Diesels require high compression ratios to work efficiently. Thus they were simpler to produce in heavier and larger engines that could have the mass to make up for a lack of design and technology. It became apparent that supercharging the engine was an easy method of increasing compression. On many of these engines two pistons are used. It increases the compression via low grade technology, and offers a valve system at the same time. The Commer Knocker used two pistons and a supercharger. The pistons were horizontally opposed to each other in a bank of three cylinders, so six pistons. The supercharged mix was thus further compressed by the two pistons coming to the middle of the cylinder where the combustion occurred. By doing this there were few high stressed parts and a simple engine which was reliable and more powerful for its size than the opposition.
There were drawbacks. It was a noisy engine and always sounded is if it was reving hard as it fired every stroke. Once heard at full chat, never forgotten, as they roar in a way no other diesel does. The second issue was that they had a habit of coking up. Not in itself an issue to the truck as they decoked themselves. But for anyone else an alarming blaze of fire and glowing soot could emanate from the exhaust without much warning.
Despite its good performance and reliability the unit was dropped in favour of 'normal' technology. That is conservative technology, aided by the increase understanding of materials, design and combustion. Today small diesels can outperform their petrol equivalents as Diesel is a more calorifically dense fuel. Yet there were very successful early deisel engines that were small. The Lohman clip on cyclemotor I think. Or was Mosquitoe.
Returning to the Panther. It is therefore possible that this car had one of a number of differing '50's versions of the shared twin piston in one cylinder engine. The other option is a multiple version of the engine used in the Iso Romi. This rather odd unit probably could operate as a diesel two stroke and a twin would be about the right size. I do not know who was actually responsible for the invention and manufacturer of that unit, but it was in its hay day at the time.
