Attempt all questions. Attach the question sheet along with the answers to the f
ID: 1766450 • Letter: A
Question
Attempt all questions. Attach the question sheet along with the answers to the following questions 1. (5 points) Explain coefficient of performance of refrigeration system. Discuss the possibility and limitations of using the refrigerant as engine coolant. 2. (5 points) List the regions where engine lubricant is used to reduce the frictional losses. Identify three most critical regions and discuss the strategy to reduce the frictional losses further 3. (5 points) What are the necessary changes that could turn spark ignition engine into compression ignition engine, if at all possible. Discuss the pros and cons in detail. 4. (5 points) Explain figure 5.12 5. (5 points) What is equivalence ratio? How does equivalence ratio effects the Otto cycle efficiency (Tors) 6. (5 points) Using figure 2.7, extract the noto for the range of equivalence ratio @compression ratio 15. Plot the efficiency curve as a function of equivalence ratio and discuss the curve 7. (5 points) Outline the shortcomings of the simple ideal cycles, and explain how the fuel-air cycle model overcomes these problems 8. (5 Points): One of the steps of firing up of the engine was to make sure that "Choke" was on. What is meant by "Choke on"? 9. (5 points): Why does the optimum ignition timing change with engine-operating conditions? What are the advantages of electronic ignition with an electronic control system? critical ones that are absolutely necessary to operate/run an engine. What would be the impact of three sensors that were left behind? 10. (5 points): Sensors that will be found in a typical engine installation are listed here. Pick six most crankshaft speed/position sensor Camshaft position Throttle position sensor Air flow rate sensor Inlet manifold absolute pressure Air temperature coolant temperature Air-fuel ratio lambda sensor Knock detectorExplanation / Answer
1. A)The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work required.
B) A liquid coolant like water is more than adequate to carry away excess heat from the combustion process.
A refrigerant as R12, R22 or now R134a would need to be compressed and require more energy to change its state of liquid to gas to absorb and carry away heat.
10) The leftover is air temperature, throttle position sensor & speed sensor. Since the air-fuel ratio sensor will already be used it is not mandatory to have an air temperature sensor since the atmospheric air will be minimal, the variation in rotation or speed depends on the amount of fuel burn etc so speed sensor doesn't play a huge role, throttle positions are arranged systematically while manufacture so regular check is not required.
4) No figure is mentioned.
5) a)The equivalence ratio is defined as the ratio of the actual fuel/air ratio to the stoichiometric fuel/air ratio. Stoichiometric combustion occurs when all the oxygen is consumed in the reaction, and there is no molecular oxygen(O2) in the products.
b) The effect of equivalence ratio on the performance of an Otto cycle is the friction loss computed from the empirical correlation, the specific heat ratio of the working fluid supposed constant, the internal irreversibility described by using the compression and expansion efficiencies, and the heat transfer loss are considered
6) Figure not mentioned
7)
the fuel-air cycle can overcome since:
1.No change in the fuel or air chemical composition before combustion.
2.The process is frictionless and adiabatic.
3.The charge is in chemical equilibrium after combustion.
4.The combustion process is instantaneous.
5.Fuel is completely vaporized and perfectly mixed with the air
3)
The corresponding diesel engines generally have improved efficiencies, between 30% and 40%. Both sets of efficiency values are considerably influenced by the chosen compression-ratio and design.
The petrol engine is usually designed with a shorter stroke and operates over a much larger crankshaft-speed range than the diesel engine. This enables more power to be developed towards the upper-speed range in the petrol engine, which is necessary for high road speeds; however, a long-stroke diesel engine has improved pulling torque over a relatively narrow speed range, this being essential for the haulage of heavy commercial vehicles.
And si engines are consist of spark plugs which is only used to ignite the petrol, not diesel and diesel can only be ignited means burn by compression because of its properties.
.So no, we can't change SI engine to CI engine.
5) a)The equivalence ratio is defined as the ratio of the actual fuel/air ratio to the stoichiometric fuel/air ratio. Stoichiometric combustion occurs when all the oxygen is consumed in the reaction, and there is no molecular oxygen(O2) in the products.
b) The effect of equivalence ratio on the performance of an Otto cycle is the friction loss computed from the empirical correlation, the specific heat ratio of the working fluid supposed constant, the internal irreversibility described by using the compression and expansion efficiencies, and the heat transfer loss are considered
4) No figure is mentioned.
6) Figure not mentioned
7)
the fuel-air cycle can overcome since:
1.No change in the fuel or air chemical composition before combustion.
2.The process is frictionless and adiabatic.
3.The charge is in chemical equilibrium after combustion.
4.The combustion process is instantaneous.
5.Fuel is completely vaporized and perfectly mixed with the air
8) The choke in a vehicle is a device that reduces the amount of air going into the engine and makes it easier to start the engine or run it in cold weather. A choke gets the engine firing right, with the right air/fuel mixture and lets it warm up without being too rich or too lean.
9) a) The phenomenon behind this is timing advance, "Timing advance" refers to the number of degrees before top dead center (BTDC) that the spark will ignite the air-fuel mixture in the combustion chamber during the compression stroke. Retarded timing can be defined as changing the timing so that fuel ignition happens later than the manufacturer's specified time. hence it depends on engine operating conditions.
b) The ignition system in an internal combustion engine ignites the mixture of fuel and air in the cylinders. An electronic ignition directs an electric current to each spark plug when it needs to fire. It has many advantages over mechanically timed ignition systems.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.