JP3192055B2 - Gas turbine combustor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas turbine combustor having fuel nozzles for diffusion combustion and premix combustion.

[0002]

2. Description of the Related Art Exhaust gas discharged from a gas turbine combustor contains gases such as NOx and CO which cause air pollution, and strict emission regulations are set for these gases. As a countermeasure, the fuel is distributed in multiple stages to reduce NOx, the combustion load per stage is reduced, or lean premixed combustion is performed, thereby suppressing the occurrence of a partial high-temperature region. A method for NOx conversion has been carried out, and this method is now mainstream.

[0003] Most gas turbine combustors include diffusion combustion in which fuel and air are separately supplied from the upstream side of the combustor and burn, and premixed combustion in which fuel and air are premixed in a premixer and burned. However, in recent years, the combustion ratio of premixed combustion tends to increase in a high load region in order to reduce NOx more effectively.

[0004] Premixed combustion is an effective combustion method for reducing NOx, but the flammable range is narrower than diffusion combustion, and unstable combustion such as combustion oscillation is likely to occur. That is, the combustion oscillation is strongly affected by the ratio of the fuel flow rate to the air flow rate, that is, the so-called fuel-air ratio (fuel concentration).

As a measure for preventing such combustion oscillation, a method of installing a control valve for adjusting the flow rate of air flowing into the premixer and controlling the fuel-air ratio is disclosed in Japanese Patent Application Laid-Open No. 61-195164. Therefore, this method will be described with reference to FIG. That is, FIG. 6 (a) is an explanatory view of an air flow control valve flowing into a premixer in this known example. FIG. 6A shows an outline of a gas turbine plant equipped with the air flow control valve. Will be described.

A gas turbine plant is mainly connected to a gas turbine combustor 1, a gas turbine described later, and a gas turbine to obtain compressed air for combustion and cooling.
It is constituted by a compressor described later.

The compressed air discharged from the compressor is guided to the gas turbine combustor 1 and burns together with fuel in a combustion chamber 5 formed in a combustor liner 4 of the gas turbine combustor 1 and is generated at that time. The high-temperature and high-pressure combustion gas is injected into the gas turbine via the transition piece 6 to drive the gas turbine. In general, power is generated by a generator (not shown) connected to the gas turbine.

The main structure of the gas turbine combustor 1 is a combustor liner 4, a diffusion fuel supply system 7,
It comprises a premixed fuel supply system 8 and an air supply system.
It is attached to.

On the upstream side of the combustor liner 4, a diffusion combustion liner 12 having a smaller diameter than the combustor liner 4 is provided.
Further, a fuel nozzle 13 for diffusion combustion and an inner cylinder 14 are provided on the upstream side in the liner 12 for diffusion combustion. A plurality of diffusion combustion fuel nozzles 13 are provided in the circumferential direction,
The fuel ejected from the fuel nozzle 13 for diffusion combustion is used for diffusion combustion in the diffusion combustion chamber 15 downstream from the entire region from the start of the gas turbine to the rated operation.

A premixer 16 is provided on the outer peripheral side of the liner 12 for diffusion combustion, and a plurality of fuel nozzles 17 for premixed combustion are arranged in the circumferential direction on the upstream side thereof. The compressed air flowing out of the compressor flows into the premixer 16 through an air flow path 18 formed by the outer cylinder 9 and the combustor liner 4, and is premixed with the fuel ejected from the fuel nozzle 17 for premixed combustion. The mixture is mixed inside the vessel 16 to form an air-fuel mixture.

The air-fuel mixture is injected into the combustion chamber 5 in the combustor liner 4 to obtain heat energy by diffusion combustion in the diffusion combustion liner 12 to perform premix combustion. This premixed combustion
It is mainly implemented in the region from the partial load zone of the gas turbine to the rated operation.

In the configuration of the gas turbine plant as described above, the above-mentioned known example includes an air flow control valve 28 for adjusting the flow of air flowing into the premixer 16 as shown in FIG. It is disclosed that the fuel cell is installed to control the fuel-air ratio and suppress the combustion oscillation.

