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Measurement and validation of hole-to-hole fuel injection rate from a diesel injector
Flow Measurement and Instrumentation 61 (2018) 66–78
Contents lists available at ScienceDirect
Flow Measurement and Instrumentation journal homepage: www.elsevier.com/locate/flowmeasinst
Measurement and validation of hole-to-hole fuel injection rate from a diesel injector Tong Luoa, Su Jianga, Adams Moroa,b, Chuqiao Wanga, Liying Zhouc, Fuqiang Luoa,
T
⁎
a
School of Automotive and Traffic Engineering, Jiangsu University, Zhenjiang 212013, China School of Mechanical Engineering, Accra Technical University, Accra, Ghana c School of Mechanical Engineering, Guiyang University, Guiyang 550005, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Diesel engine Injector Injection rate Momentum flux
Hole-to-hole fuel injection characteristic differences that occurs during injection, results in non-uniform fuel distribution and compromised combustion and emission in direct injection IC engines. Hence the instantaneous determination of these differences could help in understanding and the improvement of combustion characteristics. In this paper, a hole-to-hole transient measuring method based on the spray momentum flux theorem was developed and used to determine the fuel injection rate from each nozzle hole of a multi-hole diesel injector. The customized measuring method, was further used to study the characteristics of injection from multi-hole nozzle. Injection rates from the multi-hole nozzle, were compared with those measured with an EFS IFR-600 which is widely used to measure the total injection rate of diesel injector. And about 1% discrepancy in terms of cycle fuel injection quantity, was obtained. Additionally, the fuel injection rate from each nozzle hole of a double layered eight-hole diesel injection nozzle were measured and analyzed. It was found that the cycle fuel injection quantities of the lower layered nozzle holes (4 holes) were 5–15% greater than the cycle fuel injection quantities of the upper layered nozzle holes (4 holes). This was attributed to the different degrees of flow resistance encountered by the nozzle holes. The lower layered nozzle holes encountered relatively less flow resistance than the upper layered ones. This result validates the experiment results obtained from the same nozzle, where the mean fuel injection quantities from eight fuel tunnels connected to the holes, showed the same trend.
1. Introduction The performance and emission characteristics of diesel engines are largely governed by fuel atomization and spray processes which in turn are strongly influenced by the internal flow dynamics of injection nozzles [1–3]. With stringent emission regulations and increasing demand for fuel economy, injectors have become one of the most important parts of fuel injection system in diesel engines [4–6]. For a multihole injector, differences in injection rates between individual injection nozzle holes, result in non-uniform fuel distribution in space and time during spray combustion and therefore affect combustion quality and emission characteristics of diesel engines [7–9]. Bosch method [10–13] and Zeuch method [14–16] are currently two of the most common methods used to determine the instantaneous mass flow through diesel injectors. However, Charge measuring method [17] and Laser Doppler Anemometer [18] can also be used for fuel injection rate measurements. Although all of the above measuring methods are used to determine the total injection rate from multihole diesel injectors, they cannot be used to estimate hole-to-hole differences ⁎
of a multi-hole nozzle. In this regard, the development of a hole-to-hole injection rate measuring system, will be immensely significant since it could serve as a guide for the optimization of multihole injectors during manufacturing [11]. Even though the deformation test method developed by Marčič et al. [7] and mass flow rate test bench constructed by Payri et al. [19] are used to determine the injection rate of nozzle holes from a multihole injector, they can only acquire data from one hole at a time. This present some limitations since data from each hole has to be acquired one at time before hole-to-hole characteristics could be analyzed, or results obtained from a single hole could be assumed to be the same with the other nozzle hole (in the case of symmetric multi-hole nozzles). However research have shown that, even in symmetric multiholes, hole-to-hole injection rate are not the same due off-axis needle displacement, geometrical differences and internal flow characteristic difference. A transient measuring test rig, which uses the principles of spray momentum flux theorem [20–24], was used to study the behavior and stability of injection from each nozzle hole, simultaneously [1]. The experimental test rig that was used for the simultaneous data
Corresponding author. E-mail address: [email protected] (F. Luo).
https://doi.org/10.1016/j.flowmeasinst.2018.03.014 Received 11 December 2017; Received in revised form 27 February 2018; Accepted 21 March 2018 Available online 22 March 2018 0955-5986/ © 2018 Elsevier Ltd. All rights reserved.
Flow Measurement and Instrumentation 61 (2018) 66–78
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Nomenclature
∆1 ∆vm ρf Δ
geometrical outlet section (m2) discharge coefficient non-uniform coefficient spray impact force (N) Nozzle exit and sensor surface distance (m) mass flow rate (kg/s) spray momentum flux (kgm/s) injection pump speed (rpm) cycle fuel injection quantity (m3) time (s) time delay (s) Velocity (m/s) Pressure drop (Pa)
Ageo Cd Cn F L ṁ Ṁ n Q t t’ u ΔP
Subscript
m th below upper max min f
The customized spray momentum flux experimental setup is shown in Fig. 2. Although the experimental approach used in this study and in [22] are the same, the fuel injection systems and the injectors analyzed, were different. In the study conducted by Luo et al. [22], 5 hole asymmetric injector, used mainly in off-road machinery was investigated, whereas in this study a 6 hole symmetric nozzle injector and an eight hole double layered asymmetric nozzle injector were investigated. In [22], validation of fuel injection rates from each hole was performed by comparing the cycle fuel injection quantity of each hole (obtained by integrating the instantaneous injection rates through a complete injection cycle) to measured total fuel injected from it. Whereas in this study, the validation of fuel injection rate from the 6 hole injector, was performed by comparing the sum of the hole-to-hole cycle fuel injection rates to the total fuel injection rate (measured with an EFS IFR-600 m) from all the holes. For the 8 hole injector, the validation was performed by comparing the cycle fuel injection quantity from each hole to those measured with eight specially designed fuel separators. That is eight fuel tunnels, connected to each hole of the nozzle, were used to collect and measure the mean fuel injection quantities from them. A high-pressure common rail fuel injection system was used for fuel supply instead of a pump-line nozzle system.
