Experimental Study on the Effects of Nozzle Temperature on Internal

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Fossil Fuels

Experimental Study on the Effects of Nozzle Temperature on Internal Deposits of a Gasoline Direct Injector Jin Xiao, Haoyi Song, Xian-Pei Yang, Kai Yu, Zhen Huang, Qi Yin, Xiaojin Bai, and Xuewei Pan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01195 • Publication Date (Web): 02 Aug 2018 Downloaded from http://pubs.acs.org on August 3, 2018

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Energy & Fuels

Experimental Study on the Effects of Nozzle Temperature on Internal Deposits of a Gasoline Direct Injector

Jin Xiao1*, Haoyi Song1, Xianpei Yang1, Kai Yu1, Zhen Huang1*, Qi Yin2, Xiaojin Bai2, Xuewei Pan2 1. Key Lab. for Power Machinery and Engineering of M. O. E Shanghai Jiao Tong University 200240, Shanghai, P. R. China. 2. SAIC Motor Corporation Limited Passenger Vehicle CO. 201804, Shanghai, P. R. China.

Abstract

Internal deposit formation in the injector nozzle can both restrict the fuel flow and alter the spray characteristics of the injectors, which will lead to the loss in power and fuel economy, as well as the increase of exhaust emissions. Injector temperature is considered as a fundamental element among the parameters influencing the formation of deposits inside the injector. Although all the relative investigations have declared that the injector tip temperature showed significant relations with the formation of deposits inside, the exact relationship between the tip temperature and deposit formation was controversial since they reported a quite different result. As a result, how the temperature affects the quantity and positions of deposit formation inside the injector remained unclear. In the present work, an experimental facility that simulated the heat environment when a GDI injector was working in the engine was employed to make internal deposits form inside the injector nozzle as well as to investigate the effects of the injector tip temperature on the formation of internal injector deposits. Besides, an experimental investigation concerning the spray behaviors before and after internal deposit forming was reported. According to the results, it can be found that a suitable temperature interval existed, when beyond this temperature interval, it was not easy for deposits to form inside the injector. In addition, the positions of deposits that accumulated in the injector were significantly different under different injector tip temperatures, which leads to the *Corresponding author: E-mail address: [email protected]. Tel.:+86-21-34206858; Fax: +86-21-34205949

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conclusion that the higher the tip temperature is, the deeper the positions of deposits are. Keywords: GDI, Deposits, Nozzle temperature, Spray

1. Introduction In recent years, gasoline direct injection (GDI) engines have experienced a fast development as it exhibited high performance and excellent fuel economy. In addition, it was considered to be the proper powertrain to satisfy the severe legislation in future as well as other requirements. At the same time, the market share of vehicles with the GDI engine increased dramatically and was predicted to reach 40% of vehicles sold globally by 2030[1]. Besides, it was reported that the benefits of fuel consumption from the GDI engine could reach 15% in comparison with the PFI engine [2-6]. As a result, less CO2 would be emitted. Moreover, it was regarded to have great potential to downsize the gasoline engine[7]. However, the nozzle of the GDI injector was designed to extrude into the combustion chamber and had to be directly exposed to the high temperature combustion gas, making it easier for deposits to accumulate on. Admittedly, the injector deposits both restricted the fuel flow[8-10] and altered the spray characteristics of the injectors[11, 12]. In addition, low levels of flow restriction could be adjusted by the ECU, yet high levels of that and any levels of spray distortion could not be adequately controlled electronically, which would impose a negative influence on combustion in cylinders, causing power loss[13-15] and fuel consumption increase[13-15] and exhausting emission deterioration[13-17]. Xu et al[18] has reviewed the studies on GDI injector deposits in recent years and believed that further investigation for controlling fuel injector deposits was required in several key areas, including the deposit formation mechanism, the overall effects of nozzle temperature and T90 of the fuel on injector deposit formation. Temperature was a fundamental element among the parameters that influence the formation of deposits inside the injector, which directly determined the pathway of fuel transforming into the internal deposits[19]. Kinoshita et al.

[20]

has

proposed a deposit formation model concerning temperature after conducting several single-cylinder engine tests. They presented that deposit precursors dispersed homogeneously in the residual fuel after a fuel injection. Besides, with the passage of time, the fuel would partly evaporate, and the cohesion of the deposit precursors would accordingly progress.


