With reference to the above and below prior art documents,
supposing that the two 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 in the C combustion chamber, when the two combustion chambers Ca and C will start communicating after the TDC, the remaining expansion ratio is
I.e. even if the combustion completes instantly when the two combustion chambers Ca and C unite into one united combustion chamber Cu, the following expansion ratio is too low (5.5:1) for an
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 combustion chamber C undergoes a relatively high compression (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 Ca and C unite into a united combustion chamber Cu and the not yet burnt mixture is burnt, the following 5.5:1 expansion ratio, is low expansion ratio for efficient thermodynamic cycle.
Another drawback of the prior art is that after the TDC, as the burnt gas expands inside the cup-like recess (the combustion chamber Ca inside the auxiliary cylinder), it cools down, the active radicals formed during the preceding combustion are progressively de-activated, the pressure drops; simultaneously, in the other combustion chamber C the expansion of the compressed air-fuel mixture reduces its pressure and temperature; worse even, just
before the moment the two combustion chambers Ca and C unite into a united combustion chamber Cu, the pressure and temperature in the combustion chamber C are lower than they
were the moment the united combustion chamber Cu was divided into the two sealed combustion chambers Ca and C.
According the preceding, the moment the two combustion chambers Ca and C unite into one united combustion chamber Cu, the reduced pressure and temperature in the combustion chamber C degrade
its auto-ignition capability, while the exiting burnt gas from the cuplike recess (the auxiliary cylinder) is not too hot, nor too active, nor at too high pressure to cause the required pressure shock to trigger the auto-ignition of the not yet burnt air-fuel mixture. I.e.
both combustion chambers are at worse condition than they were at the TDC.
Among the objects of the PatBam is to address the above disadvantages of the closest prior art.
For instance, in the PatBam the ignition of the air-fuel mixture inside the combustion chamber takes place when the volume inside the combustion chamber is adequately smaller (and
the pressure inside the combustion chamber substantially higher) than 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 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:
The PatBam is applicable in rotary engines, too, wherein instead of pistons there are rotors, and instead of cylinders there are casings.