I.C. ENGINES

1. I.C. ENGINES LECTURE NO: 10 (14 Apr 2014)

2. Fuel Spray Formation • Spray Formation Boundary 15 mm 15 mm Core Boundary 40 mm 75 mm

3. Fuel Spray Formation • Fuel issues from the jet in a liquid stream • The surface of the liquid come in contact with air and the friction between the two results in the formation of ligaments or threads, that break into small particles and form an envelope surrounding the core of the spray • Core consist of highest velocity particles

4. Fuel Spray Formation • Dispersion of the droplets in any one cross section of the spray becomes more even: • As the distance is increased from the orifice to cross section • As the air density is increased • As the oil viscosity is decreased • As the injection is increased

5. Fuel Spray Formation • Measurement of the drop size indicate: • Greatest number if droplets are less then 5 microns in diameter • Increased the injection pressure decreased the mean droplets size • Increase the air density decreased the mean droplet size • Increase the oil viscosity increase the mean droplet size • Increase the orifice size increase the size of the droplet

6. Fuel Spray Characteristics • Degree of Atomization • Penetration • Dispersion

7. Fuel Spray Characteristics • Diesel engine requires hard sprays because soft sprays do not have adequate penetration in the dense air • Spray must be direct to various parts of the combustion chamber by multiple orifices of the nozzle or by using more than one nozzle in open chambers in the absence of strong air motion • Inlet inducted swirl is not necessary with divided chambers. These chambers can give satisfactory performances with single nozzle • Spray duration at full load should not exceed 30˚ crank angle

8. Degree of Atomization • Fuel velocity is the most important factor affecting the degree of atomization • Therefore increase the injection pressure reduces the mean diameter of the particle as well as variation in size • Nukiyama and Tansawa develop an empirical equation for computing the average drop diameter which has the same surface –volume ratio as that obtained by the entire spray

9. Degree of Atomization • d = average drop diameter in microns (10-4 cm) • ω = relative velocity between air and liquid stream (m/s) • ρ = liquid density ( 0.7 to 1.2) ( g/cm3 ) • σ = liquid surface tension ( 0.003 to 0.5) ( poise) • This value is very small • Therefore • because surface tension is very important

10. Numerical Example • Determine the average drop diameter for the 31.5 kgf/cm2 injection pressure. Values of fuel density and surface tension may be taken as 0.86 g/cc and 28 dynes/cm respectively • Formula

11. Numerical Example • Formula • = 80 m/s

12. Penetration • Jet Velocity • An increase in injection pressure increase jet velocity • Spray tip penetration increases with jet velocity • Air Density • An increase in combustion chamber air density decreases the penetration

13. Penetration • Orifice Diameter • An increase in orifice diameter increase the penetration of the spray tip. • Orifice length to diameter ratio between 4:1 and 6:1 results in maximum penetration. • The minimum penetration is reached with ratio 1:1 and 3:1

14. Penetration • Orifice Diameter • As per schwitzer • Where • S = Penetration time • 𝝙p = Pressure difference across orifice • d = Orifice diameter • da = air density in atm

15. Numerical Example • Penetration of 20 cm in 15.7 millisec is obtained with 140 kgf/cm2 injection pressure. Values of fuel density and surface tension may be taken as 0.86 g/cc and 28 dynes/cm respectively • Formula

26. Electronic ignition system (EIS) Electronic spark timing (EST) Flyback voltage Hall-effect switch High energy ignition (HEI) Igniter Ignition coil Ignition control (IC) Ignition control module (ICM) Ignition timing Inductive reactance Initial timing Ion-sensing ignition Iridium spark plugs Knock sensor (KS) Magnetic pulse generator Magnetic sensor Married coil Mutual induction Optical sensors Paired cylinder Pickup coil (pulse generator) Ping Platinum spark plugs Polarity Primary ignition circuit Saturation Schmitt trigger Secondary ignition circuit Self-induction Spark knock Spark output (SPOUT) Switching Tapped transformer Transistor Trigger True transformer Turns ratio Up-integrated ignition Waste-spark ignition KEY TERMS

27. Function • An ignition system is a system for igniting a fuel-air mixture at the right instant. • It is best known in the field of internal combustion engines but also has other applications, e.g. in oil-fired and gas-fired boilers. • Hot spark across spark plug gap • Distributes high voltage to each plug in correct sequence • Time the spark so it arrives as piston nearing TDC • Adjusts spark timing with load & speed

28. History • The earliest internal combustion engines used a flame, or a heated tube, for ignition • These were later replaced by systems using an electric spark. The instant of sparking is decided by the ignition system.

