Click here for the complete GB1,156,821 patent document.
With reference to the above and below prior art documents wherein, at a point of the cycle, the united combustion chamber (Cu in the following) is divided into a main (C in the following) and an auxiliary (Ca in the following, that in the cup-like recess) combustion chambers,
and supposing that the main and the auxiliary combustion chambers are sealed from each other only for the last 10% of the piston stroke (this means that for an 80mm piston stroke, the auxiliary piston has only 8mm stroke inside the cup-like-recess / auxiliary cylinder),
supposing also a 2:1 connecting rod to stroke ratio,
the last 10% of the stroke of the piston corresponds to a crankshaft rotation from 33 degrees before, to 33 degrees after the TDC.
With a compression ratio of, say, 11:1, when the main and the auxiliary combustion chambers will start communicating after the TDC, the remaining expansion ratio is only 5.5:1.
I.e. even if the combustion completes instantly when the main and the auxiliary combustion chambers unite into a united combustion chamber, the following expansion ratio is too low (5.5:1) for an efficient cycle.
For example, for the constant volume air-fuel cycle for a lean mixture (say, 80% of stoichiometric), with 11:1 CR (compression ratio) the theoretical thermal efficiency is 50%, while with 5.5:1 CR the theoretical thermal efficiency drops to 40%.
The air-fuel mixture in the main combustion chamber undergoes a relatively high compression (say, 11:1 which is below the critical for auto-ignition) that increases its temperature; the colder walls cool it down (which causes a pressure drop); then it expands returning only a part of the energy consumed for its compression (due to the pressure drop) and then, when the two combustion chambers unite and the not yet burnt mixture is burnt, the remaining 5.5:1 expansion ratio is a low expansion ratio for an efficient thermodynamic cycle.
Another drawback of the prior art is that after the TDC, as the burnt gas expands inside the cup-like-recess (auxiliary combustion chamber), it cools down, the active radicals formed during the combustion are progressively de-activated, the pressure drops; simultaneously, in the main combustion chamber the expansion of the compressed air-fuel mixture reduces its pressure and temperature; worse even, just before the moment the two combustion chambers unite, the pressure and temperature in the main combustion chamber are lower than they were the moment the united combustion chamber was divided into the two sealed combustion chambers.
According the previous, the moment the auxiliary and the main combustion chambers unite, the reduced pressure and temperature in the main combustion chamber degrade its auto-ignition capability, while the exiting burnt gas from the cup-like recess (i.e. from the auxiliary combustion chamber) is not too hot, nor too active, nor at too high pressure to cause the required pressure and temperature shock to trigger the auto-ignition of the not yet burnt air-fuel mixture.
I.e. both combustion chambers are at worse conditions than they were at the TDC.
Among the objects of the PatBam is to address the above disadvantages of the prior art.
For instance, in the PatBam the ignition of the air-fuel mixture inside the main combustion chamber takes place at a substantially higher pressure and temperature than the pressure and temperature when the two combustion chambers were isolated from each other.
In the above PatBam version the auxiliary piston and the auxiliary cylinder are permanently engaged, which makes feasible the use of sealing ring(s) in the auxiliary piston if desirable.
With the auxiliary piston secured to the cylinder head, the auxiliary cylinder is movable along a hole / bore / guide in the cylinder head, with a restoring spring pushing the auxiliary cylinder towards the piston.
When the piston approaches its TDC, it pushes the auxiliary cylinder and compresses the restoring spring.
As the piston pushes the auxiliary cylinder "upwards", initially the ports on the auxiliary cylinder are closed by the auxiliary piston and a quantity of already compressed air-fuel mixture (previously entered into the auxiliary cylinder) is trapped and compressed until it is
auto-ignited (or ignited).
The ignited mixture is further compressed until the auxiliary piston (and its piston ring, if it has piston ring) to pass over the passageways. With the passageways (a kind of "blind ports") the piston ring is kept in place and there are formed passages for the burnt gas.
The burnt gas passes from the passageways to the backside of the auxiliary piston (the narrowing of the auxiliary piston) and then from the ports into the cylinder to trigger the ignition of the rest, already compressed, airfuel
In the above PatBam version there is no mechanical contact for the displacement of the auxiliary cylinder.
The auxiliary cylinder has a disk-like-piston secured on it; the pressure in the main cylinder pushes the disk-like-piston (and the auxiliary cylinder) upwards in a bore in the cylinder head. Initially the auxiliary piston inside the auxiliary cylinder compresses the airfuel mixture and causes its ignition, then, when the auxiliary piston is over the passageways at the inner-lower end of the auxiliary cylinder, the burnt gas passes, through the passageways and through the ports on the auxiliary combustion chamber towards the combustion chamber.
As the pressure inside the combustion chamber increases, the
auxiliary cylinder is displaced as if the main piston was pushing it
In the above PatBam version, the auxiliary piston is activated like a poppet valve by a cam lobe rotating in synchronization with the piston reciprocation.
A spring restores the auxiliary piston "upwards". For the rest, the relative motion between the auxiliary piston and the auxiliary cylinder (which, in this case, is secured to the cylinder head) traps initially a quantity of already compressed air-fuel mixture inside the auxiliary combustion chamber, then it compresses it to auto-ignite, and then, when the auxiliary piston passes over the passageways of the auxiliary cylinder, the burnt gas (arrows) passes to the combustion chamber.
