Why can’t we use the heat from combustion to make cars more efficient?

Question

Can we use the heat to boil water to turn a turbine? Or would the water never cool enough to be used again?

What about using the heat to create pressure and then releasing the pressure to help move the fly wheel?

In: 1046

Answer 1

Because the main inefficiency in cars is that you’re using 4000lbs of steel to move a 200lb person. If you want to buy a gallon of milk, you’re moving 4200lbs of material several miles to secure 8lbs of milk. It doesn’t matter how close you get to Carnot optimal, you’ve wasted 99.8% of your energy moving things that weren’t part of the objective.

And practical efficiencies in Carnot cycles require scale. The larger the engine the more efficient you can usually make it, which if you’re an engineer chasing a regulation of ‘x MPG at highway speeds’ competing with a regulation of ‘can survive a front-end collision at highway speeds’, then there are certain realities with respect to mass and power you need to accept to meet the assumptions in this calculation (that people need to travel in cars at highway speeds on infrastructure so poor that a head on collision is a likely enough occurrence that it needs to be protected against.

Note the regulations don’t say ‘don’t build a society where you need to burn a gallon of gas to secure a gallon of milk’.

There are no technical obstacles to running an energy efficiency society. All of the obstacles are cultural. We have inefficient cars because we demand inefficient cars. You had 60MPG cars in the US in the 80s. They were small, didn’t accelerate fast, and often couldn’t hit Texas highway speeds. There are more efficient cars in Europe – basically all the most popular cars in Europe are pretty efficient. None of them are sold in the US because Americans want road tanks, because we favor personal survivability over efficiency, economy, survivability of the community (pedestrians, cyclists, people who do buy small cars) and so on. Cars are inefficient because we want them to be, not because we can’t solve the problem. Climate change is a cultural, not technological problem. We know how to solve climate change. Have for quite a while. Homelessness is a cultural, not technological problem. We know how to solve that too. Same with healthcare costs, and almost everything else.