No, this is not the steam engine that we’re working on…
First off I should introduce myself, I’m Nick and I’ve been watching OSE’s efforts for the last year or so and thinking along tangential lines for a while longer. After graduating in mechanical engineering at UW-Madison and working my previous two years as an engineer at a coal power plant I came to the conclusion: a very fundamental change in the way we power our society is in order. So I have left the job with a personal commitment to try to work towards solutions that make sense for future generations to come.
If you are reading this you probably have similar sentiments – I’m excited about the possibilities of open collaboration towards local sustainable technology. I’ve been to Factor e Farm a couple of times in the past year and have pitched in on the recent compressed earth brick building. After seeing the success of the CEB press and getting a feel for the advantages of open collaboration I decided that working on developing a solar power generation system with OSE would be a good outlet for my commitment towards sustainable energy solutions.
So for the last month or so my mind has been stuck on a subject considered by most to be locked in the history books for good: steam engines. Family, friends and concerned acquaintances wonder if Iâ€™ve popped a gasket myself in devoting perfectly good time to this research . Please allow me to share my thoughts on this subject and why I think it is worthwhile to revive it and put some modern touches on it. We are developing a steam engine as the heat engine of choice for the solar power system, and we are aiming to convert our open source tractor to steam power as well.
My motives for pursuing this research are spurred on by a multitude of criteria such as: (1), finding an engine simple enough to be locally manufactured and serviced, (2), ability to take both solar thermal and biomass thermal heat inputs, and (3), operate with low maintenance requirements and costs. Engine building is no small task and is fraught with little details that are easily missed on paper but are a real world show stopper.
For example the Stirling engine looks great on paper, it uses air as a working medium, it can accept high temperature heat inputs – and therefore has a cycle that should get very close to ideal efficiencies. Realizing this in a reliable engine, however, has been very difficult. Low specific heat capacities of air mean that the engine size will be larger than a steam engine and this in turn requires much larger cylinder sizes. To counter this the cylinders usually operate with a pressurized gas, but this in turn requires perfect sealing of the cylinder, all of which puts this engine out of the reach of all but the most sophisticated machine shops.
Other engine options that can take multiple heat inputs – such as the steam turbine – are also full of difficult manufacturing and engineering barriers such as precise machining and high speed dynamic balancing.
So perhaps it should be obvious that the low speed simple steam engine was the main engine to usher in the industrial age up to the 1920â€™s. So does it have a place in our history now? Well that is the question we intend to investigate and answer in our steam engine project.
The pros to this engine are:
- Fuel Flexibility: ability to take either direct solar thermal energy or indirect solar energy in the form of combusted biomass. Given that cellulose is both the most plentiful form of biomass energy and that it doesnâ€™t have to compete with food production – we need to consider developing engines around this fuel. Since refining cellulosic materials to ethanol or diesel are not yet proven – external combustion engines like the steam engine are more attractive.
- Simplicity and Durability: With combustion occurring externally at a steady pace the engine cylinders do not experience the shock of internal fuel combustion. Additionally since full power can be obtained at very low engine speeds the life of the engine is typically orders of magnitudes higher than IC engines.
- Emissions: With either non-polluting solar energy or biomass as the power source this engine is inherently clean. Since combustion of biomass occurs externally without large pressures thermal Nox is not formed, which would be problem in an IC engine.
- Efficiency: The large con is that the steam engine is historically of lower efficiency than an IC engine. This however isnâ€™t always true and I think it need not be true in the future. Higher steam temperaturess raise the engine efficiencies and many late model compounding steam engines achieved >20% overall efficiency which is on par with a spark IC, but still half of a good diesel cycle. For stationary power applications running the engine in cogeneration mode were hot water and house heat are produced from the exhaust will eliminate this concern. In mobile applications it should be noted that a spark IC efficiencies will vary from 11% -13% at idle to 25%-28% at full load. The steam engine will remain constant through load variations and so a simple steam engine achieving 19% efficiency will in practice equal a typical gas engine in efficiency.If down the road the steam engine is adopted and developed, higher boiler temperatures and pressures and cylinder compounding could bring efficiencies up to the level of sub-critical Rankine plants, 35-37%. Give the low fuel refining requirements for steam engines, this may give steam power the edge over the slightly more efficient diesel.
- Steam Danger: Working with steam successfully has required over 150 years of trial and error to master. Luckily we can stand atop that knowledge as we move forward. The flash steam generator â€“ the boiler type of choice – has no danger of explosion.
Adding it all up it seems the steam engine deserves a modern small-scale attempt. So one option to move forward with the project is to simply dig through some old engineering books and duplicate a simple steam engine for a solar thermal boiler tube or biomass-fired flash steam generator.
After considering this option initially, I realized that there appears to be some mechanical baggage that we donâ€™t need in the digital age. Control of yester-yearâ€™s steam engine was done mechanically with a variety of steam valves and a centrifugal governor. These parts make a simple steam engine much more complicated than just a simple cylinder with an oscillating piston. Given the availability of low cost, open source control boards, optical sensors, and solenoid steam valves – why not try to improve?
Steam can be injected simply by using electronically-controlled valves – much like modern fuel injection. Down the road – steam temperatures and pressures can also be incorporated into the control board to add safety features like automatic dumping of steam if boiler temperatures and pressures go beyond design conditions.
To me, it sounds attractive enough to pursue.Â So I have decided to put my money where my mouth is and fund the first prototype. I have purchased the required valving and electronics and am finalizing my mechanical crank plan. I plan to post as I hit some project milestones and aim to have something running on steam in a few months.Â If you want to offer some info or comment on the project please post it under the steam engine construction set on the wiki, I’m also available via email at raaumn at hotmail.com.