An Optical Characterization of the Effect of High-Pressure Hydrodynamic Cavitation on Diesel

Abstract

Most modern high-pressure common rail diesel fuel injection systems employ an internal pressure equalization system in order to provide the force necessary to support needle lift, enabling precise control of the injected fuel mass. This results in the return of a substantial proportion of the high-pressure diesel back to the fuel tank. The diesel fuel flow occurring in the injector spill passages is expected to be a cavitating flow, which is known to promote fuel ageing. The cavitation of diesel promotes nano-particle formation through induced pyrolysis and oxidation, which may result in deposit formation in the vehicle fuel system.A purpose-built high-pressure cavitation flow rig has been employed to investigate the stability of unadditised crude-oil derived diesel and a paraffin-blend model diesel, which were subjected to continuous hydrodynamic cavitation flow across a single-hole research diesel nozzle. Continuous in-situ spectral optical extinction (405 nm) has been employed to identify, determine and measure variations in fuel composition as a function of the cavitation duration.The results of two high-pressure diesel cavitation experiments are reported. The first dealt with the effect of injection pressure on the rate of induced variation in chemical composition of diesel, and concluded that faster degradation of the fuel occurred at higher pressure.The second experiment involved an investigation into the variation in composition occurring in diesel fuel and the paraffin-blend model diesel, subjected to cavitating flow over a longer duration. Observed differences suggest that the high-pressure cavitation resulted in hydrodynamic sono-chemical destruction of aromatics in the diesel, which is believed to lead to carbonaceous nano-particle formation.

Dynamics of post-injection fuel flow in mini-sac diesel injectors part 1: Admission of external gases and implications for deposit formation

“…The recirculation of high-pressure fuel across control valve nozzles is capable of stressing the fuel, which may lead to premature ageing and degradation. 30–35 Four types of deposits have been observed to form throughout the fuel injection system in these studies. They are (1) a hard lacquer coating the internal stainless steel surfaces, (2) sticky brown/black deposits (likely to be caused by fuel ageing and degradation), (3) crusty brown/black carbonaceous aggregates that collect in small clearance regions and (4) black particles and aggregates with a ferromagnetic response.…”

Hydrodynamic luminescence in a model diesel injector return valve

“…16–18 A further industry study of the effect of ultrasonic cavitation on diesel fuel showed that the ultrasonic excitation produced sono-chemical pyrolysis reactions that led to the formation of sticky black gums and soot-like nano-particles and aggregated particulates. 13 In parallel with this, Jeshani, 19 Fatmi 20 and Lockett et al 12,21,22 have investigated the effect of hydrodynamic cavitation in diesel nozzles on diesel fuel. This work employed time-resolved in situ measurements of the optical attenuation coefficient of various diesel fuel samples as a function of cavitation exposure time, together with 2-column gas chromatography (2-D GC×GC) measurements of the composition of samples obtained before and after cavitation, and ultraviolet-visible (uv-vis) absorption spectrophotometry.…”