IT202100000410A1 - INTERNAL COMBUSTION ENGINE WITH IMPROVED COMBUSTION - Google Patents

Description

DESCRIPTION

of the patent for Industrial Invention entitled:

?Internal combustion engine with improved combustion?

Field of application of the invention

The present invention ? relating to the field of internal combustion engines and in particular it concerns the improvement of the internal combustion of a compression ignition engine.

State of the art

Compression ignition engines are generally referred to as diesel cycle engines. These generally comprise a cylinder closed by a head and a movable piston in the cylinder in which ? obtained the combustion chamber. An example of a combustion chamber? shown in EP3517754.

The air/fuel mixture for each complete engine cycle, in diesel engines? notoriously thin. Ignition generally takes place due to the favorable air/fuel ratio around the drops injected by the injector, creating the combustion conditions only locally. This peculiarity of the combustion called ?compression ignition? inevitably involves the production of solid particulate, linked to the carbon residue that forms in the center of each drop, and NOx, linked to the very high local temperatures of the combustion zone in the vapor phase in the volume surrounding each drop. In this volume there is a residual presence of oxygen that pu? bind to atmospheric nitrogen forming thermal NOx. A low compression ratio involves a temperature, at the end of compression proportionally low, which can? cause misfires and/or high HC.

On the other hand, a very high compression ratio causes an excessive production of NOx due to the high average and local temperatures, linked to the fact that the temperature generated by combustion adds up to the starting temperature of the air which is? proportional to the RC.

AND? known in fact that a low RC ? advantageous for the reduction of particulate matter and NOx, precisely because of the greater time available for the fuel to evaporate and mix before self-igniting, while it is? pejorative for the production of HC due to the lower average temperatures of the gases which do not favor their complete oxidation.

Are known, to overcome these problems of trade off, mode? of particular combustion, denominated with Anglo-Saxon acronyms, such as the PCCI (Premixed Compression Combustion Ignition) or the HCCI (Homogeneus Compression Combustion Ignition) which seek, working on the injection times, to obtain a combustion as pi? possible in the vapor phase, to avoid the localized combustion process around the liquid droplets. These combustions have for? the big limit of making it difficult to control the moment of the beginning of the combustion and to increase the stresses of pressure in the engine, why? the pre-injected fuel, once it reaches the pre-ignition conditions, self-ignites simultaneously throughout the combustion chamber. In addition to the mechanical stresses, measurable by the PCP (Peack Combustion Pressure), even the sound stresses become unacceptable, with the noisiness? of combustion that ?sounds? like a knock on the head.

In fact according to the prior art, as the piston moves towards the top dead center (TDC), the fuel propagates, due to the injection thrust, towards the annular periphery of the combustion chamber, where as the pressure increases and the temperature, the combustion of the mixture is determined.

The combustion, therefore, spreads from the periphery towards the center of the combustion chamber, whose volume is what? little used to be mostly? filled by a solid protrusion of the piston in the form of a truncated cone.

The dispersion of the fuel inside the combustion chamber essentially depends on the shape of the combustion chamber itself, on the times and on the injection pressure and on the reciprocal position between the injector and the piston.

The central cone helps disperse fuel outwards even when the piston is proximal to the injector, and normally has the function of filling the volume to help achieve high RC.

In all of this, the injection times play a fundamental role: according to the known art, it is not possible to anticipate the injection excessively, since the evaporated fuel before reaching the self-ignition conditions lights up all together when the latter are reached with the risk of knocking and/or excessive PCP. This why? the minimum RC of the engine must necessarily be kept above a certain value, typically 15-15.5:1, which always guarantees the ignition? even with quantity? minimum amount of fuel injected.

It is believed that the combustion strategy of the prior art can be improved.

Unless specifically excluded in the detailed description that follows, what is described in this chapter ? to be considered as an integral part of the detailed description.

Summary of the invention

Purpose of the present invention? that of indicating a fuel injection strategy which avoids the formation of carbonaceous particles, but at the same time allows the compression ratio to be kept relatively high.

