GB2568697A

GB2568697A - Controllable HCCI combustion

Info

Publication number: GB2568697A
Application number: GB1719459.8A
Authority: GB
Inventors: Pattakos Emmanouel; Pattakos Efthimios; Pattakos John; Pattakos Manousos
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-11-23
Filing date: 2017-11-23
Publication date: 2019-05-29
Also published as: GB201719459D0

Abstract

An ICE comprising a first piston and cylinder defining a first combustion chamber C, and a second, auxiliary piston and cylinder defining an auxiliary combustion chamber Ca, such that the auxiliary piston is secured on the first piston; where at BDC the first and auxiliary combustion chambers are in communication to form united cylinder Cu and, during a compression stroke, the auxiliary piston is slidably fit into the auxiliary cylinder so as to substantially isolate the first chamber C from the auxiliary chamber Ca, and where further travel during said compression stroke, but prior to the TDC position of the piston, the auxiliary chamber communicates freely with the first chamber. Auxiliary chamber Ca has an increased compression ratio in comparison to first chamber C, such that a fuel-air mixture is taken above a threshold for auto-ignition during the compression stroke. The compression ignited fuel-air mixture passes from the auxiliary chamber to the first chamber around TDC. The auxiliary piston may be secured on the first piston (figure 3), or on the first cylinder with the auxiliary cylinder formed in the first piston (figure 4). The auxiliary cylinder may be actuated by the first cylinder (figures 5-27). The auxiliary piston may be cam driven (figure 28-30). May be HCCI engine and/or rotary engine.

Description

Closest prior art is the US6,557,520 patent (Roberts) and the US2017/0204777A1 patent application publication (Riley).

The first closest prior art document (US6,557,520) discloses a cuplike recess (or auxiliary cylinder) formed in the piston and a small diameter piston (or auxiliary piston) secured on the cylinder head. The second closest prior art document (US2017/0204777A1) discloses a cup-like recess (auxiliary cylinder) formed in the cylinder head, and a small diameter piston (auxiliary piston) secured on the piston.

In both cases, the shape of the cylinder head fits with the shape of the piston so that, when the piston is near its TDC (Top Dead Center), the auxiliary piston is getting inside the auxiliary cylinder dividing the united combustion chamber Co, into a combustion chamber C and an auxiliary combustion chamber Ca.

The geometry is such that the compression ratio in the two combustion chambers is substantially different.

The high compression ratio inside the auxiliary combustion chamber Ca causes the auto-ignition of the air-fuel mixture, while the lower compression ratio in the combustion chamber C is below the critical threshold required for its auto-ignition.

During the motion of the piston towards the TDC, there is a crankshaft angle f before the TDC at which the auxiliary piston enters into the auxiliary cylinder dividing the united combustion chamber Co into two combustion chambers C and Ca.

After that angle and till approximately f degrees after the TDC (i.e. when the auxiliary piston exits from the auxiliary cylinder), the C and Ca combustion chambers are sealed from each other.

At f degrees after the TDC burnt gas exits from the auxiliary cylinder and triggers the auto-ignition of the compressed air-fuel mixture in the rest cylinder, enabling a controllable HCCI autoignition that, according the inventors of the closest prior art offers a high thermal efficiency.

However, there are some significant drawbacks in the closest prior art; these drawbacks greatly reduce the thermal efficiency as explained in the following.

Supposing that the two combustion chambers Ca and C are sealed from each other only for the last 10% of the piston stroke, Fig 31 (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 only 5.5:1.

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 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 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 closest 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 present invention is to address the above disadvantages of the closest prior art.

For instance, in the present invention 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.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the basic arrangement I operational principle of the closest prior art US6,557,520 patent

Fig. 2 shows the basic arrangement I operational principle of the closest prior art patent application US 2017/0204777A1.

Fig. 3 shows the operational principle of the present invention. In comparison to the closest prior art arrangement of Fig. 2: with properly shaped auxiliary piston and auxiliary cylinder (cup-like recess), the drawbacks of the prior art are overcome.

Fig. 4 shows the operational principle of the present invention. In comparison to the closest prior art arrangement of Fig. 1, with properly shaped auxiliary piston and cup-like recess (auxiliary cylinder), the drawbacks of the prior art are overcome.

Fig. 5 shows details of the present invention: the auxiliary cylinder (it corresponds to the cup-like recess) is at its outmost position. Fig. 6 shows details of the present invention: the ports on the auxiliary cylinder have just closed by the auxiliary piston.

Fig. 7 shows details of the present invention: the air-fuel mixture trapped in the auxiliary cylinder has been heavily compressed and is ignited.

Fig. 8 shows details of the present invention: the passageways at the lower end of the auxiliary cylinder allow the burnt gas to pass to the back side of the auxiliary piston and then, through the ports, to the combustion chamber outside the cup-like recess and ignite the rest air-fuel mixture.

