Evaluating Energy Systems in Cars
Energy storage has revolutionized how we produce and use energy. One of the best examples is the Electric Car. A few years ago King and Donihue each needed a new car. This is what we learned from our purchasing research.
As I was investigating car options I visited the local car dealerships and test drove a number of cars. Being an unrepentant techno geek I asked why the Prius gets better fuel efficiency in the city rather than the highway. I also wanted to know why the diesel VW Golf had better fuel economy than the gasoline version. The car sales folks were clueless. Clearly not a product of a liberal arts education. I started to do some digging to get the answers to my questions.
Cars move when we apply power to the wheels (Read about horsepower). Traditionally, the power came from an internal gasoline engine. Today we have cars powered with gasoline, diesel, and electric engines. This is what I learned starting with a conventional gasoline engine:
Another Example of the Hybrid Drive
If we assume the transmission is close to 100% efficient we can calculate the maximum efficiency of an internal combustion engine driven car based on the Carnot equation and the maximum temperature stability of steel. An ideal internal combustion engine would have an efficiency of 37%, but in practice it is often half this value (Read more about gasoline engines). Diesel Engines are more efficient than gasoline engines (Read about Diesel Engines). Electric motors have efficiencies of over 85% (reference).
The three videos below illustrate the engineering behind the superior fuel economy of hybrid electric cars.
https://youtu.be/4CFxQGWAaho
Read more about Toyota hybrid drive train. It is important to note that the Toyota V uses a combined electric/gasoline engine with 100% of the energy from the car coming from gasoline!