Contemplating the [very small, but clearly non-zero] power output of this engine somehow led me to find this site:

**LINK** http://bettigue.blogspot.com

It is full of wonders and I think you will enjoy a visit

… The text is in German, but that’s no great problem these days.

MichaelG.

Here is a German patent from 2015 which cites Henry Wood, and briefly describes the working of the engine:

**LINK**

https://patents.google.com/patent/DE202015004768U1/de#

The text is viewable in English

MichaelG.

Very good!

Going back to the efficiency question the set-up is close to being able to take actual measurements, which I'm always interested in.

• A close estimate of the heat produced by the lamp can be got by weighing the amount of oil or spirit burnt over, say 10 minutes. The heat value of most liquid fuels is available on the web, so the heating lamp's output can be expressed in Watts.
• Adding an ammeter would allow the watts going into the LED to be calculated. (W=V x I)

The ratio between power in and power out will be scary low: my guess is considerably less than 1%, because only the small proportion of the flame sucked into the cylinder is available for work. Most of the flame's energy is wasted.

Another possibility is to substitute a rheostat for the lamp (an ordinary potentiometer should do). This would allow the load to be varied to find the systems peak power output. Possible but unlikely that the LED is a perfect load, so the engine may do even better by tweaking the rheostat for best results.

When the output from the generator in watts is known, the output of the engine can be guesstimated. Roughly the engine is outputting about twice the wattage of the load because the generator can be assumed to be about 50% efficient.

Working out the efficiency of the engine itself is harder. The pressure changes inside the cylinder have to be traced whilst the engine is running at constant speed, which isn't easy to do with a small engine. You can get an idea of the mechanical inefficiency by driving the cold engine with an electric motor, again assuming it's about 50% efficient, and measuring how many watts are needed to spin the flame licker: this gives a rough idea of the power consumed by friction and accelerating the piston, con-rod, crank and valve masses.

Good work, and much neater than my efforts!

Dave