Title: Combustion apparatus
Abstract: A combustion apparatus 2 has a fuel spraying nozzle 12, a feed canal 16 and a return canal 17, both the canals connected to the nozzle, with the former canal 16 feeding a fuel to the nozzle and with the latter canal 17 allowing an unsprayed portion of the fuel to flow back. An electromagnetic pump 18 disposed in the feed canal 16 serves to compress the fuel towards the nozzle 12, and an injector valve 25 is disposed in the return canal 17. A controller 40 regulates the operation of the injector valve 25 in the manner of duty-ratio control so as to adjust the flow rate of the fuel being sprayed out of the nozzle 12.
Patent Number: 6,908,299 Issued on 06/21/2005 to Asano, et al.
| Inventors:
|
Asano; Kimiaki (Kobe, JP);
Hara; Hitoshi (Kobe, JP);
Hamada; Tetsurou (Kobe, JP);
Kanda; Yoshinori (Kobe, JP);
Hasegawa; Hiroki (Kobe, JP);
Hori; Toshihiro (Kobe, JP)
|
| Assignee:
|
Noritz Corporation (Hyogo, JP)
|
| Appl. No.:
|
650660 |
| Filed:
|
August 28, 2003 |
Foreign Application Priority Data
| Aug 29, 2002[JP] | 2002-250546 |
| Feb 25, 2003[JP] | 2002-046859 |
| Current U.S. Class: |
431/12; 431/72 |
| Intern'l Class: |
F23N 005/00 |
| Field of Search: |
431/12,72,73,18
|
References Cited [Referenced By]
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| 6581573 | Jun., 2003 | Nimura et al.
| |
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| |
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| |
Primary Examiner: Basichas; Alfred
Attorney, Agent or Firm: Wood, Phillips, Katz, Clark & Mortimer
Claims
1. A combustion apparatus comprising:
a spraying means for spraying a fuel to be burnt and comprising a fuel spraying
nozzle for jetting fuel,
a fuel channel for flowing the fuel therethrough,
the fuel channel comprising a fuel feed canal for communicating fuel to the fuel
spraying nozzle,
the fuel channel further comprising a fuel return canal for returning fuel from
the fuel spraying nozzle that is communicated to the fuel spraying nozzle through
the fuel feed canal and not jetted by the fuel spraying nozzle,
a fuel pump disposed in the fuel channel so as to compress the fuel flowing towards
the spraying means,
an intermittently operating valve disposed in the return canal of the fuel channel
so that a valve body of the valve is driven to close and open the return canal
intermittently or periodically, and
a valve controller to control the timing at which the valve body is driven to
close and open the return canal.
2. The combustion apparatus as defined in claim 1, wherein the valve controller
is designed to perform a duty ratio control or PWM control for the closing and
opening of the valve body.
3. The combustion apparatus as defined in claim 1, wherein the valve controller
is designed to control the valve body to open and close the return canal synchronously
with an alternating current driving the fuel pump.
4. The combustion apparatus as defined in claim 1, wherein the valve controller
is designed to control the valve body to open and close the return canal synchronously
with the timings of zero-crossing signals generated in an alternating current driving
the fuel pump.
5. The combustion apparatus as defined in claim 1, wherein the valve controller
is designed to control the valve body to open the return canal upon detection of
every zero-crossing signal that is generated in an alternating current driving
the fuel pump.
6. The combustion apparatus as defined in claim 1, wherein pressure relief is
executed either after or before a combustion process, by keeping open the intermittently
operating valve for a given duration.
7. The combustion apparatus as defined in claim 1, wherein a pre-combustion pressure
relief is executed before a combustion process, with a post-combustion pressure
relief being executed after the combustion process, such that in the pre-combustion
pressure relief the intermittently operating valve is kept open for a shorter time,
with this valve being kept open for a longer time in the post-combustion pressure relief.
8. The combustion apparatus as defined in claim 1, wherein lapse of time is measured
from a preceding termination of a combustion process until a succeeding resumption
thereof, the apparatus further comprising an ignition controller for modifying
the spraying rate of fuel at the beginning of a resumed combustion process and
on the basis of the measured time lapse.
9. The combustion apparatus as defined in claim 1, wherein lapse of time is measured
from a preceding termination of a combustion process until a succeeding resumption
thereof, the apparatus further comprising an ignition controller such that the
spraying rate of fuel when re-igniting it will be reduced if the measured time
lapse is equal to or longer than a given reference time, than other spraying rates
intended for any other time lapse shorter than this reference time.
10. The combustion apparatus as defined in claim 1, further comprising an air-blowing
means for positively supplying air to be consumed in combustion of the fuel, as
well as an ignition controller for modifying the spraying rate of fuel at the beginning
of a resumed combustion process, and on the basis of such a measured time lapse.
11. The combustion apparatus as defined in claim 1, further comprising an ignition
controller such that the spraying rate of fuel when re-igniting is reduced if a
measured fuel pressure is lower than a given reference value, than other spraying
rates intended for any fuel pressures equal to or higher than this reference value.