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Energy & Fuels When the nozzle temperature was lower than 90 vol. % distillation temperature (T90) of the fuel, the residual fuel would not evaporate completely and leave some in a liquid state, making the deposit precursors still exist at a state of dispersion in the fuel and easy to be washed away by the next injection. On the contrary, if the nozzle temperature was higher than 90 vol. % distillation temperature, as most of the residual fuel evaporated, the deposit precursor would cohere to each other and adhere strongly to the nozzle wall, which was not easily washed away[20]. This model accorded with the experimental results conducted by themselves and part of results given by some other researchers, such as Aradi [21]. However, those results from Aradi et al[22]did not always fit the model that a tip temperature higher than T90 leads to high deposit formation in some case, and the flow rate losses at a temperature of higher than T90 were much lower than that at a lower temperature. In addition, the experimental results given by Ashida et al.[23] also failed to conform to the model above as no obvious connection was found between T90 and the fuel flow decline caused by deposits. Although all the relative investigations had suggested that the temperature of the injector tip had shown a significant relationship with the formation of deposits inside when few of them exhibiting the exact relationship. Besides, how the temperature impacted the quantity and the position of deposit formation inside the injector remained unclear. Besides, most of the researches that tended to identify the effects of some parameters on injector deposits were carried out based on engine tests[7, 10, 13, 22-25], where too many parameters should be considered to get the results, and the high labor and capital cost should be paid to support the extremely long running of the engine bench. Therefore, the impacts of one single parameter were not easy to be distinctly identified, and the high cost hindered the development in this field. To develop a bench rig with low cost for simulating DISI injector deposit formation and penetrate into the effects that injector tip temperature have on deposit formation alone, a specific facility and procedure that can realize the changes of one single variable was developed to make deposits form inside the nozzle similar to the processes in a real engine. The flow rates injectors adopted in experiments had been measured before and after the deposit formation procedure to identify the quantity of deposits under each condition. Besides, the spray characteristics of each injector had also been investigated to get the positions of deposits that form in the nozzle under different temperatures and the roles that internal deposits play in the injection processes.


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2. The Experimental System and Setup 2.1 The Experimental System The deposit formation facilities consisted of a fuel source, an injection control system, a temperature control system and an injector mounting seat, as shown in Fig.1.

Figure 1 The Schematic Diagram of the Experimental System

The fuel source was made up of a high pressure nitrogen bottle, a pressure reducing valve, an energy accumulator and a piezometer. The high pressure nitrogen gas was used to pressurize the injection fuel in the energy accumulator, and the injection pressure was controlled by a pressure reducing valve. The piezometer displayed the pressure of fuel in the fuel delivery line. The injection process was controlled by a Standard Direct Injector Driver system of NATIONAL INSTRUMENTS. The temperature of the injector tip was controlled by a closed-loop control system consisting of a temperature controller, a patch thermocouple and a heating coil. The patch thermocouple was pressed on a fixed position close to the nozzle hole on injectors’ tip surface. The control precision of the temperature fell within the range of -0.5 ⁰C~0.5 ⁰C around the setting point. After the deposit formation procedure (seen in Section 2.3), the single injection fuel quantity of each injector which represents the flow rate of the injector, was measured and compared with the data before experiment. The drop value was considered as the quantity of deposits forming inside the nozzle. The measurement was conducted by virtue of the injection


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Energy & Fuels system and a number of reagent bottles of 100ml. Each bottle was weighed before and after 100 times of injection by an electronic balance with the accuracy of 0.01mg under the injection pressure of 9 MPa and an injection duration time of 1ms. The averaged single injection quantity of each injector was used to represent the flow rate of the injector. During spray experiments, a FASTCAM high-speed photography camera was adopted to obtain the spray development images. To match the spray size and the image size when observing the spray shape, the sampling rate was determined as 10000 fps (frames per second) and the image resolution was 512×256 pixels. The camera shutter rate was 1/24000s. The time interval between two recorder images was 0.1ms. When the injection processes of different injectors with deposits forming under different temperatures were investigated, the sampling rate was set as 120000 fps and the image resolution was 128×16 pixels. The time interval between these two recorder images was 0.00833ms. A DG535 digital delay and pulse generator was employed to synchronize the start of high speed photograph cameras and that of the spray. The fuel used in spray experiments was n-heptane, while the injection pressure was 9 MPa. 2.2 Test Fuel and Injectors Two kinds of fuel were used in the deposit formation experiments. To be specific, one was commercial 95# gasoline, named A; the other was the specific gasoline with certain constituents, named B. The key characteristics of Gasoline A and B are shown in Table.1, and the distribution of the main compositions in Fuel A and Fuel B was shown in Appendix A and Appendix B, respectively. No detergent additive or other deposit-regarding additives were added to these two kinds of

