ICE exam 1

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ICE exam 1
2013-09-24 13:25:47
internal combustion engines

review questions for exam
Show Answers:

  1. Name the five processes in an internal combustion engine in order starting with compression
    • Compression
    • Combustion
    • Expansion
    • Exhaust
    • Intake
  2. What is the range of power produced by internal combustion engines and what order of power is produced by the vast majority of engines?
    • Range: 0.01 kW to 20x10^3 kW
    • Order: 10^2 kW
  3. What components of a reciprocating engine have remained basically the same since the later 1800s?
    • reciprocating internal combustion engine
    • engine
    • block
    • piston
    • valves
    • crankshaft
    • connecting rod
  4. Can both the spark ignition (SI) and compression ignition (CI) engines use the four stroke and the two stroke cycles?
  5. What does knock limit in an Otto cycle engine?
    the maximum compression ratio of the Otto cycle engines
  6. What controls the power in a SI engine?
    the throttle
  7. What controls the power in a CI engine?
    the amount of fuel injected into the cylinder
  8. What limits the power of a CI engine?
    the formation of smoke (forms if there is inadequate mixing of the fuel and air)
  9. Does a diesel or C.I. engine have a throttle?
  10. What is scavenging in a two stroke cycle?
    the pushing out of exhaust by the incoming air
  11. What is short circuiting in a two stroke engine?
    when some of the air goes straight through the cylinder and out the exhaust port
  12. Why is short circuiting particularly bad for carbureted engines?
    Instead of being in the crankcase, there is an air-fuel mixture. So, if short-circuiting occurs, fuel is wasted and there is increased hydrocarbon emissions.
  13. Which is greater, the brake power or the indicated power and why?
    Indicated power; due to friction
  14. bsfc is a valid measure of efficiency provided what parameter is held constant?
    q_c (the heat of combustion)
  15. Is the volumetric efficiency defined in Ferguson and Kirkpatrick chapter 1 dependent on the atmospheric or intake density?
    intake density
  16. What is a typical bmep and mean piston speed for an engine, independent of the size?
    • bmep = 5 bar
    • mean piston speed = 5 m/s
  17. What causes the torque at maximum throttle to decrease as at high engine speeds.
    Viscous friction effects
  18. Which occurs at lower speed, maximum torque or maximum power?
    maximum torque
  19. Turbocharged
    intake pressure is greater than exhaust pressure
  20. units of Joule
  21. units of Watt
  22. n_R
    • # revolutions/cycle
    • 2 stroke = 1
    • 4 stroke = 2
  23. N
    engine speed, rpm
  24. MEP
    mean effective pressure

    the average pressure acting on the expansion stroke that will produce the same amount of work as is produced by the cycle


    goes up when you turbocharge
  25. sfc
    • specific fuel consumption
    • mdot_f/power or m_f per cycle/work per cycle

    can only compare engines that use the same fuel
  26. e_v
    volumetric efficiency
  27. n_c
    • combustion efficiency
    • 99% +
  28. n_th
    • fraction of heat converted to work
    • Wout/Qin
  29. n_f
    fuel conversion efficiency
  30. e_vi is less than or equal to 1.0
  31. V_d
    • displacement volume
    • units: m^3/cycle
  32. Naturally aspirated
    an internal combustion engine, in which fuel intake depends solely on atmospheric pressure
  33. indicated
    identifies work being produced by the cylinder gases on the piston of the engine
  34. Brake
    the work measured from the output shaft
  35. R
    • Rod/Crank ratio
    • rod length/crank radium (1/2 stroke)
  36. When does r_c apply?
    • Otto: 1-2 and 3-4
    • Diesel: only 1-2
    • r_c=V1/V2