FR2638819A1 - METHOD AND DEVICE FOR PREPARING A COMBUSTIBLE-AIR MIXTURE FOR COMBUSTION - Google Patents

Abstract

For the optimum preparation of an air-fuel mixture intended for combustion, the proportions of combustion air and fuel of said mixture are determined as a function of the electrical conductivity of the combustion zone 4. The conductivity is measured at the using an ionization electrode 14 and a ground electrode cooperating with it, incorporated in an electrical circuit 17 extending in the combustion zone; the measured value is compared with an empirically established reference value, the air coefficient of the mixture being adjusted according to the result of this comparison.

Description

The present invention relates to a method and a

  positive for the preparation of a fuel-air mixture

intended for combustion.

  The invention aims to ensure from the beginning of the

  combustion and despite the changing conditions to which

  it is subject to immediate adjustment

  optimal position of the mixture according to the case.

  The differences in the air coefficient with respect to

  their optimum, which determines the composition of the mixture, may have different causes. This is how the

  fuel composition may vary, or that the temperature

  air varies, or that pressure varies in

  exhaust gas discharge, or - at the beginning of combustion - the burner plate is cold. In each case, such variations of the air coefficient are

  cause of combustion disturbances and may

  cease limiting the scope of the burners.

  Especially if the mixture consists of gas and air and is burned to the more or less extensive area of a burner, it is found that the air coefficient, so the

  ratio between the proportion of gas and that of combustion air

  which guarantees a more or less complete combustion

  Te, therefore optimal, essentially determines the current of flaring ionization, which at 1 '

  using an appropriate device for the measurement of ioni-

  and placed in the combustion zone, can be

measured exactly.

  Starting from the direct ratio between the effective air coefficient of a fuel mixture, on the one hand, and the

  ionisation current, on the other hand, measured by a

  flame control system using an ionization electrode, it can be determined empirically, for a given area o the air coefficient is greater than 1, so superstoechiometric, a set value

  for the characteristic ionization current for a

optimal bustion.

  For a given nominal setting of a burner supplied with a standard test gas, taking into account the arrangement of the electrode as well as the nature of the burner plate and the combustion chamber, it is established. measurable and usable report, interdependence

  between the actual value of the ionization current at

  the flames, on the one hand, and the air coefficient ef-

fective, on the other.

  Because of this interdependence, it can be established

  a given measurable value of the ionization current, la-

  which corresponds to an optimum air coefficient, a con-

sign of air coefficient X.

  If at the time of starting the burner or

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  the actual value of the ionizing current

  sation deviates from the established standard, the cost

  The air pressure can be adjusted accordingly, for example by varying the speed of the fan,

  the quantity of fuel, or with the aid of

  or similar, to return to the instruction.

  For this purpose, according to the invention,

  the combustion air or fuel part of the

  is adjusted according to the electrical conductivity

  that of the combustion zone, that is to say for example in

  function of the given ionization current.

  In concrete, it is the electrical conductivity of the combustion zone which is measured and compared with a

  established empirically, the proportion of combustion air

  tion and fuel of the mixture being adjusted to

  the result of this comparison until the

  sign for the conductivity of the combustion zone is reached. The solution according to the invention provides

  other advantage that the time for heating the

  burner, in case of cold start, can

  be significantly shortened. In addition, we obtain a

  Constant busting even though gas quality or admission

of air undergoes variations.

  Compared to an air ratio regulator equipped with an O2 probe, the solution according to the invention is distinguished by a substantially simpler construction.

  and allows an almost instantaneous measure of the ef-

  of the air coefficient, which is particularly important

  both for any cold start.

  A device suitable for the application of the method

  in accordance with the invention comprises a burner fed with

  an air-fuel mixture, an electrical circuit

  on the combustion zone of this burner with an ionization electrode arranged in this zone as well as

  a ground electrode cooperating with it, and a device

  measuring device of the current, disposed in said circuit e-

  electrical power and which, by an appropriate line, transmits the

  their measurement of the current to a regulator who compares this

  the actual value with a setpoint communicated by a setpoint signal generator to

  given the result of this comparison, the value of the

  of air and fuel composing the mixture.

