- Email: [email protected]
A new method for measuring fuel-injection rate
Flow Measurement and Instrumentation 10 (1999) 159–165
A new method for measuring fuel-injection rate ˇˇ Milan Marcic
*
University of Maribor, Smetanova 17, 2000 Maribor, Slovenia Received 29 October 1998; received in revised form 12 November 1998; accepted 10 December 1998
Abstract The paper deals with the basic principles of use and testing of the new method for measuring injected volumes of liquids. The above method was employed in measuring the injected fuel volume in diesel injection systems, where fuel is injected at time intervals of up to 4 ms. It works by measuring the electric charge deposited by liquid droplets impacting a metal electrode. The electric charge is generated mainly in the injection nozzle, where the fuel rubs against the metal parts of injection nozzle, resulting in one portion of free electrons moving from the metal to the fuel. The fuel then transfers this electric charge to the sensor electrode. Rubbing merely serves to bring many points of the surface into good contact. The electric current appears also due to the temperature gradient in the sensor electrode. The temperature gradient in the electrode is a result of the transformation into heat of kinetic energy of fuel droplets hitting the electrode at velocities of 100–300 m s−1. The electric charge is led from the electrode to the charge amplifier, where it is converted into electric current. The test results showed a very reliable operation of the sensor and a linear dependence of the area under the injection rate curve upon the injected fuel volume. The comparison of the injected rates measured with the charge and Bosch measuring method, which is most frequently utilised today, showed a good matching of results in any operating regime. 1999 Elsevier Science Ltd. All rights reserved. Keywords: Injection rate; Charge measuring method; Thermodynamics
1. Introduction The importance of fuel injection system in the operation of diesel engines has been recognised since its early days. The rate at which the fuel is introduced into the combustion chamber determines the performance of the engine. Hence, knowing the characteristics of the fuel injection rate is extremely important in designing the engine. So far, many fuel injection rate measuring methods have been developed among which Zeuch’s [1] and Bosch’s [2] are most frequently used today. The paper shows a new fuel injection rate measuring method, which measures the fuel electric charge. Its major advantages are simplicity and low price.
fuel becomes electrically charged when it rubs against the sensor electrode (Fig. 1) [3] and the other injection system parts. Fuel droplets hit the sensor electrode at a velocity of 100–300 m s−1. Thus, the fuel is electrically charged and this charge is then emitted on contact with the electrode. Due to high velocity, the dispersed fuel droplets have a relatively high kinetic energy, which is transformed into heat; when the droplets hit the electrode, a time varying temperature gradient is obtained, itself being a minor source of electric current.
2. Physical principles of charge measuring method With the charge measuring method, fuel detection is based upon the measuring of electric charge of fuel. The * Tel.: ⫹ 38-662-220-7500; e-mail: [email protected]
fax:
⫹
38-662-220-7990;
0955-5986/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 5 - 5 9 8 6 ( 9 8 ) 0 0 0 5 3 - 3
Fig. 1.
Sensor of charge measuring method.
160
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
The device for injection rate measuring (Fig. 2) consists of two parts: sensor A which is used for the detection of fuel and amplifier B which receives and amplifies the charge. The voltage obtained at the output from the amplifier can be measured with an appropriate measuring instrument, e.g. an oscilloscope. The housing 1 of sensor A is made of a material with good insulating properties, and the electrode 2 used for fuel detection, on the other hand, of a material which conducts electric current. The electrode 2, onto which the fuel is injected, must be inclined at an angle of 80° to the fuel jet axis, which allows better outlet of the fuel. The electrode surface must be polished, as the volume of the charge generated while the fuel slides against the metal is dependent upon the finish quality of the surface. Fuel outlet from sensor A must be as fast as possible so that the fuel remaining in the sensor does not interfere with the next jet. We tested several types of amplifiers. We obtained the best results with high input resistance amplifiers. The most important are the resistor R5, for which we experimentally established the value R5 ⫽ 1 M⍀, and the capacitor C, for which the experimentally established value is C ⫽ 0.5 pF. With those values, we achieved the best results. The amplifier was designed so as to ensure amplification between 2 to 20 times. Amplification is controlled with the potentiometer R1. Fig. 3 illustrates the measured injection rate with voltage Uosc plotted on the vertical axis and time on the horizontal axis. 3. Physical description of charge measuring method With the charge measuring method, when the fuel rubs against the injection system parts, one portion of
Fig. 2.
