US3368401A - Measurement of heat content of combustible fuel mixtures - Google Patents

Description

United States Patent ABSTRACT OF THE DISCLOSURE A bomb calorimeter for measuring heat of combustion includes electrical means for measuring heat required to ignite the fuel and means for subtracting the heat produced by energizing the firing wire from the total measured heat.

This invention is related generally to the measurement of the heat liberated during combustion of a combustible fiuid, and more particularly to a bomb calorimeter and apparatus associated therewith for making extremely accurate heat measurements by measuring the heat added to to the system by ignition of the firing means thereof.

Bomb calorimeters have been used for many years for the purpose of making accurate heat measurements. In j the past few years various fuels have been developed for applications in which it is important to know the energy content of the particular fuels to an extremely high degree of accuracy. It is desirable to use bomb calorimeters for such applications because of the convenience and the ease of operation thereof.

It has now been discovered that a major cause of error in bomb calorimeters is the variable amount of heat liberated by the firing means thereof during a heat measurement. The most desirable type of bomb calorimeter for use in highly accurate heat measurements is a type mak ing use of a low resistance firing wire that fuses during the ignition of the explosive fluid mixture which is undergoing an energy content determination.

In accordance with one aspect of the invention, there is connected between the firing means of a bomb calorimeter and an electrical terminal means to which connection to an electrical source may be made, a circuit means for measuring the electrical power consumed by the firing means when the firing means is electrically energized. Preferably, the circuit means includes a multiplying circuit means for connecting the firing means to the terminal means adapted to produce an output voltage proportional to the power consumed by the firing means, along with integrating means for producing an output indication of the time integral of the output power of the electrical circuit means. In addition, means is provided electrically connected to the firing means for detecting the fusing of the firing means and for disconnecting the integrating means from the electrical circuit means upon said detection, which it has been found will produce an exceedingly accurate power measurement.

Objects and features of the invention which are not apparent from the above discussion will become evident upon consideration of the following detailed description of the invention when taken in connection mm the accompanying drawing, wherein the single figure illustrates a preferred embodiment of the invention in the form of an electrical schematic diagram, partially in block form.

With reference now to the figure, there is shown a bomb calorimeter 1 in block form, which bomb calorimeter is of the type having a low resistance wire firing device 3 which, when electrically energized, will produce heat sufliciently high to ignite a fluid combustible mixture in the bomb calorimeter. The firing wire 3 may be an element of nichrome or other alloys of about 5 3,368,401 Patented Feb. 13, 1968 ohms resistance. The wire may be 1 to 4 inches in length.

There is also provided a plurality of terminals 73, 75, and 79 for connection to a three-wire alternating current source, which may be a 110 volt A.C. single phase source. Terminal is grounded, and terminals 73 and 79 are connected to the primary 57 of power transformer 59 through contact 67 of push-button switch 69. Power from the alternating current souce is supplied to firing device 3 from the secondary winding 55 of transformer 59 through the electrical circuit described below.

Reference numeral 5 designates a multiplying device adapted to produce an output voltage at terminals 15, 17 proportional to the product of the current flowing therethrough (applied to terminals 7, 9) and the voltage applied thereto (applied to terminals 11, 13). The function of multiplying device 5 is to, in effect, measure the power consumed by firing means 3 responsive to a voltage applied thereto. Thus, firing means 3 is connected in series circuit relationship with terminals 7, 9, current limiting resistor 53, and the secondary winding 55 of power transformer 59. The voltage input terminals 11, 13 of multiplying device 5 are connected respectively to one side of firing device 3 and to terminal 9 through resistor 19. The multiplying device 5 may be of the type manufactured by Bell, Inc. of Columbus, Ohio, Model No. HM3011.

The output voltage of multiplying circuit 5 is integrated by an integrating amplifier including an integrating capacitor 63. The input circuit of the integrating amplifier 61 is connected to output terminals 15, 17 of multiplying device 5 through a normally closed contact 43 of relay 45, and a series resistor 21. A resistor 23 is connected in parallel across the lines between the output terminals 15, 17 and the input circuit of amplifier 61. The function of resistors 21, 23 is to establish specified load to multiplier such that this device will meet specified output, linearity, and temperature compensation. The output signal of integrating circuit 61 is measured by a voltmeter 71 which may be a Weston Model 911 DC. voltmeter having a sensitivity of 20,000 ohms per volt.

