IT202300002826A1 - ENGINE WITH RESONATOR ON THE EXHAUST DUCT AND VEHICLE COMPRISING SAID ENGINE - Google Patents

Description

ENGINE WITH RESONATOR ON THE EXHAUST DUCT AND VEHICLE

INCLUDING SAID ENGINE

DESCRIPTION

TECHNICAL FIELD

[0001] The present invention relates to improvements in internal combustion engines. In particular, the present invention relates to improvements in exhaust systems for reciprocating internal combustion engines.

EARLY ART

[0002] Internal combustion engines, in particular reciprocating internal combustion engines, comprising cylinder-piston systems for the production of mechanical power, are widely used in the automotive sector. The use of fuels to power internal combustion engines has an environmental impact also due to the presence of unburned fuels and other impurities in the combustion gas.

[0003] In order to reduce environmental pollution, catalytic converters are increasingly being used on the exhaust pipe, upstream of the silencer. These devices are configured to remove pollutants from the exhaust gases coming from the engine combustion chamber(s), before releasing the exhaust into the environment.

[0004] Catalytic converters, also known as catalytic converters, are responsible in particular for transforming carbon monoxide (CO) into carbon dioxide (CO2) and for converting unburned hydrocarbons into water vapour and carbon dioxide, through oxidation processes. Catalytic converters also have the function of transforming nitrogen oxides (NOx) into nitrogen (N2) and oxygen, through a reducing transformation.

[0005] Catalysts inserted in the exhaust pipe provide a valid aid in reducing pollutants released into the atmosphere, but have a negative impact in terms of engine performance, since their presence in the exhaust pipe generates pressure waves in the exhaust gas flow that are reflected towards the engine exhaust port(s). These pressure waves increase the engine exhaust pressure and therefore reduce its efficiency. Reduced efficiency of the internal combustion engine has a negative impact on fuel consumption and therefore, ultimately, on the environmental impact.

[0006] The invention aims to reduce the above-mentioned drawbacks of internal combustion reciprocating engines equipped with a catalyst.

SUMMARY

[0007] In one aspect, to solve in whole or in part the drawbacks of the prior art, an internal combustion engine is described herein, comprising at least one cylinder-piston system with an intake port and an exhaust port, in which an exhaust duct is connected to the exhaust port, along which a catalyst and a silencer are arranged in sequence. The catalyst is placed upstream of the silencer with respect to the direction of the flow of exhaust gases along the exhaust duct. Characteristically, the engine comprises a resonant system connected to the exhaust duct. The resonant system comprises a resonant duct and a resonant cavity. The resonant duct provides a fluid connection between the exhaust duct and the resonant cavity, and the resonant duct is connected to the exhaust duct upstream of the catalyst with respect to the direction of the flow of exhaust gases along the exhaust duct. In illustrated embodiments, the resonant duct and the resonant cavity are arranged in such a way that the resonant duct is connected to the exhaust duct. resonant have different cross-sections, the resonant duct having a smaller cross-section than the resonant cavity.

[0008] Further advantageous features and embodiments of the engine according to the invention are described below and defined in the attached dependent claims.

[0009] The invention also includes a motorcycle comprising an engine as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention will be better understood by following the description and the attached drawings, which illustrate an exemplary and non-limiting embodiment of the invention. More specifically, the drawing shows:

Fig.1 is a side view of a vehicle equipped with an engine according to the invention;

Fig.2 is a schematic view of the engine according to the invention, complete with exhaust system;

Figs. 3 and 4 are experimental diagrams relating to the characteristics of the engine according to the invention;

Fig.5 is a schematic of an improved resonant cavity; and

Fig.6 is a diagram of an exhaust system according to the invention in a further embodiment.

DETAILED DESCRIPTION

[0011] In Fig.1 a commercial vehicle is schematically shown on which an engine of the type described can be installed. The vehicle 1 can comprise a single steerable front wheel 3 or two steerable front wheels 3, and a pair of rear drive wheels 5, for example.