12. A combustion apparatus comprising:
a spraying means for spraying a fuel to be burnt and comprising a fuel spraying
nozzle for ietting fuel,
a fuel channel for flowing the fuel therethrough,
the fuel channel comprising a fuel feed canal for communicating fuel to the fuel
spraying nozzle,
the fuel channel further comprising a fuel return canal for returning fuel from
the fuel spraying nozzle that is communicated to the fuel spraying nozzle through
the fuel feed canal and not jetted by the fuel spraying nozzle,
a fuel pump disposed in the fuel channel so as to compress the fuel flowing towards
the spraying means and,
an intermittently operating valve disposed in the return canal of the fuel channel
so that a valve body of the valve is driven to close and open the return canal
intermittently or periodically at regular and variable intervals by a duty-ratio
control,
wherein the duty-ratio control is repeated at a frequency that is adjusted responsive
to a required amount of heat to be generated.
13. The combustion apparatus as defined in claim 12, wherein the duty-ratio control
involves a plurality of hypothetical regions that have different frequencies of
the duty-ratio control in relation to the required amount of heat to be generated
per unit time.
14. The combustion apparatus as defined in claim 12, further comprising a valve
controller for controlling the intermittently operating valve with action relying
on a plurality of electronics reference tables each being an array of valve-operating
data, such that the frequencies of the duty-ratio control differ from each other
between the tables, and one of them is selected to match a desired flow rate of
the fuel being sprayed and burnt.
15. The combustion apparatus as defined in claim 12, wherein the one cycle time
in the duty-ratio control is prolonged for comparatively lower amount of heat required
to be generated per unit time.
16. A combustion apparatus comprising:
a spraying means for spraying a fuel,
a fuel channel for flowing the fuel therethrough,
a fuel pump disposed in the fuel channel so as to compress the fuel flowing towards
the spraying means, and
an intermittently operating valve disposed in the fuel channel so that a valve
body of this valve close and open the channel periodically at regular and variable
intervals by the duty-ratio control,
the valve body fully closing the channel when it is at a first position,
the valve body fully opening the channel when it is at a second position,
wherein the duty-ratio control is repeated at a frequency that is adjusted responsive
to the current flow rate of the fuel being burnt, in such a manner that if the
ratio of a first time length for the valve body to move once from the first position
to the second position and then back from the second position to the first position
divided by a second time length in which said valve body remains at the second
position during one cycle of said duty-ratio control does exceed a threshold, then
one cycle time in the duty-ratio control is prolonged.
17. The combustion apparatus as defined in claim 16, wherein the duty-ratio control
is conducted in such a manner that if the duty ratio for causing the intermittently
operating valve to open does exceed a reference value, one cycle time in the duty-ratio
control is prolonged.
18. The combustion apparatus as defined in claim 16, wherein the valve controller
is designed to drive the valve body synchronously with the timings of zero-crossing
signals generated in an alternating current driving the fuel pump.
19. A combustion apparatus comprising:
a spraying means for spraying a fuel,
a fuel channel for flowing the fuel therethrough,
a fuel pump disposed in the fuel channel so as to compress the fuel flowing towards
the spraying means,
an intermittently operating valve disposed in the fuel channel so that the valve
is closed and opened periodically at regular and variable intervals by a duty-ratio
control, and
a temperature sensing means also disposed in the fuel channel in order to detect
the temperature of fuel flowing through the fuel channel,
wherein the intermittently operating valve is driven at a frequency that is adjusted
based on the temperature detected by the sensing means during combustion.
20. The combustion apparatus as defined in claim 19, wherein the frequency of
electric current for driving the intermittently operating valve is lowered if and
when the temperature detected by the sensing means is above a reference temperature.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustion apparatus for burning a liquid fuel.
2. Description of Related Art
Some combustion apparatuses known in the art are of the type as disclosed in
Patent Laying-Open Gazette No. 10-227453. A fuel spraying nozzle incorporated in
this apparatus operates to blow a fuel mist to be burnt continuously. This nozzle
is of the so-called return type that has an internal return path such that a portion
of the fuel supplied from a fuel tank will flow back toward the tank through the
internal return path and a return channel provided out of the nozzle.
FIG. 18 is a flow diagram showing the flow of fuel in the related art combustion
apparatus that includes the return type nozzle. A fuel spraying nozzle
205
built in this apparatus
201 has a spray mouth for jetting a fuel mist. A
fuel channel (or "a fuel canal")
209 connected to the nozzle
205
is composed of a feed channel (or "a feed canal")
210 reaching the spray
mouth and a return channel (or "a return canal")
211 leading back therefrom
to an upstream region of said channel. The feed channel
210 starting from
a fuel tank
214 so as to terminate at an inlet of the spraying nozzle
205
does include electromagnetic valves
212 and
213 and an electromagnetic
pump
215 that are arranged in series along the feed channel. On the other
hand, the return channel
211 connected to a returning side of the nozzle
205 does include a check valve
216 and a proportional control valve
217, that are likewise arranged in series. A downstream end of the return
channel
211 merges into the feed channel
210, at a junction intervening
between the electromagnetic valve
212 and the electromagnetic pump
215.
The proportional control valve
217 disposed in the return channel
211
is the so-called "ball type" valve that cannot absolutely close this channel
211.
Therefore, the one electromagnetic valve
212 is interposed between the junction
and the fuel tank
214 so as to avoid any excessive or undesired flow of
fuel from or towards this tank.
