Infernal Combustion Engine Again

I was reading an article recently where it stated that an internal combustion engine produces more energy in heat than it does in motive power. If this is the case, why has this heat not been used for any other purpose than the heater in the car or heating up the outside air. Surely there must be a use for this heat to generate some other form of power or even airconditioning?

It appears that they are working on such a system. Toyota appears to have some kind of Waste heat auxiliary power unit on the drawing boards.

In stationary applications, the heat is used (for space heating, for heating water or even, as you suggest, for cooling).

Turning waste heat into power (i.e. adding an additional bottoming cycle to the Otto cycle or Diesel cycle), you quickly run into a situation of diminishing returns. The waste heat is fairly low grade, so you can hope to extract very little power, but you would have all the complexity of putting an additional working fluid through a cycle.

Turning waste heat into cooling is achieved using an absorption chiller (I saw one installed on a stationary gas engine just last week), but it too is a lot of extra complexity.

I hope you are aware that while recovery of some of the energy lost to heat is possible (but may not be practical), recovery of all the energy lost is not. You won’t be able to feed the output back to the input and come out ahead, for that would be perpetual motion.

Isn’t perpetual motion allowed?

On this board, we obey the laws of thermodynamics, Son!

I saw a plant that tries to recover as much heat from a diesel engine. The engine was connected to a generator. And The engine had no radiator or waste heat oil cooler. That heat was recovered to pre heat boiler water. The exhaust gases ran a low pressure boiler which was used to heat the hospital.

Turbochargers are said to use some of this heat energy to provide additional power.

For cars, of course, the added weight of the system to extract additional useful energy from waste heat is a downside, even apart from the additional complexity and cost.

There are a few experimental six stroke engine designs intended to use the heat generated from fuel combustion for an extra power stroke:

The Crower engine, which got some press a few years ago dispenses with having a water jacket to cool the engine, and injects water into the cylinder after the exhaust stroke. The water turns into steam and provides an additional power stroke. According to that Wiki article, it turned out that somebody had a similar idea in 1915.

Whether this sort of thing could be made to work in a production vehicle is another question, of course.

Steam engines commonly used a “triple expansion” design, where there were primary, secondary and tertiary pistons that used the exhaust steam from the previous piston in the cascade. This was practical because even mobile steam engines like locomotives or ship engines were large and heavy anyway, and the fuel economy meant that the extra engine size was offset by the tons of coal saved. By contrast internal combustion engines are compact, powerful and use a high-energy fuel, so in terms of vehicle performance scavenging waste heat wasn’t worth it- you’d get more milage from extra fuel than that fuel’s weight in secondary generation. Only if absolute fuel consumption due to high price or scarcity is a factor does it become worth it.

I think the last major innovation in the Otto Cycle internal combustion engine was the addition of the turbocharger in the mid-Twenties. All of the other basic improvements predate what is recognized as an automobile (1888).

There have been incremental improvements but like the toaster, the basic idea was worked out long ago.There have been all manner of experiments into better engines and more radical engine designs, but the Otto and Diesel seem to be the best and most practical. My personal opinion is that they will once again outlast the electric car.

In a shout-out to another thread, this is why auto manufacturers use the same basic engine for decades. Individual components may be improved upon, but the basic product rarely needs updating.

Combined-cycle power plants use the idea of the OP to make electricity generation far more efficient. But as has been mentioned, it makes things far more complicated.

Interesting replies. Gary T, no, the Turbo purely uses the exhaust gasses to turn the turbine blades. Heat is a bit of a bother due to the bearings in the turbine having to be force fed oil to keep them from glowing red and seizing. I have Two Lotus cars with Turbo chargers and when they are run up on the dynomometer the whole manifold and turbo glows red.