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TDI Page Diesel Quiz
Thanks to tdimeister for this diesel Quiz.

Enjoy.

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PART I: Warm up
1.Which engine layout has the least reciprocating imbalance?

a) 60-degree V6 b) 90-degree V6
c) Horizontally-opposed six cylinder
d) 90-degree V10

 

PART II: Diesel specific questions

2.Diesel clatter:

a) Is related to the ignition delay. b) Can be reduced by reducing the compression ratio.
c) Can be reduced by significantly retarding the ignition timing and using Diesel fuel of higher cetane number. d) All of the above.

3.Pilot injection:

a) Is intended to reduce the combustion noise, or "clatter," in a direct-injected Diesel engine. b) Decreases the thermal efficiency of an engine.

c) Can decrease emissions of Nitrogen Oxides (NOx)
. d) All of the above.

4) In a common-rail fuel injection scheme:

a) A mechanical pump delivers a constant high pressure to the fuel injectors. b) The pump does NOT control fuel injection quantity nor timing.
c) Maximum pressures are currently limited to approximately 1650 atmospheres because of the possibility of leaks. d) All of the above.

5) In a unit fuel-injection scheme,

a) Pressure is raised, and fuel-injection commences by, powerful electronic solenoids. b) Pressure is raised to over 2000 atmospheres by an electric pump.
c) Pressure is raised by a mechanical cam acting on a plunger. d) Delivers a 15% improvement in fuel efficiency over a common-rail setup because of its extremely high pressure.

PART III: Fill `er up!

6) Like the octane rating for gasoline, the cetane number of a fuel is an indication of its ignition quality. Which of the following statements is true?

a) A high cetane fuel will have a low octane number. b) A high cetane fuel will have a higher energy (heating value) than a low cetane fuel.
c) A high cetane fuel will have greater knock resistance than a low cetane one if used in a spark ignition engine. d) There is no correlation whatsoever between octane and cetane ratings.

7) Which of the following is false about the cetane rating of a fuel?

a) The cetane index is a calculated value using the ASTM mid boiling point and API gravity. b) Aromatic (i.e. benzene-containing) compounds as a rule have lower cetane numbers than liquid paraffinic (i.e. saturated alkyl) hydrocarbons.
c) A direct relationship is observed between a fuel's cetane rating and its energy of combustion. d) A correlation is observed between a fuel's cetane rating and its volatility and specific weight.

PART III: General thermodynamics

8) The ratio of the heat equivalent of work done in an engine to the total heat supplied in the same unit of time is refereed to as its?

a) Compression efficiency b) Thermal efficiency
c) Mechanical efficiency d) Absolute efficiency

9) The ratio of brake horsepower output of an engine to the indicated horsepower developed in the cylinders is called the ________________ of the engine?

a) Compression efficiency b) Thermal efficiency
c) Mechanical efficiency d) Absolute efficiency

PART III: More advanced thermodynamics

10) A modern high-speed Diesel engine can best be approximated by an ideal thermodynamic cycle with what characteristic?

a) Constant-pressure heat addition. b) Constant-volume heat addition.
c) A combination of constant-volume and constant-pressure heat addition. d) None of the above.

11) Given a pair of engines of identical compression ratios, displacements, etc., one operating on a ideal Diesel cycle and the other an ideal (throttle-less) Otto cycle; which of the following is a true statement?

a) The Diesel engine would require a cooling system with greater capacity. b) The Diesel engine would have higher peak cycle pressure.
c) The Otto engine would have higher indicated thermal efficiency. d) The Diesel engine would have higher indicated thermal efficiency.

12) A direct-injected Diesel engine typically has a lower compression ratio but still achieves better fuel economy and roughly equivalent cold-starting abilities (neglecting the contribution of glow plugs) than an indirect-injected engine. Why?

a) Reduced surface-to-volume ratio reduces heat transfer to the combustion chamber walls. b) Reduced throttling losses from the swirl chamber orifice.
c) Reduced heat losses from turbulent motion of air in the pre-chamber in an indirect-injection engine. d) All of the above.

13) What can be said of the thermal efficiencies in real-world spark-ignition (SI engines)? Select one true statement:

a) At a fixed RPM, the thermal efficiency of an SI engine increases relatively steadily with increasing throttle input. b) An SI engine is operating at maximum thermal efficiency when idling and at very light cruising.
c) Neglecting heat transfer, the temperature at the end of the compression stroke of an SI engine decreases at closed throttle. d) All of the above.

14) What can be said of the thermal efficiencies in real-world compression-ignition (CI engines)? Select one true statement:

a) A CI engine is operating a maximum thermal efficiency at the maximum power limit. b) A CI engine is operating at maximum thermal efficiency when idling and at very light cruising.
c) The net efficiency of a CI engine is unaffected by gas pedal input because there is no throttle plate. d) None of the above.

15) A compression-ignition engine gets its improved thermal efficiency over a spark-ignition engine because:

a) Diesel fuel has a higher energy content than gasoline per unit mass. b) Higher compression ratio
c) Higher compression ratio and elimination of the throttle plate. d) A and B above.

PART IV: Turbochargers

16) A well designed automotive turbocharger can achieve about 75% isentropic (adiabatic) efficiency. Why aren't there devices with 100% efficiency?

a) Friction b) Heat transfer
c) A truly isentropic process is impossible to achieve in the real-world. d) All of the above.

17) Which of the following statements is true?

a) turbocharger increases the net efficiency of an engine because some of the exhaust energy that would otherwise be wasted is recovered. b) A turbocharger decreases the net efficiency of an engine because it adds backpressure in the exhaust.
c) All else being equal, a VNT turbocharger will have greater peak isentropic efficiency than a fixed-geometry turbo because of the directability of the gas flow. d) A VNT turbocharger varies the compressor-wheel blade geometry, allowing faster response.

18) What is the correct general rank of isentropic efficiencies of the following various turbo- and supercharging schemes?

a) Efficiencies between turbo- and superchargers cannot be compared because the former is driven by exhaust gases while the latter is driven mechanically. b) Axial turbocharger > Radial turbocharger > Rootes supercharger.
c) Radial turbocharger > Axial turbocharger > Rootes supercharger. d) Rootes supercharger > Radial turbocharger > Axial turbocharger.

PART V: Cool-down

19) In general, how does the introduction of Exhaust Gas Recirculation (EGR) in a Diesel engine affect thermal efficiency, smoke output and emissions of Nitrogen Oxides (NOx)?

a) Thermal efficiency remains constant, smoke increases, NOx increases. b) Thermal efficiency increases, smoke increases, NOx increases.
c) Thermal efficiency decreases, smoke increases, NOx decreases. d) Thermal efficiency decreases, smoke decreases, NOx remains constant.

20) Catalytic converters:

a) Are of the reducing type to reduce emissions of carbon monoxide and unburned hydrocarbons. b) Are not really required in Diesel engines because they produce less emissions.
c) Are different from those employed in gasoline engines because of the excess oxygen in the exhaust gases of Diesel engines. d) All of the above.

 

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