Mass and Momentum Flux Measurements With a High Pressure Common Rail Diesel Fuel Injector

The combined optimization of diesel engine power, fuel consumption, and emissions output significantly drives the development and tuning of engines. One leading subsystem that continues to receive major development and advancement is the fuel system. High pressure common rail systems lead fuel injection technology and utilize both solenoid and piezoelectric actuated injectors with a wide range of pressure and injection scheduling control. To optimize engine operation the fuel system’s capability is implemented through complex fuel scheduling coupled with charge preparation. With the number of parameters to control, fuel delivery (including dynamic flow characteristics) is one that must be well understood. Most rate of injection systems provide mass flow rate; however, studies have shown that momentum flux is a critical parameter controlling spray entrainment and penetration. To obtain the mass flow rate and momentum flux for a high pressure common rail diesel fuel injector, a rate of injection meter was designed, constructed, and tested allowing for the dynamic measurement of fuel injection with the capability of in-situ operation in a combustion vessel. Measurements were obtained by recording the force signal from a fuel spray jet impinging on the anvil of a force transducer. Combining the force signal with a measure of cumulative injected mass enables calculation of mass and momentum dynamics. The injection system consisted of a Bosch Generation 2 CRIP 2.2 solenoid controlled fuel injector with a single hole 0.129 mm diameter injector nozzle, driven by a custom programmable injector driver from Southwest Research Institute. Testing control variables were injection pressure and injection duration while using #2 ULSD fuel. Initial results showed high repeatability with a COV of less than 1.1 percent for all injection parameters with an average C_d of 0.92 and C_a of 0.97 for a mean injection pressure of 852 bar. A six point injection pressure sweep from 1000 to 1810 bar showed a 1.74 mg/ms overall increase in injection rate and a 0.16 ms overall decrease in fuel discharge duration. A six point injection duration sweep from 0.25 ms to 1.50 ms showed a 3.36 mg/ms total injection rate increase and a 0.68 ms overall increase in fuel discharge time while maintaining a consistent start-of-injection delay. The results show that this injection rate apparatus provides needed information on injection characteristics to assist engine manufacturers with achieving goals of high power with minimal emissions. Furthermore, it has been shown that this system is versatile for future injector characterizations over a wide range of pressures and durations, along with fuel type and injector parameters including nozzle hole diameter.