HK1172668B - Split-cycle engine - Google Patents

Description

Split cycle engine

Technical Field

The present invention relates to "split-cycle" (split cycle) compression-ignition engines that introduce fuel and a combustion-supporting fluid in an expansion cylinder during the combustion phase.

Background

As is known, a conventional compression-ignition engine cycles in a single cylinder, where air is first admitted and then compressed; then injecting fuel and igniting the fuel as a result of the compression bringing the air to a high temperature; followed by an expansion step and a venting step. The result of the engine's characteristic combustion mode is the emission of highly polluting carbonaceous dust and nitrogen oxides.

Various solutions have been proposed to reduce said emissions, based on the improvement of the injection system according to the homogeneous combustion principle, and on specific strategies of the intake system and the mixture of fuel and air, among which known techniques such as HCCI, PCCI, MK, etc.

In all these techniques, however, in order to control the combustion process, a high percentage of burnt gases must be present in the cylinder, which limits the effective specific power. Other drawbacks due to some of these techniques are high pressure gradients in the combustion stage, which involves noise and high mechanical stresses.

Solutions are also known, called split-cycle engines, in which the steps of intake and compression are carried out outside the cylinder, the steps of combustion and exhaust being carried out in the cylinder (expansion cylinder). More specifically, the chamber in which the intake and compression steps are performed constitutes the second cylinder (compression cylinder). Split-cycle solutions have been proposed and used in compression ignition engines and spark ignition engines for different purposes.

In WO2009020488, WO2009020489, WO2009020490, WO2009020491 and WO2009020504 in the name of Scuderi, a split-cycle engine is described having a cylinder block with a compression cylinder and an expansion cylinder closed by a cylinder head in which one or more passages 78, called crossover passages, are provided, closed at the respective ends by a compression-side valve 84 and a combustion-side valve 86. Each crossover passage defines a pressurization chamber 81 in which pressurized gas may accumulate when both the compression-side valve and the combustion-side valve are closed. In the channel 78, an injection of gasoline is provided by an injection nozzle 90, the injection nozzle 90 injecting gasoline into the compressed air present in the exchange channel. At least one spark plug 92 is provided in the expansion cylinder for igniting the mixture.

Even though the possible application of the system to compression ignition engines is cited in the cited patent document, it should be noted that this application is not feasible. In fact, unlike in the case of spark-ignited engines, in the case of compression ignition, the injection in the crossover passage can also cause ignition of the fuel therein. This will create unacceptable thermal stresses on the combustion side valve. The presence of the combustion side valve also reduces efficiency due to pressure drop during the passage of combustion gases through the valve.

Moreover, in the engine described in the cited document, there is a large pressure difference between the compression cylinder and the expansion cylinder when the combustion side is open, with consequent loss of efficiency due to large hydrodynamic losses.

In US6340004 the same kind of engine as described above is described, providing a crossover channel with respective valves at the inlet and outlet openings. The piping also comprises a regenerator (regenerator) of the combustion gases, which accumulates part of the heat of the cycle and applies it to the subsequent cycle.

In US4157080A and DE28122199, an engine is described which provides a supercharging step and a compression cylinder and two pistons of a combustion cylinder which are phase-shifted by 180 ° with respect to each other.

Disclosure of Invention

It is a feature of the present invention to provide a compression ignition split-cycle engine that produces low dust emissions.

It is a further feature of the present invention to provide a compression ignition engine that produces low nitrogen oxide emissions.

It is a further feature of the present invention to provide a compression ignition engine that makes it possible to obtain high values of efficiency and specific power.

It is another feature of the present invention to provide a compression ignition engine for reducing the pressure gradient in the combustion stage and thus reducing the noise and high mechanical stresses generated by such pressures.

It is still another feature of the present invention to provide a compression ignition engine that is simple in construction and inexpensive to manufacture.

