Injector nozzle coking can severely limit engine performance by limiting the amount of fuel delivered to the combustion chamber and altering the spray pattern. Injector nozzle coking is also one of the most sensitive measures of diesel fuel quality. Formation of deposits within the holes of the injector nozzle or on the outside of the injector nozzle may have an adverse effect on overall system performance.
There is no single factor that results in nozzle coking but can be classified in four major areas e.g. spray hole geometry, application duty cycle, nozzle localized temperature and the fuel quality.
This paper provides a critical review of the current understanding of the main factors affecting the deposit formation. Engine was tested by motoring dynamometer using test cycle generated by Cummins Inc, as an attempt to try to simulate field conditions. This cycle involves test conditions like running engine at maximum power, maximum engine braking condition, cycling between high & low loads and engine shut down and restart for definite time to achieve a soak period, different load and braking conditions.
For injector nozzle coking test the fuel shall be blended with a specified oil to achieve a required concentration of Zn ppm to accelerate coking.
The intention of doing this experimental analysis was to check the robustness of nozzle configuration to prevent nozzle coking under worst conditions. After the complete injector coking experimental analysis, test cell results indicate 1.26% average injector nozzle coking with injector open loop vs. 0.64% average with injector close loop which was well within 5% of cup flow loss, which is acceptable.