Fig. 9 shows what Fig. 5 from another viewpoint.

Fig. 10 shows what Fig. 6 from another viewpoint.

Fig. 11 shows what Fig. 7 from another viewpoint.

Fig. 12 shows what Fig. 8 from another viewpoint.

Fig. 13 shows what Fig. 5 from another viewpoint.

Fig. 14 shows what Fig. 6 from another viewpoint.

Fig. 15 shows what Fig. 7 from another viewpoint.

Fig. 16 shows what Fig. 8 from another viewpoint.

Fig 17 shows details of the present invention; at (d) the auxiliary piston and the auxiliary cylinder are assembled.

Fig. 18 shows an application of the present invention; the mechanism of Fig. 17(d) is secured on the cylinder head of an internal combustion engine; the piston is at its BDC (Bottom Dead Center).

Fig. 19 shows what Fig. 18 at another crankshaft angle: the auxiliary cylinder is displaced by the upwardly moving piston, and the ports have been closed.

Fig. 20 shows what Fig. 19 at a later crankshaft angle; the air-fuel mixture into the auxiliary cylinder is heavily compressed and ignited.

Fig. 21 shows what Fig. 20 with the piston at its TDC; the auxiliary piston is on the passageways at the lower end of the auxiliary cylinder allowing the burnt gas to exit through the ports to ignite the compressed air-fuel mixture in the rest cylinder.

Fig. 22 shows a version wherein the auxiliary cylinder is activated by the pressure of the gas in the cylinder (and not mechanically by the piston).

Fig. 23 shows what Fig. 22 at a later crank angle: the ports have been closed and the air-fuel mixture is trapped in the auxiliary cylinder.

Fig. 24 shows what Fig. 23 at a later crank angle: the heavily compressed air-fuel mixture is ignited.

Fig. 25 shows what Fig. 24 at a later crank angle: through the passageways on the lower end of the auxiliary cylinder the front side starts and continuous to communicate with the back side of the auxiliary piston allowing the burnt gas to exit through the ports to ignite the compressed air-fuel mixture in the combustion chamber.

Fig. 26 shows details of the auxiliary cylinder of Fig. 22.

Fig. 27 shows details of the auxiliary cylinder of Fig. 22.

Fig. 28 shows a version wherein the auxiliary cylinder is secured on the cylinder head of an internal combustion engine and wherein the auxiliary piston is activated by a rotating eccentric cam.

Fig. 29 shows what Fig. 28 at a later crankshaft angle: the ring of the auxiliary piston is over the passageways at the lower end of the auxiliary cylinder, and the ignited air-fuel mixture passes through the passageways and the ports to the main cylinder to ignite the compressed air-fuel mixture.

Fig. 30 shows details of the mechanism in Fig. 28; the auxiliary piston ring is disassembled from its groove.

Fig. 31 shows the pressure versus the crankshaft angle for adiabatic compression expansion.

DETAILED DESCRIPTION OF THE INVENTION

This invention is about an internal combustion engine comprising at least: a cylinder;

a piston slidably fitted in said cylinder, said piston sealing one side of a combustion chamber defined by said piston and by said cylinder;

an auxiliary cylinder, an auxiliary piston slidably fitted in said auxiliary cylinder, said auxiliary piston sealing one side of an auxiliary combustion chamber defined by said auxiliary piston and by said auxiliary cylinder;

said piston and said auxiliary piston move relative to said cylinder and said auxiliary cylinder, respectively, performing, among others, compression strokes followed by expansion strokes, during a portion of a compression stroke of the piston in the cylinder, air-fuel mixture inside the combustion chamber is compressed, with the auxiliary combustion chamber communicating freely with the combustion chamber at least during the last part of said portion, during a successive portion of the same compression stroke of the piston in the cylinder, the combustion chamber and the auxiliary combustion chamber stay substantially sealed from each other with a part of said air-fuel mixture being trapped inside the auxiliary combustion chamber wherein the auxiliary piston is performing an auxiliary compression stroke as it moves relative to the auxiliary cylinder, causing the compression of the trapped in the auxiliary chamber air-fuel mixture above the critical threshold for an autoignition, with the compression inside the combustion chamber remaining below the critical threshold for an auto-ignition of the airfuel mixture therein, wherein the auxiliary piston and the auxiliary cylinder are such that before the end of the auxiliary compression stroke, the auxiliary combustion chamber communicates freely with the combustion chamber, enabling gas from the auxiliary combustion chamber to pass to the combustion chamber and trigger the combustion of the air-fuel mixture therein.

