Instabilities and soot formation in spherically expanding, high pressure, rich, iso-octane-air flames

Flame instabilities, cellular structures and soot formed in high pressure, rich, spherically expanding iso-octane-air flames have been studied experimentally using high speed Schlieren cinematography, OH fluorescence, Mie scattering and laser induced incandescence. Cellular structures with two wavelength ranges developed on the flame surface. The larger wavelength cellular structure was produced by the Landau-Darrieus hydrodynamic instability, while the short wavelength cellular structure was produced by the thermal-diffusive instability. Large negative curvature in the short wavelength cusps caused local flame quenching and fracture of the flame surface. In rich flames with equivalence ratio φ > 1.8, soot was formed in a honeycomb-like structure behind flame cracks associated with the large wavelength cellular structure induced by the hydrodynamic instability. The formation of soot precursors through low temperature pyrolysis was suggested as a suitable mechanism for the initiation of soot formation behind the large wavelength flame cracks

Instabilities and soot formation in high pressure explosion flames

Flame instabilities, cellular structures and soot formed in high pressure, rich, spherically expanding iso-octane-air flames have been studied experimentally using high speed Schlieren cinematography, OH fluorescence, and laser induced incandescence. Cellular structures with two wavelength ranges developed on the flame surface. In rich flames with equivalence ratio ?> 1.8, soot was formed in a honeycomb-like structure behind flame cracks associated with the large wavelength cellular structure

A length-scale analysis of instabilities in high pressure explosion flames,

Cellular flame structure in high pressure iso-octane-air explosion flames, obtained in the Leeds combustion bomb, was investigated using Schlieren cinematography and OH laser induced fluorescence. High pressure, stoichiometric, iso-octane-air explosion flames were observed to develop a relatively large wavelength cellular structure (3 mm to 7 mm) as a result of the Darrius-Landau hydrodynamic instability. High pressure, rich, iso-octane-air explosion flames ( = 1.4) were observed to develop a cellular structure with two distinct wavelengths present on the flame surface, a large wavelength cellular structure that was comparable with before (3 mm to 7 mm), and a smaller wavelength cellular structure (~ 1 mm). It is suggested that the small wavelength cellularity is caused by the thermal-diffusive instability. It is further suggested that at high pressures, the hydrodynamic instability and the thermal-diffusive instability decouple from each other, resulting in a dual wavelength cellularity

Instabilities and soot formation in high-pressure, rich, iso-octane-air explosion flames - 1. Dynamical structure

Simultaneous OH planar laser-induced fluorescence (PLIF) and Rayleigh scattering measurements have been performed on 2-bar rich iso-octane–air explosion flames obtained in the optically accessible Leeds combustion bomb. Separate shadowgraph high-speed video images have been obtained from explosion flames under similar mixture conditions. Shadowgraph images, quantitative Rayleigh images, and normalized OH concentration images have been presented for a selection of these explosion flames. Normalized experimental equilibrium OH concentrations behind the flame fronts have been compared with normalized computed equilibrium OH concentrations as a function of equivalence ratio. The ratio of superequilibrium OH concentration in the flame front to equilibrium OH concentration behind the flame front reveals the response of the flame to the thermal–diffusive instability and the resistance of the flame front to rich quenching. Burned gas temperatures have been determined from the Rayleigh scattering images in the range 1.4⩽ϕ⩽1.9 and are found to be in good agreement with the corresponding predicted adiabatic flame temperatures. Soot formation was observed to occur behind deep cusps associated with large-wavelength cracks occurring in the flame front for equivalence ratio ϕ⩾1.8 (C/O⩾0.576). The reaction time-scale for iso-octane pyrolysis to soot formation has been estimated to be approximately 7.5–10 ms

Fuel distribution measurements in a model low NOx double annular combustor using laser induced fluorescence

Planar laser induced fluorescence (PLIF) was employed in a three sector, low NOx double annular combustor in order to characterise the combusting fuel spray. Naphthalene was employed as a fluorescent agent in odourless kerosene in order to determine the behavior of the light fractions in the fuel vapour, and the light to medium fractions in the fuel spray, while 2,5 di-phenyl oxizol (ppo) was employed to determine the behavior of the heavy fractions in the fuel spray. Counter-swirl air blast atomizing fuel injectors employing a nominal fuel spray included cone angle of 90 deg were employed to inject the kerosene fuel into the double annular combustor. Radial and axial measurements were performed on the combusting spray. Spatial variations in fuel spray placement were observed, together with radial anisotropy

The optical characterisation of spray and soot formation in a diesel engine

Laser sheet drop-sizing (LSD) measurements of a Diesel spray and simultaneous laser induced incandescence/Mie scattering measurements of soot have been performed in an optically accessible, common rail, 1.9 litre, turbo-charged, direct injection Diesel engine. The diesel fuel injectors employed in this study were prototype five hole injectors, supplied by R. Bosch. An oxygenated surrogate Diesel fuel with an estimated cetane number of 54 was employed in order to reduce the amount of soot formed during combustion. The prototype five-hole injector employed produced spray jets that were distinguishable in terms of the liquid volume fraction, drop-size distribution and spray penetration distance produced. The soot volume fraction formed during combustion was found to be correlated with drop-size distribution, and local soot particle size distribution was observed to be inversely correlated with local soot volume fraction