The basic idea of the present invention ? that of performing a pre-injection of fuel between the conclusion of the exhaust phase and the beginning of the consequent intake phase, in order to optimize the evaporation of the fuel in the comburent.

Preferably, this pre-initiation ? carried out when the exhaust valves are closed, as the present invention describes injections of fuel intended to be fully burned in the engine.

Preferably, the piston is in a position with respect to the injector such that the jet of fuel generated by the injector affects only the piston.

Another object of the present invention ? to allow a ratio of air/fuel more? lean compared to the prior art, minimizing the risks of misfires and increased NOx production.

According to a preferred variant of the invention, the central cone ? modified so as to create, in it, a second combustion volume which allows to obtain a synergistic effect with respect to the execution of the pre-injection.

The injector ? arranged in the engine head in an approximately central position and comprises annular openings for generating fuel jets distributed over a cone-shaped surface, the vertex of which is approximately in the tip of the injector and the base affects the so-called crown of the piston.

The spray predominantly affects the second combustion volume, centrally arranged, when the piston ? next to the top dead center, while, the spray affects more and more? the first combustion volume, having a toroidal and annular shape with respect to the second combustion volume and less and less of the second combustion volume, as the piston moves away from the top dead centre.

Preferably, in the compression phase, a further first injection of fuel is carried out aimed at dispersing fuel in the first volume, i.e. in the periphery of the combustion chamber. Therefore, the piston is in an intermediate position between bottom dead center and top dead center.

Subsequently, a further second fuel injection is performed in the second combustion volume so as to reach a local air/fuel ratio suitable for guaranteeing flammability? of the mixture and preferably close to, coinciding with or slightly greater than the stoichiometric ratio.

While the fuel injected in the pre-injection phase, cio? approximately at top dead center between the exhaust and intake strokes, has time to evaporate and disperse throughout the combustion chamber, the fuel injected approximately at top dead center (TDC) in the compression stroke remains substantially localized until it is neutralized by combustion.

Preferably, a further third injection of fuel in the first volume is achieved in the expansion phase, i.e. when the piston moves towards the bottom dead center in order to reach a preordained global air/fuel ratio.

By preordained air/fuel ratio we mean the ratio that is obtained globally in an entire cycle.

Advantageously, the second volume allows to obtain a prearranged fuel-air ratio relatively rich with respect to the first combustion volume, since it confines the fuel injected into it, avoiding its mixing with the rest of the charge, and guaranteeing that the first ignition takes place in it, when the piston ? next to the TDC, triggering a diffusion of the flame front from the center to the periphery of the combustion chamber, cio? in the opposite way to the solutions of the prior art.

At this point, the further third injection of fuel, which ? the fourth counting the pre-injection, ? made while the combustion has already? started, cooperating with the diffusion of the flame front towards the periphery of the combustion chamber with the effect of obtaining a complete and optimal oxidation of the fuel and of reaching a significant increase in power of the engine, although? the air/fuel ratio remains overall lean.

The further third injection, in addition to increasing the engine power, also favors the complete combustion of the mixture dispersed by the pre-injection, spreading burning fuel drops outwards from the chamber which act as further ignition triggers for the lean mixture, which is highly dispersed and not very reactive.

Even if the air/fuel ratio in the first combustion volume ? under the self-ignition ratio, the second combustion volume, by triggering combustion, causes an increase in temperatures and pressures in the entire combustion chamber, forcing combustion also in the first combustion volume.

The most relevant of the present variant of the invention? that the injection of fuel in the second volume of combustion takes place near? of the PMS, does this mean that ? is it possible to control in a very precise way?the moment of ignition of the local mixture obviating the problems of uncontrollability? of the known art. According to a further preferred variant of the invention, a further pre-injection is performed in the intake phase to obtain optimal fuel dispersion throughout the combustion chamber.

The dependent claims describe preferred variants of the invention, forming an integral part of the present description.

Brief description of the figures

Further objects and advantages of the present invention will become clear from the detailed description that follows of an embodiment of the same (and of its variants) and from the annexed drawings given for purely explanatory and non-limiting purposes, in which:

in figure 1 ? shown is a view according to a longitudinal section of a combustion chamber according to a preferred variant of the present invention;

in figure 2 ? shown a view from? top of the face of the piston in which ? obtained the combustion chamber according to the variant of figure 1;

Figures 3 and 4 show two different operating conditions of the variant according to Figures 1 and 2, in which fuel injections are performed.

