Stirling Engines, Low Temperature Alternatives For Power Plants

For as long as 200 years, the studies have been going on it after Robert Stirling had invented this concept of Stirling engines. Teruyuki Akazawa of Estir Co pondered on the reuse of the lost heat from the Panasonic plant. The re-implementation of the Stirling engines was in fact a fantastic business strategy to be considered which gives more productivity.

The air cylinder has got a piston that moves up and down. This forms a cycle due to the repeated expansion and contraction. There is expansion when heated by the air and contractions encountered when cooled by the water.

One of the reasons for this continuing in the analysis for the replacement of the Stirling engines with that of the gasoline is due to the drawback of the working temperature of the Stirling engine. The power plant could supply only 500 A, but the Stirling engine needs very high temperature for its working around 1000 A.

Panasonics plants the Akazawa though of cutting down the internal friction so as to enable the engines to work at lower temperatures. This came to reality by the usage of the oil instead of the lubricants. The lubricants when heated to several hundred degrees will cause the engine to burn and clog.

It was needed to change the linear motion of the piston into a rotary motion. For this Akazawa had devised a new concept called the Scotch yoke. The Scotch yoke is a mechanism for converting the linear motion of a slider into rotational motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part. The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed.

There was a thought of converting the linear motion of the piston into a rotary motion. For this Akazawa had conducted trial and error methods so as to convert linear motion into a rotary motion. This mechanism was named to be the Scotch yoke. The Scotch yoke is a mechanism for converting the linear motion of a slider into rotational motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part. The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed.

The advantages compared to a standard crankshaft and connecting rod setup are:
1. Fewer moving parts.
2. Smoother operation.
3. Higher percentage of the time spent at top dead center (dwell) improving theoretical engine efficiency of constant volume combustion cycles, though actual gains have not been demonstrated.
4. In an engine application, elimination of joint typically served by a wrist pin, and near elimination of piston skirt and cylinder scuffing, as side loading of piston due to sine of connecting rod angle is eliminated.

The disadvantages are:
1. Rapid wear of the slot in the yoke caused by sliding friction and high contact pressures.
2. Increased heat loss during combustion due to extended dwell atop dead center offsets any constant volume combustion improvements in real engines.
3. Lesser percentage of the time spent at bottom dead center reducing blowdown time for two stroke engines, when compared with a conventional piston and crankshaft mechanism.
This setup is most commonly used in control valve actuators in high pressure oil and gas pipelines.
It has been used in various internal combustion engines, such as the Bourke engine, SyTech engine, and many hot air engines and steam engines.

Experiments have shown that extended dwell time will not work well with constant volume combustion (Otto, Bourke or similar) cycles. Gains might be more apparent using a stratified direct injection (diesel or similar) cycle to reduce heat losses.

Akazawa tried of not using the motor oil when they ere developing an air conditioning system and they succeeded. Later this group also developed an engine that did not use any kind of lubricating oil.
Since 2009, the Stirling engine was used and it provided power to about 500W. Now, the second version of the engine was built that gave power of about 10KW. The president of stir Co, Akazawa said that it could power to about to about 12 to 2 houses 7 days a week. He said that “I hope it’ll become standard procedure for all manufacturing plants to be equipped with Stirling engines to generate electricity from waste heat.” He also added that “I want to revive the abandoned engine mechanism using the latest technologies, which are more sophisticated.”

As of 2000, 95 % of the wasted heat is from industrial plants and has temperatures of under 400 degrees Celsius, and only 3% is 500 degrees or hotter, this was according to a study performed by the Energy Conservation Center in Japan, so the engine revival by Akazawa is indeed welcomed by the industry.

Tags: Akazawa, Panasonic, Scotch yoke, Stirling engines

Category: Energy News