Greensteam leverages external combustion to simplify engine design and to enhance clean combustion of solid waste fuels. But external combustion is agnostic regarding heat source(s). An external combustion power generation system can draw upon hybrid heat sources, including solar, sewage methane digestion, geothermal or even nuclear. These can be mixed in varying proportions diurnally or seasonally, depending on context, and changing supply and demand. (For instance, solar panels could preheat boiler feedwater).

The furnace/boiler (for efficient production of steam) and the ‘engine’ (for conversion of steam to mechanical power) are two separate and separable projects. We will address both, with emphasis on engines in the early stages.

To leverage 100 years of materials, metallurgical and mechatronic advances since steam engine design development ceased.

A. To research and apply new plastics, composite materials, ceramics, and alloys (etc) to reduce wear, manage thermal expansion, thermal radiation, etc.
B. To find sweet spots between simplicity and efficiency, recognising that increase in efficiency are often coupled ort increases in complexity
C. To reduce moving parts and masses to a minimum, especially parts that wear or must be adjusted.
D. To seek application of mechatronics (sensor, microcontroller, powered output devices) to create autonomous self-regulation (homeostasis), to reduce mechanical parts count, increase energy efficiency and create real-time response. Note that, in a self-contained system, this implies generating the electrical power for the mechatronics from the engine itself and this generation is a cost.
E. To explore novel design solutions to problems such as valve control and drive trains.
F. Constraining design space - Engines are stationary and small scale - for domestic/small community electrical generation and mechanical tasks - pumping, grinding, driving machinery. Hence it has an optimal and fixed rpm range.

A. To leverage automated controls and the luxury of extended combustion time to build a furnace capable of cleanly burning a diverse range of combustible solid waste - including domestic waste, agricultural waste, industrial/medical waste and plastic waste.
B. To develop a mechatronic system of water temperature, oxygen, CO2, and steam temperature and pressure (etc) sensors and automatic valves and dampers (etc) to maximise efficient combustion and steam generation.
C. To use passive, low-tech and sustainable solutions wherever possible.

• Historical/technical review of steam engine design.
• Development of several small-scale prototype engines based on Penny’s design/research (solidworks, etc) resulting in design refinement and dimensions and specifications for parts for several engine designs.
• Resolution of design issues - valve design, valve actuator design, drive train design, overall topology. Materials and components research.
• Fabrication training and tests.
• Prototype parts production using CNC router/mill and conventional mill/lathe machinery.
• Sensor/control research
• small scale high speed high pressure mechatronic steam valve development
• Design/build small scale generator/battery backup for onboard mechatronics

• Detailed modelling, specification and feasibility of Greensteam Furnace/boiler1. Including: fuel feed, combustion column, high pressure steam storage, safety valves, instrumentation and control components.
• Construction of prototype furnace/boiler.

Steam is dangerous. High pressure steam more so.

Explosions are to be avoided at all costs. Steam causes horrible burns to flesh.
All systems will be built with constant attention to safety issues.

All experimental procedures will be conducted with constant attention to safety issues.

Preliminary tests will always be made using compressed air and other ‘partially simulated’ methods.

A steam engine converts energy liberated by expansion of supplied high-pressure steam to (conventionally) linear movement of a piston. The critical component of such a system is neither the piston nor the drive train but the valve mechanisms that regulate steam inlet and exhaust.

For historical reasons, mechanical power systems have gravitated towards rotational modes of power transfer. The reciprocating piston appears to be unavoidable, small scale turbines being impractical. Some applications exist for direct reciprocating output - steam hammers, reciprocating pumps, pile drivers etc. Reciprocating to rotational conversion (and vice versa) is inherently inefficient, but seemingly, a necessary evil. Simple and energy-efficient solutions are sought in all cases, including drive trains and valve control. Central to these are development of drive trains that do not require crankshafts (cam, eccentric and overhung) and alternatives to reciprocating valves and valve drive systems - belt and chain drives, eccentrics and swash plates, and rotating valves of various forms.

The rotary valve has been a holy grail of engine design for nearly two centuries. Rotary valves possess several significant advantages over reciprocating forms, including higher compression ratios and speeds, reduced complexity, meaning higher reliability and lower cost. Regrettably, competitive designs have been elusive, owing mainly to sealing and wear issues. Joseph Riedl developed a rotary valve for brass instruments in 1832. The famous Corliss steam valve was a hybrid reciprocating rotary kind. Some remarkable WWII aviation engines used them, as did some mid-century automotive and motorcycle experiments.

Though there is much to learn from internal combustion engine (ICE) design, it is important to denaturalize some design aspects. First, the ICE includes - obviously, internal combustion. External combustion eliminates some of the complexities of ICE. A major efficiency of the steam engine (compared to a 4 stroke ICE) is that every second stroke (or in the case of double acting cylinders - every stroke) is a power stroke. So, engines can be 25% of the size (cylinder volume) for the same power output. A conventional IC engine is dependent on a technically sophisticated crankshaft, and complex and energy consuming valve mechanisms.