These and other objects are achieved by a compression-ignition split-cycle engine comprising:

a cylinder block;

an expansion cylinder having an expansion piston adapted to be alternately moved in said expansion cylinder between a top dead center (ETDC) and a bottom dead center (EBDC) by a crankshaft mechanism which always has a predetermined position of said expansion piston corresponding to a predetermined crankshaft angle;

a compression cylinder having a compression piston adapted to move alternately in said compression cylinder between a top dead center (ETDC) and a bottom dead center (EBDC) according to a delay of a predetermined angular phase shift (angular phase shift) relative to a crankshaft angle of said expansion cylinder, said compression cylinder being arranged adjacent to said expansion cylinder;

a cylinder head closing the compression and expansion cylinders and in which at least one crossover passage is provided, which is connected to the cylinders and comprises a compression-side opening and an expansion-side opening, the cylinder head comprising at least one intake valve, which faces the compression cylinder, for introducing a combustion-supporting fluid in the compression cylinder, and at least one exhaust valve, which faces the expansion cylinder, for discharging combustion exhaust gases discharged from the expansion cylinder;

at least one transfer valve arranged at a compression-side opening of the exchange channel;

means for opening and closing the delivery valve at predetermined times of the alternating cycle of the piston;

means for opening and closing the exhaust valve at predetermined times of the alternating cycle of the piston;

means for injecting fuel into said crossover passage or into said expansion cylinder at a predetermined time of the alternating cycle of said piston to compression ignite the injected fuel by compression until an auto-ignition temperature is reached;

the method is characterized in that:

the exchange passage and the expansion cylinder are combined to define a combustion chamber, and the exchange passage is always communicated with the expansion cylinder;

the method is characterized in that:

said means for causing the opening and closing movement of said delivery valve opens said delivery valve in advance with respect to the crankshaft angle of said ETDC, the advance opening movement being greater than or equal to 20 ° of crankshaft angle, by:

the instantaneous pressure between the compression cylinder and the expansion cylinder is substantially equal from the moment of opening of the delivery valve until the ETDC is reached; and is

Between the ETDC and the CTDC, substantially all of the delivery of the combustion-supporting fluid between the compression cylinder and the expansion cylinder occurs through the crossover passage;

is characterized in that:

the fuel injection means injects the fuel starting from the expansion piston reaching the ETDC, so that the injection of the fuel takes place simultaneously with respect to the delivery of the comburent fluid through the exchange channel.

Thus, before opening the delivery valve, there are basically only two chambers, one defined by the compression cylinder and the other by the exchange channel associated with said expansion cylinder. Thus, when opening the delivery valve, which is at least 20 ° advanced with respect to the ETDC, there is no significant delivery of the comburent fluid into the exchange channel, since the pressure in the expansion cylinder is approximately equal to the pressure of the compression cylinder. As the cycle progresses, the pressure increases in a similar manner everywhere by the simultaneous lifting strokes of the two pistons until the ETDC is reached, since the two cylinders communicate with each other through the crossover passage. Then, beyond the ETDC, the compression piston continues to rise and the expansion piston starts to descend, allowing the combustion fluid between the two pistons to be completely conveyed through the exchange channel. Injection takes place simultaneously with delivery, followed by combustion of the entire fuel. The evaporation phenomenon and the mixing between the fuel and the comburent fluid take place in a better way than in a conventional diesel engine, since the delivery causes high disturbances. In particular, the evaporation proceeds in a faster manner and the mixture obtained is more homogeneous. In this way, a very efficient combustion is obtained, and subsequently a very small fraction of unburnt particles, in particular carbon-containing dust, is present in the exhaust gas.

Moreover, since the pressure between the compression cylinder and the expansion cylinder is substantially similar or very close during the valve opening and closing moments between the expansion cylinder and the exchange channel, the losses due to stratification are very low.

In particular, the means for causing the opening and closing movement of the delivery valve advance the opening of the delivery valve according to an advance angle setting comprised between-80 ° and-25 °, in particular between-35 ° and-30 °.

In particular, the means for injecting fuel are adapted to inject a small amount of fuel in advance with respect to the ETDC, in a manner adapted to heat the combustion environment, so-called pilot injection. In this way, pilot injection allows ensuring that the injected fuel ignites directly from reaching the ETDC.

