Durability Study of a High Pressure Common Rail Fuel Injection System Using Lubricity Additive Dosed Gasoline-Like Fuel - Additional Cycle Runtime and Teardown Analysis 2019-01-0263

This study is a continuation of previous work assessing the robustness of a Cummins XPI common rail injection system operating with gasoline-like fuel. All the hardware from the original study was retained except for the high pressure pump head and check valves which were replaced due to cavitation damage. An additional 400 hour NATO cycle was run on the refurbished fuel system to achieve a total exposure time of 800 hours and detect any other significant failure modes. As in the initial investigation, fuel system parameters including pressures, temperatures and flow rates were logged on a test bench to monitor performance over time. Fuel and lubricant samples were taken every 50 hours to assess fuel consistency, metallic wear, and interaction between fuel and oil. High fidelity driving torque and flow measurements were made to compare overall system performance when operating with both diesel and light distillate fuel. Injector rate shapes were measured as a function of time, and high resolution x-ray imaging of the nozzle tips was performed as part of the final teardown analysis. At the end of testing, there was a loss of rail pressure control at low fueling rates due to cavitation of the pump inlet check valve, consistent with prior findings. Excessive fuel-in-oil dilution was not observed under normal operating conditions, and there was no indication of significant fuel contamination by oil as evidenced by elemental analysis. The gasoline-like fuel required higher fuel system driving power and had a lower hydraulic efficiency than diesel due to a combination of higher vapor formation and leakage flow. Injectors exhibited reduced fueling rates after 600 hours of exposure and showed significant signs of cavitation damage within the nozzle tip. However, fuel wetted components in sliding contact did not show extraordinary signs of wear, potentially due to the use of lubricity additive.