In accordance with the principle of parsimonious engineering (Penny) - also known as the KISS principle (keep it simple, stupid), and with consideration of the IIABDFI protocol (if it aint broke, don’t fix it), several novel designs have been developed that minimise moving parts and sophisticated manufacturing processes. Greensteam designs seek alternatives to the crankshaft, and alternatives to the spring return poppet valve.

1. complete and clean combustion of dirty fuels

2. optimized harvesting of liberated heat as steam. Given the goal of complete combustion of dirty fuels, a sophisticated monitoring and control system is assumed. How simple this can be is a subject for R+D. Maximising heat harvest implies: efficient heat transfer; minimization of heat exhaust; thermal insulation.

Prototype design is a vertical cylinder in form. Involves a pair of concentric vertical cylinders, the inner one being a fire-brick lined vertical combustion chamber with rising helical steam-coil. Fuel and air are fed in at the bottom where ignition occurs. At the top of the combustion chamber, combustion gasses are fed down a surrounding annular chamber, also insulated, containing a descending water preheat coil. This is topped by a spherical and insulated steam reservoir. Waste gasses exit to further heat scavengers, scrubbers, etc. Water is fed in via a (hopefully passive) feedwater system perhaps driven by exhaust gasses from furnace, or steam-condenser pump from engine. Condensate from engine exhaust is fed hack into feedwater system.

a. small fuel particle size. This may involve chippers or shredders that may be driven by power takeoff from engine.

b. optimizing temperature, oxygen and flow at various points in the column. This will involve instrumentation and active flow valves and dampers. intuitive understanding of forces and mechanisms Ability to pursue self-directed research, have a methodical research design development process, meet deadlines and communicate/collaborate with others. Experience with materials, tool use and hands-on making practices (not just 3D printing).

This review examines various designs and topologies of piston engines, primarily steam and internal combustion (IC) engines, but including compressors, pumps and other machines. The ‘age of steam’ - especially on west coast USA - is for most little more than a historical fantasy. We must remember that for 150 years, external combustion steam engines were the source of motive power for industry and transport, and were the context in which the discipline of engineering developed.

The distinction between external and internal combustion is fundamental here. External combustion was abandoned for historical reasons not directly related to engines themselves. It must be remembered that in 1920, there were more steam cars in the USA than internal combustion (diesel and gasoline combined). The viability of the combination of combustion and power-stroke in engine design is integrally connected with the discovery and exploitation of easily extracted oil, and the development of systems for handling a liquid fuel. This stimulated the growth of IC engines - it is just more convenient to squirt fuel than shovel it. That is why USA was largely home to the development of the automobile. If oil had been easy to find in UK (coal was just lying about), steam engines would have been oil-fired from the start, and we might still be driving steam cars.

Early engines (marine and stationary) operated at low pressures and single digit rpm and tended to be quite large. Many had cylinders so big you could walk inside them. The general trend in the evolution of piston engines has been toward higher pressure, higher rpm and smaller displacement. This could only occur in parallel with increasing precision in manufacture, better understanding of balance, lubrication and wear, and more sophisticated materials. For examples of all the aspects of the history of engines, the reader is directed to Douglas Self’s (wonderful) Museum of Retro-Technology

Ironically, the aspect of these designs that is simplest is the piston/cylinder system. Standard variants are single acting and double acting. In IC engines, single acting pistons include little end bearings or wrist pins. In older steam engines, this bearing took the form of cross slide.

In a standard IC cylinder, fuel/air is introduced between piston and cylinder head. In a conventional four stroke engine, this results in a power stoke every 4th stroke intake/compression/power/exhaust. In a two-stroke engine, power stroke happens every second stroke: power/exhaust. A single acting steam cylinder is two-stroke. Some steam cylinders are sealed at both ends (with piston rod emerging via a seal) and there are valves at both ends so one side of the piston is exhausting while the other is in power stroke. This means every stroke is a power stroke. The efficiencies are obvious.

In the conventional piston engine, reciprocating movement of pistons is concerted to rotary motion of a driveshaft. This is an inherently inefficient mechanical conversion and usually requires a substantial selection of precision engineered and dynamically balanced components. The crankshaft is the best understood piston engine drive train. Though common, their complexity should not be underestimated.

Almost always, valves are actuated from the crankshaft, which provides both timing and motive power. Main types include:

• Eccentric/cam actuated pushrod
• Chain/belt
• Bevel gear
• Wobble plate actuated rocking shaft

Timing refers to when valves open and close (and therefore how long they are open for) with respect to the position of the piston in its stroke. Mechanical valve mechanisms are normally driven off the crankshaft. Combined inlet/exhaust valve mechanisms have the (potential) drawback that timing cannot be separately adjusted.

In an IC engine, combustion time is fixed, so the higher the rpm, the sooner fuel must be ignited in order to extract all expansion energy from the explosion before BDC. In a steam engine, drive is produces in two ways, first the introduction of high-pressure steam into the cylinder, then expansion of same steam. These are two separate processes. In both cases, for efficient functioning, valve timing must be advanced as rpm rise. Flexible, quickly responsive and independent control of valve ‘advance’ and open times is central to an efficient engine.