Currently, testing additives for their tendency to form deposits—known as “no-harm” testing—is very time-consuming and expensive due to the use of engine tests. The engines used are technologically outdated and no longer reflect the state of the art. The continued development of injection systems—driven by increasingly stringent emissions regulations and changes in fuel composition—requires a completely new approach in this area. By combining the Diesel Deposit Formation laboratory test (DDFT) with the ENIAK test bench test, an alternative to engine testing was evaluated.
The investigations were based on five reference fuels/fuel blends (B0, B10, B100, R50, and HVO) and twelve different additives from the categories of cold-flow improvers, lubricity improvers, and antioxidants. The test is applicable to both internal and external deposits in common-rail injectors, although the focus of the work was on oxidative deposits at the nozzle tip.
DDFT has proven to be a cost-effective and rapid screening method for a wide range of fuel-additive combinations, capable of modeling various deposit formation mechanisms. Additives that cause noticeable deposit formation can thus be identified in advance of test bench or engine testing. The results show that the DDFT is highly sensitive to additive additions. For fuels B0, B10, and R50, both a significant increase and a complete reduction in deposits were determined based on the measured deposit volume compared to the corresponding reference fuel. The influence of additives on deposit formation depends on the composition of the reference fuel. Biofuel components (B10, R50) have a reducing effect on deposit formation in the DDFT. The reference fuels B100 and HVO showed no deposit formation in the DDFT up to 300 °C. Even with the addition of selected additives, no deposits formed.
At the same time, selected tests were conducted using the same reference fuels on the ENIAK test bench in „closed-loop“ mode. The ENIAK test bench simulates a complete common-rail system with a central high-pressure pump and a shared pressure vessel for all four installed solenoid valve-injector test strings (EURO 6). The correlation of the results from both methods (DDFT and ENIAK) is good with regard to deposit formation and nozzle coking for the reference diesel (B0), but is limited for the other fuel systems for various reasons.
The goal of the research project has been achieved.