fuel. Fuel A was the main fuel used to study the effects of the injector tip temperature on internal deposit formation while Fuel B was adopted to verify the rule obtained by using Fuel A. Table 1 Main characteristics of Fuel A and B Parameters

Fuel A

Fuel B

Octane Number 90% distillation temperature/T90 Final boiling point Sulphur content Aromatics content Olefin content

95.2

95.0

155ºC

172 ºC

189ºC 1 mg/kg 33.8% 5.3%

202 ºC 31 mg/kg 40.0% 11.8%

The injector used in this study was a seven-hole non-uniform GDI injector, and the diameter of each hole is 0.2mm.


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The injector nozzle is designed as the stepped hole which is the major type of injector used in GDI engines currently. The distribution of the nozzle holes and the diagram of internal configuration are shown in Fig. 2.

Figure 2 The distribution of the nozzle holes and the diagram of internal configuration 2.3 The Deposit Producing Procedure The deposit producing procedure made some reference to the ASTM D6421[26] procedure for fuel evaluation. The deposit producing procedure began with a 4-min heating period, during which the tip temperature reached the target temperature, and then the injection began at the simulated speed of 800 rpm (400 /min), the injection pressure of 9 MPa and the duration time of 0.9ms. The injection period lasted for 15s. After the injection period, the temperature of the injector tip would be maintained at the target temperature for 40 minutes to facilitate the formation of the deposits. Subsequently, the heating would be stopped and a fan run to cool the injector tip. Then, the injector tip temperature would decline to about 90ºC as it did in a real GDI engine after key-off, as reported in Ref. [25]. This period lasted for 16 min and then a new cycle began. After 44-cycle operation, the system would be stopped and the injector was taken down. Then the flow rate was measured, and the spray pattern and the injection process were photographed again. As known to related researchers, it is not extremely easy for deposits to accumulate during the running of the engine while it is relatively easy when a soak period is added to the experimental procedure. Thus, the test rig simulates the key-on and key-off of the engine and extends the high-temperature soak time to accelerate the accumulation of internal deposits. During the forming process of injector deposits, after gasoline injection, most components of the residual gasoline in the


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Energy & Fuels injector nozzle evaporate in several seconds, and then the remaining species began to transform into potential deposits through chemical reactions which were the relatively long process (dozens of minutes). Thus, as the droplet evaporation was determined by tip temperature, the reactants of the subsequent reactions to form deposits would be determined in these several seconds, and the tip temperature would further and merely affect the reaction rates rather than reaction paths, which has been demonstrated in the reference [27]. Therefore, the long soak period in the cycle is an effective way of accelerating the formation of deposits as the potential deposits really need time to form and adhere tightly to the nozzle wall, though the injector temperature would not last so long in a real GDI engine.

Figure. 3 The schematic diagram of the deposit producing procedure 3. Results and Discussion The deposit formation experiments had been conducted using the deposit formation facilities in accordance to its procedure, and the flow rates and sprays of each injector were measured before and after the deposit formation procedure. The operating conditions in this paper are shown in Table 2. The experiment was repeated three times under every condition, and the reported data are the performance of the whole injector.