FIG. 19 shows the structure of proportional control valve
217 employed
in the related art combustion apparatus
201. This valve has an internal
fuel passage
221 formed in a casing
220 and extending between a fuel
inlet end
222 and a fuel outlet end
223, with the inlet end
222
leading to the check valve
216. A valve seat
225 is formed at an
intermediate point in the internal passage
221, and a spherical valve body
226 rests on this seat
225. A plunger
227 in contact with
the valve body
226 is surrounded by an electromagnetic coil
228.
With this coil being turned on with an electric current, it will make a stroke
along the axis of casing so as to move the valve body
226 up and down.
As the plunger
227 displaces the valve body
226, the cross-sectional
area of internal passage
221 will vary to change the flow rate of fuel advancing
from the inlet end
222 to outlet end
223. A current regulator not
shown but varying the intensity of electric power applied to the proportional control
valve
217 will serve to control the fuel flow rate through the return channel.
The fuel stream effluent from the tank
214 will continuously be compressed
in the electromagnetic pump
215, before entering the spraying nozzle
205.
The thus compressed fuel stream of a high pressure will reach the spray mouth
that is located at a distal end of the spraying nozzle
205, so that a noticeable
portion of such a fuel stream is blown outwards to form a mist. The remainder of
said fuel stream will flow back from this nozzle
205, through the check
valve
216 and into the inlet end
222 of proportional control valve
217. The remainder having entered this valve
217 through its inlet
end
222 is delivered to an upstream region of the feed channel, at a flow
rate determined by the intensity of current being applied to said coil
228.
Gradual change or certain fluctuation in the temperature of the proportional
control valve
217 has been observed in the related art combustion apparatus
201 during its operation. Such a change or fluctuation as being caused by
the change in ambient temperature and/or the like will in turn change the temperature
of coil
228 installed in the casing
220. Electric resistance of the
coil
228 will vary in response to the change in its temperature, thereby
rendering unstable the current intensity applied to the coil
228. Consequently,
the flow rate at which the remainder of fuel stream flows back through the return
channel will become unreliable. It has been somewhat difficult for the related
art apparatus
201 to precisely regulate the spraying rate of fuel, failing
to stabilize the condition of combustion state.
Such an unstable combustion in the related art apparatus does mean that the
amount of a fuel sprayed out of said nozzle would not be burnt completely. Incomplete
combustion will result in the discharge of a non-burnt fraction, bringing about
a poorer efficiency of energy. In addition, an unnegligible amount of toxic gasses
such as carbon monoxide is likely to be discharged to the outside, and an undesirable
accumulation of soot will take place inside the apparatus. Thus, the problem of
environmental pollution has been inherent in the related art combustion apparatuses,
not only rendering them likely to become out of order.
SUMMARY OF THE INVENTION
An object of the present invention made in view of the problems and drawbacks
mentioned above is therefore to provide an advanced combustion apparatus that is
simplified in structure, but is nevertheless possible to accurately regulate the
sprayed rate of a fuel to ensure complete combustion.
In order to achieve this object, a combustion apparatus provided herein has to
comprise, as defined in the accompanying claim 1, a spraying means for spraying
a fuel to be burnt, a fuel channel (otherwise known as "a fuel canal") for flowing
the fuel therethrough, and a fuel pump disposed in the fuel channel so as to compress
the fuel flowing towards the spraying means. The combustion apparatus has to comprise
further an intermittently operating valve disposed also in the fuel channel so
that a valve body of the valve will be driven to close and open the channel intermittently
or periodically, and also a valve controller to control the timing at which the
valve body is driven to close and open the channel.
A valve body of the intermittently operating valve is to be driven to intermittently
or periodically close or open the channel, for the purpose of changing or varying
a flow rate of the fuel. Instead of operating the proportional control valve to
directly change the degree itself to which it is opened, the present apparatus
can now be controlled to regulate the frequency at which it must repeat to open.
Such a mode of adjusting the spraying rate of fuel will not be adversely affected
by any change in ambient temperature or the like, thus avoiding any fluctuation
or variation in the spraying rate that would otherwise make it difficult to ensure
stable combustion.
In the present apparatus, the timing at which the intermittently operating valve
is repeatedly closed and opened will be regulated to control the flow rate of the
fuel flowing through a fuel return channel. Any disturbance such as a variation
in the pressure of the fuel being fed to the nozzle, will be canceled or compensated.
This action is effected herein by adjusting the timing of closing and opening this
valve, thereby further stabilizing the combustion process.
Stable combustion now afforded herein will minimize the amount of toxic gases
such as carbon monoxide and the amount of soot likely to be produced during a combustion
process. The apparatus is favorable from a viewpoint of protecting environment
from pollution and also protecting the apparatus itself from any damage.
As defined in the accompanying claim 2 dependent on claim 1, the
valve controller may be designed to perform a duty ratio control or PWM control
for the closing and opening of the valve body.
In this case, the flow rate of the fuel flowing through the return channel will
be controlled based on the ratio to a unit time of an overall period in which the
valve body is repeatedly open. Ambient temperature around or in the intermittently
operating valve will not affect the accuracy of control, thus ensuring stable combustion
of sprayed fuel of a volume corresponding to any required or desired amount of
heat to be generated.
