Design and Technology – Energy and control systems | e-Consult
Energy and control systems (1 questions)
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Answer: A 4-stroke internal combustion engine converts chemical energy (from fuel) into mechanical energy through a cyclical process. The four strokes are: Intake, Compression, Combustion (Power), and Exhaust.
Stages of the Engine Cycle:
- Intake Stroke: The piston moves downwards, creating a vacuum in the cylinder. The intake valve opens, allowing a mixture of air and fuel to be drawn into the cylinder. Energy Transformation: Chemical energy (potential in the fuel) is not yet being converted.
- Compression Stroke: The intake valve closes, and the piston moves upwards, compressing the air-fuel mixture. This increases the temperature and pressure of the mixture. Energy Transformation: Chemical potential energy is converted into thermal energy (heat).
- Combustion (Power) Stroke: At or near the top of the compression stroke, the air-fuel mixture is ignited (by a spark plug in a petrol engine or by compression in a diesel engine). The rapid expansion of the burning gases forces the piston downwards. Energy Transformation: Thermal energy (heat) is converted into mechanical energy (piston movement). This is the power stroke.
- Exhaust Stroke: The exhaust valve opens, and the piston moves upwards, pushing the burnt gases out of the cylinder. Energy Transformation: Mechanical energy (piston movement) is used to expel the exhaust gases.
Factors Affecting Efficiency:
- Compression Ratio: A higher compression ratio generally leads to higher thermal efficiency.
- Friction: Friction between moving parts reduces efficiency.
- Heat Loss: Heat lost through the cylinder walls and exhaust gases reduces efficiency.
- Incomplete Combustion: Incomplete burning of the fuel reduces efficiency.
- Valve Timing: Incorrect valve timing can reduce efficiency.
Methods to Improve Efficiency:
- Higher Compression Ratio: Within the limits of engine design to avoid knocking.
- Reduced Friction: Using low-friction coatings and improved lubrication.
- Improved Cooling: More efficient cooling systems to reduce heat loss.
- Optimised Combustion: Precise fuel injection and ignition timing to ensure complete combustion.
- Turbocharging/Supercharging: Forcing more air into the cylinder to increase power and efficiency.