Acoustic noise reduction of a gaseous fuel injector

Abstract

A fuel system for supplying CNG to an internal combustion engine. The system includes a fuel rail, a CNG fuel injector, and an engine manifold. The CNG fuel injector includes a fuel inlet in fluid communication with the fuel rail, and a fuel outlet disposed along a longitudinal axis and in fluid communication with the engine manifold. A member is disposed at the fuel outlet that dispersing the CNG in a direction skewed from the longitudinal axis as the CNG flows from the fuel outlet into the engine manifold.

Description

FIELD OF THE INVENTION

This invention relates generally to noise suppression of a fuel injector for an internal combustion engine, and more particularly to noise suppression of a compressed natural gas (CNG) fuel injector.

BACKGROUND OF THE INVENTION

As consumer vehicles and commercial vehicles have evolved, it has been a desirable feature to have lower noise, vibration and harshness (NVH) for improved driver and passenger comfort. In the course of vehicle evolution, various components have been designed for function, safety and minimal NE. As part of this effort, the overall background noise of the vehicle chassis and powertain components have been reduced to a point such that the fuel injectors have become an objectionable noise source. This objectionable noise is exaggerated in CNG injectors. A known way to reduce the NVH of CNG injectors is to provide an acoustic barrier that covers the CNG injectors and/or the manifold in which the injectors are mounted.

It is believed that there is a need for a method and apparatus for reducing the NVH of CNG injectors without providing an acoustic barrier that covers the CNG injectors and/or the manifold.

SUMMARY OF THE INVENTION

A preferred embodiment provides a fuel system for supplying CNG to an internal combustion engine. The system includes a fuel rail, a CNG fuel injector, and an engine manifold. The CNG fuel injector includes a fuel inlet in fluid communication with the fuel rail, and a fuel outlet disposed along a longitudinal axis and in fluid communication with the engine manifold. A member is disposed at the fuel outlet that dispersing the CNG in a direction skewed from the longitudinal axis as the CNG flows from the fuel outlet into the engine manifold.

Another preferred embodiment provides a method of supplying CNG to an internal combustion engine. The method includes flowing the CNG through a fuel rail, flowing the CNG through a CNG fuel injector, flowing the CNG into an engine manifold, and suppressing an expanding volume of the CNG as the CNG flows from the fuel injector into the engine manifold.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain features of the invention.

FIG. 1 is CNG fuel system for an internal combustion engine, according to an embodiment of the invention.

FIG. 2A is a cross-sectional view of a CNG fuel injector including a device that suppresses noise, according to an embodiment of the invention.

FIG. 2B is a cross-sectional view of the device for suppressing noise of FIG. 2A, at axis 2B-2B.

FIG. 3 is an apparatus for testing noise in a CNG fuel injector.

FIG. 4A is a photogragh of CNG dispensed in a manifold for an internal combustion engine.

FIG. 4B is another photogragh of CNG dispensed in a manifold for an internal combustion engine.

FIG. 5A is a photogragh of CNG dispensed in a manifold for an internal combustion engine through the device for suppressing noise of FIG. 2A.

FIG. 5B is another photogragh of CNG dispensed in a manifold for an internal combustion engine though the device for suppressing noise of FIG. 2A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a preferred embodiment of a CNG fuel system for an internal combustion engine. In the preferred embodiment, CNG is flowed from a CNG tank 2, through a fuel rail 4, to a CNG fuel injector 10. When the fuel injector 10 is actuated, CNG is released from the fuel injector outlet though a noise suppression device 26, and into the manifold 22.

FIG. 2A illustrates a CNG fuel injector 10, according to an embodiment of the invention. Fuel injector 10 includes a seat 5, an orifice 6, a closure member 7, an actuator 8, and the noise suppression device 26. The actuator 8 moves the closure member 7 between a first configuration, such that the closure member 7 forms a fluid tight seal with the seat 5 and prevents fluid flow through the orifice 6, and a second configuration, such that the closure member 7 is spaced from seat 5 and allows fluid flow through the orifice 6. Device 26 is a member that is disposed proximate the fuel injector outlet within the engine manifold, and that suppresses the expanding volume of CNG as the CNG exits the fuel injector into the manifold. Device 26 may be a monolithic member having a cylindrical side wall 28 disposed around a longitudinal axis A-A, an open first end 30, and a closed second end 32. The open first end 30 may be fixed at the fuel injector outlet by a seal weld 34. The seal weld provides a fluid tight seal around the perimeter of the first open end. The cylindrical side wall 28, the fuel injector exit, and the closed second end 32 define a chamber 36 into which CNG may be dispersed. The monolithic member is formed of a sintered metal so that the cylindrical sidewall and closed second end are porous and allow CNG to pass therethrough into the manifold. As shown in FIGS. 2A and 2B, suppressor 26 is formed from sintered 316L stainless steel having a 40 μm pore size, a cylindrical wall length L of 25 mm, an outer diameter D of 12.5 mm and a wall thickness t of 2.5 mm. As CNG exits the orifice 6, the CNG enters the chamber 36 and is suppressed from flowing in the direction of longitudinal axis A-A. The CNG fills the chamber 36, permeates the cylindrical side wall 28 and the closed second end 32, and is dispersed radially outward in a direction skewed to, e.g. transverse to or oblique to, axis A-A, as well as in a direction along axis A-A.