Advantageously, said means for opening and closing the exhaust valve are adapted to block the exhaust valve with a predetermined advance with respect to the expansion piston reaching the ETDC moment, so as to perform compression of part of the exhaust gases in the expansion cylinder up to a predetermined pressure, and said means for opening and closing the delivery valve open the delivery valve when the compression piston has compressed the comburent fluid in the compression cylinder to a pressure substantially equal to that present in the expansion cylinder, so as to perform said delivery of the comburent fluid from the compression cylinder to the expansion cylinder through the exchange channel substantially simultaneously with the auto-ignition of the fuel. This makes it possible to eliminate the mechanical problem and the airtightness caused by the presence of the further expansion-side delivery valve disposed at the opening of the crossover passage facing the expansion cylinder.

In this way, during the combustion phase, after the delivery valve is opened, the compressed fuel and the combustion-supporting fluid supply is delivered into the combustion cylinder through said exchange channel. The exchange channel thus has a pure delivery function and is not merely a pressurized storage vessel for the comburent fluid.

Alternatively, said means for opening and closing the delivery valve open the delivery valve in advance with respect to the closing of the exhaust valve, so that in the expansion cylinder the exhaust gases are flushed out by the fresh comburent fluid before closing the exhaust valve. Even in this case, when closing the exhaust valve, there is an equal increase in pressure in both the expansion cylinder and the compression cylinder to achieve higher power.

Advantageously, the angular phase shift of the crankshaft angle of the compression piston relative to the crankshaft angle of the expansion piston is set between 10 ° and 45 °, preferably between 20 ° and 30 °, in particular 25 °. The purpose of the angular phase shift between the compression piston and the expansion piston is to cause the delivery of the comburent fluid compressed by the compression cylinder to the expansion cylinder.

Advantageously, means are provided to adjust said angular phase shift between said compression piston and said expansion piston with respect to the operating conditions of said engine.

In particular, the crankshaft mechanism comprises separate drive shafts for operating the compression piston and the expansion piston.

Alternatively, the crank shaft mechanism includes a first drive shaft operating the expansion piston, and a second drive shaft operating the compression piston, the first and second drive shafts being connected to each other to maintain the same rotational speed.

In a possible exemplary embodiment, the crankshaft mechanism of the pistons of the compression and expansion cylinders is of the main connecting rod-connecting rod type.

In particular, the means for injecting comprise at least one injector, in particular a pressurized injector, facing the crossover passage or arranged in the expansion cylinder.

In yet another exemplary embodiment of the engine, a plurality of crossover passages are provided between the expansion cylinder and the compression cylinder, wherein each of the crossover passages has at least one respective transfer valve disposed at a compression-side opening of the crossover passage and is in constant communication with the expansion cylinder. This solution is feasible for e.g. high power engines.

Advantageously, the engine incorporates a supercharger, which is adapted to obtain a higher specific power of the engine, and a better thermodynamic efficiency.

In particular, the compression cylinder and the expansion cylinder have the same displacement or different displacements, in which case it is advantageous for the displacement in the expansion cylinder to be higher, thus obtaining a cycle with more complete expansion.

In a possible exemplary embodiment, the engine may include a plurality of compression cylinders respectively associated with a plurality of expansion cylinders, the expansion cylinders and compression cylinders being arranged and combined differently from one another.

In a possible exemplary embodiment, the crossover passage provides an adjustment element adapted to adjust the cross-section and/or volume of the crossover passage to adapt it to different operating conditions of the engine.

In particular, the adjusting element may be formed by a bolt or a blade.

Drawings

The invention will become more apparent from the following description of exemplary, but not limiting, embodiments thereof, with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a cross-sectional view of an exemplary embodiment of a compression ignition engine at an engine cycle stage according to the present disclosure;

FIG. 2 schematically illustrates a cross-sectional view of an exemplary embodiment of a compression-ignition engine in a subsequent stage of an engine cycle;

FIG. 3 shows a pressure curve in response to crank angle of the crankshaft mechanism, wherein near ETDC, open and close valve timings and phase shift of fuel injection are labeled;

FIG. 4 schematically shows a cross-sectional view of an exemplary embodiment of the engine of FIG. 1 having a supercharger.