[0012] In Fig.2, an engine 9 is schematically illustrated which can be installed in the vehicle 1. The engine 9 comprises an exhaust system indicated as a whole by 11 and a cylinder-piston system 13, which can comprise a single cylinder 13.1 in which a piston 13.2 is slidably housed. 13.3 indicates a connecting rod-crank system which converts the reciprocating motion of the piston 13.2 in the cylinder 13.1 into a rotary motion of the output shaft. 13.4 indicates an intake port and 13.5 indicates an exhaust port of the cylinder-piston system 13. 13.6 indicates the combustion chamber defined inside the cylinder 13.1.

[0013] Although the present description refers to an engine with a single cylinder-piston and single intake and exhaust ports, the possibility of realizing the engine 9 with a plurality of cylinder-piston systems and/or of providing more than one intake port and/or more than one exhaust port is not excluded.

[0014] The exhaust system 11 comprises an exhaust duct 17, with an inlet end 17.1 and an outlet end 17.2. The inlet end is connected to the combustion chamber 13.6 through the exhaust port(s) 13.5. The outlet end 17.2 is adapted to release into the environment the exhaust gases generated by the combustion of the fuel in the combustion chamber 13.6.

[0015] A catalyst (or pre-catalyst) 19 is arranged along the exhaust duct 17. Downstream of the catalyst 19, with respect to the direction of flow G of the exhaust gases in the exhaust duct 17, a muffler or silencer 21 is arranged. Between the catalyst 19 and the silencer 21, or integrated into the latter, further elements (not shown) can be arranged to reduce the pollutants contained in the exhaust gases.

[0016] At a point in the exhaust duct 17 located upstream of the catalytic converter 19, between an inlet side 19.1 of the catalytic converter 19 and the exhaust port 13.5, there is a branch 23, in which a resonating duct 25 is inserted into the exhaust duct 17.

[0017] The resonant duct 25 extends from the branch 23 to a resonant cavity 27. The resonant duct 25 and the resonant cavity 27 cumulatively form a resonant system collectively indicated by 29.

[0018] In advantageous embodiments, as shown in Fig. 2, the resonant duct 25 is approximately tangent to the exhaust duct 17 at the point of mutual connection, i.e. at the bifurcation 23. By approximately tangent is generally meant a configuration such that the overall flow of exhaust gas in the exhaust duct 17 is approximately tangent to the flow in the resonant duct 25. For example, the median lines, i.e. the axes of the exhaust duct 17 and the resonant duct 25 may be tangent to each other. In Fig. 2 the axis or median line of the exhaust duct 17 is indicated by 17.1 and the axis or median line of the resonant duct 25 is indicated by 25.1. The rectilinear extension of the axis 25.1 is tangent to the curve defining the axis 17.1 of the exhaust duct at a point upstream of the bifurcation 23 with respect to the direction of flow of the exhaust gas in the exhaust duct 17.

[0019] During operation of the internal combustion engine 9, the opening and closing of the exhaust port by the operation of the exhaust valve (not shown) in synchrony with the execution of the engine cycles causes pressure waves in the exhaust duct 17. These pressure waves are reflected on the material contained in the catalyst 19 at the inlet end 19.1 of the latter, generating reflected pressure waves that propagate in the opposite direction to the direction of the exhaust gas flow (arrow G in Fig.2).

[0020] The reflected pressure waves cause an increase in pressure at the exhaust port 13.5, which increases the back pressure at the outlet, which the combustion gases must overcome in the exhaust phase of the operating cycle of the engine 9. This increase in back pressure due to the pressure waves reflected by the catalytic converter 19 has a negative impact on the efficiency of the engine 9, as the higher the back pressure, the lower the power output of the engine.