Fig. 3.
Injection rate.
the free electrons moves from the injection system parts into the fuel, which obtains negative electric charge. Rubbing merely serves to bring many points of the surfaces into good contact [3]. The rubbing of the fuel is the highest in the injection nozzle and in the sensor, where finely dispersed fuel droplets hit the sensor electrode at high velocity. The charge brought with the fuel droplets and the charge generated in the sensor is led to the amplifier, where it is transformed into the electric current, amplified and recorded on the measuring instrument (Figs. 1 and 14). The amplifier also inverts the sign of the electric voltage from negative to positive. The injected fuel was Shell Calibration Fluid B. It is an oil derivative and a mixture of several hydrocarbons. The hydrocarbon atoms are bound into molecules by a mixed ionic–atomic bond. A substance with such a bond is, in most cases, non-conducting as is Shell Calibration
Charge measuring method.
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
Fluid B. As there are many components of hydrocarbons in Calibration Fluid B, and none is prevailing, we could not do even an approximate calculation of the electrostatic fuel charging which occurred while the fuel was rubbing against the metal. The next reason for the occurrence of electric current is the temperature gradient in the electrode 1, i.e. the crystal in which the gradient T(r) exists is a generator of electric voltage. In our case we have the gradient T(r) on the electrode (Fig. 1) against which fuel droplets hit at the velocity of 100–300 m s−1. When the droplets hit the plate, the kinetic energy of droplets is instantly transformed into thermal energy which results in the occurrence of the gradient T(r) between points 1 and 2 on the electrode (Fig. 1). In order to calculate the current of the electrons which are a consequence of the gradient T(r), we used the equations of the quantum statistics distribution. For electrons which are fermions (particles with spin s ⫽ 1/2), we used the Bose–Fermi distribution. The current of electrons is: →
→
j ⫽ E ⫹ K1(ⵜT) ⫽
冕
2e (F ⫺ F0)→ v d3k (2)3
(1)
161
The calculation of the integral gives us an explicit expression of the constant k1 as a function of: m ⫽ electron mass; kB ⫽ Boltzmann constant; ⫽ mean time between two consecutive scatterings of electrons
⫽
m* e0
where m* is effective mass of electron;  is mobility of h electrons and ប ⫽ ; h is Planck’s constant. 2 The solution of the integral Eq. (2) is: jz ⫽
3 2e 4 m 2 2 3 dT ( ) 2 ·(kB)5·(T) 2 ·f(x) · · 3 (2) 3 ប m dz
⫽ k1
(3)
dT dz
The result of the calculation of the Eq. (3): k1 ⫽ ⫺ 4624. From Eq. (1) we get: 0 ⫽ ·EZ ⫹ k1
dT dz
→
k
where E is the electric field strength, is electric conductivity, e is the elementary charge, k is the wave vector of electron, d3k is the volume element in the wave vector
EZ(z) ⫽ ⫺
k1 dT dU · ⫽ dz dz
space representation, → v is velocity of electrons and T is temperature.
k1 U⫽⫺
冕 z
dT k1 dz ⫽ ⫺ ·⌬T dz
(4)
0
∂F0 → F ⫺ F0 ⫽ → v ( ⫺ r )) )(F ⫺ ⵜWF(→ ∂W ⫹
From the energy equation we calculate how much the
W ⫺ WF ⵜT(→ r) T
where F is the electric field force, F0 the external electric field force, WF the Fermi energy and W the energy of electrons at room temperature. We introduce spherical coordinates into the Eq. (1) and have to calculate the current in one direction only: jz ⫽
2e 兰兰兰(F ⫺ F0)v cos·k sinddkdk (2)3
Thus, we obtain the integral we have to solve: jz ⫽
2e ∂F0 W ⫺ WF 兰 · (2)3 ∂W T
冕 冕
2
mdW ·v2·k· 2 ប
d· cos2 sin d·( ⫺
0
(2)
0
dT )· dz
Fig. 4.