The device 26 is not required to be a monolithic member, cylindrical in shape, fixed at the fuel injector exit, or formed of sintered metal, so long as device 26 suppresses the expanding volume of CNG as the CNG exits the fuel injector into the manifold. For example, device 26 could be a member that is not fixed to the fuel injector but is fixed to the manifold. Device 26 could be formed of a wire mesh, a sheet metal with slots formed therein, or a porous solid member that suppresses the CNG. In the embodiment where device 26 is formed of sintered metal, pore size and device dimensions may be altered.

Applicant has conducted testing to show the effects of Applicant's invention. FIG. 3 illustrates an apparatus for testing the acoustic pressure, or noise level, of CNG fuel injectors generally of the type disclosed in commonly assigned U.S. Pat. No. 5,494,224 and U.S. Pat. No. 6,508,418, each being incorporated by reference herein in the entirety. In the preferred embodiment, testing is carried out in accordance with SAE 1832J, which is also incorporated by reference herein in the entirety. A fuel inlet of a CNG fuel injector 10 is connected to a CNG fuel supply 12, and a fuel outlet of the CNG fuel injector 10 is disposed in a baffle 14 to reduce noise transmission from exiting gas. First and second microphones 16, 18 are disposed proximate the injector connector and body, respectively, as shown in FIG. 3. Measurement is carried out with the fuel injector and microphones disposed in an anechoic chamber.

Testing of one standard flow and two high flow CNG fuel injectors was performed. The standard flow CNG fuel injector, identified as calibration 30020, has a nominal flow rate of 2.75 g/sec at 9.29 Bar abs. One high flow CNG fuel injector, identified as calibration 30019 has a nominal flow rate of 4.0 g/sec at 9.29 Bar abs. Another high flow CNG fuel injector, identified as calibration 30025 has a nominal flow rate of 3.9 g/sec at 9.29 Bar abs. The acoustic pressure of each CNG fuel injector was measured at pressures of 1, 5, 7, 9 and 11 Bar abs, with the measured data being tabulated in Table 1 below. Acoustic pressure units are in dB, A-weighted, over a standard reference level of 20 micro Pascal, and are the average of measurements taken from microphone 16 and microphone 18.

TABLE 1
Pressure, Abs.
Bar	Calib, No. 30019	Calib, No. 30020	Calib, No. 30025
1	58.0	55.1	57.4
5	70.4	66.7	71.6
7	73.9	69.5	73.3
9	75.5	71.2	76.1
11	77.0	72.7	78.0

The results indicate a strong correlation between fuel rail pressure and acoustic pressure of CNG fuel injectors. Fuel injector noise due to gas flow is a major contributor to the magnitude of noise over the same injector with no flow. Average injector noise at ambient rail pressure for any calibration tested is less than 60 dBA, and at 9 Bar absolute rail pressure this increases at least 10 dBA, also for any calibration tested.

The CNG fuel injectors display significantly more noise than similar mass flow liquid fuel injectors. It is believed that the increase in noise of CNG fuel injectors is due to sonic flow of an expanding gas volume of the fuel from a CNG injector, in contrast to the constant volume displacement of liquid fuel from a liquid fuel injector. The sonic flow of the expanding gas volume causes acoustic shock waves inside the engine manifold as the CNG fuel injector dispenses CNG into the manifold and the CNG impinges on the air in the manifold. FIG. 4A is a photogragh of CNG 24 dispensed from a fuel injector 20 in a manifold 22 for an internal combustion engine, taken 2.4 ms after the CNG is dispensed. The sonic flow of the expanding volume of the CNG 24 into the manifold 22 causes acoustic shock waves as shown in the figure. FIG. 4B is a photogragh of the CNG 24 dispensed from the fuel injector 20, taken 3.8 ms after the CNG is dispensed. The sonic flow of the expanding volume of the CNG 24 across the manifold 22 causes acoustic shock waves as shown in the figure.