In the Fig. 31 the extra-fat-line curve is the pressure inside the combustion chamber C (CR 11:1), the fat-line curve is the pressure inside the auxiliary combustion chamber Ca (CR 20:1), the thin-line curve is the total volume inside the cylinder (the center-to-center connecting rod length to the piston stroke ratio is taken 2:1, the offset of the crankshaft rotation axis from the line along which the center of the piston wrist pin reciprocates is taken zero).

At f=33 degrees before the TDC, i.e. when the volume in the cylinder is 10%+10% = 20% of the capacity of the cylinder (the one 10% is the dead volume (for compression ration 11:1), the other 10% is because the piston has already covered the 10% of its stroke), the auxiliary cylinder of the closest prior art (Figs. 1 and 2) receives and contains the auxiliary piston forming two sealed combustion chambers. The auxiliary combustion chamber inside the auxiliary cylinder undergoes a compression of CR=20:1, while the rest combustion chamber inside the cylinder undergoes a compression of only 11:1.

While the combustion chamber C remains under the critical threshold for auto-ignition, the auxiliary combustion chamber Ca goes over the critical threshold for auto-ignition and auto-ignites. Then the burnt gas in the auxiliary combustion chamber Ca is compressed until the piston to reach its TDC, and then it expands until the 33 degrees after the TDC when the two combustion chambers C and Ca reunite into a united combustion chamber Cu; then the burnt gas expands into the main cylinder igniting the rest mixture.

The remaining small expansion ratio (5.5:1 in this case) decreases substantially the BTE.

According the present invention, the air-fuel mixture in the auxiliary cylinder (Figs. 3, 4) is sealed and compressed and ignited (or autoignited) as before; however the geometry of the auxiliary piston and of the auxiliary cylinder is such that it enables the two sealed combustion chambers to reunite before the exit of the auxiliary piston from the auxiliary cylinder (as the arrows show, when the piston is at its TDC the compressed I ignited mixture from inside the auxiliary cylinder can pass from the widening of the auxiliary cylinder bore to the narrowing of the auxiliary piston and then to the combustion chamber in the main cylinder feeding it with active radicals, causing a significant pressure sock in the un-burnt mixture in the cylinder and allowing a full expansion (11:1 in this case).

In Fig. 17(d), the auxiliary piston is at a position (relative to the auxiliary cylinder) allowing air-fuel mixture from the cylinder to enter through the ports of the auxiliary cylinder, as the arrows show.

When the auxiliary piston and its piston ring are over the passageways at the one end of the auxiliary cylinder, the ignited air-fuel mixture passes (as the arrows show in the Figs. 17(c), 17(e)) through the passageways, to the back side of the piston at the narrowing of the piston and then, through the auxiliary cylinder ports it exits to trigger the ignition of the compressed air-fuel mixture in the cylinder.

In a similar way, as shown in the Figs. 28 and 29, when the auxiliary piston is at its “up most” position, it allows air-fuel mixture to enter, through the auxiliary cylinder ports (arrows in Fig. 28); when the piston reaches its “down most” position, the burnt gas passes through the passageways to the back side of the piston crown (where the narrowing of the piston is) and then trough the ports of the auxiliary cylinder (as the arrows show in Fig. 29). By timing the cam lobe that actuates the auxiliary piston, the moment the two combustion chambers re-unite can be optimized.

In Fig. 3 middle-left and middle-right, the two combustion chambers Ca and C are sealed from each other. The more the piston approaches its TDC, the bigger the pressure difference between the two combustion chambers (properly selected “dead volumes” for the two combustion chambers).

At middle-right the compression inside the auxiliary cylinder is adequately high to cause the auto-ignition of the air-fuel mixture inside the auxiliary cylinder. The ignited mixture in the auxiliary combustion chamber Ca and the not-yet-ignited mixture in the combustion chamber C are further compressed as the piston continues its motion towards its TDC.

At right (piston at TDC) the shape of the auxiliary piston and the shape of the auxiliary cylinder form a way / a path through which the compressed / burnt gas from the auxiliary cylinder passes to the cylinder triggering the ignition of the air-fuel which was compressed inside the combustion chamber C.

In Fig. 4 the functioning is the same as in the arrangement shown in Fig. 3. The only difference is where the auxiliary piston and the auxiliary cylinder are secured / formed. As the piston moves towards its TDC the auxiliary piston (on the cylinder head) enters into the auxiliary cylinder (formed on the piston) and the united combustion chamber Cu is divided into two sealed combustion chambers Ca and C. The compression in the combustion chamber C is lower than the critical for auto-ignition, while the compression in the auxiliary combustion chamber Ca is high enough to initiate auto-ignition. Later (still before the TDC) the two combustion chambers unite into one (Fig. 4 at right) and the compressed airfuel mixture in the main cylinder ignites.