2. Theoretical background and experiment Employing the law of conservation of mass and momentum at the exits of the holes [21,25], together with the Bernoulli's theorem [26], the injection rate (Vḃ ) expression in Eq. (1) was obtained
̇ geo Ca MA ρf
(1)
where (Ṁ ) is the momentum at the exits, Ageo is the geometric area of the holes, Ca is the area coefficient and ρf is the fuel density. From the spray momentum flux experiment, the momentum at the exits was obtained. The experiment was conducted by mounting piezoelectric force sensors, perpendicularly to the axial directions of the injected fuel from the various holes as shown in Fig. 1. The sensor were carefully positioned and orientated at a distance (L) that ensured that the fuel will not rebound after impact and also the effect of inertia forces were eliminated. More detailed description of the theory and the experiment procedure adopted in this study are presented in [22]. By ensuring that the effect of rebound velocity and inertia forces on the results were negligible, the momentum flux (M (t ) ) and the instantaneous injection rates at the exits (Vḃ ), were expressed as
M (t ) = F (t + t ′)
mean theoretical Lower layer Upper layer maximum minimum liquid
2.1. Experimental method
acquisition, was developed and validated with experimental results from other experimental method. After the validation, the test rig was used to acquire and analyze the hole-to-hole injection rate differences from a double layered eight hole nozzle, at various operating conditions. In this paper, the theory governing the measuring principle and the experimental setup, are described in Sections 2 and 3 respectively. The results, are presented in Section 4 and a summary conclusion in section 5.
Vḃ =
relative difference between Qbelow and Qupper Mean velocity difference(m/s) Fuel density (kg/m3) Relative error
(2)
F (t + t ′) Ageo Ca
Vḃ =
ρf
(3)
Integrating Eq. (3) over the complete injection cycle, the cycle fuel injection quantity from each nozzle hole (Q ) was obtained.
q=
Q=
∫ ∑q
F (t + t ′) Ageo Ca ρf
dt
Fig. 1. Test principle of spray momentum flux.
(4) (5)
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Fig. 2. High-pressure common rail system injection rate measurement set-up for each nozzle hole. 2500
Sensor 1 Sensor2 Sensor 3 Sensor 4 Sensor 5 Sensor 6 Sensor 7 Sensor 8
2000
Voltage (mV)
Fig. 3. Force sensor installation position. Table 1 Specifications of the piezoelectric quartz crystal force sensor. Range Natural frequency Linearity Repeatability Medium temperature Weight
0–3 N ≥ 40 kHz ≤ 1%FS ≤ 1%FS − 20–70° C 16 g
1500
1000
500
0 0
1
2
3
4
5
Force (N) Fig. 4. Corresponding relationship between output voltage and weight force.
Piezoelectric quartz crystal force sensors were mounted perpendicular to the axial direction of their corresponding nozzle hole in the first compartment of the data acquisition system test cabinet, as shown in Fig. 3. From the figure it can be seen that the orientation of the holes, ensured that the sensors had to be tilted in other to be perpendicular to the emerging spray jets. At this oriented position and under the influence of gravity, spray jets rebounds are minimized or eliminated [27]. This is because after the fuel impacts the sensor surface, it freely drops downwards. The piezoelectric force sensors, translates the force impacted on them by the spray jet, into charge signals. The signals were amplified with a charge amplifier (PPM-12KA-610) and then transmitted to a sixteen-channel data acquisition system (UA326H-16) for analysis. The data is analyzed visually on a computer and recorded for subsequent processing. After the experiment, the evaporated fuel in the fuel mist dispersal chamber, were removed with an explosion-proof fuel mist filter. The filter, extracts the fuel from the extracted air-fuel mixture in the chamber and stores it for further usage. The specifications of the piezoelectric quartz crystal force sensor, are shown in Table 1. The sensors were positioned at distances that ensured the elimination of factors that could compromise the results
[22,27]. The method adopted in calibrating the piezoelectric force sensors is the same as described in [28]. From Fig. 4, it can be seen that linear relationship were obtained for all the sensors during the calibration.
3. Results and discussion 3.1. Uniform-distributed 6-hole injector The symmetric 6-hole injector that was experimentally analyzed with the customized test rig is from a four-valve direct injection engine. Fig. 5 and Fig. 6 show the injector and the 3D model of its nozzle respectively. The injector had a nozzle hole diameter of 0.155 mm and hole length of 0.8 mm. Each nozzle hole had an inclination angle of 72.5°. As conducted in [1], the total fuel injection rates from each nozzle hole of the injector, were compared with the total fuel injection rate measured by an EFS IFR-600 m. Considering the uncertainty of a
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Experiments conducted with the customized test rig and the EFS IFR-600 m at the operating condition shown in Table 2, were compare with one another. The compared results are shown in Fig. 8(a), (b), (c). Fig. 8(a′), (b′), and (c′) shows the hole-to-hole injection rates, measured with the momentum flux test rig. The rail pressures were taken as the injection pressures and atmospheric pressure as the back pressure. As seen in Fig. 8(a′), (b′), and (c′), the global shapes of the hole-tohole injection rate time-histories, were similar at all the operating conditions. Under both methods, the injection rate time-histories, followed the same trend. This is consistent with the research results in [21,29]. From Fig. 8(a), (b), (c), it is evident that at constant injection pressure, injection rate rises rapidly with increase in needle lift. At full needle lift, the curve remains constant with slight increment, while at the closing stages, the injection rate decreases sharply. However under the injection pressures of 80, 120 and 160 MPa, it is clear that, the higher the injection pressure, the steeper the gradient of the injection rates at the transient stages (opening and closing). This is because the higher the injection pressure, the quicker the hydraulic system of the injector responds, hence resulting in a relative faster needle dynamics. It can also be observed from Fig. 8 that, with the increment of injection pressure not only increases the injection stop time but increases the peak injection rate gradually. The cycle fuel injection quantities from the injection nozzle were analyzed for the two measuring technique and compared as shown in Fig. 9. Those from the momentum flux experimental setup were computed using Eq. (5) as explained in Section 2. The difference between the computed and the measured quantities from the EFS IFR-600 m, were evaluated using:
Fig. 5. The experimental symmetric 6-hole injector.