[0013]

As described above, premixed combustion is effective for reducing NOx in a gas turbine combustor. However, premixed combustion has a narrow flammable range as compared with diffusion combustion, and unstable combustion such as combustion oscillation is likely to occur.

The combustion vibration of the gas turbine combustor depends on the natural frequency of column resonance determined by the structure and operating conditions (combustion temperature, flow velocity, pressure) of the gas turbine combustor, and the combustion frequency of the fuel burner and flame stabilizer. It is thought that when the fluctuation period of the heat energy generated by the stabilization coincides with the fluctuation period, the heat energy increases rapidly.

FIG. 6B is a block diagram showing the combustion oscillation of the gas turbine combustor, and FIG. 6A and FIG.
The combustion oscillation of the gas turbine combustor will be described with reference to FIGS.

When a combustion oscillation occurs in the combustion chamber 5, the pressure in the combustion chamber 5 fluctuates with the occurrence of the combustion oscillation in a cycle of the combustion oscillation as shown in FIG. 6 (b)-(1). . Combustion chamber 5
Fluctuates, the fluctuation propagates to the premixer 16, the diffusion combustion chamber liner 12, and further to the air flow path 18, and the flow rate of the air flowing into the premixer 16 and the diffusion combustor liner 12 becomes as shown in FIG. (B)-(2).

On the other hand, in the diffusion fuel supply system 7 and the premixed fuel supply system 8, the fuel supply pressure is higher than the pressure in the combustion chamber 5, so that it is shown in FIG. 6 (b)-(3). Thus, the fuel is hardly affected by the pressure fluctuation of the combustion chamber 5, and a substantially constant amount of fuel is supplied. For this reason, the concentration of the air-fuel mixture supplied to the combustion chamber 5, that is, the fuel-air ratio varies as shown in (b)-(4) of FIG.

The period of change of the concentration of the mixture supplied to the combustion chamber 5 is determined by the flow rate of the mixture in the premixer 16 and the distance from the fuel supply position to the flame formation position.
When the fluctuation period of the mixture concentration matches the natural frequency of the air column resonance of the combustor, the pressure fluctuation increases due to the resonance phenomenon. Then, the pressure fluctuation feeds back to the air supply system and may gradually increase.

In the conventional gas turbine combustor, since the distance from the fuel supply position to the flame formation position is the same in the circumferential direction, when combustion vibration occurs, the concentration of the air-fuel mixture supplied to the combustion chamber is reduced in the circumferential direction. It fluctuates in phase.

Therefore, in this case, when a high-concentration air-fuel mixture is supplied to the combustion chamber, the calorific value increases in the circumferential direction, so that the pressure rapidly increases, while a low-concentration air-fuel mixture is supplied. Then, the calorific value decreases in the circumferential direction, so that the pressure decreases. As a result, there is a case where the combustion vibration increases.

The method of controlling the fuel-air ratio by installing an air flow control valve for adjusting the flow rate of air flowing into the premixer as in the above-mentioned known example is effective in suppressing combustion oscillation. However, this method has the trouble of moving the air flow control valve one by one according to the combustion state of the gas turbine combustor, and it is necessary to install an apparatus for that.

The present invention has been made in view of such circumstances, and when periodic pressure fluctuations occur in a combustor due to combustion oscillation, the present invention prevents gas pressure fluctuations from increasing and performs gas combustion for stable combustion. It is intended to provide a turbine combustor.

[0023]

The above object can be achieved as follows.

(1) A cylindrical diffusion combustion chamber, a plurality of diffusion combustion fuel nozzles arranged circumferentially in the diffusion combustion chamber for supplying fuel to the diffusion combustion chamber, and openings in the peripheral wall of the diffusion combustion chamber A plurality of air supply ports for supplying combustion air to the diffusion combustion chamber, a premixer located on the outer peripheral side of the diffusion combustion chamber and premixing fuel and air, A gas turbine combustor provided with a plurality of premixed combustion fuel nozzles arranged in a circumferential direction for supplying fuel to a premixer, and a combustion chamber for generating combustion gas downstream of the premixer. In the above, the axial positions of the fuel ejection holes of the plurality of diffusion combustion fuel nozzles are different, and the axial directions of the fuel ejection holes of the plurality of premixed combustion fuel nozzles are different. The positions are also different.

