The International Steam Pages
The Possibility of a Steam-Water Turbine Railway Locomotive
An innovative British company, Pursuit Dynamics of Hertfordshire, has devised a steam-water engine for marine propulsion. This engine has no moving or sliding parts and injects high-pressure steam and a stream of air into water flowing in a pipe system, with a resulting water jet being expelled at the engine exit. A further description of this engine is at Pursuit's webpage at http://www.pdx.biz/, including a j-peg schematic illustrating the engine's operational characteristics.
This steam-water power engine concept holds the potential that its rapidly expelled jet of luke warm water could drive a turbine. Such a turbine could operate at high levels of efficiency since it converts energy from a relatively slow moving jet of high-density liquid. This is in contrast to conventional steam turbines which convert power from a rapid jet of extremely low-density hot gas. Since most of the steam injected into the water stream condenses into the water, a conventional water turbine with its blades coated with hard ceramic, may be used. This turbine concept has the potential to offer higher levels of efficiency than low-power (below 1,000-Hp) steam turbines, most of which deliver maximum thermal efficiencies in the 4% to 10% range.
In a marine application, the steam-water jet emerges at 3 to 4-degrees above the inlet water temperature. It may be possible to increase this temperature range in a closed-cycle steam-water turbine system, in which some reject heat would be reclaimed in a heat-exchanger prior to entering the boiler. A large proportion of the waste heat would be rejected in a radiator, prior to the cooled water re-entering the steam-water jet. The use of liquid rather than gas allows for a greater heat transfer efficiencies in the heat exchanger and radiator, while also minimizing the problems associated with rejecting the latent heat of vapourization in order to condense waste steam back into a liquid.
A railway locomotive using a steam-water jet driven water turbine, could operate in a variety of applications where small, efficient, low-powered railway motive power would be required to run on some form of combustible solid fuel renewable energy. Since this concept is in its early stages of research and development, the full power potential of the steam-water turbine system is presently unknown. It may eventually be able to power railway locomotives offering an excess of 1,000-drawbar horsepower. There are many applications for such power levels in developing nations, where railway track conditions do not allow train speeds in excess of 25 or 30-miles per hour.
During its early stages of development, the steam-water turbine system may be restricted for use in renewable energy fueled shunting locomotives, where the turbine may drive into a Voith-type railway gearbox. For higher turbine power output levels, a choice of electrical traction or Voith-type railway gearboxes could be considered as higher turbine power levels become available. In the under 2,000-Hp traction sector, a future steam-water turbine locomotive could be cost and efficiency competitive against other rival non-fossil fueled locomotives. This power level is near the limit of the cooling system of a closed-cycle steam or steam-water based railway locomotive power system.
A steam-water turbine locomotive may be able to operate using a small high-pressure water-tube boiler, instead of a larger low-pressure firetube boiler. The high pressure steam is injected into the water stream at supersonic speeds, generating shock waves. This not only propels the water stream but also enables the steam to condense into the water. Prior injection of air into the water stream assists in this process, raising efficiency. In future development, it may become possible to recirculate the air by separating it downstream of the turbine, cooling it, then re-injecting it via an air pump. The steam-water jet system has the potential to become an efficient, compact and competitive option for future solid renewable fueled railway traction.
Harry Valentine, Transportation Researcher, firstname.lastname@example.org
Click here to return to the modern steam locomotive developments page.