Detailed Description

Referring to fig. 1 and 2, a compression-ignition split-cycle engine 100 according to the present invention includes a cylinder block 200 having an expansion cylinder 6 in combination with an associated expansion piston 7, the expansion piston 7 being adapted to be alternately moved between an upper dead center (ETDC) and a lower dead center (EBDC) in the expansion cylinder 6 by a crankshaft mechanism 20. In particular, the crank shaft mechanism 20 makes the predetermined position of the expansion piston 7 always correspond to a predetermined crank angle. In particular, as shown in fig. 3, the ETDC of the expansion piston 7 corresponds to a crank angle of 0 °.

Moreover, the cylinder block 200 comprises a compression cylinder 2 associated with a compression piston 1, said compression piston 1 being adapted to move alternatively between a top dead centre (ETDC) and a bottom dead centre (EBDC) in the compression cylinder 2 according to a predetermined delay with respect to the crankshaft angle of the expansion piston 7. The compression piston 1 is in turn connected by a crank member 7a to a crank mechanism 20. The expansion cylinder 6 is disposed adjacent to the compression cylinder 2. In particular, the compression cylinders 2 and the expansion cylinders 6 have the same displacement, or alternatively they may have different displacements. With different displacement, it is advantageous for the expansion cylinders 6 to have a higher displacement.

The cylinder block 200 further includes a cylinder head 30 which closes the cylinders 2 and 6, and in which at least one crossover passage 5 is provided, the crossover passage 5 connecting the two cylinders 2/6, and including a compression-side opening 5a toward the compression cylinder 2 and an expansion-side opening 5b toward the expansion cylinder 6. The cylinder head 30 also comprises at least one intake valve 3, facing the compression cylinder 2, for sucking a comburent fluid, for example air, into the compression cylinder 2, and an exhaust valve 9, facing the expansion cylinder 6, for discharging the combustion exhaust gases at the outlet of the expansion cylinder 6. Specifically, the intake valve 3 selectively opens/closes the intake conduit 13, and the exhaust valve 9 selectively opens/closes the exhaust conduit 19.

In particular, in the crossover passage 5, the delivery valve 4 is arranged at the compression-side opening 5a, while the expansion-side opening 5b is always in communication with the expansion cylinder 6, the expansion cylinder 6 forming a separate combustion environment 6a together with the expansion-side opening 5 b. On the other side, only the compression cylinder 2 defines a second combustion environment 2 a. Therefore, there is no valve between the expansion cylinder 6 and the crossover passage.

Furthermore, the engine 100 comprises means for causing the opening and closing movement of the delivery valve 4 at predetermined moments of the alternate cycle of the piston 1/7, in particular in the compression phase of the compression cylinder 2 and in the expansion phase of the expansion cylinder 6, respectively.

In addition, means are provided for causing the opening and closing movement of the exhaust valve 9 at alternate predetermined times of the piston 1/7, as described in detail below.

In particular, the means for opening and closing the delivery valve 4 and the means for opening and closing the exhaust valve 9 and the intake valve 3 comprise, for example, a mechanism comprising a camshaft (not shown) which, following the opening and closing of the valves 3/4 and 9, receives the actuation motion through the crank-shaft mechanism 20 and allows the appropriate phasing (phasing) of the alternating motion of the two pistons 1/7. In particular, the crank shaft mechanism 20 includes a shaft 21 that operates the respective pistons 1 and 7 through crank members 1a and 7a, as shown in fig. 1,2 and 4. In a possible exemplary embodiment, the crank shaft mechanism 20 of the pistons 1 and 7 is of the main connecting rod-connecting rod type.

Alternatively, in a manner not shown, the crank shaft mechanism 20 includes a first drive shaft that operates the expansion piston, and a second drive shaft that operates the compression piston. The first and second drive shafts are connected to each other so as to maintain the same rotational speed.