Linearity diagram.
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
162
Fig. 7.
Fig. 5.
Injection rate at 400 rpm.
fuel has been heated when hitting the electrode, on the assumption that the phenomenon happens very quickly and that only the fuel is heated at the first moment: mv2 ⫽ mcp⌬T; ⌬T ⫽ 10°C 2 where v, the velocity of droplets, is 200 m s−1 and cp is the specific heat of Shell Calibration Fluid B. We get the voltage U ⫽ 0.79 mV from Eq. (4). Compared to the voltage we obtained as a result of the previous two effects, this voltage is low. We tested 27 different sensor types. We attempted to charge the fuel droplets in such a way that the jet, prior
Fig. 6.
Injection rate at 200 rpm.
Injection rate at 500 rpm.
to hitting the sensor, flew through the electric field between the capacitor plates. The voltage on the capacitor was 3000 V d.c. We did not observe a substantial increase of droplets’ electric charge, in spite of a high voltage on the capacitor. Therefore, we decided to omit the electric charging of fuel droplets. The testing results did not meet our expectations. In terms of reliability, price and accuracy, the sensor illustrated in Fig. 1 is the best model of the charge measuring method we tested. The charge measuring method was tested on a test stand made by R. Bosch, which is especially designed for diesel injection system testing. The test stand always uses the same fuel with constant electrical properties. The fuel was Shell Calibration Fluid B used for injection system testing. It contained no impurities which might have damaged the injection system. The fuel tem-
Fig. 8.
Linearity diagram at 500 rpm.
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
Fig. 9.
Fig. 10.
Fig. 11.
Injection rate at 500 rpm.
Fig. 12.
Injection rate at 600 rpm.
Fig. 13.
Injection rate at 700 rpm.
163
Linearity diagram at 600 rpm.
Linearity diagram at 1000 rpm.
perature during testing ranged between 30°C and 35°C, as required by the injection system testing regulations. The fuel temperature, varying between 30°C and 35°C, had no effect whatsoever on the operation of the sensor.
4. Charge measuring method test results The Bosch diesel injection system test stand can be used to measure only the injected fuel volume in a single
injection cycle, whereas it is impossible to measure the timing of injection rate, crucial in diesel engine design. Equally important is the injected fuel volume in individual time intervals of the injection process. The area under the injection rate curve represents the injected fuel
164
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
Fig. 14.
Block diagram of the data acquisition system.
volume in a single injection cycle. By knowing the latter and the area under the curve, it is possible to compute the volume of injected fuel in individual injection time intervals. Thus, Figs. 4, 8–10 show the injected fuel volume in relation to the area under the curve of injection. During the sensor development process, voltage Uosc (Fig. 3) was located on the vertical axis for practical reasons. What is essential for the applicability of the method is linearity, i.e. the dependence of the area under the curve of injection rate (Fig. 3) from the quantity of the injected fuel. Fig. 4 shows the diagram with the injection rate Q on the vertical axis and the area under the curve in cm2 on the horizontal axis. It is evident from the diagram that the linearity of the measuring method is good. The same dependence is illustrated in Figs. 8–10. Fig. 5 illustrates the injection rate (lower curve) and pressure pII (pressure in front of the injection nozzle) at n ⫽ 400 rpm of the pump and Q ⫽ 130 mm3. Fig. 6 shows the injection rate at low pump rpm (n ⫽ 200 rpm) and Q ⫽ 105 mm3. Fig. 7 shows the injection rate at n ⫽ 500 rpm and Q ⫽ 120 mm3. Figs. 8–10 are linearity diagrams at various pump rpm. The diagrams show that the linearity of the method is good. Fig. 11 shows the injection rate at n ⫽ 500 rpm and Q ⫽ 124 mm3. Fig. 12 shows the injection rate at n ⫽ 600 rpm and Q ⫽ 131 mm3. Fig. 13 shows the injection rate at n ⫽ 700 rpm and Q ⫽ 162 mm3. Figs. 11–13 show the comparison between the injection rates measured with the charge
and Bosch measuring methods. The injection rates were measured using both the Bosch and charge methods with equal injected fuel volumes, and subsequently the shapes of injection rates were compared. The charge method was scaled to fit the Bosch method. Fig. 14 shows the block diagram of the data acquisition system. All the signals were recorded on a magnetic tape. By means of the oscilloscope, it was possible to visually monitor the recording of the injection rates simultaneously. The signal was transmitted from the tape recorder to the A/D converter in order to transform it from analogue to the digital form. The signals were then fed into the computer, whereupon a comparison between the injection rates measured with Bosch and charged method was made. In the analogue form, both the injection rates measured with Bosch and charged measuring method were then plotted. The comparison of the injection characteristics obtained with Bosch and charged measuring method shows (Figs. 11–13): 1. The congruity of the results obtained with both measuring methods is satisfactory. 2. A bigger difference in the shape of both curves appears at the end of the injection. With the Bosch method the end is sharper. 3. The charge method has a considerably lower zerodrift than Bosch’s method.
