A multi-nozzle combustor comprising a pilot nozzle for flame retention and a plurality of main nozzles arranged around the pilot nozzle, each of the nozzles including an outer cylinder, an inner cylinder, and an annular passage defined between the outer and inner cylinders and forming therein a mixture-evaporation region for a fuel ejected and atomized by an airflow.

BACKGROUND OF THE INVENTION 
The present invention relates to a multi-nozzle combustor having a pilot 
nozzle for flame retention in the center and a plurality of main nozzles 
around the pilot nozzle, and more particularly, to a multi-nozzle 
combustor suitably used as a gas turbine combustor. 
FIG. 1 is a sectional view of a conventional combustor. This combustor 
comprises a pilot nozzle 3 in its central portion and a cone 4 for flame 
retention around it. A plurality of main nozzles 1 are arranged in the 
circumferential direction between the cone 4 and an inner cylinder 5. 
Each main nozzle 1 includes a shaft 6 for fuel supply and a nozzle guide 2. 
FIG. 2 is an enlarged view showing one main nozzle 1 and its surroundings. 
As shown in FIG. 2, a region for flame propagation from a pilot flame to a 
main fuel is formed between the flame-retention cone 4 of the pilot nozzle 
3 and the inner cylinder 5. In this propagation region, a distribution 12a 
of the fuel ejected from the main nozzle 1 is an uneven distribution, 
involving a fuel-lean region corresponding to a flow area 11 behind the 
shaft 6 and a fuel-rich region 12b around it. 
Since the fuel is ejected at a certain fuel ejection angle 10 to an 
airflow, as shown in FIG. 2, the distribution 12a of the fuel ejected from 
the main nozzle 1 between the flame-retention cone 4 and the inner 
cylinder 5 involves a fuel-overrich region. 
As shown in FIG. 2, moreover, the length of a mixture-evaporation region 16 
from a fuel ejection position to a firing position is so short that a 
liquid fuel cannot be mixed satisfactorily with air. Accordingly, there 
exist also microscopic fuel-overrich regions. 
When a gas turbine is subject to a high load, furthermore, the fuel 
concentration has a distribution 12a such that it is low in the region 
around a main nozzle shaft center 7 and higher on the wall side, as shown 
in FIG. 3A. When the turbine load is low, on the other hand, the fuel 
concentration has a distribution 12b such that it is high in the region 
around the shaft center 7, as shown in FIG. 3B. 
In the fuel nozzle of the conventional combustor, as described above, the 
use of the fuel supply shaft 6 entails the existence of the fuel-rich 
region 12b. 
The gas turbine combustor is subject to the problem of reduction of 
NO.sub.X in exhaust gas. An NO.sub.X generating region is a region in 
which the fuel is overrich and its concentration is locally high. Since 
the fuel distribution of the conventional fuel nozzle is uneven, it 
involves the fuel-rich region 12b, as shown in FIG. 2, so that the 
delivery of NO.sub.X is substantial. 
Further, the fuel distribution varies depending on the load. When the load 
is high, a flame propagation 14 can be effected smoothly with the main 
fuel distributed very close to a pilot flame 19, as shown in FIG. 3A. When 
the load is low, however, the main fuel is distributed at a distance from 
the pilot flat 19, so that a flame propagation 18 from the pilot flame 19 
to the main fuel cannot be effected smoothly, as shown in FIG. 3b, and 
therefore, a combustible is left inevitably. 
BRIEF SUMMARY OF THE INVENTION 
The object of the present invention is to provide a multi-nozzle combustor 
having a pilot nozzle for flame retention in the center and a plurality of 
main nozzles around the pilot nozzle, in which the fuel distribution is 
uniform despite the change of the fuel flow rate, so that NO.sub.X and 
combustibles are produced at lower rates. 
In order to achieve the above object, a multi-nozzle combustor according to 
the present invention is designed so that each of its main nozzles is 
composed of an outer cylinder and an inner cylinder, a fuel is ejected 
from an annular passage defined between the outer and inner cylinders and 
atomized by means of an airflow around the ejected fuel, and a 
mixture-evaporation region is formed thereafter. According to this 
arrangement, the fuel ejection angle substantially corresponds to the 
course of the airflow. 