[0021] The resonant system 29 is configured to reduce or eliminate this negative effect due to the presence of the catalyst 19 in the exhaust duct 17. To this end, the resonant system 29 is sized so that, under normal conditions of use of the engine 9, i.e. in the rpm range at which the engine is usually maintained to maximize the torque and/or power delivered, the resonant system 29 resonates generating pressure waves at the bifurcation 23 having the same frequency as the pressure waves reflected by the catalyst 19 and in counterphase with respect to the reflected pressure waves.

[0022] The pressure waves reflected by the catalyst 19 and the pressure waves generated by resonance of the resonant system 29 tend to cancel each other out in the section of the exhaust duct 17 between the exhaust port 13.5 and the bifurcation 23. This is because the pressure waves give rise to a phenomenon of destructive interference.

[0023] In practice, it happens that the pressure waves generated in the resonant system 29 destroy the pressure waves reflected by the catalyst 19, or at least reduce their intensity.

[0024] The end result of this phenomenon is a reduction or elimination of the negative effect of the reflected pressure waves in terms of increased back pressure at the exit port 13.5.

[0025] Typically, the solution proposed here is advantageous for reciprocating internal combustion engines which have, for example, an operating speed typically between 2400 rpm and 5000 rpm, and more specifically between 3600 rpm and 4200 rpm.

[0026] In some embodiments, the resonant cavity 27 may have a fundamental resonant frequency of between 10 Hz and 30 Hz, preferably between 14 Hz and 18 Hz, even more preferably between 16 Hz and 18 Hz, at the temperature of the exhaust gases under steady-state operating conditions of the internal combustion engine. Typically, the fundamental resonant frequency may be approximately 16 7 Hz, where the variation in frequency is attributable to the variation in temperature of the exhaust gas which, by modifying the speed of sound in the exhaust gas, affects the fundamental resonant frequency. The latter is in fact given by the formula

in which:

c is the speed of sound in the fluid medium contained in the resonant system, called speed c being a function of the temperature and of the ratio between the specific heat at constant pressure and the specific heat at constant volume;

S ? the section of the duct 25

L ? the length of the duct 25

V is the volume of the resonant cavity.

[0027] The value of 16 - 18 Hz of the resonance frequency chosen is linked to the idea of optimizing the engine in maximum torque and in particular in maximum power. Since with a fixed geometry of the resonator it is not possible to obtain the two advantages, it may be advantageous to choose a value of the resonance frequency capable of giving a certain positive contribution to the maximum torque and which allows the energy contribution of the pressure waves to be used in the best possible way to enhance the maximum power.

[0028] To do this, in the embodiment described, a resonator geometry was chosen that allows it to work between 16 and 18 Hz. In fact, at 2300 rpm of the engine, a fundamental engine frequency of 2250 (?50)/60=37 Hz is obtained, which corresponds approximately to a resonant frequency of the resonator of 37/2 =18 Hz (2 because it is a 4-stroke engine and the energy contribution occurs every 2 revolutions of the crankshaft). In practice, using a numerical simulator, it is possible to configure the dimensions of the resonator such that, using the Helmholtz relation, the resonance frequency is equal to approximately 16 Hz. With this optimised geometry, it is possible to exploit the energy contribution of the first order frequency (16 - 18 Hz) to obtain an increase in torque and a multiple of this frequency to enhance the maximum power. In fact, the maximum power with the resonator is around 4300 rpm and the fundamental frequency of the motor is around 4300/60=71 Hz or a resonance frequency of around 71/2=36 Hz which is exactly double the first order resonance frequency mentioned previously.

[0029] Ultimately, a system was obtained that has a fairly wide bandwidth for a slow engine category such as an APE 300 engine, the main characteristics of which are indicated below.

[0030] As seen in Fig.2, the resonant cavity 27 has a larger cross-section than the cross-section of the resonant duct 25. Typically, in particularly advantageous embodiments, the ratio of the cross-sectional area of the resonant cavity to the cross-sectional area of the resonant duct is between 35 and 55, preferably between 40 and 50, more preferably between 43 and 48.

