Figure 2: Two – stroke diesel engine (Left) Four – stroke diesel engine (Right)
Project 2:
In company that designs road cars and heavy trucks, it important to make the proper selection of the engines. Your part as a system energy engineer is to make a proper selection between an engine operates on Otto cycle/gasoline engine or Diesel cycle/diesel engine. Your head of department asked you to provide a detailed technical report that shows your selection for engine to be used with heavy truck vehicle. This is best achieved by performing the following tasks: Section.1:
1. Which engine does operate at lower ??? and has higher air-fuel mass ratio?
2. Which engine does burn fuel more completely?
3. Which engine has lower fuel cost?
4. Explain what compression ratio for Otto and Diesel cycles means
5. Explain what cut-off ratio for Diesel cycles means
6. Explain the limitations of SI engines in terms of their ability to operate at much higher compression ratios. What is this limitation called?
7. Provide general plot(s) for thermal efficiency, ? vs compression ratio, r for air with ? = 1.4 and show the typical compressions ratios for gasoline and diesel engines. Compare your plots in terms of the typical compression ratio values.
8. Using your plot of the thermal efficiency, ? vs compression ratio, r for air with ? = 1.4 for a diesel engine, show how will the thermal efficiency, ? would change with the cut-off ratio values.
9. Explain mathematically how the thermal efficiency, ? of Otto cycle is always higher than diesel cycle if-and-only-if both engines are operated at same compression ratio, ?.
10. Based on Part.6, 7, indicate which engines has more tendency to work at higher compression ratio values.
11. Based on Part.1, 2, 3, 10, explain why diesel engine would have higher overall efficiency than gasoline engine and explain how this would not violate your results in Part.9.
12. Assume you have Otto cycle operates at compression ratio of 9 and Diesel cycle operates at ratio of 23, which engine will have better overall efficiency?
13. Which engine has heat transfer addition at constant pressure and constant volume, how does this affect the overall efficiency?
14. Compare the compression process of both engines in terms of the working fluid (air-fuel mixture or air only)
15. Compare both engines in terms of the way that the combustion is initiated.
Based on what you have explained and explored previously, make your recommendations to select an engine for heavy truck in which the following design requirement must be met:
− Operates at lower rpms with less fuel consumption.
− Lower operational cost.
− Higher overall efficiency.
Also, give an example of a well-known design of the engine you have selected, showing its overall efficiency value, number of cylinders, power output, operating rpm, date of manufacturing, estimated total engine cost, country of manufacture and brand, availability of spare parts in local market, warranty period, and supplier name.
Section.2:
In case you select the diesel engine, evaluate the performance a four-cylinder two stroke 2.4 ? diesel engine that operates on ideal Diesel cycle has a compression ratio of 23 and cut off ratio of 1.75. Air is at 75?? and 105 kPa at the beginning of the compression process. This is best achieved by:
Determine the required power the engine will deliver at 3500 ???.
In case the diesel engine is four stroke what required power, it will deliver, compare this value with two stroke diesel engines.
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