Alternatively, a glow plug on the auxiliary piston can cause the ignition of the air-fuel mixture inside the auxiliary combustion chamber Ca (for cold starting, for instance, or for safety at normal operation).

In practice the inevitable clearance of the piston inside its cylinder (piston tilting, piston slapping) makes difficult the achievement of the required small clearance between the auxiliary cylinder and the auxiliary piston. According the plot in the Fig. 31, after their separation the two combustion chambers have substantially different pressures: for instance, 15 degrees before the TDC there is a pressure difference of some 15 bars between the two combustion chambers; this pressure difference requires a tiny clearance between the auxiliary cylinder and the auxiliary piston. However, the one part is secured onto the moving I tilting and slapping piston, while the other part is secured on the cylinder head. Small clearance means risk for piston to cylinder head collision. Big clearance means problematic sealing.

In the Figs. 5 to 21 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 I bore I guide in the cylinder head, with a restoring spring pushing the auxiliary cylinder towards the piston (shown in Figs. 18 to 21). When the piston approaches its TDC (as in Fig. 19), it pushes the auxiliary cylinder and compresses the restoring spring. For the rest, it works as the mechanism in the Fig 4: 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), Fig. 20. 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 mixture.

In another version, shown in the Figs. 22 to 27, 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 mechanically (as in Fig. 20).

In another version, Figs. 28 to 30, 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 in Fig. 29) passes to the combustion chamber. All the previous are applicable in case of rotary engines, wherein instead of pistons there are rotors, and instead of cylinders there are casings.

The previous make also obvious how a general-purpose mechanical igniter / lighter can be formed / function. For instance, putting a droplet of fuel in the auxiliary chamber (Fig. 28) and rotating the eccentric cam manually, the air-fuel mixture formed inside the chamber auto-ignites and the flames exit from the ports to ignite anything.

A look at the plot / example of Fig. 31 is indicative for the problems of the prior art and for the solutions of the present invention. 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-yetburnt 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 present invention 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.

Claims

1. An internal combustion engine comprising at least:

a cylinder;

2. An internal combustion engine as in claim 1 wherein: the auxiliary piston is secured on the piston

3. An internal combustion engine as in claim 1 wherein: the auxiliary cylinder is formed in, or secured on, the piston.

4. An internal combustion engine as in claim 1 wherein:

the auxiliary piston is secured on the cylinder head and wherein the auxiliary cylinder is slidably fitted in a bore in the cylinder head, and wherein the piston at the last part of the compression stroke actuates the auxiliary cylinder to move relative the auxiliary piston.

5. An internal combustion engine as in claim 1 wherein:

the auxiliary cylinder comprises ports through which the auxiliary combustion chamber communicates with the combustion chamber, said ports being controlled by the auxiliary piston.

6. An internal combustion engine as in claim 1 wherein:

the auxiliary cylinder comprises passageways, near the end of the auxiliary compression stroke, the auxiliary piston passes over the passageways enabling the communication of the combustion chamber with the auxiliary combustion chamber through said passageways.

7. An internal combustion engine as in claim 1 wherein:

the motion of the auxiliary piston relative to the auxiliary cylinder is activated by an eccentric cam rotating in synchronization with the reciprocation of the piston.

8. An internal combustion engine as in claim 1 wherein:

the motion of the auxiliary piston relative to the auxiliary cylinder is activated by the pressure inside the combustion chamber.

9. An internal combustion engine as in claim 1 wherein: said auxiliary piston comprising piston rings for an improved sealing between the combustion chamber and the auxiliary combustion chamber

10. An internal combustion engine as in claim 1 wherein:

said auxiliary cylinder having a bore, the bore in cooperation with a crown of the auxiliary piston providing sealing between the combustion chamber and the auxiliary combustion chamber, said auxiliary cylinder also having at one end a widening of its bore, said auxiliary piston having a narrowing of its diameter after the crown, near the end of the auxiliary compression stroke the crown of the auxiliary piston inserts in the wider bore area of the auxiliary cylinder enabling gas from the auxiliary combustion chamber to pass at the back side of the crown and then, through the narrowing of the auxiliary piston to pass to the combustion chamber.

11. An internal combustion engine as in claim 1 wherein:

the ignition of the air-fuel mixture inside the combustion chamber takes place when the volume inside the combustion chamber is substantially smaller than the volume in the combustion chamber at the beginning of said “successive portion of the same compression stroke of the piston in the cylinder”.

12. An internal combustion engine as in claim 1 wherein:

the piston is a rotor of a rotaty engine, the cylinder is the casing of a rotary engine.

13. An internal combustion engine as in claim 1 wherein:

14. An internal combustion engine as in claim 1 wherein:

the piston besides performing compression strokes followed by expansion strokes, it also performs intake strokes and exhaust strokes.