Effect of diesel injector tip deposits on transient spray behavior

Abstract

The structural characteristics of high pressure diesel sprays have been investigated using two different complementary techniques, and the impact of injector fouling on the spray development has been assessed. In the first novel technique, fuel was injected into a reservoir of water, a liquid that offered high density ambient conditions. In a second technique, fuel was injected into a pressurised constant volume chamber.

The fuel spray cone angle from a fouled injector was found to increase by 10-140% when sprayed into water, as compared to the cone angle from a new injector. The presence of carbonaceous deposits accumulated during regular vehicle operation was found to particularly affect the early stages of spray evolution, and led to a marked increase in the cycle to cycle variability of the spray shape, with the variability in the cone angle being some 2 – 3 times greater for a fouled injector as compared to a clean one. Transient radial bulges were noted in the case of the fouled injector which could potentially reduce the axial momentum and hence detrimentally impact the combustion performance of the diesel engines.

Droplets and ligaments formed at the end of injection from a multi-orifice injector were observed to be random and chaotic, varying from injection to injection and from orifice to orifice. Despite the adverse early fuel spray evolution from the deposit rich injector compared to the new injectors, the end of injection ligament and droplet formations showed no qualitative difference based on the condition of the injectors.