[0031] In some embodiments, the resonant cavity 27 has a substantially cylindrical shape with a circular cross-section, with a first diameter D1, and the resonant duct has a circular cross-section with a second diameter D2, smaller than the first diameter D1.

[0032] The resonant cavity 27 may have for example an internal volume of between 2800 and 3400 cm<3>, preferably between 3000 and 3200 cm<3>. In some embodiments the resonant duct has a length of between 90 and 100 cm, preferably between 92 and 97 cm.

[0033] The connection point between the exhaust pipe 17 and the resonating pipe 25, i.e. the bifurcation 23, can be located at a distance between 90 and 115 mm, preferably between 100 and 105 mm from the exhaust port 13.5.

[0034] Figs. 3 and 4 show results of experimental tests performed on an APE 300 engine produced by the applicant, equipped with an exhaust system 11 made as illustrated in Fig. 2. In particular, the APE 300 engine is a four-stroke Otto cycle engine with the following characteristics:

Number of cylinders: 1

liquid refrigeration

Number of valves per cylinder: 2

Cylinder tilt: 75?

Aluminum cylinder head

Cylinder material: cast iron

Displacement: 306 cm<3>

Compression ratio 9.5+/-0.5:1

Bore x stroke: 72 x 75 mm.

[0035] The exhaust system used for testing was configured as follows:

- length of the resonant duct: 950 mm

- internal diameter D2 of the resonant duct: 19 mm

- internal volume of the resonant cavity 27: 3150 cm<3>

- axial length of the resonant cavity 27: 245 mm

- external diameter of the resonant cavity 27: 130 mm

- thickness of the resonant cavity sheet 27: 1.2 mm

- distance of fork 23 from exhaust port: 100 mm

- cross-section of the resonant duct 25 and the resonant cavity 27: circular

[0036] In the diagram in Fig.3, the values of the rotation speed in rpm are shown on the abscissa and on the ordinate, on the left, the power delivered in kW and on the right, the torque delivered in Nm. The curves W0 and C0 represent respectively the power and torque delivered by the engine without the resonant system 11. The curves W1 and C1 represent respectively the power and torque delivered by the engine equipped with the resonant system 11.

[0037] From Fig. 3 it can be observed that at any rpm value between approximately 2400 rpm and approximately 5000 rpm both the torque C1 and the power W1 are higher than the torque and power delivered by the same engine without the resonant system.

[0038] The diagram in Fig.3 therefore shows how the resonant system described here provides advantages in terms of engine efficiency.

[0039] Similar advantages can be seen in terms of fuel consumption reduction. The diagram in Fig.4 shows the engine rotation speed (rpm) on the abscissa. The specific fuel consumption expressed in g/kWh is shown on the left ordinate. The hourly fuel consumption in kg/h is shown on the right ordinate.

[0040] The Ch0 curve and the Cs0 curve indicate respectively the hourly consumption and the specific consumption of the engine without the resonant system 11. The Ch1 and Cs1 curves indicate respectively the hourly consumption and the specific consumption of the engine equipped with the resonant system 11. Both the hourly consumption and the specific consumption are reduced by approximately 4-5% in the case of using the resonant system 11 in the entire useful rotation speed range, between approximately 2400 rpm and approximately 5000 rpm.

[0041] The efficiency of the vehicle 1 on which the engine 9 is installed can be further improved by associating the resonant system 11 with an electric generator. This can be achieved by using an electric generator 31, for example a linear alternator, applied to a bottom 27.1 of the resonant cavity 27, as schematically shown in Fig. 5. The linear alternator 31 converts the energy transmitted from the vibrating bottom 27.1 of the resonant cavity 27 to the moving component of the linear alternator 31. The generated electric energy can be converted into direct current in a rectifier 35 placed on an electric line 33 connecting the linear alternator 31 to a battery 37 of the vehicle 1.