Table 2 Operating conditions Operating condition Tip Temperature / ºC Fuel

1#

2#

3#

4#

5#

6#

7#

8#

9#

10#

11#

12#

13#

14#

15#

16#

17#

80

130

140

150

160

170

180

190

200

250

80

140

160

180

190

210

250

A

A

A

A

A

A A A A A ACS Paragon Plus Environment

A

B

B

B

B

B

B

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3.1 The Influence of Temperature on Quantities of Deposits The quantity of deposits forming in the injector nozzle was indicated by the decrease of flow rates before and after the deposit formation procedure. After all the measurements, the deposited injectors were cleaned using ultrasonic vibrating cleaners, and the single injection fuel quantities were measured again to confirm that the changes of flow rates after the deposit formation procedure were attributed to deposits. During ultrasonic vibrating cleaning, the solution was n-heptane dissolving a kind of deposit detergent and the time duration was 60 minutes. The tests have proved that the flow rate variation of injectors only resulted from the deposits forming during the deposit formation procedure as the single injection fuel quantity of injectors after cleaning was equivalent to that before the deposit formation procedure. Some of these data were shown in Table 3. Table 3 Flow rates of injectors before and after deposit formation and after cleaning Flow rate

Injector

Injector #1

Injector #2

Injector #3

Before deposit formation

8.36 mg

8.27 mg

8.25 mg

After deposit formation

8.22 mg

8.05 mg

7.92 mg

After cleaning

8.37 mg

8.27 mg

8.26mg

Figure 4 shows the variation of flow rates decrease after deposits forming of injectors with injector tip temperature. As can be seen in Fig.4, the quantities of deposits varying with the injector tip temperature exhibit an overall trend of firstly increasing and then decreasing for both kinds of fuels. Within the temperature range from 160 ºC to 180 ºC, more deposits formed inside the nozzle. For Fuel A, 180 ºC is the most suitable temperature for deposit formation among the temperature ranges studied in this experiment. When the tip temperature is low to 80 ºC, there are fewer deposits after the deposit formation procedure, indicating that the forming rates of deposits under this temperature were also significantly low. Nevertheless, it should be noted that deposits do exist. Similarly, the amount of deposits decreased as the temperature increased after 180 ºC. It is not easy to measure when the temperature reached 200 ºC, not to mention the measurement of higher temperature, where no trace of deposits was observed. It indicates that there exists a proper temperature interval, ACS Paragon Plus Environment

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Energy & Fuels where the chemical processes related to deposit formation like autocatalytic oxidation of residual fuel in the nozzle are faster than other conditions.

Figure 4 The decrease of flow rates under different tip temperatures As concluded from the results above, the tip temperature of the injector is a fundamental element for injector fouling. The temperature impacts the rates of deposit production derived from the residual fuel and evaporation of the residual fuel, as well as the adhesive strength of the deposits to the nozzle wall. Therefore, the effects that injector tip temperature have on deposit formation inside the nozzle are embodied in three aspects. Firstly, as the temperature increases, the growing processes of deposits, which are related to chemical processes of gasoline autoxidation, are accelerated and thus generate more deposits in unit time. Secondly, the increase of the temperature accelerates the evaporation of the residual fuel, which suggests the decrease of the total reacting time for deposit production. Thirdly, the temperature may affect the adhesive strength between deposits and the nozzle wall (this effect is only considered on a theoretical basis and fails to lend itself to actual measurement). Taking the relationship between the appropriate temperature for deposit formation and fuel characteristics into consideration, as analyzed above, the FBP (final boiling point) of fuel is a key parameter for internal injector deposits. When the injector tip temperature exceeds the FBP of the fuel, the residual fuel after injection evaporates at an extremely


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high speed, resulting in little time left for deposit production. Apparently, the comparison between the FBP of Fuel A, as shown in table 1, and the experimental results agrees well with this conclusion. Considering the experimental results of these two kind of fuel, it turned out that the nozzle temperature interval of 160-180 ºC is the ideal temperature range for deposits to accumulate in the nozzle hole. The main difference between the results of the two kinds of fuel is that the ideal temperature interval for deposit accumulation of Fuel A is broader than that of Fuel B, probably due to the broader boiling range of Fuel A, based on the analysis above regarding evaporation and processes involved in autoxidation of the residual fuel. As a result, for all versions of gasoline, 160-180 ºC should be the ideal temperature range for deposit formation inside the nozzle as long as the FBP of gasoline exceeds 180 ºC. The breadth of the temperature interval that is suitable for growing deposits varies with the boiling range of the fuel, and the upper limit should be below the FBP. When compared these results with those of Aradi[21, 22], a significantly interesting conclusion could be made. To be specific, if the fuel had the high T90 (higher than 180 ºC), then the most suitable temperature for deposit formation must be lower than T90, while if the fuel had the low T90 (lower than 160 ºC), then the most suitable temperature for deposit formation must be higher than T90. However, if the T90 of the fuel was between 160 ºC and 180 ºC, the most suitable temperature will be either lower or higher than T90. However, at all events, the most suitable temperature will be located among 160 ºC to 180 ºC. A measurement of the range of the injector tip temperature for central mounted and side mount GDI engine had been reported as Figure 3 in Ref. [28]. It is very interesting that the range of the tip temperature for central mount GDI engine right cover the 160-180 ºC deposit formation range, while that of the side mount GDI engine is much lower than this. Moreover, all relevant research showed that the deposit tendency of injector of central mount GDI engine was much severer than that of the side mount GDI engine. These results accorded well with the conclusions above. Thus, to make the tip temperature stay out of 160-180 ºC would be a good way to reduce the deposit formation inside the injector.