C.A.R.S. temperature measurements and chemical kinetic modelling of autoignition in a methanol-fuelled internal combustion engine

Bibliography: p. 258-268.The temperature inside the cylinder of a methanol-fuelled single-cylinder Ricardo E6 research engine running under knocking conditions, is measured by means of Coherent Anti-Stokes Raman Spectroscopy (CARS), and the pressure is measured with a pressure transducer. In order to obviate any errors arising from deficiencies in the spectral scaling laws which are commonly used to represent nitrogen Q-branch spectra at high pressure, a purely experimental technique is employed to derive temperatures from CARS spectra by cross-correlation with a reference library of spectra recorded in an accurately calibrated high-pressure high-temperature optical cell. The temperature and pressure profiles obtained from the engine running under knocking conditions, are then used as input data for chemical kinetic modelling of end-gas autoignition. Five published mechanisms (Grotheer et al 1992, Grotheer and Kelm 1989, Norton and Dryer 1989, Dove and Warnatz 1983, .and Esser and Warnatz 1987) are used in the autoignition study, and the results for the different mechanisms are compared. A good qualitative understanding of the mechanism underlying end-gas autoignition in the engine is obtained, although the calculated autoignition points occur slightly earlier than the observed point. A sensitivity analysis of the methanol autoignition system is undertaken, and the importance of the decomposition of hydrogen peroxide and the hydroperoxyl chemistry is demonstrated. The discrepancies between the predicted results of the different mechanisms is shown to be caused by a small number of sensitive reactions for which there are conflicting data. Finally, a linear mode analysis from the geometric qualitative theory of differential equations is performed on the non-linear chemical rate equations. The equilibrium points in the generalised phase space of the non-linear chemical system are shown to be defined in terms of three regions. The equilibrium points are unstable improper nodes in the first region (T 1170K)

The characterisation of diesel cavitating flow using time-resolved light scattering

A conventional six-hole valve-covered orifice (VCO) injector nozzle has been modified in order to provide optical access to the region below the needle, and the nozzle passages. This has been achieved through the removal of the metal tip, and its replacement with a transparent acrylic tip of identical geometry. Elastic scattering of light obtained from the internal cavitating flow inside the nozzle holes of the optically accessible diesel injector tip was captured on a high speed electronic camera. The optical image data was obtained from a nozzle with a common rail pressure of 400 bar, and for two diesel fuels, in order to identify differences in cavitation behaviour. A set of 100 mean diesel fuel injection images were obtained from 30 fuel injection pulses, for each operating condition. The imaged mean cavitation occurring in the nozzle holes was converted to the mean proportion of nozzle hole area producing cavitation scattering. The mean cavitation area images were then analysed, and were able to demonstrate the inverse relationship between fuel mass injected and the relative area producing cavitation scattering

The search for innovators and early adopters of e-collaborative technologies within small and medium sized enterprises in the UK

New product diffusion theory predicts that innovators and early adopters are critical to the success of new innovations. The rate at which enterprises adopt e-Science technologies must therefore rely upon reliable market intelligence so that the critical early stages of adoption are successfully navigated by developers and planners. Failure to understand attitudes towards new technologies can lead to even useful technologies being under-adopted. This paper applies a survey based methodology to develop estimates of demand for web based virtual Collaborative technologies. We show that approximately 76% of the 1029 firms that we interviewed are technologically ready to deploy these technologies. We also show that 10% of all firms are ready look at these technologies as solutions to collaborative problem solving

Entrepreneurs'' attitude towards the computer and its effect on e-business adoption

This paper presents research exploring further the concept that many SMEs do not adopt computer based technologies due to decision maker's negative attitudes towards computers generally. Importantly, by assessing the entrepreneur's belief structure, we provide quantitative evidence how SMEs, particularly micros, are affected. Earlier research that addresses technology acceptance model (TAM) suggests that TAM parameters are particularly influential factors of e-commerce adoption, as perceived by top managers of SMEs. The model we develop is tested using a sample of 655 enterprises. The information was gathered, via a telephone survey of UK SMEs, from decisions makers in the enterprise. Technically, the paper uses k-means cluster analysis to segment respondents using the TAM perceptions, ease of use, usefulness and enjoyment. Based on two determined segments we look at the differential rate of adoption of internet, and the potential adoption of new e-collaborative technologies like video conferencing and electronic whiteboards. The diffusion of internet for low IT utility (LIT) segments was considerably slower than in the high utility segment (HIT). Similarly, the anticipated adoption of e-collaboration technologies was much lower for LIT than HIT. Interestingly, we find that LIT is populated by more micro SMEs than HIT. The results we present are limited however as our sample is considerably underweight in micro SMEs, suggesting that the problem may be much larger in the economy than our model predicts. For policy makers, this research confirms the value of knowledge transfer programs to SMEs in the form of technology support. Our research shows that organisations which have dedicated IT support will tend to be more advanced technologically than those that do not. The implication for entrepreneurs is if they can be persuaded that a technological route is beneficial to them, and that suitable support can be provided via KT, then operational efficiency gains could be made. This paper contributes to knowle