  It is inevitable that there is interdependence

between these shares.

  The aforementioned regulator can therefore for example be connected by a suitable line to the device controlling a gas valve supplying a mixing chamber, or to a device controlling the operation of a ventilator supplying air to a chamber of mix, or it can

  act on an organ that adjusts the width of the

  destroying the amount of combustion air.

  In the following, the invention is described with the figures of the drawing in support, which represent

  Fig. 1, a diagram showing the interdependence between

  be the varations of the air coefficient in-

  written on the abscissa, and the current of ioni-

following the ordinate,

  Fig. 2, the diagram of a device suitable for

  application of the process according to the invention.

  According to fig. 1, within the range R, that is to say part of the zone marked by B, where the coefficient

  is greater than 1, a given value of this coefficient

  is a given intensity I of the current of io-

  so that, conversely, one can choose,

  Given the measured value of the ionization current, the way in which the air coefficient and the parts of the mixture must be influenced in order to obtain optimum combustion with

an air coefficient Xn.

  Fig. 2 shows in detail a device 1 heated by a burner and whose heat exchanger 2 is heated

  by the flue gases flowing to an evacuation pipe

  cuation 3, from the combustion zone 4 of a burner plate 5 whose beaks are fed in a

  gas-air mixture from a distribution chamber 6.

  This mixture arrives in this distribution chamber 6 by the action of a fan 8 driven by a motor 7, from a mixing chamber 9 fed with gas.

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  by a pipe 10 via a valve 12 com-

  mandated by a member 11, and combustion air through

a slit 13.

  In the combustion zone 4 of the burner 5 are dis-

  the ionization electrode 14 and a foam electrode

  which are part of a 17-way electrical circuit

  by a current source 16, and which extends, in step

  between the two electrodes 14 and 15, through the area

  4 and includes an apparatus 18 for measuring

  re of the intensity of the current, which transmits the value of

  measured by a line 19 to a regulator 20.

  To this regulator 20 is further connected by a line

  21, a reference signal generator 22 which transmits to it

  sets a valid instruction for a given operating state. The regulator 20 comprises a comparator assembly which compares the measured value supplied by the apparatus 1% 8

  ionization current with the set point. Following the

  As a result of this comparison, the regulator 20 can, via lines 23 or 24, transmit signals to both the fan motor controller 7 and the controller.

  11 of the gas valve 12 which determines the proportion of

fuel mixture.

  It goes without saying that there are more numerous other possibilities to act on the air coefficient and to obtain

an optimal setpoint.

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Claims (6)

Claims R e v e n d i c t i o n s   1. Process for the preparation of a fuel mixture   for combustion, characterized in that the proportion of combustion air or fuel in the   mixture is adjusted according to the electrical conductivity   of the combustion zone, for example according to   corresponding ionization current.   2. Method according to claim 1, characterized in that the electrical conductivity of the combustion zone is measured and compared with a value of   set out empirically, and that on the basis of the   As a result of this comparison, the proportion of combustion air and fuel of the mixture is adjusted until the combustion zone conductivity target is reached. 3. Device for the application of the following process   claims 1 and 2, characterized by a burner (5)   supplied with an air-fuel mixture, an electrical circuit   scale (17) extended over the combustion zone (4) of said burner   their (5) and comprising an ionisation electrode (14)   In the zone (4) and a ground electrode (15) and a measuring element (18) for measuring the current, which, via a line (19), transmits the actual value of the current   a controller (20) which compares this value with a value   their setpoint sent by a signal generator of   setpoint (22) to adjust, depending on the result of this-   comparison, the share of combustion and combustion air fuel forming the mixture.   4. Device according to claim 3, characterized   in that the regulator (20) is connected by a line (24) to the control member (11) of a regulating valve   supplying fuel to a mixing chamber (9).   5. Device according to claim 3, characterized   in that the regulator (20) is connected by a line (23) to a fan providing the air supply a mixing chamber (9).   6. Device according to claim 3, characterized   in that the regulator (20) acts by a line   (23) on a member disposed in the intake pipe   air flow of the mixing chamber (9) and which adjusts the width of the slot (13) determining the amount of combustion air.