Engine efficiency is closely linked to a principle called the First Law of Thermodynamics. This law says that energy cannot be created or destroyed; it can only change from one form to another.

In engines, this means that the chemical energy from fuel is changed into mechanical energy, which is what makes the engine work.

When we burn fuel in an engine, the chemical energy turns into thermal energy (heat). This heat builds up pressure in a part of the engine called the combustion chamber. However, not all the heat produced is used to do work. Some of it gets lost as heat, friction, and sound.

Let’s break it down:

1. Energy Input: This is the total energy that comes from the fuel.
2. Useful Work Output: This is the mechanical energy that powers the vehicle.
3. Waste Energy: This is the energy lost as heat or other inefficiencies.

We can express the efficiency, which we can call $\eta$, of an engine like this:

$$\eta = \frac{\text{Useful Work Output}}{\text{Energy Input}} \times 100\%$$

This formula shows how the First Law affects efficiency: the best an engine can do is limited by how much energy can be turned into useful work.

In the real world, knowing about these energy losses helps engineers create better engines that work more efficiently. They might use special materials, improve how fuel burns, or add systems that recover energy to make engines use energy better.

In summary, the First Law of Thermodynamics helps us understand how energy works. It is key to making engines better and more efficient, showing the difference between what engines could do and what they actually do.