressure, density of compressed air, physical properties of fuel (self-ignition temperature, vapor pressure, viscosity).
  3. Prevention of Impingement on Walls  ↣  Reduce direct striking of fuel particles on walls.
  4. Mixing  ↣  For non-turbulent type of C/C, nozzle should take care of proper mixing of air and fuel.

Types of Nozzle:

  1. Pintle Nozzle  ↣  Stem nozzle is pin, low injection pressure 8-10MPa, cone angle is 60°, no dribbling effects.
  2. Single Hole Nozzle  ↣  Cone angle is 15°, injection pressure 8-10MPa, dribbling effects.
  3. Multi-hole Nozzle  ↣  multi-holes in tip of nozzle about 4-18, hole angle 20° upward, injection pressure 18MPa, very small hole so clogging does happen.
  4. Pintaux Nozzle  ↣  Type of pintle nozzle with auxiliary hole in nozzle body. At low pressure, nozzle valve does not open, so fuel is injected through aux-hole.       

Note: Want to learn about Car Engine Operations then see the video given below:

And, 

References:

  • University notes + my knowledge.
  • Videos from YouTube.
  • Images from Google Images.
  • Book: IC Engines by V Ganesan (4th Edition).
  • Class Lectures.

Comments

  1. Amazing Car Operations but can you tell me how ignition timing is set up?

    ReplyDelete
    Replies
    1. For ignition timing, you need to do the following things:
      1. Open the side housing (case) of engine.
      2. Check whether the piston is at TDC or not.
      3. Now rotate the flywheel and align the triangle shaped sign on the pulley mechanism on its outer surface with indentation on the crankcase.
      Thereby ignition timing is set up.
      You can watch this by clicking the link below:
      https://youtu.be/8y3nq61yhcM

      Delete
    2. Impressive❤️❤️❤️

      Delete

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