Exergy Engineering LLC — Department of Defense SBIR Phase II: A19-089

Description

Project scope addressed hardware solutions not additive solutions to aviation turbine fuel used on existing engine systems as applied to the Denso HP4 pump used in the General Motors Duramax L5P diesel engine.  This hardware solution would address critical wear component interfaces, during use of low lubricity fuels applied to medium-duty military diesel engines, such as the U.S Army’s Joint Light Tactical Vehicle (JLTV) and associated applications (ground or marine engines). Exergy Engineering completed investigation into failure modes and operation of a Denso HP4 Common Rail fuel injection pump using Jet-A aviation fuel under inlet temperature conditions greater than 70 degree Celsius and high fuel pressures greater than 200 MPa.  A successful accelerated test was developed to induce failures on a test rig simulating engine like conditions including, gear radial and thrust loads on the input shaft, heat loads from the gear case, and ambient air around the pump.  The final developed test cycle produced consistent pump failures for baseline assessment. Failures initiated in four areas of the pump.  The successful development of the test cycle set the stage for initial testing and validation of improvements to the HP4 design.  Analysis of the bearings identified the lubrication mechanism is not classical shaft hydrodynamics but a squeeze film mechanism that collapses with time transitioning into a thin film boundary lubrication.  The extent to which the film thickness is degraded, with the use of low viscosity fuel and the higher temperature, was calculated and compared to operation with Diesel Fuel Grade 2 (DF-2) at both normal and elevated temperatures.  This highlighted the importance of new component design strategies with low lubricity fuels. Design concepts to eliminate the critical failures were developed and analytically assessed to confirm increased lubrication film thicknesses in excess of those of the pump operating on DF-2 fuel at 40 degree Celsius.  In addition, bearing materials and coatings have been identified that offer better dry-running lubrication. Exergy Engineering has identified three core design improvement opportunities to address, not only the critical failure areas, but overall pump robustness.  During Phase I these pump component designs were developed simultaneously with applicable vendors needed for procurement.  Components were then made to test design concept fit and form. The Phase II project objective is to develop a pump technical hardware solution to demonstrate the innovative design advancements necessary for robust pump operation with low lubricity aviation turbine fuels.  Validation testing of the final design would be completed on a motorized test stand, including a 400-hour NATO test to meet applicable pump performance standards.