3.2 Injection Duration


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Energy & Fuels Based on the spray system and high speed photograph system, the variation of injection duration before and after the

deposit production procedure of each injector had been investigated under the same injection conditions. The injection pressure was 9 MPa, and the injection pulse width was 1ms. The injection fuel was n-heptane. The sampling rate of the high speed camera was 120000 fps, and the interval between two adjacent images was 8.33 µs. The injection processes were recorded by the camera, from which the start time and the end time of injection could be obtained, so that the effects of deposits generating at different temperatures on injection processes could be examined. The injection process of every injector was photographed at least 20 times. The averaged testing results are shown in Table.4 and Fig.5.

Table 4 Decrease of injection duration after the deposit formation procedure Operating Condition number

1#

2#

3#

4#

5#

6#

7#

8#

9#

10#

Tip temperature / ºC

80

130

140

150

160

170

180

190

200

250

Decrease of flow rate

0.43%

1.02%

2.09%

1.52%

2.68%

3.22%

4.05%

0.85%

0.73%

0.01%

Injection duration decrease after deposit /µs

1.7

8.3

18.3

23.7

31.1

33.3

35

41.3

46.1

0.4

It is generally believed that the deposits that affect the start time and the end time of injection are located on the ball surface and the seat surface[29], as illustrated in Fig.2. Due to the presence of deposits on these locations, the changes of the needle valve lift or the impact on fuel flow would be responsible to the variation of injection duration. Hence, it is believed that the decline of actual injection duration before and after deposit formation inside only results from the deposits on the ball surface and the seat surface. As can be seen from Fig. 5, the actual decline of injection duration increased with the increase in the tip temperature of injectors when the temperature was below 200 ºC, and then decreased. The injection duration nearly remained unchanged at a nozzle tip temperature of 250 ºC, based on which it was assumed that there was low deposit formation on the ball surface and the seat surface at this condition. Hence, the decline of injection duration also presents a shape of single peak with the increase of tip temperature as well as the decrease of flow rates. Apparently, the temperature corresponding to the peak decline of the injection time is higher than that of the flow rate, as shown in Fig.5, which indicates that the tip temperature ACS Paragon Plus Environment

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of injectors influences not only the quantity but also the positions of deposit formation in the nozzle, and that the influences on the deposit position lag behind that on flow rates. As discussed above, the ideal temperature interval for deposit formation is 160-180 ºC. When the tip temperature exceeds the range from 180 ºC to 200 ºC, due to the heat conduction, the temperature of the ball and the seat will be a little lower than the tip temperature, which probably falls within the temperature interval of 160-180 ºC, which is conductive to the formation of deposits. When the tip temperature further rises and reaches 250 ºC, for example, the temperature of the ball and the seat would be much higher than the appropriate temperature (180 ºC). As a result, few deposits are generated at this position under this condition.

Figure 5 the flow rate decrease and injection duration decrease with nozzle temperature

3.3 Spray Characteristics The spray characteristics were acquired based on the images captured by the high-speed photography system. During the image processing procedure, the color images were first converted to the grayscale style via the MATLAB program, and then a preset threshold value was chosen for all the images to extract the spray contour, when depending on measurement of the spray angle and the penetration distance. Definitions of spray parameters are shown in Fig. 6. The spray penetration distance is defined as the distance from the nozzle tip to the spray front along one of the sprays. L0 in Fig. 6 is the plane projector distance from the spray front to the nozzle tip. The actual distance is:


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Energy & Fuels

L ⁄

(1)

where L is the actual spray penetration distance and is the angle between the nozzle centerline and the selected spray centerline, which can be obtained from the design parameters. The spray cone angle is defined as the angle covered by those two tangent lines, and it connects the nozzle tip and the periphery points at the position of 1/2 penetration distance from the nozzle tip.

