Stirlingengineforum.com

The Chevy celebrity engine is not where the bar is anymore. modern otto cycle engines are cracking the 40% efficiency barrier.
https://www.sae.org/news/2018/04/toyota ... percentage.
Toyota with atkinson cycle engines is providing real world engines, with high horsepower, high HP/weight and good environmental performance. These engines are not high in NOx with modern cat convertors. I think the stirling engine is great for waste heat, off grid stationary power generation possibilities, and anywhere good quality fuel is not available.
I think any transportation application has to include fast start up, good dynamic power output range, low weight, affordability. The Stirling would be great for stationary power generation, since one could make steady output, weight would not be an issue, and very poor qualtiy fuel use would be an a huge advantage. I don't see anything in the stirling that comes as close to the carnot cycle as, say, a diesel engine by the way. there's nothing fundamental from a heat cycle that makes it more efficient. The regenerator is more os a necessity to patch up hot reservoir / cold reservoir heat transfer difficulaties. In a diesel, ever higher hot side temperatures and pressures can be raised as materials technology improves, for example a ceramic engine could raise temperature and pressure far higher, and the cold side is always the ambient dump temperature.
An energy.gov website lists stretch goals for advanced boosted diesel engines at 50%.

https://www.energy.gov/sites/prod/files ... p_2018.pdf

with otto cycle engines already passing 40%, who knows what might come next? If you want sky high diesel efficiency, just jack up the operating temperatures and evolve the materials technology of the engine.
But known of these engines will work with primitive simple fuels, such as agri-waste, wood, crude oil, coal, etc.

I've thought a solar hybrid Stirling/electric vehicle might be useful. The Stirling could chug along steadily, as Stirling engines mostly do, keeping batteries topped off, while an electric motor took care of rapid acceleration, stop and go.

On a sunny day, a car roof can get pretty darn hot sitting in a parking lot or traffic jam. Or just sitting at home in the driveway.

At one time, Stirling engines were potentially much more efficient than photovoltaics. I'm not sure if that is still true with advances in both technologies.

A Stirling solar/electric hybrid could also be kept charged with virtually any available combustible fuel at night or on cloudy days.

To understand an Alpha Stirling Engine, or any engine, it is best to look at the ideal case and later put in the effects of a real working engine.

An ideal Alpha can be explained using four strokes, or phases, performed by the two pistons working together, but without any crankshaft:
1. Hot piston in top dead center. Cold piston compressing moving in. Heat of compression is absorbed by the cold side. Heat removed. < Squeeze.

2. Transfer of air from cold to hot. No change in volume. Both Pistons must move to do this phase. Heat transfered out of the regenerator. Hottest and highest pressure attained. < Bang.

3. Hot piston is expanding. Cold piston top dead center. Heat loss from expansion is replaced from the hot side. Heat added to the air. < Power stroke.

4. Transfer of air from hot side to cold side. No change in volume. Both Pistons must move to do this phase. Heat is stored/absorbed in the regenerator. Lowest temperature and pressure attained. < Blow/Suck.

Then back to phase 1.

Just as in an internal combustion engine (IC), (1. Compresses cool air < Squeeze. 2. Heats < Bang. 3. Expands hot air < Power stroke. 4. Exhausts hot air and sucks in cool < *Blow/Suck.), the Alpha gets it's power stroke after the "bang", during the hot expansion 3 , the other three strokes require momentum from the flywheel to drag it through to the end of the compression.

Add some real engine points. The two Pistons being moved by a common crankshaft, out of phase by 90 degrees, mimicks the four phases described above. The motions and pauses/dwells are blurred, intermixed in the edges of the four strokes. It helps to break the motion down to four quarter turns. Each quarter turn should be centered at a top or bottom dead center of one of the pistons.

When a piston is at the top or bottom of it's travel it's motion relative to crank speed is slowest, a pause/dwell. At the same time the other piston is at 90 crank degrees and moving fastest. Example: Hot piston at 90 moving out expanding, cold piston at top dead center, in, not moving.

Having sinusoidal motion, from a crankshaft, reduces impact loading and smooths the engines high speed operation. It is a tradeoff between efficiency and effectiveness/power-density.

* Note: The blow and suck in a four stroke IC engine are two separate strokes. They are combined here, into one phase, for comparison to the Alpha Stirling Engine. The two stroke IC engine combines them into one stroke as well.

Also the bang in an IC engine burns for part of the expansion stroke/phase. Diesels have a much shorter combustion period. It is called detonation.

Thank you.