[0042] Fig. 6 shows a further embodiment of the exhaust system according to the invention. Equal numbers indicate parts equal or equivalent to those illustrated in Fig. 2 and described above. The exhaust system 11 of Fig. 6 differs from the exhaust system 11 of Fig. 2 mainly in that the resonant cavity 27 is integrated into a single block 20 in which the muffler or silencer 21 is also inserted. The silencer 21 and the resonant cavity 27 are suitably separated from each other, for example by a sheet metal 22, to prevent the flows in the silencer and in the resonant cavity from interacting with each other.

Claims (14)

ENGINE WITH RESONATOR ON THE EXHAUST DUCT AND VEHICLE COMPRISING SAID ENGINE Claims 1. An internal combustion engine, comprising at least one cylinder-piston system with an intake port and an exhaust port, in which a long exhaust pipe is connected to the exhaust port, in which a catalyst and a silencer are arranged in sequence, the catalyst being placed upstream of the silencer with respect to the direction of the flow of exhaust gases along the exhaust pipe; characterized in that it comprises a resonant system connected to the exhaust pipe, wherein the resonant system comprises a resonant pipe and a resonant cavity, wherein the resonant pipe provides fluid connection between the exhaust pipe and the resonant cavity; and wherein the resonant pipe is connected to the exhaust pipe upstream of the catalyst with respect to the direction of flow of the exhaust gases along the exhaust pipe. 2. The internal combustion engine of claim 1, wherein the resonant duct is approximately tangent to the exhaust duct at the point of connection between the resonant duct and the exhaust duct. 3. The internal combustion engine of claim 1 or 2, wherein the resonant system is sized in such a way that at the connection point between the resonant pipe and the exhaust pipe, pressure waves generated in the resonant system are formed in counterphase to the pressure waves generated in the exhaust pipe by the catalyst. 4. The internal combustion engine of claim 1 or 2 or 3, wherein the cavity is resonant and has a fundamental resonant frequency of between 10 Hz and 30 Hz, preferably between 14 Hz and 18 Hz, even more preferably between 16Hz and 18 Hz at the exhaust gas temperature under steady-state operating conditions of the internal combustion engine. 5. The internal combustion engine of one or more of the preceding claims, wherein: the resonant cavity has a cross-section larger than the cross-section of the resonant duct. 6. The internal combustion engine of claim 5, wherein the ratio of the cross-sectional area of the resonant cavity to the cross-sectional area of the resonant duct is between 35 and 55, preferably between 40 and 50, more preferably between 43 and 48. 7. The internal combustion engine of claim 5 or 6, wherein the resonant cavity has a substantially cylindrical shape with a circular cross-section, with a first diameter, and the resonant duct has a circular cross-section with a second diameter, smaller than the first diameter. 8. The internal combustion engine of one or more of the preceding claims, wherein the resonant cavity has an internal volume of between 2800 and 3400 cm<3>, preferably between 3000 and 3200 cm<3>. 9. The internal combustion engine of one or more of the preceding claims, wherein the resonating duct has a length between 90 and 100 cm, preferably between 92 and 97 cm. 10. The internal combustion engine of one or more of the preceding claims, wherein the connection point between the exhaust pipe and the resonating pipe is between 90 and 115 mm, preferably between 100 and 105 mm from the exhaust port of the cylinder. 11. The internal combustion engine of one or more of the preceding claims, wherein the maximum engine power and the maximum engine torque are delivered at a rotational speed between 2400 rpm and 5000 rpm. 12. The internal combustion engine of one or more of the preceding claims, wherein the resonant cavity is combined with an electric generator driven by the vibration of a wall of the resonant cavity and adapted to convert the mechanical energy transmitted to the electric generator into electrical energy. 13. The internal combustion engine of one or more of the preceding claims, wherein the resonant cavity is integrated into a block containing the silencer. 14. A vehicle comprising an internal combustion engine as claimed in one or more of the preceding claims.