Further, an injection device 8 for injecting fuel in the crossover passage 5 or in the expansion cylinder 6 at a predetermined timing of alternate circulation of the piston 1/7 is provided at the crossover passage 5 to perform compression ignition of the injected fuel 8a (fig. 2) when the compression ignition temperature is reached. In detail, the injection means comprise at least one nozzle 8, in particular a pressurized nozzle, facing the exchange channel 5 or the expansion cylinder 6.

In particular, in the engine cycle, as shown in fig. 3, the delivery valve 4 opens in advance with respect to the crankshaft angle of the ETDC, with an opening movement advanced by 20 ° or more, in particular, by 30 °, as shown in the graph of fig. 3. More specifically, the delivery valve 4 opens in advance with respect to the crankshaft angle of the ETDC according to an advance angle setting between-80 ° and-25 °, in particular between-35 ° and-30 °. In this way, between the opening instant of the delivery valve 4 until the ETDC is reached, there is a substantially equal instantaneous pressure between the compression cylinder and the expansion cylinder, and between the ETDC and the CTDC, through the exchange channel 5, a substantially complete delivery of the comburent fluid is carried out between the compression cylinder 2 and the expansion cylinder 6.

Furthermore, starting from the expansion piston 7 reaching the ETDC, the nozzle 8 injects fuel so that this fuel injection step is carried out simultaneously with the delivery of the comburent fluid through the exchange channel 5.

Thus, before opening the delivery valve 4, there are basically only two environments 2a and 6a, one defined by the compression cylinder 2 and the other defined by the exchange channel 5 and the expansion cylinder 6 together, which define a separate common environment 6 a. Thus, when opening the delivery valve 4, which is advanced by at least 20 ° with respect to the ETDC, there is no substantial delivery of the comburent fluid in the exchange channel 5, since the pressure in the compression cylinder 2 is approximately equal to the pressure in the expansion cylinder 6. As the cycle progresses, the pressure increases in a similar manner everywhere, as shown in fig. 3, due to the simultaneous lifting strokes of the two pistons (fig. 2), up to the ETDC, since the two cylinders communicate with each other through the crossover passage 5. Then, beyond the ETDC, the compression piston 1 continues to rise and the expansion piston 7 starts to descend, allowing the complete transfer of the comburent fluid between the two cylinders through the exchange channel 5. Injection 8a takes place simultaneously with delivery (fig. 2), followed by combustion of the entire fuel. The evaporation phenomenon and the mixing between the fuel and the comburent fluid take place in a better way than in a conventional diesel engine, since the delivery causes high disturbances. In particular, the evaporation proceeds in a faster manner and the mixture obtained is more homogeneous. In this way, a very efficient combustion is obtained, and a very low fraction of unburned particles, in particular carbon-containing dust, is subsequently transported in the exhaust gas.

In addition, a small injection of fuel, a so-called pilot injection, may be provided ahead of time with respect to the ETDC by means of the nozzle 8 in such a way that it preheats the combustion environment 6 a. In this way, pilot injection allows to ensure the success of direct ignition of the fuel charge injected from the time of reaching the ETDC.

According to a preferred cycle of the engine, the means for opening and closing the exhaust valve are adapted to close the exhaust valve 9 with a predetermined advance with respect to the expansion piston reaching the ETDC, so as to cause a portion of the exhaust gases to be compressed in the expansion cylinder 6 up to a predetermined pressure, and when the compression piston 1 compresses the comburent fluid in the compression cylinder 2 to a pressure substantially equal to that present in the expansion cylinder 6, the means for opening and closing the delivery valve 4 open the delivery valve 4, so as to cause the delivery of the comburent fluid from the compression cylinder 2 to the expansion cylinder 6 through the exchange channel 5, and substantially simultaneously perform the auto-ignition of the fuel. In this way, the mixture of compressed fluid and comburent fluid is delivered during the combustion phase, after opening the delivery valve 4, through the exchange channel 5 into the expansion cylinder 6. The exchange channel therefore has a pure conversion function and is not a storage vessel for the pressurized comburent fluid. This makes it possible to eliminate the loss of stratification (loss of ignition) due to the presence of a further transfer valve arranged at the opening of the crossover passage 5 towards the expansion cylinder 6, similar to engines of known type.