Fig. 6. The 3-D model of the nozzle.
Δ=
Q − Q′ × 100% Q′
(6)
From Fig. 9 it is clear that, the computed cycle fuel injection quantities are slightly less than those measured by the EFS IFR-600 m. At all the operating conditions, within 5% relative error, were obtained. This shows that the accuracy of the injection rate measuring system is within acceptable limits. After establishing the accuracy of the customized injection rate measuring system, further experiments were conducted with it at the injection pressure, injection duration and injection frequency of120 MPa, 1500 μs and 6 Hz respectively. Similar trends of injection rate results between the EFS IFR-600 and the momentum flux test rig, were obtained at this condition. About 1% relative error between them, was obtained.
Fig. 7. The connection diagram of EFS IFR-600. Table 2 Operating conditions.
3.2. Two-layer eight-hole diesel injector nozzle
Parameter
Value
Injection frequency (pump speed) Injection pulse Injection pressure
6 Hz (360r/min) 1500 μs 80 MPa, 120 MPa, 160 MPa
In this section, a two layered eight-hole injector used in a four valve diesel engine, was analyzed with the customized momentum flux experimental setup. All the holes in the nozzle have diameters of 0.18 mm, length to diameter ratios of 4.17 and rounding radii of 30 µm. Holes 1, 3, 5 and 7 are the lower layered holes whiles holes 2, 4, 6 and 8 are upper layered holes of the eight-hole nozzle, as shown in Fig. 10. The test experiments operation conditions are listed in Table 3. Figs. 11–14 show the time histories of injection rate for each nozzle hole under all the operating conditions. Hole-to-hole cycle fuel injection quantities and hole-to-hole non-uniform coefficient of cycle fuel injection quantities (Cn) [22] are shown in Fig. 15 and Fig. 16 respectively. Non-uniform coefficient of cycle fuel injection quantities among nozzle holes (Cn), were analyzed with expression in Eq. (7):
single condition validation, the comparison were performed at several operating conditions. The EFS IFR-600 was equipped with a high-frequency dynamic pressure transducers, static back pressure measuring sensors and displacement sensors. It measures the total transient injection rate of all nozzle holes and the cycle fuel injection quantity of injectors with high precision. The line diagram of the EFS IFR-600 setup is shown in Fig. 7.
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Fig. 8. (a), (b), (c)are injection rate comparison between EFS IFR-600 results and experimental results. (a′), (b′), and (c′) are the hole-to-hole injection rate at different injection pressures and at the injection pulse width of 1500 μs and frequency of 6 Hz. Injection pressure in a) and a′) are 80 MPa, in b) and b′) are 120 MPa, and in c) and c′) are 160 MPa.
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Cycle fuel injection quantity of the injector (mm3)
T. Luo et al. 90
Measured by momentum flux test rig
5.0
85
Measured by EFS Relative error
4.5
quantities among them. At the same injection pulse width, increasing the injection pressure, gradually increases the hole-to-hole cycle fuel injection quantities and reduces the non-dimensional parameter (Cn). In other words, increment in injection pressure gradually stabilizes in-nozzle hole fuel flows. Thereby decreasing the hole-to-hole cycle fuel injection quantity differences. Hole-to-hole cycle fuel injection quantities compared in Fig. 15 and analyzed in Figs. 17 and 18 show that, the cycle fuel injection quantities of the lower layered nozzle holes are 5–15% greater than those from the upper layered holes. This is due to the positioning of the holes, within the nozzle geometry. With relatively less flow resistance, the discharge coefficient and the flow velocities of the lower layered nozzle holes, are higher than the discharge coefficients and flow velocities of the upper layered holes. The cycle fuel injection quantity differences between the upper and lower layered nozzle holes are larger, depending on the injection pressure. That is difference between the two layered nozzle holes reduces with the increment of either the injection pressure or the injection pulse width. This is consistent with the results obtained in the investigations of Lu Yang et al. [30]. In their studies, eight fuel separators were used to collect and measure the mean fuel injection quantities of each hole from the same type of injector with geometrically similar nozzle to one analyzed in this study. From Fig. 17 and Fig. 18, it can be seen that, the average deviation of the fuel quantities for the upper layered nozzle holes are below the zero line. Meaning, their fuel quantities are relatively lower than those from the lower layered nozzle holes. With increment in injection pulse width or injection pressure, the degree of relative difference, minimizes (nozzle holes deviation points are close to the zero line). As the injection pulse increases, the effect of the transient stages (opening and closing) on in-nozzle flow reduces, since the needle remains at the quasi steady state (full needle lift) position, relatively longer. Also as the injection pressure increases, the needle moves faster through the transients and stay at maximum needle lift relatively longer. This is as a result of the quick response of the injector's hydraulic system.