The same reference numbers and letters in the figures identify the same elements or components or functions.

It should also be noted that the terms "first", "second", "third", "superior", "inferior" and the like may be used herein to distinguish various elements. These terms do not imply a spatial, sequential, or hierarchical order for the modified items unless specifically indicated or inferred from the text.

The elements and characteristics illustrated in the various preferred embodiments, including the drawings, can be combined with each other without however departing from the scope of protection of the present application as described below.

Detailed description of examples of implementation

According to the present invention, a so-called pre-injection of fuel into the cylinder is provided between the end of the exhaust phase and the beginning of the consequent intake phase, so as to optimize the mixing of the fuel in the combustion agent.

The piston, in this operating condition, is in a position proximal to the top dead center (TDC), and completely masks the walls of the cylinder, in the sense that when the injector? operational, the related fuel jets hit the piston only.

In fact, the fuel has a relatively long time to homogenize and evaporate in the comburent. This leads to minimizing the formation of particulates and at the same time there is a better distribution of heat in the combustion chamber which leads to a more? low NOx formation.

With reference to figures 1 ? 4 shows a compression-ignition internal combustion engine E equipped with an injector N centrally located in the head H of the engine, in which the piston P is, in a known manner, slidingly coupled to a cylinder L closed by the head H.

According to the present invention in the piston P ? a combustion chamber T is defined which is essentially rotationally symmetrical with the axis X of the piston P. This combustion chamber T, as can be seen from figures 1, 3 and 4, which represent axial sections of the cylinder L, has an approximately toroidal shape.

This toroidal shape? annular with respect to a central elevation portion CP preferably having an approximately truncated conical shape.

According to the present invention, in the central elevation portion CP ? defined a second combustion volume C having an opening facing a head H of the internal combustion engine.

The injector N with the relative fuel ejection openings J arranged so that in a first interval R1 of axial positions of the piston, the fuel is? injected mainly in the first volume T of combustion and in a second interval R2 of axial positions of the piston, the fuel ? predominantly injected into the second combustion volume C.

The fuel ejection openings are arranged to form an approximately conical overall jet with the apex of the cone proximal to the injector itself.

Evidently, the shape of the fuel jet does not change over time. Therefore, the one that allows the first combustion volume T or the second combustion volume C to be predominantly affected?? the reciprocal position between piston and injector.

Therefore, how much greater ? the distance between the piston and the injector much greater ? the quantity? of injectable fuel mainly in the annular volume obtained in the piston.

In the compression phase, a further first fuel injection is made aimed at dispersing fuel in the first volume, i.e. in the periphery of the combustion chamber. Therefore, the piston is in an intermediate position between bottom dead center and top dead center.

When, in the compression phase, the piston ? in a position proximal to the top dead centre, ie in the second range of axial positions R2, a further second injection of fuel is performed, most of the fuel ? injected into the second combustion volume C, while the dispersion of fuel in the first combustion volume T ? much lower. There? it is particularly advantageous because, in this phase characterized by high pressures of the charge in the cylinder, the fact of being able to inject fuel mainly in the second combustion volume, easily allows to reach, in it, an air/fuel ratio suitable for a quick ignition of the combustible, report that typically, but not necessarily, ? close to the stoichiometric ratio which appears to represent the condition of pi? high reactivity and flammability.

This means that, unlike known compression ignition engines, combustion begins in the central part and then spreads to the periphery of the entire combustion volume.

The limit that separates the intervals of axial positions R1 and R2 depends on the radius of the annular wall that separates the first volume T from the second volume C of combustion: greater ? is the radius greater? the R2 interval in which the fuel ? predominantly injected into the second combustion volume C.

The limit that separates the intervals of axial positions R1 and R2 also depends on the opening of the ejection cone which the injector N defines with the relative ejection openings.