An amount of heat to be generated per unit time is proportional to an amount
of
fuel to be burnt per unit time, which in turn is substantially equal to an amount
of fuel to be sprayed per unit time.
As defined in the accompanying claim 3 dependent on claim 1, the
valve controller may be designed to control the valve body to open and close the
channel synchronously with an alternating current driving the fuel pump.
As defined in the accompanying claim 4 dependent on claim 1, the
valve controller may be designed to control the valve body to open and close the
channel synchronously with the timings of zero-crossing signals generated in an
alternating current driving the fuel pump.
As defined in the accompanying claim 5 dependent on claim 1, the
valve controller may be designed to control the valve body to open the channel
on the basis of detection of every zero-crossing signal that is produced in an
alternating current driving the fuel pump.
In the modes defined in the accompanying claims 3 to 5, there is
a possibility that the fuel feeding pressure appearing within the feed channel
and towards the spraying means may pulsate corresponding to the frequency of said
alternating current (power source). However, the intermittently operating valve
in the return channel will be opened and closed synchronously with an alternating
current power source driving the fuel pump, so as to cancel such pulsation of the
fuel feeding pressure. Because almost no fluctuation is thus observed in this pressure,
stable combustion will be ensured in the apparatus of the present invention.
As a result, the fuel will be sprayed in a constant pattern regardless of the
required amount of heat or the flow rate at which the fuel is sprayed and burnt.
The mixture of fuel and air will continue to be uniform and constant, also stabilizing
combustion in this apparatus.
Also, a flame of the fuel thus burnt will not pulsate, thereby diminishing
combustion noise.
As defined in the accompanying claim 6 dependent on claim 1, pressure
relief may be executed either after or before combustion process, by keeping open
the intermittently operating valve for a given duration.
A portion of the fuel that is being forced into the spraying means by the pump
in the feed channel will be left unburnt to reflux into the return channel at a
considerably high pressure.
The intermittently operating valve will remain closed after combustion of the
fuel has ceased, so that a certain zone in the return channel becomes a tightly
closed chamber. This chamber would be of a high pressure due to the compressed
fuel, thus loading said valve with an extreme pressure that is likely to impair
durability thereof In addition, a rise in ambient temperature and a consequent
rise in the pressure of stagnant fuel would also cause deterioration of the valve.
Such a consequent irregular rise of the internal pressure might happen, even
if the internal pressure of return channel is not so high immediately after combustion
has ceased in the apparatus. At an initial stage of resuming the combustion of
fuel, the internal pressure thus having irregularly risen will cause a variation
in the spraying pressure and disable smooth and stable combustion.
The pressure relief conducted after or before every combustion process, as noted
above, will make the internal pressure of return channel almost equal to atomospheric
pressure so as to avoid the problem just mentioned above.
If conducted immediately after the combustion process, the pressure relief for
relieving such an extreme pressure will be more effective to protect the intermittently
operating valve from deterioration.
As defined in the accompanying claim 7 dependent on claim 1, a pre-combustion
pressure relief may be executed before combustion process, with a post-combustion
pressure relief being executed after the combustion process. In the pre-combustion
pressure relief, the intermittently operating valve will be kept open for a shorter
time, with this valve being kept open for a longer time in the post-combustion
pressure relief.
Any initial variation of the spraying pressure is thus avoided when resuming
the combustion process. Further, any abnormal rise in pressure of the return channel,
which might result in deterioration of the intermittently operating valve, is avoided.
The post-combustion pressure relief is effective to reduce the internal pressure
of feed and return channels to such a noticeable degree that the pre-combustion
pressure relief can be completed within a shorter time. The internal pressure of
both the feed and return channels will be relieved surely to stabilize combustion.
A regular operation of the apparatus to burn the fuel can thus be started earlier
after such a shortened period of the pre-combustion pressure relief.
The present inventors seeking for stable combustion in the apparatus have found
as a result of their experiments that a certain gradual decrease in the internal
pressure of a fuel compressing means such as a pump was unavoidable. A significant
variation of said pressure was observed when resuming the next combustion processes,
thus resulting in an unstable spraying rate and incomplete combustion of the fuel.
The resolution of this problem will be given herein as defined in the accompanying
claim 8 dependent on claim 1. In this mode of invention, lapse of
time may be measured from a preceding termination of combustion process until a
succeeding resumption thereof. An ignition controller employed herein will modify
the spraying rate of fuel at the beginning of a resumed combustion process, properly
on the basis of such a measured time lapse.
The ignition controller may be designed to previously estimate and suppose, just
before re-ignition, the spraying pressure that will appear when resuming combustion
process. The spraying pressure as well as the spatial configuration of a sprayed
fuel mist are optimally controlled in this way to make smooth the resumed combustion
of said mist.
Re-ignition will thus ensure complete combustion, scarcely producing
soot or tar, under any conditions of operation of this apparatus.
As defined in the accompanying claim 9 dependent on claim 1, lapse
of time may likewise be measured from a preceding termination of combustion process
until a succeeding resumption thereof. However, the spraying rate of fuel when
re-igniting it will be reduced if the measured time lapse is equal to or longer
than a given reference time, than other spraying rates intended for any other time
lapse shorter than this reference time.
