The following gives a brief description of why SSSP should be expected to be interesting as future prime mover
1) Fuel flexibility
Like the Stirling engine the SSSP has external combustion and offers great fuel flexibility compared to the ICE and GT and the fuel cell. SSSP is also expected to offer advantages when harnessing solar energy in solar thermal power application. The multi fuel possibilities make it possible to use locally available energy (solar, bio fuel) and realize autonomous distributed off-grid power system.
2) Exhaust gas and noise emission
The exhaust gas emission has a potential to be very low. Due to the absence of preheat or pre-compression of the combustion air, the combustion temperature will be lower than for other power cycles which imply lower NOx emission. NOx emission will almost be eliminated without any catalytic conversion. By coating the steam generator surfaces with an oxidation catalytic layer other emissions such as CO and HC can be reduced in a cost effective way. The SSSP has also a potential to be very silent and vibration free power source, and hence offer an environmentally friendly power source that can be placed close to people in mobile applications as well as in buildings.
3) Energy consumption
The modern steam engine has a potential to offer low energy consumption both as a self contained stand alone system as well as a bottoming cycles in hybrid systems. The main reason for that is the high part load efficiency. In almost all applications ( automotive and stationary ) part load efficiency is more significant than full load efficiency. The advantages of high part load efficiency will be especially pronounced in small scale distributed autonomous off-grid CHP (Combined Heat and Power) and most mobile applications. RANOTOR R&D Corp. is expected to achieve about 32 % at part load in a modern steam engine, which is almost 3 times higher efficiency than a conventional ICE operating at part load.
4) Investment costs and power density
The power density for a modern SSSP can be very high (1200 kW/litre displacement volume ). Besides high power density for the steam engine proper also compact heat exchanger approach for the steam generator and the condenser will together imply low weight to power ratio ( 0.5 kg/ kW peak power) for the complete SSSP, and hence a competitive price ( $/kW peak power ) is expected. Further more , by only designing and supplying different burners the same basic SSSP system can be used at many different markets depending on the local fuel supply No after treatment of the exhaust gas is necessary. Silent and vibration free, that is, can be integrated close to the user without mufflers and suspensions.
5) Maintenance needs
The modern oil free steam engine power system will be similar to a heat pump and refrigeration system where the working fluid is well defined and operates in a closed loop. The steam engine proper is therefore expected to have a long life time without any maintenance needs. The primary energy input will be conversed to mechanical energy ( electricity ) and almost all of the rest 60 – 65 % will be rejected as heat in the condenser. The heat losses occurring in the steam generator rejected as exhaust gas is less than 5 % and at low temperature and no expensive exhaust gas system is involved which has to be replaced. In CHP applications where heat losses are utilised all heat losses are harnessed in the condenser. In order to collect and recover all heat losses from an ICE- engine several heat exchangers have to be used as for instances an exhaust gas heat exchanger , oil cooler, coolant water and intercooler. Further more , the condenser where the waste heat is collected operates with working fluids (condensing steam and water ) in closed loops which eliminate fouling problem. The only components involved in the SSSP which is expected to require maintenance is the burner and to some extent the steam generator.
6) Torque characteristic and momentary respond
The steam engine will provide very high torque already from zero shaft speed and with a proper designed engine, gear box can be eliminated in automotive applications. A steam engine will provide instant response to power demand if steam is available without any lag and delay . Modern compact steam generators and a so called steam buffer will promptly provide the steam engine with steam. The torque characteristic is excellent for automotive applications with high low end torque and an “elastic” torque profile. The prompt response is important also for CHP applications
SSSP makes it possible to realise hybrids (combicycles ) with high efficiency at significant load. Hybrids also offer APU ( Auxiliary Power Units ) features in automotive applications and backup features in CHP applications. Hybrids offer also higher flexibility to meet mismatch between electricity and heat demand. The SSSP can act as bottoming cycle together with almost any kind of prime mover as ICE and the development of the ceramic gasturbine with higher temperature should justify the micro bottoming cycle concept further. SSSP is also interesting as bottoming cycles together with the emerging high temperature fuel cells.