80 4.0 3.5
70
3.0
65 60
2.5
55
Relative error (%)
75
2.0 50 1.5
45
1.0
40 1
2
3
Operating conditions number (-) Fig. 9. Comparison between EFS IFR-600 results and experimental results at different operation conditions.
Fig. 10. The layout of nozzle holes of eight hole injector.
Table 3 Operating conditions. Parameter
Value
Injection frequency Injection pulse
6 Hz (360r/min) 500 μs , 800 μs , 1000 μs , 1500 μs , 2000 μs 40 MPa, 60 MPa, 80 MPa, 100 MPa
Injection pressure
Cn =
qmax − qmin qmean
× 100%
4. Conclusion In this paper, a customized experimental test rig based on spray momentum flux was constructed to study the behavior and stability of injection from multi-hole diesel injection nozzles. The results were validated with the results obtained from a different measuring method. The following are the summary conclusions observed. After measuring and comparing the cycle fuel injection rates from a six hole nozzle (with the customized test rig and EFS IFR-600 m), it was observed that, the injection rate curves (time histories) from both measuring techniques fits well with each other. The relative error between them, was within 5%. This shows that the customize injection rate measuring system, is within acceptable limits. The cycle fuel injection quantities of the lower layered nozzle holes (1, 3, 5 and 7) of a double layered eight hole nozzle, are 5–15% greater than the cycle fuel injection quantities of the upper layered nozzle holes (2, 4, 6 and 8). With increment in injection pulse width or injection pressure, the degree of relative difference between the upper and the lower layered nozzle holes, minimizes. This is as a result of a faster needle movement due to pressure increment or as a result of a lesser effect of the transient stages (opening and closing stages) due injection pulse width increment.
(7)
As shown in Figs. 11–16, at the same operation conditions, local injection rate differences from the nozzle holes exist, although the time histories are relatively consistent. At the injection pulse width of 500 μs under all the operating condition, the injection rate curves from all the nozzle holes are triangular in shape. As the injection pulse width increases, the hole-to-hole injection rate curve, gradually transforms into a rectangular shape. The cycle fuel injection quantity of each nozzle hole, gradually increases while the non-dimensional parameter (Cn) gradually reduces, till it attains stability. Generally at the same injection pressure, increasing the injection pulse width, gradually stabilizes the injection rate curve of each nozzle hole and also, gradually decreases the differences in cycle fuel injection
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Fig. 11. Injection rate of each nozzle hole at the injection pulse width of (a) 800, (b) 1000, (c) 1500 and (d) 2000 μs, injection frequency of 6 Hz, and injection pressures of 40 MPa.
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Fig. 12. Injection rate of each nozzle hole at the injection pulse width of (a) 500, (b) 800, (c) 1000, (d) 1500 and (e) 2000 μs, injection frequency of 6 Hz, and injection pressures of 60 MPa.
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Fig. 13. Injection rate of each nozzle hole at the injection pulse width of (a) 500, (b) 800, (c) 1000, (d) 1500 and (e) 2000 μs, injection frequency of 6 Hz, and injection pressures of 80 MPa.
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Fig. 14. Injection rate of each nozzle hole at the injection pulse width of (a) 500, (b) 800, (c) 1000, (d) 1500, (e) 2000 μs, injection frequency of 6 Hz, and injection pressures of 100 MPa.
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Fig. 15. Cycle fuel injection quantities of each nozzle hole under the injection pressures of (a) 40 MPa, (b) 60 MPa, (c) 80 MPa and (d) 100 MPa at injection frequency of 6 Hz.
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Fig. 16. Non-uniform coefficient of cycle fuel injection quantities among nozzle holes under the injection pressures of (a) 40 MPa, (b) 60 MPa, (c) 80 MPa and (d) 100 MPa. All were at the injection frequency of 6 Hz.
Fig. 17. The relative average deviation of the fuel quantities of each nozzle hole, at a constant injection pressure of 100 MPa and varying injection pulse width.
