The 6 stroke cycle engine

I haven't seen or installed a hydrogen enhancement system on a 5 or 6 stroke cycle reciprocal engine ever before. But after I read how it works, it actually is more suitable and safer to use for hydrogen fuel!. Please read on and hopefully you see what I am also able to see here. This is borrowed from a Ducati website.

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Is there any development potential for the reciprocating internal combustion engine, whose architecture seems to have by now settled into a classic?
Motor Union Italia devised and designed a revolutionary engine featuring exhausts, production times, overall dimensions and weight all lower than a traditional four stroke engine's.
The correct technical definition of this new type of engine is: 6-stroke isovolumetric engine with revolving con-rod and half-floating piston.

Introduction
Reciprocating engines can either be "2 stroke cycle" engines or "4 stroke cycle" engines. As is known, the difference between the two lies in their succession of four characteristic strokes: in 2-strokes, it is completed in one crankshaft revolution (360º), while in 4-strokes, it is completed every two revolutions (720º).
The traditional geometry of reciprocating engines, i.e. piston, con-rod and crankshaft, determines a symmetrical piston movement with respect to the T.D.C. (Top Dead Centre) and the B.D.C. (Bottom Dead Centre), according to the sinusoidal pattern created by the crankshaft radius or "throw".
In both instances, designers, looking for improved performance, have pushed the valve opening and closing times to extremes. This has been done to maximise the volumetric efficiency of the piston around the TDC: in fact, these are technical compromises made necessary by the variable volume combustion typical of reciprocating engines, the operation of which is based on the crankshaft/connecting rod assembly. In practice, fuel ignition must necessarily begin before the TDC, consequently, the early stage of combustion (the only working stroke of the engine) occurs while the piston is still going up: this obviously results in wasted energy at the expense of the flywheel. This traditional approach is reversed in the new design: basing on the new crankshaft assembly that they have designed, Motor Union engineers offer an isovolumic combustion engine.
The driving shaft no longer has a crank but an eccentric profile similar to a cam: it can therefore generate motion patterns basically different from the symmetric motion of a crankshaft assembly. The piston must follow the eccentric profile because it is linked with it by a roller (coaxial with the piston pin) and by a retainer (a small con-rod guided in a profiled groove in the eccentric).
The roller turns without sliding on the cam profile which, unlike a crank, does not have a fixed radius but consists of a sequences of arcs of a circle, whose parameters can be changed (obviously, in the design phase) to adjust the vertical motion of the piston during each phase (in the intake phase the piston's downward movement is actuated by the retainer).
Why did they want to create an engine in which the piston does not move according to the well-know sinusoidal pattern created by the con-rod - crankshaft assembly? To enable it to follow, more logically and more appropriately, the evolution of the thermal and fluid-dynamic cycles by which it is affected.
The distinctive characteristic of this engine is, in short, that it allows the piston to "stop;" at the TDC and at the BDC for the time necessary to obtain a 6 Stroke cycle, with considerable advantages in terms of consumption and operating smoothness, and without having to compromise like in traditional engines, to the detriment of each stroke.



STROKE 1 - Constant Volume Combustion.
It is the dream of engine designers come true. Ignition begins when the piston is stopped at the TDC. The piston stop lasts for the time calculated by the designers to complete combustion and prevent any back-pressure caused by the spark advance. This enables to make the most of the energy obtained from the fuel, with decreased consumption by up to 20%.



STROKE 2 - Full expansion stroke.
In the state of the art, the working stroke is less than 65% of the total expansion stroke, because of the exhaust opening advance, which determines an over-4% loss of possibly resulting work. In the new design, the entire expansion stroke occurs between the TDC and the BDC.


STROKE 3 - Free exhaust.
This is the first, constant-volume exhaust phase: high-pressure gases are spontaneously evacuated while the piston is stopped at the BDC.

STROKE 4 - Forced exhaust.
In this phase, the exhaust gas is low pressure gas, therefore, the piston will not require a big pumping effort going up towards TDC. Approximately 2% saved energy

STROKE 5 - Intake.
The piston travels from the TDC to the BDC where it stops: the column of fresh gases continues to flow into the cylinder by inertia, until the intake valve closes. The intake volumetric efficiency is increased.



STROKE 6 - Compression.
Complete stroke from the BDC to the TDC. Ignition occurs at the TDC without any spark advance, saving a 3÷4% of the flywheel accumulated energy.
In a traditional engine, ignition always occurs during the compression stroke, applying a back-pressure on the crown of the piston which implies a loss of driving energy.

The Motor Union research engineers have found a simple, cheap way to make the most of the most neglected and most badly wasted of all strokes, the combustion stroke: they did this by modifying the piston motion pattern (fixed and unchangeable in current engine designs, because it is determined by the crankshaft dimensions and con-rod length only), by modifying the driving shaft concept, by introducing revolutionary changes in the con-rod design and, above all, by modifying the crank design which, instead of one fixed length, has different lengths according to the required motion pattern at different times. The proposed system therefore enables to work out an unlimited number of piston motion patterns, tailored to each different application, and to be able to divide each driving shaft revolution into several, rational, operation strokes, clearly defined and well separated; this will not only enhance the essentially important strokes of combustion and expansion, but also reduce the loss of efficiency for all of the following reasons:
Less con-rod pin friction;

Less (negative) pumping work required to let out exhaust gases;
Less back-pressure caused by spark advance;
Constant compression ratio (in traditional engines, during the combustion stroke which happens before the TDC, a volume variation occurs in the combustion chamber caused by the piston movement around the TDC);
Less friction thanks to the smaller number of driving shaft supports in a multicylinder engine;

Full expansion stroke;
According to Motor Union, this design would not totally upset the operation of current engines. On the contrary: it would only be necessary to modify the driving shaft, while continuing to use the same cylinders, pistons, heads and all the timing system parts of current engines. This would enable to still use the know-how acquired so far, and the currently available tools, casting and machining techniques.
The prototypes of a 6-Stroke Engine already built not only confirmed all theoretical expectations but were also relatively easy and cheap to build, lighter and less bulky. Displacement being the same, dimensions were reduced by 35% and, the crankshaft assembly, case and cylinder materials used being the same, the total weight reduction could range between 30 and 50%.

When I was one of the many freshly-graduated engineers still full of daring dreams, back at university, my Machines II teacher used to disillusion us by saying that all sorts of "devilish" variations of the reciprocating internal combustion engine had ALREADY been designed and patented. Is the new Motor Union engine design going to break this "rule" and become successful?

by: Stefano Bianucci