(2) In (1), a plurality of diffusion combustion fuel nozzles have different fuel injection directions from fuel injection holes, and a plurality of premixed combustion nozzles are provided. The direction in which fuel is ejected from the fuel ejection holes of the fuel nozzle is also different.

(3) A pilot burner that performs diffusion combustion or premix combustion or a combination of these combustion methods on the shaft center side, and diffusion combustion or premix combustion or a combination of these combustion methods on the outer peripheral side of the pilot burner. In a gas turbine combustor comprising a multi-type combustor in which a plurality of premixers performing combined combustion are provided, and a swirling blade is provided at an outlet of the pilot burner and the premixer, on the outer peripheral side of the pilot burner. A plurality of fuel nozzles arranged in the circumferential direction for supplying fuel to the premixer have different distances from the axial positions of the fuel ejection holes to the outlet of the premixer.

(4) In (3), the fuel jet directions of the fuel jet holes of the plurality of fuel nozzles are different.

[0028]

The operation of the present invention is as follows.

(1) In the gas turbine combustor, the axial positions of the fuel injection holes in the diffusion combustion fuel nozzles and the premix combustion fuel nozzles, each of which is arranged in a plurality of circumferential directions, They differ depending on the positions of the fuel nozzles arranged in the circumferential direction. Therefore, in each case, the time required for the fuel ejected from the fuel nozzle to reach the combustion zone differs depending on the fuel nozzle.

Therefore, the fuel concentration of the air-fuel mixture supplied to the combustion zone becomes non-uniform in the circumferential direction, and the phase of the heating value change differs in the circumferential direction. In addition, an increase in pressure fluctuation can be prevented.

(2) The direction of fuel injection at the fuel injection holes provided in the fuel nozzles for diffusion combustion and the fuel nozzles for premixed combustion in a plurality of circumferential directions, respectively, Are different depending on the positions of the fuel nozzles.

Therefore, also in this case, as in the case described above, the time required for the fuel ejected from the fuel nozzle to reach the combustion region differs depending on the fuel nozzle, and the phase of the heat generation amount varies in the circumferential direction. Therefore, when a pressure fluctuation occurs in the combustor, an increase in the pressure fluctuation can be prevented.

(3) The axial position of the fuel injection holes of the fuel nozzles, which supply fuel to the premixer of the gas turbine combustor comprising a multi-type combustor and are arranged in a plurality of circumferential directions, It differs depending on the position of the arranged fuel nozzle. Therefore, a similar effect can be obtained by the same operation as in the case of the premixed combustion fuel nozzle of (1) described above.

(4) In addition, the fuel injection direction of the fuel injection holes of the fuel nozzles, which supply fuel to the premixer of the gas turbine combustor comprising a multi-type combustor and are arranged in a plurality of circumferential directions, is changed. , Depending on the position of the arranged fuel nozzle. Therefore, a similar effect can be obtained by the same operation as in the case of the fuel nozzle for premixed combustion of (2) described above.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram of a gas turbine plant provided with the fuel nozzle of the present embodiment, and FIG. 2 is an enlarged view of a main part of FIG.

The present embodiment is different from the conventional example shown in FIG. 6A in that the present embodiment employs the fuel nozzle for diffusion combustion and the fuel nozzle for premixed combustion according to the present invention. , Respectively. In FIG. 1, FIG.
The gas turbine 2 and the compressor 3 not shown in FIG.

In this embodiment, as shown in FIG. 1, a plurality of diffusion combustion fuel nozzles 1 are arranged in the circumferential direction.
This is a case where the axial lengths of the fuel nozzles 3 and 17 are different from each other.

FIGS. 2 (a) and 2 (b) are enlarged views of a main part of FIG. 1 and show two adjacent premixed combustion fuel nozzles among a plurality of premixed combustion fuel nozzles. That is, the premixed combustion fuel nozzle 17a and the premixed combustion fuel nozzle 17
b are illustrated by way of example, and these are separated by a partition plate 21.