Fig. 18. The relative average deviation of the fuel quantities of each nozzle hole, at a constant injection pulse width of 2000 μs and varying injection pressure. 77
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Acknowledgment
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This work is supported by the National Natural Science Foundation of China (No. 51476072), Scientific Research Innovation Foundation for Graduate Students of Jiangsu Province (KYLX16_0889, KYLX_1034) and Chinese Science and Technology Support Plan (2014BAG09B01). References [1] S. Som, A.I. Ramirez, D.E. Longman, S.K. Aggarwal, Effect of nozzle orifice geometry on spray, combustion, and emission characteristics under diesel engine conditions, Fuel 90 (2011) 1267–1276 (3). [2] A.K. Agarwal, A. Dhar, J.G. Gupta, W.I. Kim, C.S. Lee, S. Park, Effect of fuel injection pressure and injection timing on spray characteristics and particulate size–number distribution in a biodiesel fuelled common rail direct injection diesel engine, Appl. Energy 130 (2014) 212–221. [3] K. Mathivanan, J.M. Mallikarjuna, A. Ramesh, Influence of multiple fuel injection strategies on performance and combustion characteristics of a diesel fuelled HCCI engine – An experimental investigation, Exp. Therm. Fluid Sci. 77 (2016) 337–346 (2016/10/01/). [4] G. Li, C. Zhang, Y. Li, Effects of diesel injection parameters on the rapid combustion and emissions of an HD common-rail diesel engine fueled with diesel-methanol dual-fuel, Appl. Therm. Eng. 108 (2016) 1214–1225. [5] R. Payri, F.J. Salvador, J. Gimeno, J. De. la Morena, Influence of injector technology on injection and combustion development - Part 2: Combustion analysis, Appl. Energy 88 (2011) 1130–1139. [6] T.-M. Jia, G.-X. Li, Y.-S. Yu, Y.-J. Xu, Effects of ultra-high injection pressure on penetration characteristics of diesel spray and a two-mode leading edge shock wave, Exp. Therm. Fluid Sci. 79 (2016) 126–133. [7] M. Marčič, Measuring method for diesel multihole injection nozzles (10/15/), Sens. Actuators A: Phys. 107 (2003) 152–158. [8] M. Marčič, Sensor for injection rate measurements, Sensors 6 (2006) 1367–1382. [9] R. Payri, S. Molina, F.J. Salvador, J. Gimeno, A study of the relation between nozzle geometry, internal flow and sprays characteristics in diesel fuel injection systems, KSME Int. J. 18 (2004) 1222–1235. [10] B. W, The fuel rate indicator: a new instrument for display of the characteristic of individual injection, SAE (1966) 660749. [11] F.J. Salvador, J.J. Lopez, J. De. la Morena, M. Crialesi-Esposito, Experimental investigation of the effect of orifices inclination angle in multihole diesel injector nozzles. Part 1 – hydraulic performance, Fuel (2017). [12] R. Payri, A. García, V. Domenech, R. Durrett, A.H. Plazas, An experimental study of gasoline effects on injection rate, momentum flux and spray characteristics using a common rail diesel injection system (7//), Fuel 97 (2012) 390–399.
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Contents lists available at ScienceDirect
Flow Measurement and Instrumentation journal homepage: www.elsevier.com/locate/flowmeasinst
Measurement and validation of hole-to-hole fuel injection rate from a diesel injector Tong Luoa, Su Jianga, Adams Moroa,b, Chuqiao Wanga, Liying Zhouc, Fuqiang Luoa,
T
⁎
a
School of Automotive and Traffic Engineering, Jiangsu University, Zhenjiang 212013, China School of Mechanical Engineering, Accra Technical University, Accra, Ghana c School of Mechanical Engineering, Guiyang University, Guiyang 550005, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Diesel engine Injector Injection rate Momentum flux
Hole-to-hole fuel injection characteristic differences that occurs during injection, results in non-uniform fuel distribution and compromised combustion and emission in direct injection IC engines. Hence the instantaneous determination of these differences could help in understanding and the improvement of combustion characteristics. In this paper, a hole-to-hole transient measuring method based on the spray momentum flux theorem was developed and used to determine the fuel injection rate from each nozzle hole of a multi-hole diesel injector. The customized measuring method, was further used to study the characteristics of injection from multi-hole nozzle. Injection rates from the multi-hole nozzle, were compared with those measured with an EFS IFR-600 which is widely used to measure the total injection rate of diesel injector. And about 1% discrepancy in terms of cycle fuel injection quantity, was obtained. Additionally, the fuel injection rate from each nozzle hole of a double layered eight-hole diesel injection nozzle were measured and analyzed. It was found that the cycle fuel injection quantities of the lower layered nozzle holes (4 holes) were 5–15% greater than the cycle fuel injection quantities of the upper layered nozzle holes (4 holes). This was attributed to the different degrees of flow resistance encountered by the nozzle holes. The lower layered nozzle holes encountered relatively less flow resistance than the upper layered ones. This result validates the experiment results obtained from the same nozzle, where the mean fuel injection quantities from eight fuel tunnels connected to the holes, showed the same trend.
1. Introduction The performance and emission characteristics of diesel engines are largely governed by fuel atomization and spray processes which in turn are strongly influenced by the internal flow dynamics of injection nozzles [1–3]. With stringent emission regulations and increasing demand for fuel economy, injectors have become one of the most important parts of fuel injection system in diesel engines [4–6]. For a multihole injector, differences in injection rates between individual injection nozzle holes, result in non-uniform fuel distribution in space and time during spray combustion and therefore affect combustion quality and emission characteristics of diesel engines [7–9]. Bosch method [10–13] and Zeuch method [14–16] are currently two of the most common methods used to determine the instantaneous mass flow through diesel injectors. However, Charge measuring method [17] and Laser Doppler Anemometer [18] can also be used for fuel injection rate measurements. Although all of the above measuring methods are used to determine the total injection rate from multihole diesel injectors, they cannot be used to estimate hole-to-hole differences ⁎
of a multi-hole nozzle. In this regard, the development of a hole-to-hole injection rate measuring system, will be immensely significant since it could serve as a guide for the optimization of multihole injectors during manufacturing [11]. Even though the deformation test method developed by Marčič et al. [7] and mass flow rate test bench constructed by Payri et al. [19] are used to determine the injection rate of nozzle holes from a multihole injector, they can only acquire data from one hole at a time. This present some limitations since data from each hole has to be acquired one at time before hole-to-hole characteristics could be analyzed, or results obtained from a single hole could be assumed to be the same with the other nozzle hole (in the case of symmetric multi-hole nozzles). However research have shown that, even in symmetric multiholes, hole-to-hole injection rate are not the same due off-axis needle displacement, geometrical differences and internal flow characteristic difference. A transient measuring test rig, which uses the principles of spray momentum flux theorem [20–24], was used to study the behavior and stability of injection from each nozzle hole, simultaneously [1]. The experimental test rig that was used for the simultaneous data
Corresponding author. E-mail address: [email protected] (F. Luo).
https://doi.org/10.1016/j.flowmeasinst.2018.03.014 Received 11 December 2017; Received in revised form 27 February 2018; Accepted 21 March 2018 Available online 22 March 2018 0955-5986/ © 2018 Elsevier Ltd. All rights reserved.
