1. Heat Engines
How do we get the heat energy of the fuel and turn it into mechanical energy?
Simply put we combine the carbon and hydrogen in the fuel with oxygen.
2 reactions that occur are
C + O2  CO2 + heat energy
H2 + O  H2O + heat energy
This process is just the reverse of photosynthesis.

2. Just a little chemistry
For example, the the equation for burning heptane looks like:
C7H O2  7CO2 + 8 H2O X 106 calories per 100g of Heptane
1.15 x106 is called the heat of combustion for heptane. Every hydrocarbon has such a number
It is the maximum amount of energy for a certain amount of mass of a substance you can extract.
It represents the energy from the sun stored in the fuel since ancient times

3. So what is a heat engine?
A heat engine is any device that can take energy from a warm source and convert it to mechanical energy
Efficiency: not all of the energy from the burning of the fuel goes into the production of energy. Heat is lost as waste heat and needs to be disposed of.
For example, most energy generating plants are located near bodies of water or have cooling towers which are used to carry off waste heat.

4. How well does one work?
Your car often carries off waste heat via its cooling system. But your car recycles some of that heat—how?
No heat engine will perfectly convert all the heat energy to mechanical energy.
We need to quantify the efficiency and designers of heat engines work to maximize this efficiency.