Parametric studies of cavitation dependence on hydrocarbon and biodiesel fuel injection flows

Ndamuso, N. (2017). Parametric studies of cavitation dependence on hydrocarbon and biodiesel fuel injection flows. (Unpublished Doctoral thesis, City, University of London)

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Abstract

The parametric studies investigated the cavitation phenomena occurring in Diesel Fuel Injection Equipment using immersed jets. The studies looked at cavitation from the incipient stage, to the fully developed stage, to leaving the fuel to cavitate for a sustained period of time. The studies were conducted with the aim of understanding the cavitation phenomena occurring inside the Fuel Injection Equipment making use of purposed built continuous flow rigs.

The first part investigated the onset of cavitation taking place inside a mechanical 80 bar continuous recirculated flow rig that mimicked the flow inside the injectors spill valves as well as the flow inside the high-pressure pumps spill valves during the first stages of cavitation.
High velocity jets of variable concentration were considered, from the incipient stage to the fully developed stage, focusing on the impact that changing the fuel composition has on the jets as well as on the impact it has on the geometrical parameters of the nozzle valves. The rig made use of custom made Acrylic, Brass and Aluminum-steel nozzles of Cylindrical, Hemispherical and Conical geometries respectively.

The n-Octane, n-Decane, n-Dodecane, n-Tetradecane and n-Hexadecane mixtures were directed into an optically accessible receiver using single hole injector nozzles of 0.14mm and 0.25 mm hole diameters respectively. Parameters such as the fuel composition, the geometry and the material of the nozzles, as well as the operating conditions of the fuels were looked into where 25 repetitive sets of measurements were completed taking into consideration each parameter respectively. Incipient cavitation was associated with the flow outside of the nozzle and was visually observed at the top of the nozzle hole. Cavitation additionally occurred between the layers of the turbulent high immersed jet flow and the stagnant fluid inside the receiver.

The onset of cavitation was obtained using the fuel Upstream Pressure to Downstream Pressure ratio. At the point of onset, the results showed that the Upstream Pressure to Downstream Pressure ratio decreased with the increase of n-Octane percentage in the mixture when considering the Cylindrical and the Hemispherical nozzles. When considering the Conical nozzle on the other hand, the critical Upstream Pressure to Downstream Pressure ratio increased with the increase of n-Octane concentration. The results also showed that the jet length and width increased when varying the diameter of the nozzle hole from 0.14 mm to 0.25 mm.

Furthermore, the total Saturated Vapour Pressure increased with the increase in n-Octane concentration, where the increase in the propensity of the flowing fuel through the Cylindrical and Hemispherical nozzles, to cavitate was noted. On the other hand, the propensity of the Conical nozzles to cavitate decreased with the increase in Saturated Vapour Pressure.

The second part of the study investigated the sustained hydrodynamic cavitation taking place inside a mechanical 1650 bar continuous recirculated flow rig, mimicking the flow inside the injectors spill valves and high-pressure pumps spill valves at a later stage of cavitation as the fuel was left to cavitate for a longer period of time, leading to the degradation of the fuel due to changes in the fuel’s chemical composition taking place during cavitation.

A needleless 0.213 mm single hole diameter Cylindrical nozzle was considered, as the Commercial Diesel fuel, the biofuel Rape Methyl Ester and the Gas to Liquids paraffin blend were left consecutively to cavitate for a period of 30 hours. The volume flow rate was obtained as 1.129 Liter per minutes considering a Discharge Coefficient of 0.8.

The results showed that by passing a 405nm laser over the 30 hours period through the cavitated fuel mixtures, a decrease with time of the transmission signal of the laser beam penetrating all tested fuels respectively was noticed. The laser beams experienced a decrease in strength due to the changes in the chemical composition of the fuel as high pressures and high temperatures took place inside the receiver. The effect of heating the fuels overnight inside a modified Water Bath tea urn at 60 degrees Celsius was looked into in order to separate the impact of temperature to the impact of cavitation alone. The effect of subjecting to fuel to cavitation and heating was greater than the effect of subjecting the fuel to heating alone.

The Gas to Liquids fuel was visually transparent compared to the commercial Diesel fuel and had the highest laser transmission signal.

Of all three fuels, the Commercial Aged Diesel fuel had the lowest laser transmission signal as the impurities inside the fuel changed the chemical composition of the fuel due to sustained hydrodynamic cavitation.

Item Type: Thesis (Doctoral)
Subjects: T Technology > TJ Mechanical engineering and machinery
Divisions: City University London PhD theses
School of Engineering & Mathematical Sciences > Engineering
URI: http://openaccess.city.ac.uk/id/eprint/19228

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