If the time lapse to be measured in comparatively short, then the fuel feeding
compressing means will maintain well its high internal pressure, allowing the fuel
to be sprayed smoothly even at a relatively high rate. If in contrast the time
lapse is much longer, then said internal pressure will have leaked outwards and/or
possibly have decreased due to contraction in the apparent volume of stagnant fuel
having cooled down. The reduced spraying rate to be adopted in the latter case
as noted above will provide a proper fuel mist contributing to an optimal re-ignition.
Also in the latter case, such a reduced amount per unit time of the sprayed
fuel will be useful to diminish the quantity of soot and/or tar, even if not smoothly
ignited under any operating conditions of the apparatus.
As defined in the accompanying claim 10 dependent on claim 1, the
apparatus may further comprise an air-blowing means for positively supplying air
to be consumed in combustion of the fuel, as well as an ignition controller employed
herein that will modify the spraying rate of fuel at the beginning of a resumed
combustion process, properly on the basis of such a measured time lapse. In this
specification, an air-blowing means includes a blower, a fan and a compressor.
In this mode, the ratio of an amount of fuel being ignited and an amount of the
air being blended therewith will be optimized for the purpose of improving smoothness
of ignition and also diminishing production of soot and/or tar.
As already discussed above, the time lapse from the previous termination of combustion
to the subsequent resumption thereof is likely to be accompanied by change in volume
of the fuel during this lapse of time. These changes will render inconstant the
spraying rate or pressure and the state of combustion. Therefore, as defined in
the accompanying claim 11 dependent on claim 1, the apparatus may
further comprise an ignition controller. The spraying rate of fuel when re-igniting
it will be reduced in this case, if a measured fuel pressure is lower than a given
reference value, than other spraying rates intended for any fuel pressures equal
to or higher than this reference value.
The fuel will form in this case a well-stabilized mist to be completely burnt,
irrespective of the spraying pressure, high or low.
From a further aspect of the invention as defined in the accompanying claim
12, the combustion apparatus comprises a spraying means for spraying a fuel
to be burnt, a fuel channel for flowing the fuel therethrough, and a fuel pump
disposed in the fuel channel so as to compress the fuel flowing towards the spraying
means. The apparatus further comprises an intermittently operating valve disposed
in the fuel channel so that its valve body is driven to close and open the channel
intermittently or periodically at regular and variable intervals by the duty-ratio
control. Frequency at which the duty-ratio control is repeated may be adjusted
responsive to the required amount of heat to be generated. The duty-ratio control
relates to the whole one-cycle period in which the valve repeats to be opened and
closed, and also relates to an overall opened time in which the valve stands open
(but not closed) several or many times during the whole period.
In this case, the number of times to open the intermittently operating valve
can
be varied within a unit time and in response to the varying required amount of
heat or amount of fuel to be burnt. Even if such a frequency of duty-ratio control
actions is altered, it will be possible to maintain the overall amount of fuel
sprayed and burnt and the thus generated heat within the unit time not changed
to any significant extent. In other words, the number of times to open the intermittently
operating valve can be increased or decreased. If the said number of times is decreased,
the valve will make a reduced noise when it repeats to open or be closed.
The manner in which the intermittently operating valve operates to control the
flow rate of fuel that is flowing through the fuel channel and being sprayed out
from the spraying means, is highly precise. In other words, only an accurate portion
of the fuel corresponding to the required amount of heat will actually be sprayed
and then burnt completely and efficiently.
The present combustion apparatus will operate in a preferable manner under certain
conditions in which the duty-ratio is comparatively small. If in this case the
one cycle time that is a unit time in which the valve operates one time to open
and be closed thereafter is made considerably short, then a "theoretical open time"
estimated and necessary for valve body to be at its full open position, will become
extremely short.
The "valve-moving time" which the valve body takes in order to move to such a
full open position will not be negligible relative to the "theoretical open time",
unless the latter time is sufficiently long. In other words, if the "theoretical
open time" is made so short, then discrepancy between it and an "actual open time"
in which the valve body stands full open will become increase to an unallowable
extent. In such an event, not only the flow rate of fuel flowing through the intermittently
operating valve, but also the other flow rate at which the fuel is being sprayed
out, will become almost out of control.
According to the present invention made in view of such a possible inconvenience,
a preferably long one cycle time in which the valve operates one time to open and
be closed thereafter can be used, even if a considerably small duty-ratio is selected
corresponding to the required amount of heat to be generated. The valve-moving
time will thus be made negligible relative to the theoretical open time, thereby
minimizing non-preciseness or error in the spraying rate.
Stable and complete combustion thus ensured will diminish by-production of
toxic gasses such as carbon monoxide in favor of protection of environment, and
also will reduce the amount of soot produced and accumulated to injure the apparatus.
As defined in the accompanying claim 13 dependent on claim 12, the
duty-ratio control involves a plurality of hypothetical regions that have different
frequencies of the duty-ratio control in relation to the required amount of heat
to be generated per unit time.
This mode will also be useful to spray the fuel at a proper rate meeting the
required amount of heat to be generated in a unit time, avoiding any incomplete
combustion and reducing the noise that the intermittently operating valve will make.