The premixed combustion fuel nozzle 17a and the premixed combustion fuel nozzle 17b installed in the premixer 16 have a cylindrical shape extending in the flow direction of the premixer 16, and have a root portion outside the combustor. The fuel nozzle 19 is connected to the fuel manifold 19 connected to the fuel supply system, and a fuel ejection hole 20 for ejecting fuel is provided at the tip of the fuel nozzle.

In such a configuration, in this embodiment,
Fuel injection holes 2 of premixed combustion fuel nozzles 17a and 17b
Distance from 0 to formation position of premixed flame (La, Lb)
Are made different by adjusting the axial length of the fuel nozzles. The position where the premixed flame was formed was set as the outlet of the premixer.

When the air velocity in the premixer 16 is constant irrespective of the position in the circumferential direction, the time required for the fuel ejected from the fuel ejection holes 20 to reach the flame forming position is determined by the fuel ejection holes 20. Distance to the formation position of the mixed flame (La, L
b).

Therefore, the partition plate 21 of the premixer 16
The fuel concentration of the air-fuel mixture flowing out of each section partitioned by the above will be different in the circumferential direction. That is, even when the pressure fluctuation of the combustion chamber occurs due to the combustion vibration and the air flow rate flowing through the premixer 16 fluctuates, the frequency of the pressure fluctuation and the fluctuation period of the fuel concentration of the premixer are changed by the frequency of the premixer. Therefore, the phase of the heating value change also differs in the circumferential direction, and it is possible to prevent an increase in pressure change.

In this embodiment, the distances from the ejection holes of the two adjacent fuel nozzles to the flame formation position are each L
a and Lb, but when La / Lb = n, n =
When the conditions of 1, 2, 3,... Are satisfied, combustion oscillation may be induced at a frequency n times the frequency of the generated pressure fluctuation. Therefore, L is set so that n is not an integer.
a and Lb were set to suppress combustion oscillation. That is, in the present embodiment, when a pressure fluctuation occurs in the combustor, the fuel concentration of the air-fuel mixture ejected from the premixer is varied at circumferential positions so that n does not become an integer as described above. I made it.

In this embodiment, the distance from the fuel injection hole to the flame forming position is set to two types, La and Lb. However, any number of types may be used, and no regular arrangement is required. . The description of the fuel nozzle 13 for diffusion combustion has been omitted, but the fuel nozzle 17 for premix combustion has been omitted.
The same effect can be obtained in the case of.

A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is an explanatory diagram of the fuel nozzle of the present embodiment,
FIGS. 3A and 3B show two adjacent fuel nozzles. The main components other than the fuel nozzle in this embodiment are the same as those in the first embodiment.

In this embodiment, a plurality of fuel nozzles having the same length irrespective of the positions arranged in the circumferential direction,
As shown in FIGS. 3A and 3B, this is the case where the position of the fuel ejection hole 20 is different depending on the position of the fuel nozzles arranged in the circumferential direction. Accordingly, the same effect as that of the above-described embodiment can be obtained, and the manufacturing cost can be reduced because the shape of the fuel nozzle is one type.

In this embodiment, the fuel nozzles for premixed combustion (17a, 17b) have been described by way of example.
The same effect can be obtained for the diffusion combustion fuel nozzle.

A third embodiment of the present invention will be described with reference to FIG. FIG. 4A is a schematic illustration of a premixer including a premixed combustion fuel nozzle according to the present embodiment, and FIGS. 4B and 4C.
FIG. 4A is an enlarged view of two adjacent nozzles in the fuel nozzle for premixed combustion shown in FIG. The main components other than the fuel nozzle in this embodiment are the same as those in the first embodiment.

In this embodiment, as shown in FIGS. 4 (b) and 4 (c), the fuel injection direction from the premix combustion fuel nozzle 17 is different at the circumferential position.
That is, the tip of the fuel nozzle 17 for premixed combustion is made spherical, and FIG. 4 (b) shows the fuel injection hole 20 in this spherical part.
FIG. 4 (c) shows a case where a plurality of fuel injection holes 20 are provided in the spherical portion in such a manner that the plurality of fuel injection holes 20 are inclined at an angle of α downstream to the flow direction of the fuel in the premixed combustion fuel nozzle 17. 3 shows a case where a plurality of fuel nozzles are provided at an angle of β degrees upstream with respect to the flow direction of the fuel in the premixed combustion fuel nozzle 17.