In addition, an adjusting element, not shown, may be provided in the crossover passage 5 for adjusting changes in the engine operating conditions, which adjusting element may be formed, in particular, by a bolt or a vane.

In other words, during engine operation, as shown in fig. 1, a certain amount of air is introduced into the compression cylinder 2 through the intake valve 3 and the intake duct 13 due to the downward movement of the compression piston 1.

Then, as shown in fig. 2, this is followed by a step of closing the intake valve 3 and compression of the combustion-supporting fluid, which can be air or air mixed with the exhaust gases, which, as is known, can reduce NOX. The combustion supporting fluid may also be a desired oxygen-enriched inert gas.

Since the delivery valve 4 provided at the outlet of the compression cylinder 2 is opened by the rise of the compression piston 1 and the expansion piston 7 at the right moment as described above, so as to make the comburent fluid flow through the crossover passage 5 towards the expansion cylinder 6, the expansion piston 7 of said expansion cylinder 6 moves with a right delay angle phase shift with respect to the compression piston 1.

During the descent of the expansion piston 7 in the cylinder 6, with the appropriate timing as described above, the delivery valve 4 is closed. As the expansion piston 7 descends, the expansion step is performed in the expansion cylinder 6, while the intake step is started in the compression cylinder 2. When the expansion step in the expansion cylinder 6 is completed, the exhaust valve 9 is opened, thereby opening the exhaust passage 19, the combustion gas is discharged through said exhaust passage 19, and said valve is kept open for a suitable time during the raising stroke of the expansion piston 7 in the expansion cylinder 6.

In particular, the angular phase shift between the crankshaft angle of the compression piston 1 relative to the crankshaft angle of the expansion piston 7 is set between 10 ° and 45 °, preferably between 20 ° and 30 °, in particular 25 °. The angular phase shift between the pistons 1/7 is intended to allow the combustion fluid compressed by the compression cylinder 2 to be entirely delivered to the expansion cylinder 6.

In addition, the angular phase shift between the compression piston 1 and the expansion piston 7 can be adjusted for the operating conditions of the engine.

More specifically, as shown in fig. 3, the angular phase shift between the crankshaft angle of the compression piston 1 and the crankshaft angle of the combustion piston 7 is such that all or part of the combustion takes place when the comburent fluid is delivered from the compression cylinder 2 to the expansion cylinder 6.

Moreover, as always shown in the graph of fig. 3, it is evident that the pressure difference between the compression cylinder 2 and the expansion cylinder 6 is lower during all the steps between opening and closing the delivery valve 4, in particular both pressures are similar before opening the delivery valve 4, due to the early closing of said exhaust valve 9. This improvement reduces head loss (head load) between the crossover passage 5 and the compression cylinder 2 due to stratification during the transient period of opening and closing the transfer valve 4 in the event of very close pressure between the compression cylinder 2 and the expansion cylinder 6.

Alternatively, in a manner not shown, the delivery valve 4 can be opened early with respect to the closing of the exhaust valve 9, in order to achieve a flushing of fresh air from the exhaust gases in the expansion cylinder 6 before the closing of the exhaust valve 9. Even in this case, when the exhaust valve 9 is closed, there is an increase in pressure in both the expansion cylinder 6 and the compression cylinder 2, and it is possible to achieve a greater power.

In particular, the engine 100 uses a split-cycle scheme according to which the intake and compression steps are carried out in an environment different from the environment in which the combustion and exhaust steps are carried out (expansion cylinder 6). The engine operates on the principle of feeding stepwise a mixture of fuel 8a injected by the nozzle 8 and compressed comburent fluid during the combustion step in the expansion cylinder 6, obtaining a result of reduced emissions of dust and nitrogen oxides with respect to the values typical of conventional compression ignition engines. The delivery of the comburent fluid in the expansion cylinder 6 is carried out only by opening the valve 4 facing the compression cylinder and through the crossover passage 5, injecting the fuel 8a in the crossover passage 5 or after the crossover passage 5.