As also defined in the accompanying claim 14 dependent on claim 12,
the apparatus may further comprise a valve controller for controlling the intermittently
operating valve with action relying on a plurality of electronics tables each being
an array of valve-operating data, such that the frequencies of the duty-ratio control
differ from each other between the tables, and one of them will be selected to
match a required amount of heat to be generated.
Thus, the most preferable frequency can be preset to control the intermittently
operating valve, in order to generate an exact amount of heat required.
A series of tests was carried out by the present inventors to compare the levels
of noise made by the apparatus during its operation under varied conditions. In
a case wherein the flow rates of fuel being burnt are comparatively higher, the
noise of intermittently operating valve almost melted into combustion noise. If
however said rates are considerably lower, then said noise of the valve was somewhat
offensive to the ear.
Therefore, as defined in the accompanying claim 15 dependent on
claim 12, the one cycle time in the duty-ratio control may be prolonged
for comparatively lower amount of heat required to be generated per unit time,
corresponding to comparatively lower flow rates of the fuel being sprayed and burnt.
The number of times for the intermittently operating valve to open and then be
closed will thus be reduced to diminish the overall level of noise, not causing
any change at all in a current fuel flow rate.
From a still further aspect of the invention as defined in the accompanying
claim 16, the combustion apparatus comprises a spraying means for spraying
a fuel, a fuel channel for flowing the fuel therethrough, and a fuel pump disposed
in the fuel channel so as to compress the fuel flowing towards the spraying means.
The apparatus further comprises an intermittently operating valve disposed in the
fuel channel so that a valve body of this valve will close and open the channel
periodically at regular and variable intervals by the duty-ratio control. The valve
body will fully close the channel when it is at a first position, whereas it will
fully open the channel when it is at a second position. Frequency at which the
duty-ratio control is repeated may be adjusted responsive to the current flow rate
of the fuel being burnt, in such a manner that if the ratio of "a first time length
for the valve body to move once from the first position to the second position
and then back from the second position to the first position" divided by "a second
time length in which said valve body remains at the second position during one
cycle of said duty-ratio control" does exceed a threshold, then one cycle time
in the duty-ratio control will be prolonged.
The percentage of the first time in the second time, that is the ratio of a "valve-moving
time" which the valve body takes in order to move to its full open position and
then return to its closed position to an "actual open time" in which the valve
body remains open, may possibly exceed threshold. In such an event, a difference
between a "theoretical open time" in which said valve body must remain open and
the actual open time will increase to an undesirable extent, likely to cause impermissible
error in the actually sprayed amount per unit time of the fuel.
However, in the control mode offered in the accompanying claim 16,
the valve-moving time is rendered negligible relative to the theoretical open time,
thus stabilizing combustion of fuel.
As defined in the accompanying claim 17 dependent on claim 16, the
duty-ratio control may be conducted in such a manner that in a case wherein the
duty ratio for causing the intermittently operating valve to open does exceed a
reference value, one cycle time in the duty-ratio control will be prolonged.
In the case just mentioned above, the theoretical open time will tend to be extremely
short so that the actual open time would become much shorter than the theoretical
open time. However, the apparatus employed in the claim 17 will minimize
the difference between the actual and theoretical open times so as to almost eliminate
the error in the spraying rate and the amount of generated heat, whether the duty
ratio is undesirably large or sufficiently small.
The fuel pump as recited in the accompanying claim 16 may be driven with
an alternating current from a power source driving the fuel pump. In this case,
pulsation of the current may possibly cause the unstable spraying of fuel.
Therefore, as defined in the accompanying claim 18, the valve controller
may be designed to open and close the valve body synchronously with the timings
of zero-crossing signals generated in an alternating current driving the fuel pump.
Thus, a stable spray of fuel will be ensured even if the pump is driven with
such an alternating current.
The present inventors have conducted test operations of apparatuses that involves
intermittently operating valves as the means for regulation of the spraying flow
rate of fuel, so as to find that a stable combustion would be realized if the valve
were driven with a current of a frequency adjusted taking into account the change
in fuel temperature. In detail, in a conventional combustion apparatus employing
a return type nozzle as the spraying means and if the temperature of fuel flowing
circulatingly through the fuel channel were considerably high, the fuel having
become less viscous would form eddies in a region of the nozzle adjacent to its
spray mouth, thereby increasing flow resistance in this region against the fuel
flow. Consequently, an excessive portion of the fuel was observed to flow back
into the return section of the fuel circuit, thereby tending to show a shortage
in the amount of fuel sprayed in a unit time.
From another aspect of the invention as defined in the accompanying claim 19,
the combustion apparatus comprises a spraying means for spraying a fuel, a fuel
channel for flowing the fuel therethrough, and a fuel pump disposed in the fuel
channel so as to compress the fuel flowing towards the spraying means. The apparatus
further comprises an intermittently operating valve disposed in the fuel channel
so that the valve will be closed and opened periodically at regular and variable
intervals by a duty-ratio control, and a temperature sensing means also disposed
in the fuel channel in order to detect the temperature of fuel. The intermittently
operating valve is to be driven at a frequency that is adjusted based on the temperature
detected by the sensing means.
Even if any change in fuel temperature tends to undesirably vary the flow resistance
and the spraying rate, such a tendency will now be compensated not to affect the
spraying rate, by altering the frequency of current to adjust the feed rate of
fuel flowing towards the nozzle.