Therefore, minor ? the opening of the ejection cone, the cio? of the vertex angle of the cone with respect to its axis of rotation, and greater? the second range of axial positions R2 in which the second combustion volume C is predominantly affected.

According to a preferred operating strategy of the internal combustion engine E described above, at least one further first fuel injection is performed when the piston ? in the first interval R1 of axial positions and at least one further second injection of fuel when the piston ? in the second range R2 of axial positions.

Preferably, the first injection of fuel is carried out in the compression phase and is essentially lean and has the purpose of dispersing fuel in the first combustion volume. For lean injection we mean that the lambda ? greater than 2, in the absence of EGR. If exhausted gas recirculation (EGR) then you can? reduce the lambda proportionally.

The additional second injection of fuel into the second range of piston positions, as anticipated above, is intended to achieve a relatively lower local air/fuel ratio. rich and preferably about stoichiometric in the second combustion volume.

By compression stroke, as is known, it is meant that the motion of the piston from bottom dead center to top dead center while at least for a portion of the piston stroke the intake and exhaust valves are approximately closed.

Obviously, each of the pre-injections, further first and second injections of fuel can be sub-fractionated according to fractionation techniques known as multiple injections.

The total charge per cycle ? therefore represented by the sum of the fuel injected in the pre-fuel injection, in the further first injection, second injection and any further fuel injection.

Even the pre-injection pu? be fractionated to obtain an optimal distribution throughout the combustion chamber by carrying out fractional injections in the intake cycle so as to also hit the first combustion chamber T.

Preferably, a further third injection of fuel in the first volume is achieved in the expansion phase, i.e. when the piston moves towards the bottom dead center in order to reach a preordained global air/fuel ratio.

Preferably, the second combustion volume C ? obtained in a chamber lined with a suitable material with low conductivity? thermal, such as for example an aluminum piston with steel central chamber coating or an oxide layer obtained by anodizing aluminum.

Advantageously, the low heat transmission towards the outside considerably limits the heat losses towards the outside which are harmful to the efficiency.

According to what has been described, the second combustion volume, being concentrated in the center of the piston, has a compact shape as well as rotationally symmetrical with respect to the X rotational symmetry axis. involves a natural reduction of heat dispersion towards the outside.

Preferably, inlets (not shown) are arranged to introduce fresh air by means of a swirl with an axis coinciding with that of the cylinder.

The control of the injector ? made through a unit? of processing (not shown) in itself? Note. This ? operationally connected to several sensors including at least one among

- an engine speed sensor, generally the phonic wheel, operatively connected to the crankshaft (not shown),

- one or more phase sensors, able to give information on the effective angular position of the crankshaft, - a knock sensor, or cylinder pressure, able to give information about the instant in which combustion starts,

- Intake air and exhaust gas temperature sensors, water and EGR temperature where present,

- Intake and/or exhaust pressure sensors.

It is clear to those skilled in the art that these sensors can be partially replaced by software calculation models suitable for estimating the information that these sensors normally read in real time.

Therefore, according to the variant in which the further first, second and third injections are carried out, the further first very lean injection is carried out, to disperse fuel in the first combustion volume, i.e. on the periphery of the combustion chamber; the further second injection to create a central ignition in correspondence with the second combustion volume, while the further third injection, carried out after the ignition of the charge in the second combustion volume, has the purpose of also igniting the mixture dispersed in the first combustion volume for the fact that the injected fuel crosses the flame front, realizing a plurality? of primers directed towards the first combustion volume. According to a further preferred variant of the invention, a further pre-injection is performed in the intake phase to obtain optimal fuel dispersion throughout the combustion chamber. This fuel injection also contributes to the total air/fuel ratio computation and can? be subject to splits.

The present invention can be advantageously realized through a computer program which includes coding means for the realization of one or more? steps of the method, when this program ? performed on a computer. Therefore it is intended that the scope of protection extends to said computer program and further to computer-readable means which comprise a recorded message, said computer-readable means comprising program coding means for the realization of one or more steps of the method, when said program ? performed on a computer.

Variants of the non-limiting example described are possible, without however departing from the scope of protection of the present invention, including all the equivalent embodiments for a person skilled in the art, to the contents of the claims.