Figure 6 Definition of spray parameters Figure 7 shows the variation of the spray penetration distance with time after deposit formation of three injectors under operating condition 3#, 7# (Fuel A) and 12# (Fuel B), which begins with the energizing pulse given to injectors. As can be seen from Fig. 7(a), when ignoring the slight difference of the beginning time caused by high speed cameras, the penetration distance of the injector after the deposit formation procedure developed faster than that when it was new. Similarly, the same trend can also be found in Fig. 7(b) and Fig.7(c), which demonstrates that the penetration distance of a GDI injector will become larger due to the existence of deposits though the decrease in the flow rate of the injector is less than 5%. The experimental phenomenon is slightly different from that in Ref. 27[29], where the penetration distance of used injectors was slightly shorter than that of the new ones. This could be attributed to the decline of flow rates or the amount of deposits inside the nozzle. If the decline of flow rates is minor, deposits slightly narrow the nozzle holes, and the increase of the


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efflux velocity will be the main driver of the changes of the penetration distance. When the decline of flow rates is bigger, the decrease in the quantity and the momentum of one injection and the evaporation on spray tips will significantly affect the penetration distance, which shortens the penetration distance. However, this explanation should be verified by more spray tests of deposited injectors.

(a)

(b)

(c)

Figure 7. Variation of the spray penetration distance with time after deposit formation of three injectors under operating

condition (a) 3#, (b) 7# and (c) 12# at the injection pressure of 9 MPa

(b)

(b)

(c)

Figure 8. Variation of the spray cone angle with the penetration distance before and after deposit formation of three injectors

under operating condition (a) 3#, (b) 7# and (c) 12# at the injection pressure of 9 MPa

To eliminate the effects of the start time of different injectors, a curve of the spray cone angle based on the penetration distance was drawn to examining the transformation of the spray pattern before and after deposit formation inside. Fig. 8 presents the variation of the spray cone angle with the penetration distance before and after deposit formation in the nozzle


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Energy & Fuels

of two injectors at the injection pressure of 9 MPa. As illustrated in Fig. 8(b) and 8(c), the spray angle of the injectors is enlarged by about 3º after deposit formation, which reveals that the formation of deposits inside the injector nozzle does exert palpable effect on the spray characteristics of the injector even if the mass of deposits is small. However, the spray angle under operating condition 3# fails to change visibly, as can be seen in Fig. 8(a). This may be attributed to the randomness of deposit formation as the spray cone angle is defined through two of the seven beams of the injector. This appearance partly accords with the experimental results in Ref.[29], and the conclusion drawn by Sandquist et al.[11] is that “no flow reduction due to internal deposit formation in the injectors could be statistically proven; nevertheless, the spray geometry was significantly altered”.

4. Conclusions In the present paper, an experimental facility that simulates the heat environment where a GDI injector works in the engine was employed to make internal deposits form inside the injector nozzle and study the effects of injector tip temperature of a gasoline direct injector. Besides, the spray behaviors before and after internal deposit forming were observed via high speed cameras. The main conclusions are as follows: (1) There exists an ideal temperature interval for deposit formation inside the injector nozzle, beyond which deposit

accumulation is difficult. The nozzle temperature interval of 160-180 ºC is the ideal temperature range for deposits to accumulate in the nozzle hole as long as the FBP of the fuel exceeds 180 ºC. The breadth of the temperature interval that is ideal for growing deposits varies with the boiling range of the fuel. FBP should be a specific characteristic parameter for deposit formation. (2) The injector tip temperature also works to influence the position of deposits, forming in the nozzle: the higher the

temperature is, the deeper the positions of deposits are. (3) The deposits that caused the flow rate to decrease by 5% significantly influence the spray pattern and the injection

processes.