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
5. Summary The paper deals with a new and very simple method for measuring the injection rate. The method is based upon the measuring of fuel electric charge, which occurs due to the fuel rubbing in the nozzle and sensor and the temperature gradient in the sensor electrode. The test results prove that the linearity of the measuring method is good. The method has low zero-drift, stable signals and is reliable. It can be best applied for measuring the low and high injection rates of the pintle nozzle. The comparison with the injection rates measured with the Bosch and the charge method show good matching in
165
all injection stages, except at the end of injection where the injection rate measured with Bosch’s method is sharper than the one obtained with the charge method. References [1] W. Zeuch, Neue Verfahren zur Messung des Einspritzgesetzes und ¨ Einspritz-Regelmassigkeit von Diesel-Einspritz-pumpen. MTZ, Jahr. 22 Heft 9, 1961. [2] W. Bosch, The Fuel Rate Indicator: A New Measuring Instrument for Display of the Characteristics of Individual Injection. SAE Paper 660749, 1966. [3] F.W. Sears, M.W. Zemansky, University Physics, Addison-Wesley, Reading, Mass., 1973.
A new method for measuring fuel-injection rate ˇˇ Milan Marcic
*
University of Maribor, Smetanova 17, 2000 Maribor, Slovenia Received 29 October 1998; received in revised form 12 November 1998; accepted 10 December 1998
Abstract The paper deals with the basic principles of use and testing of the new method for measuring injected volumes of liquids. The above method was employed in measuring the injected fuel volume in diesel injection systems, where fuel is injected at time intervals of up to 4 ms. It works by measuring the electric charge deposited by liquid droplets impacting a metal electrode. The electric charge is generated mainly in the injection nozzle, where the fuel rubs against the metal parts of injection nozzle, resulting in one portion of free electrons moving from the metal to the fuel. The fuel then transfers this electric charge to the sensor electrode. Rubbing merely serves to bring many points of the surface into good contact. The electric current appears also due to the temperature gradient in the sensor electrode. The temperature gradient in the electrode is a result of the transformation into heat of kinetic energy of fuel droplets hitting the electrode at velocities of 100–300 m s−1. The electric charge is led from the electrode to the charge amplifier, where it is converted into electric current. The test results showed a very reliable operation of the sensor and a linear dependence of the area under the injection rate curve upon the injected fuel volume. The comparison of the injected rates measured with the charge and Bosch measuring method, which is most frequently utilised today, showed a good matching of results in any operating regime. 1999 Elsevier Science Ltd. All rights reserved. Keywords: Injection rate; Charge measuring method; Thermodynamics
1. Introduction The importance of fuel injection system in the operation of diesel engines has been recognised since its early days. The rate at which the fuel is introduced into the combustion chamber determines the performance of the engine. Hence, knowing the characteristics of the fuel injection rate is extremely important in designing the engine. So far, many fuel injection rate measuring methods have been developed among which Zeuch’s [1] and Bosch’s [2] are most frequently used today. The paper shows a new fuel injection rate measuring method, which measures the fuel electric charge. Its major advantages are simplicity and low price.
fuel becomes electrically charged when it rubs against the sensor electrode (Fig. 1) [3] and the other injection system parts. Fuel droplets hit the sensor electrode at a velocity of 100–300 m s−1. Thus, the fuel is electrically charged and this charge is then emitted on contact with the electrode. Due to high velocity, the dispersed fuel droplets have a relatively high kinetic energy, which is transformed into heat; when the droplets hit the electrode, a time varying temperature gradient is obtained, itself being a minor source of electric current.