In such a case, the fuel ejected from the fuel ejection holes 20 shown in FIG. 4B has a velocity component in the same direction as the air flowing through the premixer 16 and is thus obtained as shown in FIG. The fuel ejected from the fuel ejection hole 20 shown in FIG.
6 has a velocity component in a direction opposite to that of the air flowing through the inside.

Therefore, even if the fuel ejection position is almost the same, the time for the ejected fuel to reach the combustion zone will be different. That is, the phase of the fuel concentration fluctuation can be made different in the circumferential direction, and the pressure fluctuation can be suppressed.

Further, as described above, the injection angle of the fuel injection holes in the plurality of premixed combustion fuel nozzles 17 is made different, and the fuel injection speed is made different, so that the phase of the fuel concentration fluctuation is changed. Thus, it is possible to more accurately control, and it is possible to more effectively suppress combustion oscillation.

Further, as in the present embodiment, the tip of the fuel nozzle 17 for premixed combustion is made to be spherical.
There is an advantage that the ejection angle of the fuel ejection hole can be widened without disturbing the flow of the air in the inside 6. In addition, even if the fuel nozzle 17 for premix combustion has a shape as in the case of the first embodiment and the second embodiment, it is possible to obtain substantially the same effect as that of the present embodiment.

In general, when performing the premixed combustion system, it is advantageous for reducing NOx that the fuel concentration distribution is constant over time and spatially uniform. The longer the premixing distance, the more advantageous. Therefore, the fuel nozzle 17 for premix combustion as in this embodiment is
It is effective to reduce the NOx by installing the premixer as far upstream as possible from the premixer 16 and increasing the premix distance.

In this embodiment, the fuel nozzle 17 for premixed combustion is taken as an example, but the same effect can be obtained with the fuel nozzle for diffusion combustion.

A fourth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a cross-sectional view of an example in which the present invention is applied to a multi-type gas turbine combustor, and FIG.
FIG. 5B is a side sectional view.

In this embodiment, as shown in FIGS. 5A and 5B, a pilot burner 2 that performs diffusion combustion at the center of the shaft is used.
3 and a plurality of multi-combustor premixers 24 for performing premix combustion on the outer peripheral side of the pilot burner 2.
A multi-type gas turbine combustor 22 having a pilot burner swirl blade 25 and a pre-mixer swirl blade 26 at the outlets of the premixer 3 and the multi-combustor premixer 24, respectively.
In this case, the present invention is applied.

That is, in this embodiment, the axial length of a plurality of circumferentially arranged premixer fuel nozzles 27 for supplying fuel to the multi-type combustor premixer 24 is determined. This is a case where the difference is made depending on the position of the fuel nozzle 27 for the mixer. With such a configuration, the same effect as that of the premixer of the first embodiment can be obtained. The same effect as in the premixer of the third embodiment can be obtained by making the axial length of the premixer fuel nozzle 27 the same and making the direction in which fuel is ejected different as in the third embodiment. Can be obtained.

In this embodiment, the fuel nozzle for premixed combustion has been described. However, when there are a plurality of fuel nozzles for diffusion combustion, the same operations as those described above are carried out in the case of diffusion combustion. The effect can be obtained.

It should be noted that the pilot burner may not only perform diffusion combustion at the center of the shaft but also perform premixed combustion or a combination of diffusion combustion and premixed combustion. The present invention is applied not only to the premixer performing the premixed combustion, but also to the diffusion combustion, or the premixer performing the combined use of the premixed combustion and the diffusion combustion.
The same effect as in the above case can be obtained.