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Nomenclature
∆1 ∆vm ρf Δ
geometrical outlet section (m2) discharge coefficient non-uniform coefficient spray impact force (N) Nozzle exit and sensor surface distance (m) mass flow rate (kg/s) spray momentum flux (kgm/s) injection pump speed (rpm) cycle fuel injection quantity (m3) time (s) time delay (s) Velocity (m/s) Pressure drop (Pa)
Ageo Cd Cn F L ṁ Ṁ n Q t t’ u ΔP
Subscript
m th below upper max min f
The customized spray momentum flux experimental setup is shown in Fig. 2. Although the experimental approach used in this study and in [22] are the same, the fuel injection systems and the injectors analyzed, were different. In the study conducted by Luo et al. [22], 5 hole asymmetric injector, used mainly in off-road machinery was investigated, whereas in this study a 6 hole symmetric nozzle injector and an eight hole double layered asymmetric nozzle injector were investigated. In [22], validation of fuel injection rates from each hole was performed by comparing the cycle fuel injection quantity of each hole (obtained by integrating the instantaneous injection rates through a complete injection cycle) to measured total fuel injected from it. Whereas in this study, the validation of fuel injection rate from the 6 hole injector, was performed by comparing the sum of the hole-to-hole cycle fuel injection rates to the total fuel injection rate (measured with an EFS IFR-600 m) from all the holes. For the 8 hole injector, the validation was performed by comparing the cycle fuel injection quantity from each hole to those measured with eight specially designed fuel separators. That is eight fuel tunnels, connected to each hole of the nozzle, were used to collect and measure the mean fuel injection quantities from them. A high-pressure common rail fuel injection system was used for fuel supply instead of a pump-line nozzle system.
2. Theoretical background and experiment Employing the law of conservation of mass and momentum at the exits of the holes [21,25], together with the Bernoulli's theorem [26], the injection rate (Vḃ ) expression in Eq. (1) was obtained
̇ geo Ca MA ρf
(1)
where (Ṁ ) is the momentum at the exits, Ageo is the geometric area of the holes, Ca is the area coefficient and ρf is the fuel density. From the spray momentum flux experiment, the momentum at the exits was obtained. The experiment was conducted by mounting piezoelectric force sensors, perpendicularly to the axial directions of the injected fuel from the various holes as shown in Fig. 1. The sensor were carefully positioned and orientated at a distance (L) that ensured that the fuel will not rebound after impact and also the effect of inertia forces were eliminated. More detailed description of the theory and the experiment procedure adopted in this study are presented in [22]. By ensuring that the effect of rebound velocity and inertia forces on the results were negligible, the momentum flux (M (t ) ) and the instantaneous injection rates at the exits (Vḃ ), were expressed as
M (t ) = F (t + t ′)
mean theoretical Lower layer Upper layer maximum minimum liquid
2.1. Experimental method
acquisition, was developed and validated with experimental results from other experimental method. After the validation, the test rig was used to acquire and analyze the hole-to-hole injection rate differences from a double layered eight hole nozzle, at various operating conditions. In this paper, the theory governing the measuring principle and the experimental setup, are described in Sections 2 and 3 respectively. The results, are presented in Section 4 and a summary conclusion in section 5.
Vḃ =
relative difference between Qbelow and Qupper Mean velocity difference(m/s) Fuel density (kg/m3) Relative error
(2)
F (t + t ′) Ageo Ca
Vḃ =
ρf
(3)
Integrating Eq. (3) over the complete injection cycle, the cycle fuel injection quantity from each nozzle hole (Q ) was obtained.
q=
Q=
∫ ∑q
F (t + t ′) Ageo Ca ρf
dt
Fig. 1. Test principle of spray momentum flux.
(4) (5)
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Fig. 2. High-pressure common rail system injection rate measurement set-up for each nozzle hole. 2500
Sensor 1 Sensor2 Sensor 3 Sensor 4 Sensor 5 Sensor 6 Sensor 7 Sensor 8
2000
Voltage (mV)
Fig. 3. Force sensor installation position. Table 1 Specifications of the piezoelectric quartz crystal force sensor. Range Natural frequency Linearity Repeatability Medium temperature Weight
0–3 N ≥ 40 kHz ≤ 1%FS ≤ 1%FS − 20–70° C 16 g
1500
1000
500
0 0
1
2
3
4
5
Force (N) Fig. 4. Corresponding relationship between output voltage and weight force.
Piezoelectric quartz crystal force sensors were mounted perpendicular to the axial direction of their corresponding nozzle hole in the first compartment of the data acquisition system test cabinet, as shown in Fig. 3. From the figure it can be seen that the orientation of the holes, ensured that the sensors had to be tilted in other to be perpendicular to the emerging spray jets. At this oriented position and under the influence of gravity, spray jets rebounds are minimized or eliminated [27]. This is because after the fuel impacts the sensor surface, it freely drops downwards. The piezoelectric force sensors, translates the force impacted on them by the spray jet, into charge signals. The signals were amplified with a charge amplifier (PPM-12KA-610) and then transmitted to a sixteen-channel data acquisition system (UA326H-16) for analysis. The data is analyzed visually on a computer and recorded for subsequent processing. After the experiment, the evaporated fuel in the fuel mist dispersal chamber, were removed with an explosion-proof fuel mist filter. The filter, extracts the fuel from the extracted air-fuel mixture in the chamber and stores it for further usage. The specifications of the piezoelectric quartz crystal force sensor, are shown in Table 1. The sensors were positioned at distances that ensured the elimination of factors that could compromise the results
[22,27]. The method adopted in calibrating the piezoelectric force sensors is the same as described in [28]. From Fig. 4, it can be seen that linear relationship were obtained for all the sensors during the calibration.
