ZIMSEC O Level Combined Science Notes: Efficiency: Diesel vs Petrol engines
- Efficiency refers to the fuel economy of an engine
- It measures the amount of chemical energy in the fuel that is converted to kinetic energy
- The efficiency of Petrol engines is around 25%
- Diesel engines have an efficiency of around 40%
- This means diesel engines have a higher fuel efficiency when compared to Petrol engines
- That is a car with a diesel engine will in theory travel longer per each litre of fuel when compared to a Petrol car
- Efficiency can thus also be measured in fuel economy terms
- Both diesel and petrol engines however cause pollution due to incomplete combustion of their respective fuels
- This is because the air supply in the engines is limited
- Carbon (soot) and carbon monoxide are produced
- Diesel engines produce less carbon monoxide as they are more efficient
How to improve the efficiency of diesel and petrol engines?
- Cleaning/Replacing blocked and old air filters regularly to ensure an adequate supply of air
- Ensuring the choke is functioning properly
- Cleaning/Replacing blocked and worn out fuel jets
- Ensure that the piston rings fit well.
- This improves compress
- Also if air seeps past the rings it burns in the cylinders producing black smoke(soot/carbon)
- Poorly fitting rings results in an inefficient engine
Differences between Diesel and Petrol engines
|Diesel Engine||Petrol Engine|
|Diesel fuel is used||Petrol is used as a fuel|
|Fuel is injected by the fuel injector after the air has been compressed||Petrol/Air mixture is introduced into the cylinder through jets|
|Fuel is ignited by the heat of compressed air||Fuel is ignited by sparks from spark plugs|
|High compression||The compression is half that of the diesel engine|
|The engines are heavier||The engines are lighter than diesel engines|
|40% with less carbon monoxide are thus more economical||25% efficient more carbon monoxide thus less efficient|
To access more topics go to the Combined Science Notes page.
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