In the multi-nozzle combustor of the invention constructed in this manner, 
the fuel is supplied from the annular passage, so that the fuel 
distribution in the circumferential direction can be made uniform at the 
stage of fuel supply. 
Since the direction of fuel ejection substantially corresponds to the 
course of the airflow, moreover, change of dispersion attributable to the 
change of the fuel flow rate can be reduced. 
According to the combustor of the present invention, the fuel ejected from 
the main nozzles is atomized by means of the airflow, so that the particle 
size of the fuel can be reduced, and the fuel evaporation region can be 
provided for the acceleration of mixture after the atomization. Thus, the 
evaporation is promoted to ensure pre-mixture combustion. 
Preferably, in the combustor of the invention, a shaft for fuel supply is 
provided on the upstream side where the flow rate of air is low. This 
shaft serves to prevent stagnation of air at the outlet of each nozzle, 
thereby making the fuel distribution uniform. 
Preferably, moreover, the fuel mixture-evaporation region should be 
lengthened to improve the evaporation characteristics of the fuel. 
In the combustor of the invention, furthermore, an air swirler should be 
provided in the inner cylinder in order to accelerate mixture of the fuel 
and air. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
A combustor according to an embodiment of the present invention will now be 
described in detail with reference to the accompanying drawings of FIGS. 4 
to 6. In the foregoing description of the prior art and the description to 
follow, like reference numerals are used to designate like portions 
throughout the drawings for simplicity of illustration. 
The combustor of the present embodiment comprises a pilot nozzle 3 in its 
central portion and a cone 4 for flame retention around it. A plurality of 
main nozzles 1 are arranged in the circumferential direction between the 
cone 4 and an inner cylinder 5. 
Each main nozzle 1 includes a shaft 6 for supplying a fuel, a fuel ring 14 
for ejecting the fuel, and a nozzle guide 2 that serves as a region in 
which the fuel is mixed with air and evaporated. 
FIGS. 5A and 5B show the details of a nozzle portion of one main nozzle 1. 
As shown in FIGS. 5A and 5B, a fuel ejecting portion of the nozzle 1 
ejects the fuel from the fuel ring 14 that is defined by a gap between a 
fuel nozzle outer cylinder 13 and a fuel nozzle inner cylinder 15. A fuel 
ejection angle 10 to the horizontal direction is given by .theta.. An air 
swirler 17, which is provided in the inner cylinder 15, is used to apply a 
turning effort to an airflow, thereby accelerating the mixture of the fuel 
and air. 
As shown in FIG. 6, the mixture of the fuel and air is accelerated in that 
area of the nozzle which is surrounded by the cone 4 and the inner 
cylinder 5. In this region 16, therefore, a fuel distribution 12a' is so 
uniform that no fuel-overrich region exists. 
Since the air flows substantially in the same direction as the fuel 
ejection, moreover, the fuel distribution cannot be one-sided despite 
fluctuations in gas turbine load. 
Since the fuel is atomized by the airflow, furthermore, it can be reduced 
in particle size, so that its evaporation can be accelerated. Besides, the 
evaporation of the fuel is further accelerated by extending a 
mixture-evaporation region 16, so that pre-mixture combustion can be 
effected even with use of an oil fuel. 
It is to be understood that the fuel used in the combustor according to the 
present invention may be either liquid or gaseous. 
In the combustor of the invention, as described above, each main nozzle is 
composed of the inner and outer cylinders, the fuel is ejected from an 
annular passage that is formed in the gap between the two cylinders. After 
the fuel is atomized by the surrounding airflow, the mixture-evaporation 
region is formed. In this combustor, the fuel and air are mixed 
satisfactorily, so that a local high-temperature flame cannot be formed 
with ease. Thus, according to the combustor of the invention, production 
of NO.sub.X can be restrained to ensure low-NO.sub.X combustion. 
Additional advantages and modifications will readily occurs to those 
skilled in the art. Therefore, the invention in its broader aspects is not 
limited to the specific details and representative embodiments shown and 
described herein. Accordingly, various modifications may be made without 
departing from the spirit or scope of the general inventive concept as 
defined by the appended claims and their equivalents.