Due to the nature of the introduction of fuel and combustion supporting fluid in the expansion cylinder 6, the engine 100 provides low dust and nox emissions and can still operate with good combustion efficiency at higher speeds than the maximum allowed in conventional compression ignition engines.

Additionally, as shown in fig. 4, the engine 100 may be supercharged, for example by a turbocharger 10, which includes a turbine 10a and a compressor 10b of similar types to those used in conventional compression ignition engines, also for increasing the specific power of the engine. In this case, an increased pressure higher than the maximum allowable pressure in the conventional compression-ignition engine may be used because the pressure gradient during combustion is lower than those typical of the conventional compression-ignition engine in the engine 100.

In yet another exemplary embodiment of the engine, more crossover passages 5 may be provided between the expansion cylinder 6 and the compression cylinder 2, wherein each crossover passage 5 has at least one respective transfer valve 4 arranged at the inlet of the crossover passage 5 from the compression cylinder 2, and each crossover passage 5 is always in communication with the expansion cylinder 6. This solution is feasible for example for high power engines.

In the same way, for the intake in the compression cylinder and for the exhaust from the expansion cylinder, more intake and exhaust valves may be provided in combination with the respective intake and exhaust ducts.

Yet another exemplary embodiment of the engine, not shown, may include a plurality of compression cylinders respectively associated with a plurality of expansion cylinders, arranged and combined with each other in a different configuration.

The foregoing description of the specific embodiments will so fully disclose the invention in such detail as to enable others to improve and/or modify such embodiments for various applications without further research and without departing from the invention, by applying current knowledge, and it is therefore to be understood that such modifications and adaptations are to be considered as equivalent to the specific embodiments. The means and materials for performing the different functions described herein may be of different nature without for this reason departing from the scope of the present invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims (21)

1. A compression-ignition split-cycle engine comprising:

a cylinder block;

an expansion cylinder having an expansion piston adapted to be alternately moved in said expansion cylinder between a first top dead center (ETDC) and a first bottom dead center (EBDC) by a crankshaft mechanism which always has a predetermined position of said expansion piston corresponding to a predetermined crankshaft angle;

a compression cylinder having a compression piston adapted to move alternately in said compression cylinder between a second top dead center (CTDC) and a second bottom dead center (CBDC) according to a delay of a predetermined angular phase shift with respect to a crankshaft angle of said expansion cylinder, said compression cylinder being arranged adjacent to said expansion cylinder;

a cylinder head closing the compression cylinder and the expansion cylinder, wherein at least one crossover passage connecting the expansion cylinder and the compression cylinder is provided and includes a compression-side opening and an expansion-side opening, the cylinder head including at least one intake valve facing the compression cylinder for introducing a combustion-supporting fluid in the compression cylinder and at least one exhaust valve facing the expansion cylinder for discharging combustion exhaust gas discharged from the expansion cylinder;

at least one transfer valve arranged at a compression-side opening of the exchange channel;

means for causing said transfer valve to perform opening and closing movements at predetermined times of the alternating cycles of said expansion piston and said compression piston;

means for causing said exhaust valve to undergo opening and closing movements at predetermined times of the alternating cycles of said expansion piston and said compression piston;

a fuel injection device that injects fuel into the crossover passage or the expansion cylinder at a predetermined timing of the alternate cycle of the expansion piston and the compression piston such that the injected fuel is compression-ignited by compression until reaching an auto-ignition temperature;

the method is characterized in that:

the crossover passage is combined with the expansion cylinder to define a single combustion chamber, and the crossover passage is always communicated with the expansion cylinder;

said means for the opening and closing movement of the delivery valve opening said delivery valve in advance with respect to the crankshaft angle of said first top dead center (ETDC), the advance opening movement being greater than or equal to 20 ° of crankshaft angle, so as to achieve:

from the moment of opening of the delivery valve until reaching the first top dead center (ETDC), the instantaneous pressure between the compression cylinder and the expansion cylinder is substantially equal; and is

-between said first top dead centre (ETDC) and said second top dead centre (CTDC), a substantially total delivery of said comburent fluid is achieved between said compression cylinder and said expansion cylinder through said exchange channel;

said fuel injection means injecting said fuel starting from the point at which said expansion piston reaches said first top dead center (ETDC), so that the injection of said fuel is simultaneous with the delivery of said comburent fluid through said crossover passage.