The function of relay 45 is to remove the output signal of cross-multiplying circuit 5 from the input circuit of integrating amplifier 61 at the instant that firing device 3 fuses. Power for energizing the control winding of relay 45 is derived through power transformer 51 from terminals 73, 79. The secondary winding 47 of transformer 51 is connected to the relay actuating winding 45a between electrodes 41 and 37, the control rectifier will conduct to energize the actuating winding 45a and open contact 43. The actuating signal for actuating the control rectifier 35 is derived from a bridge rectifier which is in electrical circuit relationship with the firing means 3. More specifically, the input terminals of the bridge rectifier are connected between firing means 3 and resistor 53 so that when the firing means 3 fuses, the voltage drop across resistor 53 will substantially disappear, and the voltage applied to input terminals of the bridge rectifier 25 will rise to substantially the voltage across secondary winding 55 of transformer 59. The output terminals of bridge rectifier 25 are coupled between rectifier electrodes 37, 41 through a rheostat or potentiometer 27 having a variable tap 29 connected across the bridge rectifier output terminals, and a series resistor 31 connected between tap 29 and electrode 41. Resistor 33 is connected between electrodes 41 and 37 in the usual manner. Electrode 37 is connected to the negative one of the output terminals of bridge rectifier 25.

Push-button switch 69 is provided with a second contact 65 which is connected across the integrating capacitor 63 of integrating amplifier 61. Contact 65 is normally closed, and contact 67 is normally open so that when the contact 67 is closed to energize the primary winding 57 of transformer 59, and thereby energizing the firing means 3, the short-circuit across capacitor 63 is simultaneously removed.

The operation of the apparatus described above is as follows. The bomb calorimeter is initially charged with a combustible fuel and firing means 3 is checked to see that it has not been previously fused. An appropriate A.C. source is connected to terminals 73, 75, and 79. When push-button 69 is actuated to close contact 67 and open contact 65, the firing means 3 will be energized and the voltage applied to bridge rectifier 25 will be sufficiently low as not to activate control rectifier 35 so that contact 43 will remain closed. The output voltage appearing across terminals 15, '17 will be proportional to the current and voltage applied to resistive firing means 3 until the firing means fuses. At this instant, the voltage applied to bridge rectifier 25 will rise to activate the control rectifier 35 and pick up the relay 45 so that any stray output voltage from multiplying circuit 5 will be removed from the input of integrating circuit 61. Thus, the voltage output of the integrating circuit will be proportional to the energy consumed by the firing means 3 during the interval between the instant at which constant 67 was closed and the instant at which the firing means 3 fused. This output voltage can readily be converted to heat units, such as B.t.u.s from the formula where E is the voltage of meter 71, K is a calibration constant, and B.t.u.s is the measured heat.

This heat quantity will be subtracted from the heat of combustion of the exposive mixture in the horn calorimeter measured by the bomb calorimeter.

The leads between terminals 15, 17 and the input of the integrating circuit 61 should be shielded as much as possible, as illustrated, so that there will be no stray voltages picked up thereby which can be integrated by the integrating circuit during a measurement.

The invention is not necessarily to be restricted to the specific structural details, arrangement of parts, or circuit connections herein set forth, as various modifications thereof may be effected without departing from the spirit and scope of the invention.

What is claimed is:

1. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustible fuel, said calorimeter including a firing means for igniting the combustible fluid in said calorimeter when said firing means s electrically energized;

electrical terminal means for connection to an electrical energy source; and

circuit means connecting said terminal means to said firing means for measuring the electrical power consumed by said firing means when said firing means is electrically energized; said circuit means including multiplying means adapted to produce an output voltage proportional to the power consumed by the firing means, integrating means adapted to produce an output indication of the time integral of said output power, and means for detecting the heat produced by energization of said firing means and for disconnection of said integrating means on detection of said heat.

2. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustible fluid, said calorimeter including a fusible firing means for igniting the combustible fluid in said calorimeter when said firing means is electrically energized;

electrical terminal means for connection to an electrical energy source; and

circuit means selectively connecting said terminal means to said firing means, including means for measuring the total electrical energy consumed by said firing means from the instant that said firing means is electrically energized and until the instant of fusing thereof; said circuit means including multiplying means adapted to produce an output voltage proportional to the power consumed by the firing means, integrating means for producing an output indication of the time integral of the output of said circuit means, and means for detecting the fusing of the firing means and for disconnection of the integrating means on detection of said fusion.

3. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustible fluid, said calorimeter including a fusible firing means for igniting the combustible fluid in said calorimeter when said firing means is electrically energized;

electrical terminal means for connection to an electrical energy source;

electrical circuit means connecting said firing means to said terminal means for producing an output voltage proportional to the power consumed by said firing means;

integrating circuit means for producing an output indication of the time integral of said output power of said electrical circuit means; and

means electrically connected to said firing means for detecting the fusing of said firing means, and for disconnecting said integrating means from said electrical circuit means upon said detection.

4. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustible fluid, said calorimeter including a fusible firing means for igniting the combustible fluid in said calorimeter when said firing means is electrically energized;

electrical terminal means for connection to an electrical energy source;

circuit means selectively connecting said terminal means to said firing means, including means for measuring power consumed by said firing means after said firing means is electrically energized and prior to fusing thereof;

said circuit means including multiplying circuit means for producing an output voltage proportional to the product of voltage applied to said firing means and current consumed by said firing means;

a voltage integrating circuit;

a relay having contact means normally connecting said integrating circuit means to said multiplying circuit means whereby said integrating circuit will integrate the multiplying circuit output voltage, and an actuating winding for opening said contact when energized;

means including electrical valve means having a control electrode, connecting said actuating winding to said electrical terminal means, for energizing said actuating winding responsive to a predetermined control signal applied to said control electrode; and

control circuit means electrically connected to said control electrode and to said firing means, for detecting the fusing of said firing means and thereupon applying said predetermined control signal to said control electrode.

5. The combination of claim 4 wherein said control circuit means includes resistor means connected in series circuit relationship with said firing means, and rectifier means having input terminals connected between said resistor and said firing means, and having an output circuit electrically connected to said control electrode, whereby the output voltage thereof applied to said control electrode will increase when said firing means fuses.

6. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustible fluid, said calorimeter including a fusible firing means for igniting the combustible fluid in said calorimeter when said firing means is electrically energized;

electrical terminal means for connection to an electrical energy source;

circuit means selectively connecting said terminal means to said firing means, including means for measuring power consumed by said firing means after said firing means is electrically energized and prior to fusing thereof;

said circuit means including multiplying circuit means for producing an output voltage proportional to the product of voltage applied to said firing means and current consumed by said firing means;

a voltage integrating circuit including an integrating capacitor;

a relay having contact means normally connecting said integrating circuit to said multiplying circuit means whereby said integrating circuit will integrate the multiplying circuit output voltage, and an actuating Winding for opening said contact means when energized;

means including electrical valve means having a control electrode connecting said actuating winding to said electrical terminal means, for energizing said actuating winding responsive to a predetermined control signal applied to said control electrode;

control circuit means electrically connected to said control electrode and to said firing means, for detecting fusing of said firing means and thereupon applying said predetermined control signal to said control electrode, said control circuit means including resistor means connected in series circuit relationship with said firing means, and rectifier means having input terminals connected between said resistor and said firing means, and having an output circuit electrically connected to said control electrode, whereby the output voltage thereof applied to said control electrode will increase when said firing means fuses; and control switch means having first contact means connected to said integrating capacitor, and second contact means connected between said terminal means and said resistor means, for short-circuiting said capacitor when said firing means is not electrically energized, and for simultaneously removing said short circuit and electrically energizing said firing means.

References Cited UNITED STATES PATENTS 1,163,367 12/1915 Riche 73-191 OTHER REFERENCES Jessup, R. S.: Brecise Measurement of Heat of Combustion With a Bomb Calorimeter. In U.S. National Bureau of Standards Journal of Research Monograph No. 7, page 9.

JAMES J. GILL, Primary Examiner.

E. E. SCOTT, Assistant Examiner.

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