Describe the operational sequence of four-stroke spark ignition and four-stroke compression ignition engines with the aid of sketches by constructing simple sketch representing the operation and plotting the P-V diagrams for each process during the cycle to show the following: The input and output heat and net output work The expansion and compression strokes The air-fuel mixture intake and exhaust gasses The spark plug when it is in the active mode The complete cycle of ideal Otto and Diesel cycles that shows the input and output heat and net output work.
A Team of Engineers asked for an internal combustion engine to use it in a designed car. Your role is to describe the operation sequence of different types of available engines, explain their
You must follow the following steps to help the team:
STEP 1
Describe the operational sequence of four-stroke spark ignition and four-stroke compression ignition engines with the aid of sketches by constructing simple sketch representing the operation and plotting the P-V diagrams for each process during the cycle to show the following:
- The input and output heat and net output work
- The expansion and compression strokes
- The air-fuel mixture intake and exhaust gasses
- The spark plug when it is in the active mode
- The complete cycle of ideal Otto and Diesel cycles that shows the input and output heat and net output work.
STEP 2
Explain the mechanical efficiency of two and four-stroke engines by answering.
- What parameter would you use to measure the mechanical efficiency of two and four stroke engines and what parameter would you fix to compare between both types. Show your explanation using the appropriate relation.
- Compare the mechanical efficiency of both two and four-stroke engines in terms of their powerto-weight, power-to-volume ratios, and revolutions per cycle.
STEP 3
To make the proper selection of the engine between a gasoline engine or a diesel engine, you asked to provide a detailed technical report show your selection for the engine to be used with an automobile vehicle that associated with low torque but high speed and acceleration. This is best achieved by performing the following tasks:
- Which engine must you choose? Explain your answer.
- Explain the limitations of the used engine.
- Provide general plot(s) for thermal efficiency, n vs compression ratio, r for air with k=1.4 and show the typical compressions ratios for gasoline and diesel engines. Compare your plots in terms of the typical compression ratio values.
- Using your plot of the thermal efficiency, n vs compression ratio, r for air with k=1.4 for a diesel engine, show how will the thermal efficiency of the diesel engine, n would change with the cutoff ratio values.
- Explain mathematically how the thermal efficiency, n of Otto cycle is always higher than diesel cycle if-and-only-if both engines are operated at the same compression ratio, r.
- Based on your answer for 5, indicate why we can use diesel engines.
- Assume you have Otto cycle operates at a compression ratio of 10 and the Diesel cycle operates at a ratio of 20, which engine will have better overall efficiency?
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