FIG. 5A is a photogragh of CNG 24 dispensed from a fuel injector into the chamber and through the porous cylindrical sidewall and closed second end of device 26, and into a manifold 22 for an internal combustion engine, taken 2.4 ms after the CNG is dispensed. The expanding volume of the CNG 24 into the manifold 22 is suppressed and dispersed in the transverse and longitudinal direction by the porous sidewall and closed end, thus eliminating or reducing acoustic shock waves in the manifold. FIG. 5B is a photogragh of CNG 24 dispensed from a fuel injector into the chamber and through the cylindrical sidewall and closed second end of device 26, and into a manifold 22 for an internal combustion engine, taken 3.8 ms after the CNG is dispensed. Again, the expanding volume of the CNG 24 into the manifold 22 is suppressed and dispersed in the transverse and longitudinal direction, thus eliminating or reducing acoustic shock waves in the manifold.

Applicant has further confirmed the noise reduction in a high flow CNG fuel injector having two different embodiments of device 26 by measuring acoustic pressure with the testing apparatus of FIG. 3, but with the injector mounted in an engine manifold, rather than in baffle 14. Testing was performed on a high flow CNG fuel injector without a noise suppression device, with a sintered 316L stainless steel, 40 μm pore size, 25 mm long device, and with a sintered bronze, 40 μm pore size, 12 mm long device. The acoustic pressure was measured at a pressure of 9.29 Bar abs, with the measured data being tabulated in Table 2 below. Acoustic pressure units are in dB, A-weighted, over a standard reference level of 20 micro Pascal, and are the average of measurements taken from microphone 16 and microphone 18.

TABLE 2
Device for Suppressing Noise Average dBA
40 μm Bronze 12 mm           75.4
40 μm 316 L 25 mm            73.5
None                         78.2

The results show that the sintered 316L stainless steel, 40 μm pore size, 25 mm long noise suppression device reduces acoustic pressure by 4.7 dBA. The sintered bronze, 40 μm pore size, 12 mm long noise suppression device reduces acoustic pressure by 2.8 dBA.

While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the invention, as defined in the appended claims and their equivalents thereof. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims.

Claims

1. A fuel system for supplying CNG to an internal combustion engine, comprising: a fuel rail; an engine manifold; a CNG fuel injector having a fuel inlet in fluid communication with the fuel rail, and a fuel outlet disposed along a longitudinal axis and in fluid communication with the engine manifold; and a member disposed at the fuel outlet that dispersing the CNG in a direction skewed from the longitudinal axis as the CNG flows from the fuel outlet into the engine manifold.

2. The system of claim 1, wherein the member is disposed in the manifold.

3. The system of claim 1, wherein the member is fixed to the fuel outlet.

4. The system of claim 2, wherein the member is fixed to the fuel outlet.

5. The system of claim 1, wherein the member disperses the CNG in a direction that is substantially transverse to the longitudinal axis.

6. The system of claim 1, the member comprising a surface that defines a volume, the volume suppresses the flow of the CNG as the CNG flows from the fuel outlet, the surface disperses the CNG in multiple directions skewed from the longitudinal axis as the CNG flows into the engine manifold.

7. The system of claim 6, wherein the CNG flows substantially from the entire surface.

8. A method of supplying CNG to an internal combustion engine, comprising: flowing the CNG through a fuel rail; flowing the CNG through a CNG fuel injector; flowing the CNG into an engine manifold; and suppressing an expanding volume of the CNG as the CNG flows from the fuel injector into the engine manifold.

9. The method of claim 8, comprising: dispersing the expanding volume of the CNG as the CNG flows from the fuel injector into the engine manifold.

10. The method of claim 8, wherein the suppressing the expanding volume of the CNG includes flowing the CNG through a member at an outlet of the fuel injector.

11. The method of claim 10, comprising: dispersing the expanding volume of the CNG in a direction radially outward from the member as the CNG flows from the fuel injector into the engine manifold.

12. The method of claim 10, wherein the member is disposed in the manifold.

13. The method of claim 10, wherein the member is fixed to the outlet of the fuel injector.

14. The method of claim 12, wherein the member is fixed to the outlet of the fuel injector.

15. The method of claim 8, further wherein the suppressing the expanding volume of the CNG reduces the noise of the CNG fuel injector by more than 2 dBA.

16. The method of claim 8, further wherein the suppressing the expanding volume of the CNG reduces the noise of the CNG fuel injector by more than 4 dBA.