2. Physical principles of charge measuring method With the charge measuring method, fuel detection is based upon the measuring of electric charge of fuel. The * Tel.: ⫹ 38-662-220-7500; e-mail: [email protected]
fax:
⫹
38-662-220-7990;
0955-5986/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 5 - 5 9 8 6 ( 9 8 ) 0 0 0 5 3 - 3
Fig. 1.
Sensor of charge measuring method.
160
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
The device for injection rate measuring (Fig. 2) consists of two parts: sensor A which is used for the detection of fuel and amplifier B which receives and amplifies the charge. The voltage obtained at the output from the amplifier can be measured with an appropriate measuring instrument, e.g. an oscilloscope. The housing 1 of sensor A is made of a material with good insulating properties, and the electrode 2 used for fuel detection, on the other hand, of a material which conducts electric current. The electrode 2, onto which the fuel is injected, must be inclined at an angle of 80° to the fuel jet axis, which allows better outlet of the fuel. The electrode surface must be polished, as the volume of the charge generated while the fuel slides against the metal is dependent upon the finish quality of the surface. Fuel outlet from sensor A must be as fast as possible so that the fuel remaining in the sensor does not interfere with the next jet. We tested several types of amplifiers. We obtained the best results with high input resistance amplifiers. The most important are the resistor R5, for which we experimentally established the value R5 ⫽ 1 M⍀, and the capacitor C, for which the experimentally established value is C ⫽ 0.5 pF. With those values, we achieved the best results. The amplifier was designed so as to ensure amplification between 2 to 20 times. Amplification is controlled with the potentiometer R1. Fig. 3 illustrates the measured injection rate with voltage Uosc plotted on the vertical axis and time on the horizontal axis. 3. Physical description of charge measuring method With the charge measuring method, when the fuel rubs against the injection system parts, one portion of
Fig. 2.
Fig. 3.
Injection rate.
the free electrons moves from the injection system parts into the fuel, which obtains negative electric charge. Rubbing merely serves to bring many points of the surfaces into good contact [3]. The rubbing of the fuel is the highest in the injection nozzle and in the sensor, where finely dispersed fuel droplets hit the sensor electrode at high velocity. The charge brought with the fuel droplets and the charge generated in the sensor is led to the amplifier, where it is transformed into the electric current, amplified and recorded on the measuring instrument (Figs. 1 and 14). The amplifier also inverts the sign of the electric voltage from negative to positive. The injected fuel was Shell Calibration Fluid B. It is an oil derivative and a mixture of several hydrocarbons. The hydrocarbon atoms are bound into molecules by a mixed ionic–atomic bond. A substance with such a bond is, in most cases, non-conducting as is Shell Calibration
Charge measuring method.
