"square/cube rule" and engine efficiency

OK, with octane C8H10, it takes two molecules of octane to burn 21 molecules of oxygen so we start of with 23 molecules of gas, after the burn we have 16 molecules of CO2 and 10 molecules of H2O resulting in 26 molecules of gas, only a slight increase in the number of gas molecules percentage wise especially when you consider the fact about 78 % of the gases in the cylinder is nitrogen which plays no part in the chemical reaction that generates the heat.

Also, engines run just fine on pure methane, (natural gas).

The main reason there is more pressure after combustion than before is mostly because the air is now very hot. If you double the temperature of air, you double its pressure if the volume is constant or you double its volume if the pressure is constant.
Take a sealed tank of air at 0 degrees C and heat it to 273 degrees C and you have doubled its temperature, measure the pressure, (absolute pressure, not gauge pressure) and it will be twice as high.

When the engine expands the now hot air to about 8 times the volume it had when it was compressed, the temperature of the air drops dramatically. That missing heat in the expanded air has been converted into kinetic energy. Raising the compression ratio also raises the expansion ratio during the power stroke and the cooler exhaust of a high expansion ratio reflects the engine’s higher thermodynamic efficiency.

Wrong. In an internal combustion engine, heat is wasted energy.

Heat that is left over after the hot gases have been expanded is wasted energy.

Did an “OLD TIME” watchmaker build that?

Does that thing have spark plugs? If it does, the plugs and distributor must be MARVELS!

Does that thing have spark plugs? If it does, the plugs and distributor must be MARVELS!

They primarily use glow plugs. You use a battery during startup to heat the glow plug, then it stays hot from each subsequent combustion.