On the use of the laser sheet drop-sizing (LSD) technique: droplet size distribution by uncertainty analysis

Sprays are used in many combustion systems such as gasoline/diesel engines and gas turbines. In order to meet more stringent emissions regulations, advanced developments of the fuel injection systems are required. For a given type of injector design, representative spray characteristics such as droplet size, size distribution, spray tip penetration and spray angel are largely dependent upon the injection condition. To further development of fuel injection strategies, a clear understanding of the transient nature of the injector spray should be established.A laser sheet drop-sizing (LSD) technique has been applied in transient fuel spray to understand the spray characteristics of an air-assisted, direct fuel injector. Ensemble averaged, planar images of the laser induced fluorescence (LIF) and Mie scattering from the spray have been obtained to measure Sauter mean diameter (SMD). Planar droplet size distribution of the spray from the injector has been investigated by means of uncertainty analysis of the LIF and Mie scattering images. Larger droplets exist in the spray tip and periphery of the spray, and the standard deviation of droplet size distribution are also high in these region. Examining both the droplet size and size distribution images provide more details of the transient spray development.</p

Transient spray behaviour of an air-assisted liquid injector

This paper presents an experimental study of an air-assisted, direct fuel injector in a constant volume chamber. This injector is the principal component of a spray guided injection system manufactured by Orbital Australia, Pty. Ltd. Ensemble averaged, planar images of the laser induced fluorescence (LIF) and Mie scattering from the spray are obtained to measure the Sauter mean diameter (SMD) for varying injection and chamber pressures. Back-illuminated images are also obtained at the same conditions, and the penetration length and spray width are also determined. Non-dimensional parameters for both the SMD and the penetration rate are then proposed, and which achieve good collapse of the experimental results. This demonstrates the significant injection parameters that control the spray behaviour.</p

Nonlinear dynamics of thermoacoustic instability using a kinematic, premixed flame model

This paper considers a simple, nonlinear model of a ductedlaminar flame. Ducted flames are susceptible to thermoacoustic instability, in which perturbations in the flame heat release drive acoustic modes of the duct that, in turn, drive the flame perturbations. Both the forced response of the flame and the selfexcited response of system are studied numerically. The overall system demonstrates limit cycles in the heat release, duct velocityand static pressure. The effect of varying the duct geometry is examined, and the form of the system’s steady state behaviour is found to be strongly dependent on the system’s configuration. This final result infers that the use of a simple saturation element to model the flame non-linearity is inappropriate.</p

An experimental study of the transfer function of a ducted, laminar premixed flame

This paper presents an experimental study of the transfer function of a ducted, laminar, premixed flame. This transfer function is defined as the ratio of the fluctuations in flame heat release to the flow velocity modulations at the base of the flame. A conical, laminar, propane/air premixed flame stabilised at the rim of the burner and confined in a glass tube is considered. The flame is excited by incident acoustic waves generated bya loud speaker over a range of forcing frequencies. The fluctuations of heat release due to corrugation of the flame by the acoustic wave is measured using a photo-multiplier tube (PMT)while the flow velocity fluctuation is determined by considering the loud speaker diaphragm motion and assuming conservation of classical acoustic energy within the burner. In keeping with other studies, the results clearly show qualitatively the low-pass filter nature of the flame. The decay of the amplitude of theflame transfer function by increase of forcing frequency is further supported by images of the excited flame.</p

Spray behaviour of hydrous ethanol fuel (E93) under cold condition

Hydrous ethanol fuels can be used to substitute gasoline inengine applications. The behaviour of such as fuel spray (E93, 93% ethanol and 7% water) was investigated under various ambient temperatures, including sub-zero conditions, by means of high-speed direct photography and laser light sheet illumination techniques (Mie scattering). The experimental results show that the spray patterns are not significantly changed. In the case of low ambient temperature, the spray tip penetration decreases and the spray angle keeps almost constant once the spray becomes fully developed. The results also show that scaling of the spray tip penetration rate previously proposed by the authors achieves reasonable collapse of the experimental results. Normalized droplet diameter was also obtained, and shows that larger droplets formed are at sub-zero temperature.</p

Dynamic response of a ducted laminar premixed flame, part I: low amplitude forcing

This paper presents an experimental study of the dynamics of a ducted, conical, laminar premixed flame subjected to low amplitude, acoustic excitation. The heat release response of the flame to velocity disturbances is investigated through measurement of the so called ‘flame transfer function’ for a wide range of forcing frequencies. The results agree well with those predicted by existing linear kinematic theories. The level of agreement, particularly in phase, for some of the experimental conditions appeared to be higher than any other previously reported validation of these theories. In keepingwith others, high speed photography of the flame clearly shows that the flame response includes waves on the flame front which are formed at the base and then convect along the flame.</p

Experimental investigation of the linear and non-linear dynamics of a ducted, laminar premixed flame

This work investigates experimentally the linear and non-linear dynamics of a ducted, conical, laminar premixed flame under forced acoustic excitation. Upstream travelling acoustic waves hit the flame at varying amplitudes. The flame transfer function is measured. In particular, for velocity disturbance amplitudes close to the mean flow velocity the phase of the transfer function shows significant difference to that at weak excitation. Instantaneous images of the flame under excitation suggest that the non-linearity is associated with the movement of the flame base at high levelsof excitation, which is assumed fixed in the kinematic linear theory. Further work by the group will attempt to explain how non-linearity comes into play at higher forcing amplitudes.</p

Dynamic response of a ducted laminar premixed flame, part II: higher amplitude forcing

This paper presents an experimental study of the non-linear response of a conical, laminar, premixed flame to acoustic excitation. The linear dynamics of this flame were discussed in a companion paper. The amplitude of the velocity disturbances upstream of the flame is increased to about 90% of the mean upstream flow velocity. It is shown that the measured flame transfer functions at higher amplitude forcing differ significantly from those at low amplitudes. The disparity is mostly in phase and manifests itself as a systematic deviation from the linear phase response at low forcing amplitude, to a roughly constant phase at high amplitudes. The origin of this phase behaviour is then sought through analysis of the excited flame images. It is shown that the observed phase response is due to the difference in the flame disturbance evolution at low and high amplitude excitation.</p

Low temperature starting on a pure ethanol fuelled direct injection engine

In the current study cold start tests have beenperformed on a multi-cylinder, spray guided directinjection, spark ignition engine. The direct injection systemwas a centrally mounted dual fluid type injecting fuel andair simultaneously. The engine has been started on ethanolat soaked temperatures from +25?C through to -10?C.Development of engine hardware, software and calibrationwas undertaken to optimise cold start times, whilst qualitymetrics were used to evaluate the performance of the starts.Consideration has been taken to restrict hardware options toproduction viable components. Conclusions are drawn regarding the start performance of an E100 spray guide DIengine at low temperatures.</p

Transient behaviour of the fuel spray from an air-assisted, direct fuel injector

The transient behaviour of the fuel spray from an air-assisted fuel injector in a constant volume chamber has been investigated experimentally. The relative Sauter mean diameter (SMD) of the spray droplets was determined using planar laser induced fluorescence (PLIF) and planar Mie scattering. Planar images of the ensemble averaged relative SMD with various injection conditions were obtained by calculating the ratio between the two laser light intensities at a given point. The penetration length and the spray shape factor were also obtained. The ensemble averaged results suggest the existence of vortices that are shed from the injector tip, and which entrain the smaller droplets. Results also show that the characteristics of the injector vary weakly with several particular injection parameters, notably the fuel injection pressure and the delay between fuel and air injection.</p