High performance steam engines
WHAT IS THE CHALLENGE?The greenhouse problem from burning of fossil fuel, the coming shortage fossil fuels, as well as skyrocketing energy prices will require a substantial change of global energy systems. For stationary electricity generation, for efficient use of electricity, and for transportation/vehicles, development of new efficient and environmentally sustainable technologies will be required. For electricity generation particularly in warmer regions and without availability of large scale electricity generation/distribution, small scale solar energy based electricity generation would be very interesting. A first step for heavy vehicles would be to improve the diesel engine. In a longer time frame, new energy sources and engines based on non-fossil energy will be required for vehicles. Within all these applications, there is a need for small scale machines that don’t need oil for lubrication. Machines without need for oil lubrication would also be very useful for environmentally better refrigeration and heat pump units with improved performance – and hence more efficient utilization of electricity.HOW CAN THE PROJECT CONTRIBUTE TO A SOLUTION?
The project objective is to develop a physical demonstrator for a small scale vibration free piston machine that doesn´t need oil lubrication. This is a new type of axial piston machine (with so called “wobble plate” instead of a conventional crank mechanism) that can be used both as engine in a high performance steam process and as refrigerant compressor. A small scale compact steam engine with advanced steam data (high pressure and temperature) can utilize solar energy or bio fuels for electricity generation, or can utilize waste heat e.g. from diesel engine exhaust. A modern steam engine is compact and has low noise. For the applications where the steam engine is powered by bio fuel, the combustion is continuous at relatively low temperature which means very low exhaust emissions. The steam engine is also very feasible for solar energy based electricity generation.
The steam engine can also improve the diesel engine fuel economy in heavy vehicles, by utilizing the exhaust heat from the diesel engine and convert this waste energy to a useful contribution to traction. In a longer time frame, a modern advanced steam system would give several advantages as engine for e.g. cars and light trucks, particularly in city traffic. There are several advantages, e.g. as opposed to petrol (otto) and diesel engines a steam engine has its best efficiency at part load, which would be particularly advantageous in city traffic. The steam engine gives an extremely high power /displacement (cylinder) volume ratio. The starting torque is very high already from standstill, so neither gearbox nor clutch will be required.
A key component is the expander, i.e. the engine, where steam thermal energy is converted to useful work. In a small scale steam system, turbines that are used in current large scale power plants, would not be feasible. Instead, a piston machine would have the most feasible characteristic and properties. As opposed to current oil lubricated piston machines, however oil free operation will be required, that could be obtained by use of new construction materials combined with water/steam lubrication. A small oil free piston machine would also be advantageous as compressor in refrigeration and heat pump units.
WHO WILL BENEFIT FROM THE RESULTS?
Realization and commercialization of a high-performance steam system will require substantial development efforts. The MISTRA project results, to demonstrate the attractive properties of a small scale oil free piston machine, will:
- Substantially contribute to environmentally sustainable small scale electricity generation, based on solar energy and bio fuels
- Give substantial environmental improvement by elimination of lubrication oil
- Be directly applicable for new environmentally improved refrigeration and heat pump units
- Verify the usefulness of the novel oil free piston machine as key component
- Contribute to the development of a small scale high performance steam engine and support funding of continued development work
Results from the MISTRA project will be utilized in current small scale steam process projects; in the Swedish “Green Car 3” program and in a EC project with Fiat and other industrial partners.
Pedagogical values: A computer simulation model for analysis of the novel piston machine´s mechanical behavior has been developed within a PhD project at KTH, with conference presentations and journal publishing of results. Some sub-problems have been solved in the form of student projects at KTH; design and construction of a test rig for piston ring testing, prototype design and testing of a new rapid valve design, and strength calculations and dimensioning of expander components.