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Acknowledge This project is supported by the National Nature Science Foundation of China (51376116), the Science and Technology Commission of Shanghai Municipality (16DZ1203100) and the Science and Technology Foundation of Shanghai Automotive Industry. We would like to extend our sincere gratitude to sponsors. Supporting Information. The distribution of species in Fuel A and Fuel B are supplied as Supporting Information. References [1]

Imoehl W. Fuel Injection System Trends and Emissions Implications. SAE Detroit, MI, 2013.

[2]

Achleitner E, Bäcker H, Funaioli A. Direct Injection Systems for Otto Engines. In: SAE International, 2007, D O I: 10.4271/2007-01-1416.

[3]

Zhao F-Q, Lai M-C, Harrington DL. A Review of Mixture Preparation and Combustion Control Strategies for Spark-Ignited Direct-Injection Gasoline Engines. In: SAE International, 1997, D O I: 10.4271/970627.

[4]

Carlisle HW, Frew RW, Mills JR, Aradi AA, Avery NL. The Effect of Fuel Composition and Additive Content on Injector Deposits and Performance of an Air-Assisted Direct Injection Spark Ignition (DISI) Research Engine. SAE Technical Paper, 2001, NO. 2001-01-2030

[5]

Guthrie PW. A Review of Fuel, Intake and Combustion System Deposit Issues Relevant to 4-Stroke Gasoline Direct Fuel Injection Engines. In: SAE International, 2001, D O I: 10.4271/2001-01-1202.

[6]

Noma K, Noda T, Ashida T, Kamioka R, Hosono K, Nishida T, et al. A Study of Injector Deposits, Combustion Chamber Deposits (CCD) and Intake Valve Deposits (IVD) in Direct Injection Spark Ignition (DISI) Engines. In: SAE International, 2002, D O I: 10.4271/2002-01-2659.

[7]

Smith SS, Imoehl W. Measurement and Control of Fuel Injector Deposits in Direct Injection Gasoline Vehicles. SAE International. DOI: 10.4271/2013-01-2616, 2013

[8]

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[10]

China P, Rivere J-P. Development of a Direct Injection Spark Ignition Engine Test for Injector Fouling. SAE International, 2003, NO. 2003-01-2006

[11]

Sandquist H, Denbratt I, Owrang F, Olsson J. Influence of Fuel Parameters on Deposit Formation and Emissions in a Direct Injection Stratified Charge SI Engine. SAE Technical Paper, 2001, NO. 2001-01-2028

[12]

Lindgren R, Skogsberg M, Sandquist H, Denbratt I. The Influence of Injector Deposits on Mixture Formation in a DISC SI Engine. SAE Technical Paper, 2003, NO. 2003-01-1771

[13]

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[14]

Arters DC, Macduff MJ. The Effect on Vehicle Performance of Injector Deposits in a Direct Injection Gasoline Engine. SAE Technical Paper, 2000, NO. 2000-01-2021

[15]

Joedicke A, Krueger-Venus J, Bohr P, Cracknell R, Doyle D. Understanding the Effect of DISI Injector Deposits on Vehicle Performance. SAE Technical Paper, 2012, NO. 2012-01-0391

[16]

Berndorfer A, Breuer S, Piock W, Bacho PV. Diffusion Combustion Phenomena in GDi Engines caused by Injection Process. SAE Technical Paper, 2013, NO. 2013-01-0261

[17]

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[18]

Xu H, Wang C, Ma X, Sarangi AK, Weall A, Krueger-Venus J. Fuel injector deposits in direct-injection spark-ignition engines. Progress in Energy and Combustion Science, 2015, 50: 63-80.

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Kinoshita M, Saito A, Matsushita S, Shibata H. A Method for Suppressing Formation of Deposits on Fuel Injector


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for Direct Injection Gasoline Engine. SAE Technical Paper 1999-01-3656, 1999 [21]

Aradi A, Imoehl B, Avery N, Wells P. The Effect of Fuel Composition and Engine Operating Parameters on Injector Deposits in a High-Pressure Direct Injection Gasoline (DIG) Research Engine. SAE Technical Paper 1999-01-3690, 1999

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Ashida T, Takei Y, Hosi H. Effects of Fuel Properties on SIDI Fuel Injector Deposit. SAE Technical Paper, 2001, NO. 2001-01-3694

[24]

Aradi AA, Evans J, Miller K, Hotchkiss A. Direct Injection Gasoline (DIG) Injector Deposit Control with Additives. In: SAE International, 2003, D O I: 10.4271/2003-01-2024.