3. Results and discussion 3.1. Uniform-distributed 6-hole injector The symmetric 6-hole injector that was experimentally analyzed with the customized test rig is from a four-valve direct injection engine. Fig. 5 and Fig. 6 show the injector and the 3D model of its nozzle respectively. The injector had a nozzle hole diameter of 0.155 mm and hole length of 0.8 mm. Each nozzle hole had an inclination angle of 72.5°. As conducted in [1], the total fuel injection rates from each nozzle hole of the injector, were compared with the total fuel injection rate measured by an EFS IFR-600 m. Considering the uncertainty of a
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Experiments conducted with the customized test rig and the EFS IFR-600 m at the operating condition shown in Table 2, were compare with one another. The compared results are shown in Fig. 8(a), (b), (c). Fig. 8(a′), (b′), and (c′) shows the hole-to-hole injection rates, measured with the momentum flux test rig. The rail pressures were taken as the injection pressures and atmospheric pressure as the back pressure. As seen in Fig. 8(a′), (b′), and (c′), the global shapes of the hole-tohole injection rate time-histories, were similar at all the operating conditions. Under both methods, the injection rate time-histories, followed the same trend. This is consistent with the research results in [21,29]. From Fig. 8(a), (b), (c), it is evident that at constant injection pressure, injection rate rises rapidly with increase in needle lift. At full needle lift, the curve remains constant with slight increment, while at the closing stages, the injection rate decreases sharply. However under the injection pressures of 80, 120 and 160 MPa, it is clear that, the higher the injection pressure, the steeper the gradient of the injection rates at the transient stages (opening and closing). This is because the higher the injection pressure, the quicker the hydraulic system of the injector responds, hence resulting in a relative faster needle dynamics. It can also be observed from Fig. 8 that, with the increment of injection pressure not only increases the injection stop time but increases the peak injection rate gradually. The cycle fuel injection quantities from the injection nozzle were analyzed for the two measuring technique and compared as shown in Fig. 9. Those from the momentum flux experimental setup were computed using Eq. (5) as explained in Section 2. The difference between the computed and the measured quantities from the EFS IFR-600 m, were evaluated using:
Fig. 5. The experimental symmetric 6-hole injector.
Fig. 6. The 3-D model of the nozzle.
Δ=
Q − Q′ × 100% Q′
(6)
From Fig. 9 it is clear that, the computed cycle fuel injection quantities are slightly less than those measured by the EFS IFR-600 m. At all the operating conditions, within 5% relative error, were obtained. This shows that the accuracy of the injection rate measuring system is within acceptable limits. After establishing the accuracy of the customized injection rate measuring system, further experiments were conducted with it at the injection pressure, injection duration and injection frequency of120 MPa, 1500 μs and 6 Hz respectively. Similar trends of injection rate results between the EFS IFR-600 and the momentum flux test rig, were obtained at this condition. About 1% relative error between them, was obtained.
Fig. 7. The connection diagram of EFS IFR-600. Table 2 Operating conditions.
3.2. Two-layer eight-hole diesel injector nozzle
Parameter
Value
Injection frequency (pump speed) Injection pulse Injection pressure
6 Hz (360r/min) 1500 μs 80 MPa, 120 MPa, 160 MPa
In this section, a two layered eight-hole injector used in a four valve diesel engine, was analyzed with the customized momentum flux experimental setup. All the holes in the nozzle have diameters of 0.18 mm, length to diameter ratios of 4.17 and rounding radii of 30 µm. Holes 1, 3, 5 and 7 are the lower layered holes whiles holes 2, 4, 6 and 8 are upper layered holes of the eight-hole nozzle, as shown in Fig. 10. The test experiments operation conditions are listed in Table 3. Figs. 11–14 show the time histories of injection rate for each nozzle hole under all the operating conditions. Hole-to-hole cycle fuel injection quantities and hole-to-hole non-uniform coefficient of cycle fuel injection quantities (Cn) [22] are shown in Fig. 15 and Fig. 16 respectively. Non-uniform coefficient of cycle fuel injection quantities among nozzle holes (Cn), were analyzed with expression in Eq. (7):
single condition validation, the comparison were performed at several operating conditions. The EFS IFR-600 was equipped with a high-frequency dynamic pressure transducers, static back pressure measuring sensors and displacement sensors. It measures the total transient injection rate of all nozzle holes and the cycle fuel injection quantity of injectors with high precision. The line diagram of the EFS IFR-600 setup is shown in Fig. 7.
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Fig. 8. (a), (b), (c)are injection rate comparison between EFS IFR-600 results and experimental results. (a′), (b′), and (c′) are the hole-to-hole injection rate at different injection pressures and at the injection pulse width of 1500 μs and frequency of 6 Hz. Injection pressure in a) and a′) are 80 MPa, in b) and b′) are 120 MPa, and in c) and c′) are 160 MPa.