[0061]

According to the present invention, in the gas turbine combustor, the phase of the fuel concentration fluctuation of the air-fuel mixture supplied to the combustion zone is made non-uniform in the circumferential direction, and the phase of the heating value fluctuation is different in the circumferential direction. By doing so, when combustion oscillation occurs in the gas turbine combustor, an increase in combustion oscillation can be prevented, and a stable combustor can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view of a gas turbine plant having a fuel nozzle according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is an explanatory view of a fuel nozzle according to a second embodiment of the present invention.

FIG. 4 is an explanatory view of a fuel nozzle according to a third embodiment of the present invention.

FIG. 5 is an explanatory view of a fuel nozzle according to a fourth embodiment of the present invention.

FIG. 6 is a schematic diagram of a gas turbine plant having a conventional fuel nozzle.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gas turbine combustor, 2 ... Gas turbine, 3 ... Compressor, 4 ... Combustor liner, 5 ... Combustion chamber, 6 ... Transition piece, 7 ... Diffusion fuel supply system, 8 ... Premixed fuel supply system, 9 ... Outer cylinder, 10: end cover, 11: pressure vessel,
12: diffusion combustion chamber liner, 13: diffusion combustion fuel nozzle, 14: inner cylinder, 15: diffusion combustion chamber, 16: premixer,
17: fuel nozzle for premixed combustion, 18: air flow path, 19
... Fuel manifold, 20 ... Fuel outlet hole, 21 ... Partition plate, 22 ... Multi-type gas turbine combustor, 23 ... Pilot burner, 24 ... Premixer for multi-type combustor, 25 ...
Swirl vane for pilot burner, 26: Swirl blade for premixer, 27: Fuel nozzle for premixer, 28: Air flow control valve.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Inoue 502, Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. In-house (72) Inventor Tomomi Koganesawa 502 Kandachi-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. (56) References JP-A-5-52125 (JP, A) JP-A-2-208417 (JP, A) JP-A-61-22106 (JP, A) JP-A-62-294815 (JP, A) JP-A-2-169828 (JP, A) JP-A-5-332541 (JP, A) JP-A-2-183720 (JP, A) JP-A-61-195164 (JP, A) JP-A-58-83669 ( (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) F23R 3/28-3/34

Claims (4)

(57) [Claims] 1. A diffusion combustion chamber having a cylindrical shape, a plurality of fuel nozzles for diffusion combustion arranged in a circumferential direction in the diffusion combustion chamber to supply fuel to the diffusion combustion chamber, and a peripheral wall of the diffusion combustion chamber A plurality of air supply ports for supplying combustion air to the diffusion combustion chamber; a premixer located on an outer peripheral side of the diffusion combustion chamber for premixing fuel and air; A plurality of premixed combustion fuel nozzles arranged in a circumferential direction on the outer peripheral side of the chamber and supplying fuel to the premixer, and a combustion chamber for generating combustion gas on the downstream side of the premixer. In the gas turbine combustor provided with a plurality of the premixed combustion fuel nozzles, the plurality of the diffusion combustion fuel nozzles have different axial positions of the fuel ejection holes, and the plurality of the premixed combustion nozzles are provided. The axial positions of the fuel nozzles in the fuel nozzles are also different. And a gas turbine combustor. 2. The fuel injection holes of the plurality of diffusion combustion fuel nozzles having different fuel injection directions are different from each other, and the fuel injection holes of the plurality of premixed combustion fuel nozzles are different from each other. The gas turbine combustor according to claim 1, wherein the direction in which the fuel is ejected from the fuel ejection hole is also different. 3. A pilot burner which performs diffusion combustion or premix combustion or a combination of these combustion methods on the shaft center side, and diffusion combustion or premix combustion or a combination of these combustion methods on the outer peripheral side of the pilot burner. A gas turbine combustor comprising a multi-type combustor in which a plurality of premixers performing combined combustion are arranged, and a swirling blade is provided at an outlet portion of the pilot burner and the premixer, wherein the pilot burner A distance from an axial position of a fuel ejection hole of a plurality of fuel nozzles arranged in a circumferential direction on an outer peripheral side and supplying fuel to the premixer to an outlet of the premixer.
A gas turbine combustor characterized in that they are different from each other . 4. The gas turbine combustor according to claim 3, wherein the fuel injection holes of the plurality of fuel nozzles have different fuel injection directions.