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Bacho PSV, Sofianek JK, Galante-Fox JM, McMahon CJ. Engine Test for Accelerated Fuel Deposit Formation on Injectors Used in Gasoline Direct Injection Engines. SAE International, 2009, NO. 2009-01-1495

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Page 19 of 30

Injector

Accumulator

Fuel inlet

Pressure gage 1 High pressure nitrogen

1 2 3 4 5 6 7 8 9 10 11 12 13

Energy & Fuels

Heater Thermocouple

Pressure gage 2

Temperature Controller ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Page 20 of 30

Ball seat


External hole

Internal hole

Thermocouple

Temperature(ºC)

Page 21 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Energy & Fuels

Target Temperature Next heating

Soaking Injection

Cooling

Heating ACS Paragon Plus Environment 4

12

20

28

36

44

52

Time /min

60

6

Page 22 of 30

6 5

5 .0 2

G a s o lin e A G a s o lin e B

5

R a te D e c re a s e (% )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Energy & Fuels

4 3 2

3 .8 4

4

4 .0 5 1 0

1 0 0

1 5 0

2 0 0

3 .2 2

3

2 .6 8

2 .5

2 . 0 19

2

F lo w

1 .5 2 1 .0 2

1

0 .7 7 0 .4 3

0 .8 5 0 .7 5 0 .7 3 0 .1 1

0

1 0 0

1 5 0 ACS Paragon Plus Environment

2 0 0

T e m p e r a t u r e ( °C )

2 5 0

2 5 0

Energy & Fuels

4.5

50

4.0

45

3.5

Flow rates decrease Injection duration decrease

40 35

3.0

30

2.5

25 2.0

20

1.5

15

1.0

10

0.5

5

0.0

0

80 100 120 140 160 180 200 220 240 260

Nozzle temperature (°C) ACS Paragon Plus Environment

Injection duration decrease (µs)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Flow rates decrease (%)

Page 23 of 30

mm 0

Energy & FuelsPage 24 of 30

1 2 10 θ 3 4 5 20 6 L0 7 8 9 30 10 ACS Paragon Plus Environment 11 12 40

Page 25 of 30

P e n e tra tio n d is ta n c e (m m )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Energy & Fuels

s p ra y b e fo re d e p o s it s p ra y a fte r d e p o s it

5 0 4 0

F u e l A

3 0

D e c r e a s e o f f lo w r a te : 1 .6 6 %

2 0

In je c to r tip te m p e ra tu re d u rin g d e p o s its fo rm a tio n p r o c e s s : 1 4 0 °C

1 0 0 0 .0

0 .2

0 .4

0 .6

0 .8


T im e a fte r s ta rt o f in je c tio n (m s )

1 .0

Energy & Fuels


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

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5 0

F u e l A

4 0 3 0 2 0


1 0


0 0 .0

0 .2

0 .4

0 .6

0 .8



1 .0

Page 27 of 30


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Energy & Fuels


5 0

F u e l B

4 0 3 0 2 0


1 0


0 0 .0

0 .2

0 .4

0 .6

0 .8



1 .0

Energy & Fuels

1 0 5

S p r a y c o n e a n g l e ( °)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Page 28 of 30


1 0 0 9 5


9 0 8 5 8 0 7 5 7 0 6 5

F u e l A In je c to r tip te m p e ra tu re d u rin g d e p o s its fo rm a tio n p r o c e s s : 1 4 0 °C 0

1 0

2 0

3 0

4 0



5 0

6 0

Page 29 of 30

100

spray before deposit spray after deposit

95

Spray cone angle (°)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Energy & Fuels

90

Decrease of flow rate: 3.97%

85 80

Fuel A 75 70 65

Injector tip temperature during deposits formation process: 180 °C 0

10

20

30

40

Penetration distance (mm) ACS Paragon Plus Environment

50

60

Energy & Fuels

S p r a y c o n e a n g l e ( °)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

9 5

Page 30 of 30


9 0 8 5


8 0 7 5

F u e l B

7 0


6 5 0

1 0

2 0

3 0

4 0



5 0

6 0

Experimental Study on the Effects of Nozzle Temperature on Internal

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