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Cycle fuel injection quantity of the injector (mm3)
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5.0
85
Measured by EFS Relative error
4.5
quantities among them. At the same injection pulse width, increasing the injection pressure, gradually increases the hole-to-hole cycle fuel injection quantities and reduces the non-dimensional parameter (Cn). In other words, increment in injection pressure gradually stabilizes in-nozzle hole fuel flows. Thereby decreasing the hole-to-hole cycle fuel injection quantity differences. Hole-to-hole cycle fuel injection quantities compared in Fig. 15 and analyzed in Figs. 17 and 18 show that, the cycle fuel injection quantities of the lower layered nozzle holes are 5–15% greater than those from the upper layered holes. This is due to the positioning of the holes, within the nozzle geometry. With relatively less flow resistance, the discharge coefficient and the flow velocities of the lower layered nozzle holes, are higher than the discharge coefficients and flow velocities of the upper layered holes. The cycle fuel injection quantity differences between the upper and lower layered nozzle holes are larger, depending on the injection pressure. That is difference between the two layered nozzle holes reduces with the increment of either the injection pressure or the injection pulse width. This is consistent with the results obtained in the investigations of Lu Yang et al. [30]. In their studies, eight fuel separators were used to collect and measure the mean fuel injection quantities of each hole from the same type of injector with geometrically similar nozzle to one analyzed in this study. From Fig. 17 and Fig. 18, it can be seen that, the average deviation of the fuel quantities for the upper layered nozzle holes are below the zero line. Meaning, their fuel quantities are relatively lower than those from the lower layered nozzle holes. With increment in injection pulse width or injection pressure, the degree of relative difference, minimizes (nozzle holes deviation points are close to the zero line). As the injection pulse increases, the effect of the transient stages (opening and closing) on in-nozzle flow reduces, since the needle remains at the quasi steady state (full needle lift) position, relatively longer. Also as the injection pressure increases, the needle moves faster through the transients and stay at maximum needle lift relatively longer. This is as a result of the quick response of the injector's hydraulic system.
80 4.0 3.5
70
3.0
65 60
2.5
55
Relative error (%)
75
2.0 50 1.5
45
1.0
40 1
2
3
Operating conditions number (-) Fig. 9. Comparison between EFS IFR-600 results and experimental results at different operation conditions.
Fig. 10. The layout of nozzle holes of eight hole injector.
Table 3 Operating conditions. Parameter
Value
Injection frequency Injection pulse
6 Hz (360r/min) 500 μs , 800 μs , 1000 μs , 1500 μs , 2000 μs 40 MPa, 60 MPa, 80 MPa, 100 MPa
Injection pressure
Cn =
qmax − qmin qmean
× 100%
4. Conclusion In this paper, a customized experimental test rig based on spray momentum flux was constructed to study the behavior and stability of injection from multi-hole diesel injection nozzles. The results were validated with the results obtained from a different measuring method. The following are the summary conclusions observed. After measuring and comparing the cycle fuel injection rates from a six hole nozzle (with the customized test rig and EFS IFR-600 m), it was observed that, the injection rate curves (time histories) from both measuring techniques fits well with each other. The relative error between them, was within 5%. This shows that the customize injection rate measuring system, is within acceptable limits. The cycle fuel injection quantities of the lower layered nozzle holes (1, 3, 5 and 7) of a double layered eight hole nozzle, are 5–15% greater than the cycle fuel injection quantities of the upper layered nozzle holes (2, 4, 6 and 8). With increment in injection pulse width or injection pressure, the degree of relative difference between the upper and the lower layered nozzle holes, minimizes. This is as a result of a faster needle movement due to pressure increment or as a result of a lesser effect of the transient stages (opening and closing stages) due injection pulse width increment.
(7)
As shown in Figs. 11–16, at the same operation conditions, local injection rate differences from the nozzle holes exist, although the time histories are relatively consistent. At the injection pulse width of 500 μs under all the operating condition, the injection rate curves from all the nozzle holes are triangular in shape. As the injection pulse width increases, the hole-to-hole injection rate curve, gradually transforms into a rectangular shape. The cycle fuel injection quantity of each nozzle hole, gradually increases while the non-dimensional parameter (Cn) gradually reduces, till it attains stability. Generally at the same injection pressure, increasing the injection pulse width, gradually stabilizes the injection rate curve of each nozzle hole and also, gradually decreases the differences in cycle fuel injection
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Fig. 11. Injection rate of each nozzle hole at the injection pulse width of (a) 800, (b) 1000, (c) 1500 and (d) 2000 μs, injection frequency of 6 Hz, and injection pressures of 40 MPa.
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Fig. 12. Injection rate of each nozzle hole at the injection pulse width of (a) 500, (b) 800, (c) 1000, (d) 1500 and (e) 2000 μs, injection frequency of 6 Hz, and injection pressures of 60 MPa.
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Fig. 13. Injection rate of each nozzle hole at the injection pulse width of (a) 500, (b) 800, (c) 1000, (d) 1500 and (e) 2000 μs, injection frequency of 6 Hz, and injection pressures of 80 MPa.
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Fig. 14. Injection rate of each nozzle hole at the injection pulse width of (a) 500, (b) 800, (c) 1000, (d) 1500, (e) 2000 μs, injection frequency of 6 Hz, and injection pressures of 100 MPa.
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Fig. 15. Cycle fuel injection quantities of each nozzle hole under the injection pressures of (a) 40 MPa, (b) 60 MPa, (c) 80 MPa and (d) 100 MPa at injection frequency of 6 Hz.
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Fig. 16. Non-uniform coefficient of cycle fuel injection quantities among nozzle holes under the injection pressures of (a) 40 MPa, (b) 60 MPa, (c) 80 MPa and (d) 100 MPa. All were at the injection frequency of 6 Hz.
Fig. 17. The relative average deviation of the fuel quantities of each nozzle hole, at a constant injection pressure of 100 MPa and varying injection pulse width.
Fig. 18. The relative average deviation of the fuel quantities of each nozzle hole, at a constant injection pulse width of 2000 μs and varying injection pressure. 77
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Acknowledgment
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