Olawole Abiola Kuti

Effect of Injection Pressure on Flame and Soot Characteristics of the Biodiesel Fuel Spray

The authors studied the effect of injection pressure on nonevaporating spray and spray flame characteristics of biodiesel fuel injected by a common rail injection system in a constant volume combustion vessel. Two biodiesels, biodiesel from palm oil (BDFp) and biodiesel from cooked oil (BDFc) were investigated, including JIS#2 Diesel. Mie scattering technique was employed to investigate nonevaporating spray characteristics. High-speed direct photography and two-color pyrometry were applied for spray flame characteristics. Injection pressures of 100, 200, and 300 MPa and ambient environment typical of diesel engine were used. Nonevaporating spray result showed that biodiesel fuels give longer spray tip penetrations and narrower spray angles especially for BDFp. Integrated flame luminosity of BDFp and BDFc show lower values compared to that of diesel at injection pressure of 100 MPa, and integrated flame luminosity of BDFp and BDFc is even lower than that of diesel at injection pressures of 200 and 300 MPa. Flame luminosity area follows a similar trend as that of integrated flame luminosity. Two-color pyrometry measurements show that the integrated KL factor of BDFp and BDFc yields smaller values than that of diesel at injection pressure of 100 MPa, and BDFp and BDFc present even lower values of integrated KL factors than diesel at injection pressure of 200 MPa. At an injection pressure of 300 MPa, the soot formation is extremely low for BDFp and BDFc. This indicates that the effect of soot reduction by using BDFp and BDFc is increased at high injection pressures. Flame luminosity and KL factor show the same trend at each injection pressure. Flame temperatures of BDFp and BDFc are lower than that of diesel at injection pressures of 100 and 200 MPa. BDFp and BDFc give higher flame temperature than diesel at injection pressure of 300 MPa. A simplified estimate for fuel jet air entrainment was made to interpret trends between different fuels and injection pressures. Analysis indicates that oxygen from fuel molecule plays a significant role on soot formation propensity at injection pressures of 200 and 300 MPa, and poor spray atomization and low mixing rate prohibit the effect of fuel molecule oxygen on soot reduction at injection pressure of 100 MPa. Combination of nonevaporating spray and spray combustion measurements provides a unique opportunity to understand the difference of spray flame characteristics between biodiesels and diesel fuel.

An investigation of the effects of fuel injection pressure, ambient gas density and nozzle hole diameter on surrounding gas flow of a single diesel spray by the laser-induced fluorescence–particle image velocimetry technique:

The characteristics of ambient gas motion induced by a single diesel spray were measured quantitatively by using a laser-induced fluorescence–particle image velocimetry technique under non-evaporating quiescent conditions. The effects of fuel injection pressure, ambient gas density and nozzle hole diameter on the ambient gas mass flow rate into the spray through the whole spray periphery (spray side periphery and tip periphery) were investigated quantitatively according to the gas flow velocity measurements. The results show that the captured gas mass flow rate through the spray tip periphery is prominent in the whole periphery and the proportion of the gas entrainment through the spray side periphery increases with spray development. The higher injection pressure significantly enhances the total gas mass flow rate through the whole periphery; however, the increase in the ratio of ambient gas and fuel mass flow rate becomes moderate gradually with the increase in the injection pressure. The higher ambient gas density results in a slight increase in ambient gas flow velocity along the spray side periphery and the tip periphery and a reduction of the spray volume; however, the ambient gas mass flow rate was apparently enhanced. The smaller nozzle hole diameter results in a significant decrease in the ambient gas mass flow rate and an increase in the ratio of the gas and fuel mass flow rate. Numerical simulation results provide more understanding of the spray-induced gas flow field and validate the measurement accuracy of the laser-induced fluorescence–particle image velocimetry results.

Characteristics of the ignition and combustion of biodiesel fuel spray injected by a common-rail injection system for a direct-injection diesel engine

