Temperature distribution measurements in an optically accessible single-cylinder engine using phosphor thermometry

Combustion is the most important process in engine operation; the development of engine technology, therefore, relies upon the advancement of combustion technology. Homogeneous charge compression ignition (HCCI), low temperature combustion (LTC) and controlled auto ignition (CAI) have the potential to allow for better fuel economy and reduced emissions in comparison with spark ignition (SI) combustion. Transient temperature distribution is crucial for understanding combustion, especially heat and mass transfer as well as the chemical reactions of combustion. The authors attempt to measure 2D gas temperature distribution using phosphor thermometry techniques in a single-cylinder optical engine. The intensity ratio method from phosphorescence was employed to measure the temperature distribution. Dy:YAG phosphor was used as seeding particle, and excited by the 3rd harmonic of an Nd:YAG laser at a wavelength of 355nm. The phosphorescence was then captured by an ICCD camera connected to an image doubler. The relationship between the intensity ratios of the two wavelengths and therefore temperature were calculated. The temperature distribution of the compression stroke was measured and compared with the mean temperature calculated from in-cylinder pressure data. The results suggest that this technique can be used for 2D gas-phase temperature measurement. This technique was also used for combustion temperature measurement. The mean temperature from phosphorescence is generally consistent with the mean temperature calculated from in-cylinder pressure in the pre- and post-combustion processes.</p

Noise generation from methane/air premixed flames

Recent demands for high combustion loads and stringent emission requirements frequently induce combustioninstabilities. Since these are undesirable sources of noise and sometimes cause disastrous destruction ofcombustion equipment, the active control of combustion instabilities becomes one of the key interests incombustion research. In order to develop effective control technologies, it is required to understand themechanisms and the influencing factors governing combustion instabilities. Premixed methane/air flames in thelaminar thin annular jet burner have been studied experimentally to investigate the characteristics of self-excitednoise generation. The flame in the annular jets has various flame shapes, including ring shape, near conical shape,crown shape, and oscillating crown shape depending on equivalence ratio, mixture velocity, and air velocity. Theregimes of the existence of these flames were identified. Self-excited noise with about 70 dB was generated forthe unsteady crown shape flame. The frequency of sound pressure depended on the equivalence ratio and mixturevelocity. Sound pressure and CH* chemiluminescence were measured by using a microphone and a photomultipliertube. The frequency of generated noise was measured as functions of equivalence ratio and pre-mixturevelocity. The frequency doubling behaviour was also observed. The variation of sound pressure with time showedsimilar behaviour as that of the CH* chemiluminescence. The calculated sound pressure from the CH*chemiluminescence signal was in satisfactory agreement with the measured one, demonstrating the source ofsound generation is from the flame surface fluctuation near the downstream part of the crown shape flames. Thepresent study demonstrated that significant noise can be generated when a rich fuel/air mixture propagate into air.The flame stability regime was influenced sensitively to the supplying air through the inner tube. Further study isneeded in the future to identify the mechanism of flame surface corrugation, the noise source location, theinteraction with the diffusion flame surrounding it, and the mechanism of frequency doubling.</p

Investigating high temperature energy flow on the wall

Abstract is not available.</p

Self-excited noise generation from laminar methane/air premixed flames in thin annular jets

Self-excited noise generation from laminar flames in thin annular jets of methane/air premixture have been investigated experimentally. Various flames were observed in this flow configuration, including conical shape flames, ring shape flames, steady crown shape flames, and oscillating crown shape flames. Self-excited noise with the total sound pressure level of about 70 dB was generated from the oscillating crown shape flames for the equivalence ratios larger than 0.95. Sound pressure and CH* chemiluminescence were measured by using a microphone and a photomultiplier tube. The frequency of generated noise was measured as functions of equivalence ratio and premixture velocity. A frequency doubling phenomenon has also been observed. The measured CH* chemiluminescence data were analysed from which the corresponding sound pressure has been calculated. By comparing the data with those of measured ones, the noise source can be attributed to the flame front fluctuation near the edge of the oscillating crown-shape flames. The flame stability regime was influenced sensitively to the supplying air through the inner tube.</p

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

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

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

On the use of planar laser-induced phosphorescence (PLIP) for combustion temperature measurement in SI engines

Combustion is the most important process in courses of engine running, the development of engine technology, therefore, relies upon the advancement of combustion technology. Homogeneous charge compression ignition (HCCI) or controlled auto ignition (CAI) have potential to get lean burn, economy and good emission than spark ignition (SI) combustion. In order to investigate the effects of mixture charging to combustion, the formative process of mixture should be controlled to form stratified or homogeneous charge, second a new technique was put forward and used for studying stratified and homogeneous combustion. Transient temperature distribution is crucial for combustion study, especially for heat and mass transfer, physical and chemical action of overflow combustion. It is very difficult to get the transient temperature distribution. In this thesis the author try to measure the 2D gas temperature distribution using laser induced phosphorescence technique at a small optical engine. According to the excited property, intensity ratio method was used. The calibration was conducted by measuring the surface temperature of solid objects in a test cell. The Dy:YAG phosphor powder was excited by 355nm wavelength of a Nd:YAG laser. The median particle diameter was 4um. The phosphorescence was captured an ICCD camera connected with an image doubler. The relationship between the intensity ratios of two wavelengths with temperature was calculated. The temperature distribution of compression stroke was measured and compared with mean temperature calculated from pressure data, the maximum error is 8.35%, this suggest that this technique can be used for 2D gas phase temperature measurement. And this technique was used for 2D combustion temperature measurement in this optical engine. The flame propagation was studied by temperature distribution, three phases of combustion marked from temperature distribution is consistent with the result gotten from fuel burned mass fraction. The mean temperature of LIP have a good consistency with the mean temperature calculated from pressure at pre combustion and after combustion, but the error is more than 10% at main combustion because of chemiluminescence of combustion.</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

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