A look at the above plot / example is indicative for the problems of the prior art and for the solutions of the PatBam.
Starting the compression stroke with 1 bar pressure, at 33 degrees before the TDC / 12 bar in the united combustion chamber, the auxiliary combustion chamber is sealed and its pressure rises at 33 bar (wherein the threshold for auto-ignition is) some 14 degrees before the TDC (corresponding to about 2% of the piston stroke).
Then the air-fuel mixture inside the auxiliary combustion chamber auto-ignites and its pressure at the TDC is way higher than the 48 bar of the case without ignition.
The pressure of the air-fuel mixture in the main combustion chamber never exceeds the 29 bar, i.e. it is below the threshold for auto-ignition.
So, after the TDC the air-fuel mixture in the main combustion chamber expands not-yet-burnt until 33 degrees after the TDC, when the two combustion chambers unite into one, with the burnt gas from the auxiliary combustion chamber igniting the not-yet burnt mixture.
With the PatBam things are similar until the auto-ignition of the air-fuel mixture inside the auxiliary combustion chamber.
Then, a little after the auto-ignition in the auxiliary combustion chamber, the auxiliary piston passes over the passageways formed on the inner side of the auxiliary cylinder, allowing the hot
(and at high pressure and full of active radicals) burnt gas to enter into the main combustion chamber and ignite it, exploiting all the 11:1 expansion ratio and achieving a high thermal efficiency.
In the animations the slides are per 10 crankshaft degrees.
The PatBam is for the four-stroke and for the two-stroke engines.
In the following GIF animation (and "windows exe" program) it is shown the (calculated) pressure and temperature (adiabatic compression and expansion) in the main chamber and in the auxiliaty chamber of a PatBam:
Click here for the respective windows-exe program.
The compression in the auxiliary chamber is as high as required to auto-ignite the fuel used; when the two chambers unite, through the transfer ports, the burnt gas streaming into the main chamber:
1. increases the pressure (shock wave),
2. increases the temperature (heat wave),
3. and injects the radicals into the main chamber.
In the following two animations the PatBam is applied on a Pulling Piston Engine (PPE, for more click here).
The lubrication in the crankcase is 4-stroke;
the design is crosshead;
the piston is not touching the bore (only the piston rings touch the bore and need lubrication; the piston itself does not need any lubrication);
the dead volume of the "scavenging pump" can be variable and can be as small as desirable;
the reed valve is shown (without its petals) inside the bellmouth (at top).
The "piston rod" aligns precisely the auxiliary chamber (formed inside the piston) with the auxiliary piston (or "anvil") secured to the casing.
The crosshead architecture rids the "piston rod" and the hole in the center of the "anvil" from thrust loads.
Because the piston "hits", like a hammer (or like a gun trigger), the compressed homogenous mixture trapped into the auxiliary chamber onto the "anvil" to cause its auto-ignition.
The previous PPE PatBam from another viewpoint:
Here is another version of the PatBam:
wherein the piston-ring of the auxiliary piston slides permanently onto the cylinder liner of the auxiliary chamber.
Applicable in two-stroke and in four-stroke engines.
In the following two animations, the PatBam is applied on an OPRE / Tilting 2-stroke engine (for more click OPRE Tilting):
The extended piston dwell at the Combustion Dead Center (it provides some 40% extra time to the HCCI combustion, increasing proportionally the useful rev range wherein the engine runs on HCCI), the compact and fully symmetrical structure (vibration free), the absence of spark plugs / high voltage system for the ignition (reliability), the extreme capacity to weight ratio, the absence of reed valves, etc, fit especially with aviation use.
In the following animation, the PatBam HCCI is applied on a PatAT Cross-Radial engine (for more click PatAT or click PatATeco):
turbocharged (if "assisted at cranking", the turbocharger can also serve as the scavenging pump),
asymmetric transfer ending after the closing of the exhaust port,
scavenging with air,
early indirect fuel injection in the space under the piston crown (the formed air-fuel mixture is the last to enter into the cylinder, eliminating the loss of unburnt fuel towards the exhaust),
no need for high voltage electric system,
better when running on cheap low-octane gasoline.
The strange piston structure divides the combustion and the scavenging into stages.
Near the TDC the HCCI combustion is divided in two stages:
After the auto-ignition and the combustion in the auxiliary chamber, the burnt gas passes into the main chamber triggering the ignition of the air-fuel mixture therein.
Near the BDC the scavenging is divided in stages:
After the opening of the exhaust port and as the piston is further approaching the BDC, the transfer ports open and pure air from the turbocharger pushes the remaining burnt gas out of the cylinder; later the well prepared air-fuel mixture from the space underside the piston crown overfills the cylinder after the closing of the exhaust port.
The scavenging completes with a gust of clean air from the turbocharger; this air pushes any fuel in the passageways of the "asymmetric" ports into the cylinder.
The specific architecture minimizes the number of bearings and the frictional losses.
It also minimizes the weight.
Even when it runs extra lean (say, AFR=2) it can still provide top specific power.
In the following drawing (at top the piston is at the TDC, at bottom the "anvil" exits from the piston):
the auxiliary combustion chamber and the "anvil" have spherical bottoms for stiffness, lower weight and in order to provide room / space for the small end of the connecting rod:
The following animation:
Click here for the color version,
or here for color-slow-motion,
here for a youtube video,
here for a youtube video.