How Much Power Is Produced from 1 Litre of Petrol? A Comprehensive Guide

The energy content of petrol gasoline is approximately 31,536 kilojoules per litre (kJ/L). This translates to about 8.89 kilowatt-hours (kWh) of energy per litre of petrol.

When considering the efficiency of an internal combustion engine, which typically ranges from 20 to 30%, usable power can be calculated from burning 1 litre of petrol. Here's a detailed breakdown:

Efficiency of an Internal Combustion Engine

An internal combustion engine, designed to convert chemical energy from fuel into mechanical energy, operates at varying efficiencies. At an efficiency of 20%, the usable power produced from 1 litre of petrol would be approximately 1.78 kWh. At a 30% efficiency, this number rises to approximately 2.67 kWh.

These values indicate the amount of useful energy that can be harnessed from 1 litre of petrol in a typical engine, underscoring the importance of understanding the efficiency of the engine in relation to petrol's energy content.

Energy Conversion in Crude Oil Production

Depending on the study, the energy required to produce one gallon of gasoline varies. Most studies suggest the figure is made up from all energy sources, not just electricity. It is generally agreed that around 5 to 7 kWh of energy is required to produce one US gallon of gasoline.

The refining process involves fractional distillation or natural production to break down crude oil into standard gasoline types. The method and initial materials influence the energy input significantly. For instance, for US crude oil that is easy to refine, the energy required for a US gallon is around 4 kWh. In contrast, harder-to-refine crude, such as tar sands or thick oil, requires a much higher amount of energy.

In terms of the primary mechanical energy efficiency, when factoring in the main energy losses and parasitic inputs, the efficiency of oil in the best internal combustion engine is less than 10%. Despite the high energy content of gasoline, the inefficiency of these engines means that a significant portion of the energy is lost as waste heat.

The Energy in Petrol and Its Burning

The specific energy of petrol, such as 87 octane, is about 32 MJ/litre. Most motor fuels designated as petrol or gasoline (excluding diesel) are within 10% of this number. Each litre of petrol, with a density of 0.7489 g/mL, weighs 748.9 g. When burned, 1 g of petrol releases approximately 44 to 48 kJ of energy. Therefore, 1 litre of petrol releases around 750 g in energy:

Energy released by 1 litre of petrol 750 g × 46 kJ/g ≈ 34,500 kJ, or approximately 33,000 to 36,000 kJ.

This immense energy output from a relatively small quantity of petrol illustrates the significant role it plays in modern transportation and mechanical energy production, despite the poor efficiency of the engines that consume it.

Conclusion

Understanding the energy content and efficiency of petrol is crucial for optimizing energy usage in vehicles and improving overall fuel economy. While the efficiency of engines can be improved, the fundamental properties of petrol remain key in discussions about energy conversion and sustainability.