Petrol vs Diesel

Question 1

What are the differences between petrol and diesel engines?

Answer 1

• Ignition: Petrol uses spark plugs, Diesel requires compression of hot air
• Engine cycle: Petrol engine uses the 4-stroke, Diesel engine uses the 2-stroke cycle
• Compression Ratio: Petrol low, Diesel high
• Vehicle application: Petrol is used in light vehicles, diesel used in heavy vehicles

Question 2

Describe the stages in the 4-stroke cycle

Answer 2

• Intake: Piston descends and air-fuel mixture enters through intake port with both inlet valves open
• Compression: Piston ascends, compressing the mixture for more powerful combustion
• Power: Spark plug ignites the compressed mixture resulting in combustion which forces the piston to reach BDC. Connecting Rod transfers the power to the crankshaft
• Exhaust Piston ascends, pushing the spent mixture out through the exhaust valves and port

Question 3

Describe the stages in the 2-stroke cycle

Answer 3

• Intake and Compression: Air is drawn into the intake port and compressed, increasing its temperature. New fuel enters the crankcase
• Power and Exhaust: Air-fuel mixture is ignited by spark and combustion occurs. Exhaust gases escape the outlet port