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
Fluid B. As there are many components of hydrocarbons in Calibration Fluid B, and none is prevailing, we could not do even an approximate calculation of the electrostatic fuel charging which occurred while the fuel was rubbing against the metal. The next reason for the occurrence of electric current is the temperature gradient in the electrode 1, i.e. the crystal in which the gradient T(r) exists is a generator of electric voltage. In our case we have the gradient T(r) on the electrode (Fig. 1) against which fuel droplets hit at the velocity of 100–300 m s−1. When the droplets hit the plate, the kinetic energy of droplets is instantly transformed into thermal energy which results in the occurrence of the gradient T(r) between points 1 and 2 on the electrode (Fig. 1). In order to calculate the current of the electrons which are a consequence of the gradient T(r), we used the equations of the quantum statistics distribution. For electrons which are fermions (particles with spin s ⫽ 1/2), we used the Bose–Fermi distribution. The current of electrons is: →
→
j ⫽ E ⫹ K1(ⵜT) ⫽
冕
2e (F ⫺ F0)→ v d3k (2)3
(1)
161
The calculation of the integral gives us an explicit expression of the constant k1 as a function of: m ⫽ electron mass; kB ⫽ Boltzmann constant; ⫽ mean time between two consecutive scatterings of electrons
⫽
m* e0
where m* is effective mass of electron;  is mobility of h electrons and ប ⫽ ; h is Planck’s constant. 2 The solution of the integral Eq. (2) is: jz ⫽
3 2e 4 m 2 2 3 dT ( ) 2 ·(kB)5·(T) 2 ·f(x) · · 3 (2) 3 ប m dz
⫽ k1
(3)
dT dz
The result of the calculation of the Eq. (3): k1 ⫽ ⫺ 4624. From Eq. (1) we get: 0 ⫽ ·EZ ⫹ k1
dT dz
→
k
where E is the electric field strength, is electric conductivity, e is the elementary charge, k is the wave vector of electron, d3k is the volume element in the wave vector
EZ(z) ⫽ ⫺
k1 dT dU · ⫽ dz dz
space representation, → v is velocity of electrons and T is temperature.
k1 U⫽⫺
冕 z
dT k1 dz ⫽ ⫺ ·⌬T dz
(4)
0
∂F0 → F ⫺ F0 ⫽ → v ( ⫺ r )) )(F ⫺ ⵜWF(→ ∂W ⫹
From the energy equation we calculate how much the
W ⫺ WF ⵜT(→ r) T
where F is the electric field force, F0 the external electric field force, WF the Fermi energy and W the energy of electrons at room temperature. We introduce spherical coordinates into the Eq. (1) and have to calculate the current in one direction only: jz ⫽
2e 兰兰兰(F ⫺ F0)v cos·k sinddkdk (2)3
Thus, we obtain the integral we have to solve: jz ⫽
2e ∂F0 W ⫺ WF 兰 · (2)3 ∂W T
冕 冕
2
mdW ·v2·k· 2 ប
d· cos2 sin d·( ⫺
0
(2)
0
dT )· dz
Fig. 4.
Linearity diagram.
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
162
Fig. 7.
Fig. 5.
Injection rate at 400 rpm.
fuel has been heated when hitting the electrode, on the assumption that the phenomenon happens very quickly and that only the fuel is heated at the first moment: mv2 ⫽ mcp⌬T; ⌬T ⫽ 10°C 2 where v, the velocity of droplets, is 200 m s−1 and cp is the specific heat of Shell Calibration Fluid B. We get the voltage U ⫽ 0.79 mV from Eq. (4). Compared to the voltage we obtained as a result of the previous two effects, this voltage is low. We tested 27 different sensor types. We attempted to charge the fuel droplets in such a way that the jet, prior
Fig. 6.
Injection rate at 200 rpm.
Injection rate at 500 rpm.
to hitting the sensor, flew through the electric field between the capacitor plates. The voltage on the capacitor was 3000 V d.c. We did not observe a substantial increase of droplets’ electric charge, in spite of a high voltage on the capacitor. Therefore, we decided to omit the electric charging of fuel droplets. The testing results did not meet our expectations. In terms of reliability, price and accuracy, the sensor illustrated in Fig. 1 is the best model of the charge measuring method we tested. The charge measuring method was tested on a test stand made by R. Bosch, which is especially designed for diesel injection system testing. The test stand always uses the same fuel with constant electrical properties. The fuel was Shell Calibration Fluid B used for injection system testing. It contained no impurities which might have damaged the injection system. The fuel tem-
Fig. 8.
Linearity diagram at 500 rpm.
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
Fig. 9.
Fig. 10.
Fig. 11.
Injection rate at 500 rpm.
Fig. 12.
Injection rate at 600 rpm.
Fig. 13.
Injection rate at 700 rpm.
163
Linearity diagram at 600 rpm.
Linearity diagram at 1000 rpm.
perature during testing ranged between 30°C and 35°C, as required by the injection system testing regulations. The fuel temperature, varying between 30°C and 35°C, had no effect whatsoever on the operation of the sensor.