Under such a condition that higher temperatures of the fuel are likely to decrease
the viscosity and increase the flow resistance against the fuel within the spraying
means, it may be preferable to adopt a lower level of the duty ratio for the intermittently
operating valve.
However, lower duty ratios would increase the percentage "valve-moving time"
in the "actual open time" for the valve body to remain open, as discussed above.
In such an event, a difference between "theoretical open time" in which said valve
body must remain open and the actual open time will increase to undesirably cause
impermissible error in the actually sprayed amount of fuel per unit time.
Therefore, as defined in the accompanying claim 20 dependent on
claim 19, the frequency of electric current for driving the intermittently
operating valve will be lowered if and when the temperature detected by the sensing
means is above a reference temperature.
Flow rate of the fuel being sprayed and burnt will thus be maintained at a desired
level so as to maintain amount of heat generated per unit time, without any fear
of suffering from any disturbance that would otherwise be caused by the varying
fuel temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic front elevation of a combustion apparatus provided in
an embodiment of the present invention;
FIG. 2 is a diagram showing a fuel pipe line that is constructed in the apparatus
shown in FIG. 1;
FIG. 3 is a cross section of an injector valve incorporated in the apparatus
of FIG. 1;
FIG. 4 is an array of graphs (a) to (e), in which the graph (a) represents the
periodic variation in an electric current that is applied from a power source to
a pump of a combustion apparatus provided in an embodiment of the present invention,
the graph (b) represents a sequence of zero-crossing signals that will be generated
based on the periodic variation shown in the graph (a), the graph (c) represents
the periodic variation in the electric current shown in the graph (a) but rectified,
and the graph (d) represents a sequence of periodically varying discharging pressure
of the pump to which the electric current shown in the graph (c) is applied, with
the graph (e) representing a train of pulse signal applied to an injector valve;
FIG. 5 is a graph showing the relationship found between the "required amount
of heat to be generated per unit time" and the "overall time length in which the
injector valve repeatedly stands open";
FIGS. 6 and 7 are flow charts of an operational mode of the combustion apparatus
shown in FIG. 1 and driven by the data processing shown in these figures;
FIG. 8 is a pair of graphs (a) and (b), in which the graph (a) represents a
sequence of data signals obtained by a temperature sensor installed in the apparatus
of FIG. 1, with the graph (b) representing a sequence of the pulse signals output
to the injector valve;
FIG. 9 is another array of graphs (a) to (e), that respectively correspond to
those (a) to (e) included in FIG. 4;
FIGS. 10 and 11 are further flow charts of a modified operational mode of the
combustion apparatus shown in FIG. 1 and driven by the data processing shown
in these figures;
FIG. 12 is a graph showing the relationship designed between the "the "required
amount of heat to be generated per unit time" and the "ratio of overall open time
of the injector valve to a unit time";
FIG. 13 is still another array of graphs (a) to (f), with (a) to (e) corresponding
respectively to those (a) to (e) included in FIG. 4;
FIG. 14 is still another flow chart of a further modified operational mode of
the combustion apparatus shown in FIG. 1 and driven by the data processing
shown in this figure;
FIG. 15 is a graph showing the relationship designed between the flow rate of
fuel being sprayed and the ratio of overall open time of the injector valve to
a unit time;
FIG. 16 is a further graph showing the relationship found between the time lapse
of the injector valve held in its ON state and the extent to which this valve is opened;
FIG. 17 is a still further graph showing the relationship found between the
time lapse of the injector valve held in its ON state and the flow rate of the
fuel being sprayed;
FIG. 18 is a diagram showing a fuel pipe line in the related art combustion
apparatus; and
FIG. 19 is a cross section of a proportional control valve employed in the related
art apparatus.
THE PREFERRED EMBODIMENTS
In FIG. 1, a combustion apparatus of a first embodiment is generally denoted
at
the reference numeral
2. This apparatus
2 comprises a nozzle block
8 having an end opened in a hollow shell
7, and a combustion chamber
10 is attached to the end of nozzle block
8. A fan or blower
11
mounted on the shell
7 will operate to feed the ambient air into the combustion
chamber
10. A fuel spraying nozzle (as the spraying means)
12 is
installed in the nozzle block
8 in order to spray a fuel towards and into
the combustion chamber
10.
The spraying nozzle
12 has a spray mouth (not shown) for jetting the fuel.
An internal feed path (not shown) and an internal return path (not shown) leading
to or starting back from the spray mouth are formed in or for the nozzle
12.
Thus, the fuel spraying nozzle
12 will operate to jet a portion of the fuel
that is being fed from the outside through the internal feed path. The remainder
of said fuel will be left unsprayed to subsequently flow back through the internal
return path.
As seen in FIG. 2, a fuel pipe line
13 connects the fuel spraying nozzle
12 to a fuel tank
15 holding therein a mass of the fuel. The pipe
line
13 consists mainly of a fuel feed canal (i.e., a feed channel)
16
and a return canal (i.e., a return channel)
17, such that the former canal
communicates with a fuel feed path formed in the nozzle
12 and the latter
canal
17 communicates with a return path also formed in the spraying nozzle
12. As shown in FIG. 1, pipes
5 forming those feed and return canals
16 and
17 extend outwardly of the shell
7 so as to lead to
an injector valve
25 and an electromagnetic pump
18, that are detailed
below. Those pipes
5 also connected to the nozzle
12 are each bent
several times at substantially right angles between the nozzle and the valve
25
or pump
18. Bends formed thus in said pipes will make same more tenacious
on one hand, and will attenuate any vibration being transmitted from said pump
18 or injector valve
25 on the other hand. Thus, such a vibration
will scarcely reach the spraying nozzle
12, thereby protecting it from damage.
