The Efficiency of Diesel Fuel: Why It Offers Better Gas Mileage
Diesel fuel and petrol are two common types of fuel used in vehicles today. While petrol is a spirit-based fuel that burns readily, diesel is an oil-based fuel that burns more slowly, leading to better energy efficiency. This article explores the reasons why diesel fuel offers better gas mileage, focusing on factors such as density, compression ratios, and calorific value.
Why Diesel Fuel Offers Better Gas Mileage
One of the main reasons diesel fuel provides better gas mileage is due to its higher density compared to petrol. Diesel has a density of approximately 0.85, while petrol has a density of about 0.75. This means that a litre of diesel contains between 15-20% more fuel than a litre of petrol. Consequently, diesel engines can travel further on the same amount of fuel, leading to improved gas mileage.
Higher Compression Ratios and Efficiency
No explanation has yet addressed the impact of compression ratios on diesel engine efficiency. The reason lies in the relationship between compression and expansion ratios.
In a typical gasoline engine, the air and fuel vapour mixture is compressed about 10 times during the compression stroke. This results in an expansion ratio of 10 during the power stroke. In contrast, a diesel engine compresses the air much more intensely, about 18 times during the compression stroke, leading to an expansion ratio of 18 during the power stroke. This higher expansion ratio allows for more effective conversion of heat energy into mechanical energy, enhancing overall engine efficiency.
Combustion Temperature and Wasted Heat
Another key factor is the combustion temperature. Diesel engines operate at a higher combustion temperature of about 2500°C, compared to around 2000°C in gasoline engines. Despite this higher combustion temperature, diesel engines have a slightly lower exhaust gas temperature, indicating that more heat energy has been converted into mechanical energy. This results in less wasted heat, leading to better overall efficiency.
Higher Calorific Value and Turbocharging
Diesel fuel also has a higher calorific value per litre or gallon, which is a crucial factor in determining the fuel efficiency of vehicles. This higher calorific value means that diesel engines can extract more energy from the same amount of fuel, contributing to better gas mileage. Additionally, the high exhaust temperatures in diesel engines make them ideal for driving turbochargers, which further improves engine efficiency and performance.
Conclusion
In summary, diesel fuel offers better gas mileage due to its higher density, more controlled combustion process, and higher calorific value. The higher compression ratios in diesel engines also contribute to greater efficiency by allowing for more effective conversion of heat energy into mechanical energy. These factors combined make diesel fuel an attractive option for drivers looking to enhance their vehicle's fuel efficiency and performance.