4. Charge measuring method test results The Bosch diesel injection system test stand can be used to measure only the injected fuel volume in a single
injection cycle, whereas it is impossible to measure the timing of injection rate, crucial in diesel engine design. Equally important is the injected fuel volume in individual time intervals of the injection process. The area under the injection rate curve represents the injected fuel
164
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
Fig. 14.
Block diagram of the data acquisition system.
volume in a single injection cycle. By knowing the latter and the area under the curve, it is possible to compute the volume of injected fuel in individual injection time intervals. Thus, Figs. 4, 8–10 show the injected fuel volume in relation to the area under the curve of injection. During the sensor development process, voltage Uosc (Fig. 3) was located on the vertical axis for practical reasons. What is essential for the applicability of the method is linearity, i.e. the dependence of the area under the curve of injection rate (Fig. 3) from the quantity of the injected fuel. Fig. 4 shows the diagram with the injection rate Q on the vertical axis and the area under the curve in cm2 on the horizontal axis. It is evident from the diagram that the linearity of the measuring method is good. The same dependence is illustrated in Figs. 8–10. Fig. 5 illustrates the injection rate (lower curve) and pressure pII (pressure in front of the injection nozzle) at n ⫽ 400 rpm of the pump and Q ⫽ 130 mm3. Fig. 6 shows the injection rate at low pump rpm (n ⫽ 200 rpm) and Q ⫽ 105 mm3. Fig. 7 shows the injection rate at n ⫽ 500 rpm and Q ⫽ 120 mm3. Figs. 8–10 are linearity diagrams at various pump rpm. The diagrams show that the linearity of the method is good. Fig. 11 shows the injection rate at n ⫽ 500 rpm and Q ⫽ 124 mm3. Fig. 12 shows the injection rate at n ⫽ 600 rpm and Q ⫽ 131 mm3. Fig. 13 shows the injection rate at n ⫽ 700 rpm and Q ⫽ 162 mm3. Figs. 11–13 show the comparison between the injection rates measured with the charge
and Bosch measuring methods. The injection rates were measured using both the Bosch and charge methods with equal injected fuel volumes, and subsequently the shapes of injection rates were compared. The charge method was scaled to fit the Bosch method. Fig. 14 shows the block diagram of the data acquisition system. All the signals were recorded on a magnetic tape. By means of the oscilloscope, it was possible to visually monitor the recording of the injection rates simultaneously. The signal was transmitted from the tape recorder to the A/D converter in order to transform it from analogue to the digital form. The signals were then fed into the computer, whereupon a comparison between the injection rates measured with Bosch and charged method was made. In the analogue form, both the injection rates measured with Bosch and charged measuring method were then plotted. The comparison of the injection characteristics obtained with Bosch and charged measuring method shows (Figs. 11–13): 1. The congruity of the results obtained with both measuring methods is satisfactory. 2. A bigger difference in the shape of both curves appears at the end of the injection. With the Bosch method the end is sharper. 3. The charge method has a considerably lower zerodrift than Bosch’s method.
ˇˇ M. Marcic / Flow Measurement and Instrumentation 10 (1999) 159–165
5. Summary The paper deals with a new and very simple method for measuring the injection rate. The method is based upon the measuring of fuel electric charge, which occurs due to the fuel rubbing in the nozzle and sensor and the temperature gradient in the sensor electrode. The test results prove that the linearity of the measuring method is good. The method has low zero-drift, stable signals and is reliable. It can be best applied for measuring the low and high injection rates of the pintle nozzle. The comparison with the injection rates measured with the Bosch and the charge method show good matching in
165
all injection stages, except at the end of injection where the injection rate measured with Bosch’s method is sharper than the one obtained with the charge method. References [1] W. Zeuch, Neue Verfahren zur Messung des Einspritzgesetzes und ¨ Einspritz-Regelmassigkeit von Diesel-Einspritz-pumpen. MTZ, Jahr. 22 Heft 9, 1961. [2] W. Bosch, The Fuel Rate Indicator: A New Measuring Instrument for Display of the Characteristics of Individual Injection. SAE Paper 660749, 1966. [3] F.W. Sears, M.W. Zemansky, University Physics, Addison-Wesley, Reading, Mass., 1973.