Old steam engines vented their steam, losing 95% of the heat. Recycling steam engines are already in service.
What we do, is link in another wagon, and this takes in the exhaust steam at 8 atmospheres, 720oC. This holds so much energy. It loops back and forth along the cooling vessel, and emerges as warm water, at 90oC. It passes its heat to a Carnot gas at low pressure.
It enters at the bottom at 20oC, 0.4 atmospheres. It emerges as hot gas, 680oC, 5 atmospheres: my PhD supervisor assured me it was better to bottom feed the cold Carnot gas.
It sets you little flow cycles, at emerges at the top, with 85% of the 95% of the wasted heat. So we vent no steam – no puff-puff. So we only need to burn 1/9th of the fuel. Diesel oil would be most efficient, and least polluting.
Really we would like to replace the fire box – and there is a way. Lightening does Molecular Nuclear Fusion
1 lightening bolt releases 2.5x1030W of heat. So a 1mx2cm steam plasma at 4 atmospheres releases 8.6MW.
So we have a steam plasma tube in a 1m water bath, and get at 8.6MW of heat. From 0.0053cc of regular water a year – constant 'burn'.
We feed this heat into a steam turbine, and get our 4.4MW of power. Now a steam engine only needs 250kW. We distribute this power to all the carriages – using power electronics to control the frequency.
The frequency determines the train speed. We have distributed drive – so no spinning of the drive wheels. No current drawn from the grid. So no electric cables or gantry required.
4.4MW – we are going to travel between cities at super sonic speed. No CO2 released – or the train, or remotely in a power station.
For countries like Australia, this will compete with air craft for travel times. So no coal, oil or gas burn. The Green train.