Abstract The effect of injection pressures at 100 MPa and 200 MPa respectively on the ignition and combustion characteristics of biodiesel fuel spray injected by a common-rail injection system for a direct-injection diesel engine was investigated. Two biodiesel fuels (namely biodiesel fuel from palm oil (BDFp) and biodiesel fuel from cooking oil (BDFc)) and JIS#2 diesel fuel were utilized in this research. The Mie scattering technique was used to characterize both the non-evaporating and the evaporating spray formation processes. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. Two-colour pyrometry was applied for the soot formation processes. At all injection pressures, the biodiesel fuels (especially BDFp) gave a longer spray tip penetration and a smaller spray angle under the non-evaporating conditions while the liquid-phase penetration length was longer for the biodiesel fuels than for diesel under the evaporating conditions. From estimation using a simplified model for air entrainment by the sprays, the BDFp and BDFc exhibited lower mass ratios of air to fuel than diesel did. The ignition delay was longest for the BDFc while it was shortest for the BDFp. Both the experimental and the predicted flame lift-off lengths for the BDFp were the shortest, indicating the least percentage of entrained stoichiometric air upstream. There was no significant difference between the integrated and averaged KL factors at 100 MPa injection pressure for the BDFc and diesel fuels. At 200 MPa, the BDFc presented much lower integrated and averaged KL factors than diesel did. The averaged flame temperatures of the BDFc were found to be lower than that of diesel. The oxygen content in the BDFc played a significant role in the soot formation in comparison with the oxygen from the percentage of stoichiometric air entrained upstream of the lift-off length.

Effect of Injection Pressure on Ignition, Flame Development and Soot Formation Processes of Biodiesel Fuel Spray

The effect of injection pressure ranging from 100 to 300MPa on the ignition, flame development and soot formation characteristics of biodiesel fuel spray using a common rail injection system for direct injection (D.I.) diesel engine was investigated. Experiments were carried out in a constant volume vessel under conditions similar to the real engine condition using a single hole nozzle. Biodiesel fuels from two sources namely; palm oil (BDFp) and cooked oil (BDFc) with the commercial JIS#2diesel fuel were utilized in this research. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. The natural luminosity technique was applied to study the flame development and the two color pyrometry was applied for the soot formation processes. Ignition delay decreased as the injection pressure progressed from 100 to 300MPa. This was as a result of the enhanced mixing achieved at higher injection pressures. The BDFp’s higher cetane number facilitated shortest ignition delay when compared to the other fuels under all injection pressures. For all the fuels, the lift-off length increased as the injection pressure increased. The percentage of the stoichiometric air entrained upstream of the lift-off length by the BDFp was the lowest. The integrated, average natural luminosities and flame areas of the BDFp and BDFc were smaller at increasing pressures as compared to that of the diesel fuel flames. At the 100MPa injection pressure, the two color pyrometry measurements indicated that there was no significant difference in the integrated and averaged KL factors for all the fuels. At 200 and 300MPa injection pressures, the BDFp and the BDFc presented much lower integrated and averaged KL factors than diesel. The averaged flame temperatures of the BDFp and the BDFc were found to be lower than that of diesel except at the 300MPa injection pressure. The oxygen contents in the BDFp and the BDFc fuels played a significant role on the soot formation process.

Fuel Spray Combustion of Waste Cooking Oil and Palm Oil Biodiesel: Direct Photography and Detailed Chemical Kinetics

Ignition processes in engines is characterized by physical processes i.e. atomization and vaporization and chemical processes i.e. influence of cetane, oxygen content, and fuel molecular structure. Due to its future prospects in reducing emissions, it is crucial to investigate the physical and chemical ignition processes of biodiesel fuel whose physical and chemical properties are different from the conventional diesel fuel.

Modelling Ignition Processes of Palm Oil Biodiesel and Diesel Fuels Using a Two Stage Lagrangian Approach

The ignition characteristics of palm oil biodiesel and conventional diesel fuels are simulated using the two stage Lagrangian (TSL) 0-D modeling technique. For the diesel fuel surrogate, thermochemical and reaction kinetic data of n-heptane detailed mechanism was utilized. For the palm biodiesel, simulations were done using the reduced mechanisms for the palm oil biodiesel using mixture of methyl decanoate, methyl decenoate and n-heptane as surrogates. Validations of the simulated data were performed against experimental results. The simulation results were able to reproduce the experimental trends in the ignition delay. The chemical kinetic processes responsible for controlling ignition were investigated using the TSL model.

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

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.

An Investigation into the Effect of Hydrodynamic Cavitation on Diesel using Optical Extinction

A conventional diesel and paraffinic-rich model diesel fuel were subjected to sustained cavitation in a custom-built high-pressure recirculation flow rig. Changes to the spectral extinction coefficient at 405 nm were measured using a simple optical arrangement. The spectral extinction coefficient at 405 nm for the conventional diesel sample was observed to increase to a maximum value and then asymptotically decrease to a steady-state value, while that for the paraffinic-rich model diesel was observed to progressively decrease. It is suggested that this is caused by the sonochemical pyrolysis of mono-aromatics to form primary soot-like carbonaceous particles, which then coagulate to form larger particles, which are then trapped by the filter, leading to a steady-state spectral absorbance.