Fuel Injection Spray Patterns: A Comprehensive Guide

Fuel injection spray patterns are a critical aspect of engine performance, influencing factors such as fuel efficiency, emissions, and combustion stability. The spray pattern is primarily determined by the injector nozzle design, fuel pressure, and injection timing. In low-pressure direct injection gasoline engines, several key parameters, including the injector spray pattern, injection timing, and fuel pressure, significantly impact mixture formation.

Injector Nozzle Design and Spray Characteristics

The design of the injector nozzle is a crucial factor in determining the fuel spray pattern. Factors such as the number of holes, hole size, and hole arrangement can significantly impact the spray characteristics. A study by Hung et al. (2007) investigated the effect of an eight-hole nozzle configuration on spray patterns:

• The internal nozzle geometry and geometrical parameters were designed to offer different spray characteristics.
• Spray geometrical parameters, such as spray angle, offset angle, and spray tip penetration, were extracted from Mie-scattered spray images.
• The spray angle ranged from 60 to 90 degrees, with an offset angle of 10 to 20 degrees.
• Spray tip penetration varied from 20 to 40 mm, depending on the nozzle design and operating conditions.

Fuel Pressure and Injection Timing

Fuel pressure and injection timing also play a significant role in shaping the fuel spray pattern. Higher fuel pressure can result in a narrower spray angle and increased spray tip penetration, while lower pressure leads to a wider spray angle and reduced penetration.

• Fuel pressure in low-pressure direct injection gasoline engines typically ranges from 3 to 10 MPa.
• Injection timing is critical, as it determines the fuel spray pattern relative to the intake valve and piston position.
• Optimal injection timing can improve mixture formation, leading to better combustion efficiency and reduced emissions.

Spray Measurement and Characterization

Accurate measurement and characterization of fuel spray patterns are essential for understanding their impact on engine performance. Various techniques are employed, including:

1. High-Speed Flow Visualization:
2. Spray images are captured using a high-speed camera and strobe light.

3. Spray geometrical parameters, such as spray angle, offset angle, and spray tip penetration, are extracted from the Mie-scattered spray images.

4. Phase Doppler Interferometry (PDI):

5. PDI is used to measure spray drop sizing, including statistical drop diameters and volume flux.

6. This data provides insights into the atomization and mixture formation processes.

7. Injector Spray Testing:

8. Injector spray tests are conducted on a test bench to evaluate the spray geometry, drop sizing, and dynamic flow characteristics.
9. The test setup, procedure, and reporting guidelines are based on the SAE Gasoline Fuel Injection Standards Committee recommendations.

Predictive Methods for Injector Performance

In addition to experimental studies, researchers have explored predictive methods for assessing injector performance. Rudnitzki (2005) investigated the feasibility of using planar Mie scattering images and statistical analysis to identify good and bad injectors:

• Visual analysis of the injector images could only identify the known good and worst injectors.
• Statistical analysis of the spray using the Insight 3G pattern factor tool produced better results.
• Identification of good and bad injectors was possible using a capture delay time of 4.1 ms, a vessel pressure of 377 kPa, and a fuel-air delay of 0.952 ms.
• Similar results were obtained with a capture delay time of 3.6 ms.

Factors Affecting Spray Patterns

Several factors can influence the fuel injection spray patterns, including:

1. Injector Nozzle Design:
2. Number of holes
3. Hole size
4. Hole arrangement

5. Internal nozzle geometry

6. Fuel Pressure:

7. Higher pressure leads to narrower spray angle and increased penetration

8. Lower pressure results in wider spray angle and reduced penetration

9. Injection Timing:

10. Optimal timing improves mixture formation and combustion efficiency

11. Affects the fuel spray pattern relative to the intake valve and piston position

12. Fuel-Air Mixture Formation:

13. Spray pattern influences the air-fuel ratio and homogeneity of the mixture

14. Impacts combustion stability, emissions, and engine performance

15. Environmental Conditions:

16. Ambient temperature and pressure can affect the spray characteristics
17. Fuel properties, such as viscosity and surface tension, also play a role

Understanding and optimizing these factors are crucial for achieving efficient and clean engine operation.

Conclusion

Fuel injection spray patterns are a critical aspect of engine performance, and their optimization is essential for improving fuel efficiency, reducing emissions, and ensuring combustion stability. The spray pattern is primarily determined by the injector nozzle design, fuel pressure, and injection timing. High-speed flow visualization studies, Phase Doppler Interferometry, and statistical analysis of spray patterns can provide valuable insights into the effect of fuel spray patterns on mixture formation and injector performance.

References:

1. Hung, D. L. S., Zhu, G. G., Winkelman, J. R., Stuecken, T., & Schock, H. (2007). A High Speed Flow Visualization Study of Fuel Spray Pattern Effect on Mixture Formation in a Low Pressure Direct Injection Gasoline Engine. SAE Technical Paper Series 2007-01-1411.
2. Spray Pattern suitability – Engine & fuel engineering – Eng-Tips (2006). Retrieved from https://www.eng-tips.com/viewthread.cfm?qid=173522
3. Sykes, D., Turner, D., Stetsyuk, J., de Sercey, V., Gold, G., Martin, P., … & Crua, C. (2021). Quantitative characterisations of spray deposited liquid films and post-injection discharge on diesel injectors. Applied Thermal Engineering, 189, 116732.
4. Rudnitzki, R. M. (2005). Optical Spray Patternation of Gasoline Fuel Injectors (Master’s thesis). University of Wisconsin-Madison.
5. Park, J., Lee, K., & Suhan, K. (2018). Spray angle of port fuel injector at different pressures for gasoline-ethanol blend. Journal of Engineering and Technology Research, 2(2), 189-193.