Conventional reciprocating engines
The trouble with this type of engine, whether it be petrol, diesel, or coal generated steam, is the constantly changing direction of the piston. This means that momentum is always being lost which results in a low efficiency. Wikipedia says: 'Most steel engines have a thermodynamic limit of 37%. Even when aided with turbochargers and stock efficiency aids, most engines retain an average efficiency of about 18%-20 %.'
The fact that this type of engine wastes about 80% of the fuel it uses, is something that the motor trade generally does not like to remind us of.
Hybrid engines such as that used in the 'Toyota Prius' are too complex to manufacture and offer little benefit for general motorway cruising.
Wikipedia says that replacing the reciprocating action of this type of engine with a rotary one, leaps the thermal efficiency to about 60%. Attempts have been made to make a rotary internal combustion engine in the past, but after some short term success have had to be abandoned, due to an inability to seal the rotors. It is probably impossible to make a rotary internal combustion engine, due to the need of compressing the mixture.
It is much more likely that a rotary external combustion combustion engine, such as a steam engine, can be successful. This is because driven pressure is reasonably constant. There is an additional benefit that the fuel used does not have to be oil, and could be bottled gas (either natural or coal gas), which is a cleaner fuel, and is in good supply at the moment.
My design utilises the principle of 'Newtons Balls' to transfer momentum from one piston to the next . It is a toroidal engine. It probably would not be suitable for a large steam locomotive, which is better driven by electric pick-up.
It should offer considerable advantages for a large truck, as these types of vehicle spend much of their time cruising on a motorway. The need to wait to come up to pressure would thus not be too much of a disadvantage.
A steam engine develops full power from zero R.P.M., so this would eliminate the need for a gearbox. (With a large truck considerable momentum must be being lost when changing gear.)
Lubrication of my engine design would be achieved by oil being fed from the central hub. It would then be fed to the pistons where it would escape and then coat the inside of the bores. Oil would have to be lost in the steam.
The rotors would be turning at a similar R.P.M. to the road wheels, therefore there would be no need for a high pressure lubrication system.
Another possible motive power for a large lorry would be a scaled down version of a diesel electric train engine . This also needs no gearbox.
Note: 3 more illustrations complete the engine cycle.