29. FUNDAMENTAL ELECTRICAL PRINCIPLES • Electricity is lazy • Electricity wants to go to ground • electron theory (-) to (+) • conventional theory (+) to (-) • Conductors • Insulators

30. ELECTRICAL UNITS OF MEASUREMENT • Volts---- Push V • Current ---Quantity A • Resistance ----Resistance to flow 

31. OHM’S LAW • E = I x R • E / I = R • E / R = I E I R

32. MAGNETISM • Alike charges repel (-) (-) • Dissimilar charges attract (-) (+)

33. MAGNETS & ELECTRICITY • Magnets can be used to for electricity • Electricity can be used to form magnets • Electricity when applied to magnets make stronger magnets

34. IGNITION COILS • Coils of wire wrapped around an iron core • Step up transformer

35. SPARK PLUGS • Spark plugs contain an air gap for electricity to create a spark and make a seal

36. HEAT RANGES The difference between a "hot" and a "cold" spark plug is in the shape of the ceramic tip. • The manufacturers will select the right-temperature plug for each engine. • Some engines with high-performance naturally generate more heat, so they need colder plugs. • If the spark plug gets too hot, it could ignite the fuel before the spark fires • It is important to stick with the right type of plug • Engine that burn oil may need hot plugs

37. MEASURING SPARK PLUG TEMPERATURE

38. TYPES OF ELECTRODES • Center electrode • Side electrode

39. SWITCHING DEVICES • Breaker points • Electronic

40. BREAKER POINTS • Ran by cam shaft

41. ELECTRONIC SWITCHING DEVICES • NO breaker points to burn or wear out

42. Basic Ignition System Operation • Charge builds up in coil (12 volts in) • Creates a magnetic field (windings of wire) • Voltage is stepped up (secondary windings) • Switch open (magnetic field collapses) • High voltage discharged (to plug)

43. IGNITION SYSTEM • Provides a method of turning a spark ignition engine on & off. • Operates on various supply voltages (Battery & Alternator) • Produces high voltage arcs at the spark plug electrode. • Distributes spark to each plug in correct sequence. • Times the spark so that it occurs as the piston nears the TDC on the • compression stroke. • Varies the ignition timing as engine speed, load and other conditions • change.

44. IGNITION PARTS BATTERY provides power for system. IGNITION SWITCH allows driver to turn ignition on and off. IGNITION COIL changes battery voltage to 30,000V during normal operation and has a potential to produce up to 60,000V. SWITCHING DEVICE mechanical or electronic switch that operates Ignition coil(Pick-up coil, Crank sensor, Cam sensor). SPARK PLUG uses high voltage from ignition coil to produce an arc in the combustion chamber. IGNITION SYSTEM WIRES connect components.

45. IGNITION CIRCUITS PRIMARY CIRCUIT • Includes all the components • working on low voltage • (Battery, Alternator). SECONDARY CIRCUIT • Consists of wires and points • between coil out-put and the • spark plug ground.

46. IGNITION COIL Primary Windings are made up of several hundred turns of heavy wire wrapped around or near the secondary windings. Secondary Windings consist of several thousand turns of very fine wire, located inside or near the secondary windings.

47. DISTRIBUTOR • Actuates the on/off cycle of current flow through the ignition coil primary windings. • It distributes the coils high voltage to the plugs wires.

48. DISTRIBUTOR • It causes the spark to occur at each plug earlier in the compression stroke as engine speed increases, and vice versa. • Changes spark timing. • Some distributor shafts operate the oil pump.

49. POINT IGNITION SYSTEM PARTS Distributor Cam, Breaker Points, and Condenser.

50. POINT IGNITION SYSTEM Points are wired in Primary Circuit – When the points are closed, a magnetic field builds in the coil. When the points open, the field collapses and voltage is sent to one of the spark plug.