The feed canal
16 combining the nozzle
12 with the fuel tank
15
in series does serve to supply the nozzle with the fuel stored in the tank. Disposed
in this canal
16 are the electromagnetic pump
18, an electromagnetic
valve
20 and a check valve (as a feed channel checking means)
21.
The check valve
21 normally stands closed, and an activation pressure (that
is a minimum actuating pressure) for opening this valve is higher than a maximum
hydrostatic head of the fuel in tank
15 standing in fluid communication
with the feed canal
16. In other words, the hydrostatic pressure caused
by the fuel stored in the tank
15 will never exceed the minimum pressure
for activating the checking valve
21 to open. For example, in the combustion
apparatus
2 of the present embodiment, the fuel tank
15 is disposed
higher than the valve
21 by 0.5 meter. The minimum actuating pressure is
0.2 Kgf/cm
2 (viz., 2.0×10
4 Pa) for this valve
21,
that is much higher than the hydrostatic head 0.04 Kgf/cm
2 (viz., 0.39×10
4
Pa) for the fuel in tank
15. Thus, the fuel will not flow towards
the spraying nozzle
12 unless the pump
18 compresses it. Although
the minimum actuating pressure for said valve
21 is selected herein to be
high by about 5 times of said hydrostatic head of said fuel, the ratio of the former
to the latter may fall within a range from 3 to 5.
The fuel tank
15 may alternatively be positioned at any height, from 1.5
m above to 2.0 m below the valve
21, thus making the hydrostatic head not
higher than 0.12 Kgf/cm
2 (viz., 1.2×10
4 Pa).
As noted above, the normally closed check valve
21 shall not naturally
open merely due to hydrostatic head of the fuel in tank
15. There may be
a possibility that the electromagnetic valve
20 would unintentionally open,
though fuel feed to the nozzle
12 had to be interrupted for the combustion
apparatus
2 then standing inoperative. Even in such an accident, the check
valve
21 will surely stop the fuel not to leak out towards a downstream
canal region. If and when the fuel from the tank
15 has to be sprayed, it
will be compressed by the pump
18 and enabled to pass through the valve
21 and flow to the nozzle
12.
A portion of the fuel fed to the nozzle
12 will be left there unburnt,
and
such a remainder will flow back towards the tank
15 through the return canal
17. A downstream end (near the tank
15) of the return canal
17
merges into the feed canal
16 at its intermediate point located on the upstream
side of electromagnetic pump
18 (and facing the tank
15). Disposed
at another intermediate point of the return canal
17 is a temperature sensor
(viz., temperature sensing means)
22 for detecting the temperature of fuel
flowing back through this canal. A further check valve (as the return channel checking
means)
23 is disposed downstreamly of the sensor
22 so that the fuel
can flow towards the tank
15 but is inhibited from flowing in a reversed
direction away from this tank. Disposed on the downstream side of the check valve
23 is the injector valve (viz., intermittently operating valve)
25
that will be opened and closed periodically at given time intervals. An accumulator
26 intervening between the injector valve
25 and the further check
valve
23 will serve to buffer fluctuation in pressure of the fuel flowing
through the return canal
17.
The injector valve
25 will operate at an extreme high frequency to be
opened and then instantly closed. As shown in FIG. 3, this valve
25 comprises
a casing
30, an actuator
31 held therein, an electromagnetic coil
32 for driving the actuator
31, and a valve body
33 movable
in unison with the actuator
31. Formed at opposite ends of the casing
30
are a fuel inlet
35 and a fuel outlet
36, with an internal fuel passage
37 extending between them
35 and
36 and through the casing
30.
The casing
30 has a terminal
38 leading to the electromagnetic
coil
32 so that power supply through this terminal
38 will activate
said coil
32. Consequently, the actuator
31 will be energized within
the casing
30, thereby simultaneously driving the valve body
33 to
open the passage
37 that is a part of the return canal
17. The valve
body
33 of the present embodiment thus opens the passage
37 instantly
in response to the coil
32 energized with an electric current, and said
body
33 will close the passage instantly upon inactivation of said coil
32. The injector valve
25 in such a closed state in response to inactivated
coil
32 will have its valve body
33 very tightly shutting the fuel
passage
37 to absolutely close the return canal
17.
The terminal
38 is connected to a controller
40 that is incorporated
to regulate the spraying rate of fuel jetting from the nozzle
12 and also
to regulate the operation of fan or blower
11. The controller
40
is designed to periodically or intermittently activate the coil
32 to displace
the valve body
33 to open and to close the passage, thus controlling the
flow rate of fuel being sprayed from the nozzle
12.
The controller
40 will apply to the electromagnetic coil
32 a pulse
current that is generated synchronously with pulse wave of the power source for
electromagnetic pump