2. An engine according to claim 1, wherein said means for opening and closing the delivery valve open said delivery valve in advance with respect to the crankshaft angle of said first top dead centre (ETDC), the advance opening movement being set between-80 ° and-25 °.

3. An engine according to claim 1, wherein the early opening movement is set between-35 ° and-30 °.

4. An engine according to claim 1, wherein said fuel injection means is adapted to inject a small amount of fuel in advance with respect to the first top dead center (ETDC), a so-called pilot injection, to preheat the combustion environment.

5. An engine according to claim 1, wherein said means for opening and closing the exhaust valve are adapted to block the exhaust valve at a predetermined advance angle with respect to the moment when the expansion piston reaches the first top dead centre (ETDC) to perform compression of part of the exhaust gases in the expansion cylinder up to a predetermined pressure, and said means for opening and closing the delivery valve open the delivery valve when the compression piston has compressed the comburent fluid in the compression cylinder to a pressure substantially equal to the pressure present in the expansion cylinder, so that the delivery of the comburent fluid from the compression cylinder to the expansion cylinder through the exchange channel is substantially simultaneous with the auto-ignition of the fuel.

6. An engine according to claim 5, wherein said determined advance angle of closure of said exhaust valve relative to said first top dead centre (ETDC) is at least 40 °.

7. An engine according to claim 1, wherein the angular phase shift of the crankshaft angle of the compression piston relative to the crankshaft angle of the expansion piston is set between 10 ° and 45 °.

8. An engine according to claim 7, wherein the angular phase shift is set between 20 ° and 30 °.

9. The engine of claim 8, wherein the angular phase shift is 25 °.

10. An engine according to claim 7, wherein means are provided to adjust the angular phase shift between the compression piston and the expansion piston for the operating conditions of the engine.

11. An engine according to claim 1, wherein the means for opening and closing the delivery valve opens the delivery valve in advance with respect to the closing of the exhaust valve to flush the exhaust gases out of the fresh combustion fluid in the expansion cylinder before closing the exhaust valve, so that when the exhaust valve is closed there is an increase in pressure in both the expansion cylinder and the compression cylinder to achieve higher power.

12. An engine according to claim 1, wherein the crankshaft mechanism comprises separate drive shafts for operating the compression and expansion pistons.

13. An engine according to claim 1, wherein the crank shaft mechanism comprises a first drive shaft operating the expansion piston and a second drive shaft operating the compression piston, the first and second drive shafts being connected to each other to maintain the same rotational speed.

14. An engine according to claim 1, wherein the crankshaft mechanism of the compression piston of the compression cylinder and the expansion piston of the expansion cylinder is of the main connecting rod-connecting rod type.

15. An engine according to claim 1, wherein a plurality of crossover passages are provided between the expansion cylinder and the compression cylinder, wherein each of the crossover passages has at least one respective transfer valve arranged at the crossover passage compression side opening and is in constant communication with the expansion cylinder.

16. An engine according to claim 1, wherein a plurality of intake and exhaust valves are provided in association with respective intake and exhaust conduits for intake in the compression cylinder and for exhaust from the expansion cylinder.

17. An engine according to claim 1, wherein said engine incorporates a supercharger adapted to obtain a higher specific power of the engine, and a better thermodynamic efficiency.

18. An engine according to claim 1, wherein the compression and expansion cylinders have the same displacement or different displacements, with the displacement in the expansion cylinder being higher at different displacements.

19. An engine according to claim 1, wherein the engine comprises a plurality of compression cylinders respectively associated with a plurality of expansion cylinders, the expansion and compression cylinders being arranged and coupled to each other in a predetermined manner.

20. An engine according to claim 1, wherein the crossover passage provides an adjustment element adapted to adjust the cross-section and/or volume of the crossover passage to suit different operating conditions of the engine.

21. An engine according to claim 20, wherein the adjustment element is formed by a bolt or a vane.