From the description given above, the technician of the branch ? capable of realizing the object of the invention without introducing further construction details.

Claims (18)

1. Internal combustion engine (E) with compression ignition and direct fuel injection comprising a cylinder to which ? intended to couple in a sliding way a piston (P) defining a combustion chamber (T), and in which in the head ? an injector (N) is arranged with relative ejection openings for fuel injection into the cylinder and processing means configured to control fuel injection and to carry out a fuel pre-injection between the end of the exhaust phase and the beginning of a consequent aspiration phase. 2. Engine according to claim 1, wherein said processing means are further configured to control a further first injection of fuel, preferably lean, in the compression phase, ie. before the piston reaches TDC, so as to disperse fuel into the periphery of the combustion chamber. 3. Engine according to claim 1, wherein said further first injection is performed in a range of piston positions close to top dead centre, such that jets of fuel generated by the injector strike the piston exclusively. 4. An engine according to claim 3 wherein said processing means is further configured to control a further second injection of fuel when the piston is ? close to top dead center to obtain a local air/fuel ratio close to the stoichiometric ratio. 5. Engine according to any one of the preceding claims 1 - 4, wherein said processing means are further configured to control a further pre-injection of fuel in the intake phase so as to disperse fuel also in the periphery of the combustion chamber. 6. Engine according to any one of the preceding claims 1? 5, wherein said processing means are further configured to control a further third injection of fuel during the expansion phase to favor diffusion of the combustion front to the periphery of the fuel chamber, so as to reach a predetermined global air/fuel ratio . 7. Engine according to any one of the preceding claims 1? 6, where in the piston ? obtained a first combustion volume (T) approximately toroidal, annular with respect to a central portion (CP) of elevation, in which in the central portion (CP) of elevation ? defined a second combustion volume (C) having an opening facing the injector (N), the injector having relative fuel ejection openings arranged so that in a first interval (R1) of axial positions of the piston, the combustible ? injected mainly in the first volume (T) of combustion and in a second interval (R2) of axial positions of the piston, the fuel ? mainly injected into the second combustion volume (C). 8. Engine according to claim 7, wherein said pre-injection and/or said further second fuel injection is designed to target essentially the second combustion volume. 9. Engine according to claim 7 or 8, wherein said further pre-injection and/or said further first and/or said further third fuel injection ? designed to target essentially the second combustion volume. 10. Engine according to any one of the preceding claims, wherein an overall air/fuel ratio is lean. 11. Engine according to any one of the preceding claims, wherein said engine head comprises inlet openings arranged to introduce fresh air by means of a swirl with axis coinciding with the axis (X) of the piston (P). 12. Internal combustion engine according to any one of the preceding claims, wherein the central elevation portion (CP) has an approximately frusto-conical shape. 13. Control method of an injector (N) for injecting fuel into the combustion chamber (T, C) of an internal combustion engine according to any one of the preceding claims 1? 10 , the method comprising a first step of performing a pre-injection of fuel when the piston is in a position proximal to the top dead center, between consecutive exhaust phases and consequent intake phases, in order to optimize the mixing of the fuel in the combustion agent. The method according to claim 13, further comprising + a second step to perform a further first injection of fuel, lean, combustion during the compression phase, while the piston ? in an intermediate position between the bottom dead center and top and a third step, immediately following the second, to perform a further second injection of fuel when the piston ? close to top dead centre, in the compression phase, in order to obtain an approximately stoichiometric local air/fuel ratio. The method according to claim 14, further comprising a fourth step, immediately following the third step of performing a further third fuel injection during the expansion phase, so as to obtain a predetermined total air/fuel ratio. 16. A method according to one of claims 13 or 15, comprising a further step of carrying out a further pre-injection of fuel during the intake stroke, when the piston is ? in an intermediate position between top and bottom dead centre, in order to optimize fuel mixing. 17. A computer program comprising program coding means adapted to implement all steps of any one of claims 13 to 16, when said program is run on a computer. 18. A computer readable means comprising a recorded program, said computer readable means comprising a program coding means adapted to implement all steps of any one of claims 13 to 16, when said program ? run on a computer.