Influence of Residence Time on Fuel Spray Sauter Mean Diameter (SMD) and emissions using Biodiesel and its Blends in a Low NOx Gas Turbine Combustor

Biodiesels have advantages of low carbon footprint, reduced toxic emissions, improved energy supply security and sustainability and therefore attracted attentions in both industrial and aero gas turbines sectors. Industrial gas turbine applications are more practical biodiesels due to low temperature waxing and flow problems at altitude for aero gas turbine applications. This paper investigated the use of biodiesels in a low NOx radial swirler, as used in some industrial low NOx gas turbines. A waste cooking oil derived methyl ester biodiesel (WME) was tested on a radial swirler industrial low NOx gas turbine combustor under atmospheric pressure, 600K air inlet temperature and reference Mach number of 0.017&0.023. The pure WME, its blends with kerosene (B20 and B50) and pure kerosene were tested for gaseous emissions and lean extinction as a function of equivalence ratio for both Mach numbers. Sauter Mean Diameter (SMD) of the fuel spray droplets was calculated. The results showed that the WME and its blends had lower CO, UHC emissions and higher NOx emissions than the kerosene. The weak extinction limits were determined for all fuels and B100 has the lowest value. The higher air velocity (at Mach=0.023) resulted in smaller SMDs which improved the mixing and atomizing of fuels and thus led to reductions in NOx emissions

Effect of steam exploded treatment on the reactivity of pine wood

A commercial thermally treated biomass process known as ‘steam exploded biomass’ provided the treated biomass samples for this project together with the original yellow pine wood. The aim was to investigate the change in pulverised biomass reactivity. The steam exploded biomass is processed into pellets in the normal way and are known as black pellets (BP). The material was investigated using the Hartmann dust explosibility equipment. This enables the minimum explosion concentration (MEC) to be determined together with the initial rate of pressure rise and the flame speed and these latter parameters are measures of the mixture reactivity. BP was found to have a higher reactivity than the raw biomass with a much leaner MEC. A good correlation was found between the initial rate of pressure rise and the flame speed for the raw wood sample. Surface morphology was performed to investigate the effects of the steam exploded treatment. This showed the enhancement of the proportion of fines. The particle size distribution was determined and this confirmed the enhancement of the fineness of the treated sample. The enhanced reactivity of BP was found to be due to the greater proportion of fine particles which had a higher heating rate and a greater release of volatiles. The steam explosion treatment was found to be an effective pre-treatment in facilitating the combustion of renewable fuel and the main effect was that it was more easily milled, changes in the biomass chemistry was of secondary importance

Burning Properties and Flame Propagation of Varying Size Pulverised Rice Husks

Flame propagation in different size fractions of a rice husk (RH) crop residues were investigated using an ISO 1 m3 dust explosion vessel. This was modified to operate with coarse biomass and for the determination of flame speeds. The flame speed, burning velocity and Kst were found to be greater for the finer fractions compared to the coarser sizes. The MEC were measured at 0.27 equivalence ratio (Ø) for the finest fraction to 1.4Ø for the coarser fraction. The most reactive concentration was measured at lower Ø for fine particles and higher Ø for coarse particles. The maximum Kst for the fine particles was 83 bar m/s and 33 bar m/s for the coarse particles. The size distribution of coarse rice husk particles always has a fine fraction and the flame propagation occurs first in the fine particles, with the coarse particles burning in the hot products of combustion of the fine particles. The fine particle fraction in a coarse mixture has to be flammable and as there is a low proportion of the mixture in the fine fraction, the overall concentration of particles has to increase for the concentration of fines to be flammable. This resulted in the observed lean flammability limit that was richer than stoichiometric for coarse size mixtures

Subresultants in multiple roots: an extremal case

We provide explicit formulae for the coefficients of the order-d polynomial subresultant of (x-\alpha)^m and (x-\beta)^n with respect to the set of Bernstein polynomials \{(x-\alpha)^j(x-\beta)^{d-j}, \, 0\le j\le d\}. They are given by hypergeometric expressions arising from determinants of binomial Hankel matrices.Comment: 18 pages, uses elsart. Revised version accepted for publication at Linear Algebra and its Application

An efficient phased mission reliability analysis for autonomous vehicles

Autonomous systems are becoming more commonly used, especially in hazardous situations. Such systems are expected to make their own decisions about future actions when some capabilities degrade due to failures of their subsystems. Such decisions are made without human input, therefore they need to be well-informed in a short time when the situation is analysed and future consequences of the failure are estimated. The future planning of the mission should take account of the likelihood of mission failure. The reliability analysis for autonomous systems can be performed using the methodologies developed for phased mission analysis, where the causes of failure for each phase in the mission can be expressed by fault trees. Unmanned Autonomous Vehicles (UAVs) are of a particular interest in the aeronautical industry, where it is a long term ambition to operate them routinely in civil airspace. Safety is the main requirement for the UAV operation and the calculation of failure probability of each phase and the overall mission is the topic of this paper. When components or sub-systems fail or environmental conditions throughout the mission change, these changes can affect the future mission. The new proposed methodology takes into account the available diagnostics data and is used to predict future capabilities of the UAV in real-time. Since this methodology is based on the efficient BDD method, the quickly provided advice can be used in making decisions. When failures occur appropriate actions are required in order to preserve safety of the autonomous vehicle. The overall decision making strategy for autonomous vehicles is explained in this paper. Some limitations of the methodology are discussed and further improvements are presented based on experimental results

Steam Exploded Pine Wood: The Influence of Particle Size on Mixture Reactivity

Power generation using waste material from the processing of agricultural crops can be a viable biomass energy source. However, there is scant data on their burning properties and this work presents measurements of the minimum explosion concentration (MEC), flame speed, Kst , and peak pressure for pulverised pine wood and steam exploded (black pellets) pine wood. The ISO 1 m3 dust explosion vessel was used, modified to operate on relatively coarse paticles, using a hemispherical dust disperser on the floor of the vessel and an external blast of 20bar compressed air. The pulverized material was sieved into the size fractions <500µm, <63, 63-15-, 150-300, 300-500µm to study the coarse particles used in biomass power generation. The MEC was measured in the range of 0.6-0.85 burnt equivalence ratio, Øburnt,. The measured Kst (25-60 bar m/s) and turbulent flame speeds (~1.5 - 5 m/s) These results show that the steam exploded pine biomass was more reactive than the raw pine, due to the finer particle size for the steam explosed biomass

Flame speed and Kst reactivity data for pulverised corn cobs and peanut shells.

Power generation using waste material from the processing of agricultural crops can be a viable biomass energy source. However, there is scant data on their burning properties and this work presents flame speed and explosion Kst data for two agricultural waste materials: corn cobs and peanut shells. Both parameters were measured on the ISO 1 m3 dust explosion equipment. Two coarse size fractions of corn cobs (CC) and peanut shells (PS) of size less than 500 μm were tested using the Leeds 1 m3 vessel and were compared with two pulverized coal samples. This is typical of the size fraction used in pulverized coal power stations and of pulverized biomass currently used in power generation. The explosion parameters minimum explosive concentration (MEC), rate of pressure rise (dP/dt), deflagration constant (Kst), peak to initial pressure rise (Pm/Pi), turbulent and laminar flame speeds were determined using a calibrated hemispherical disperser in the 1 m3 vessel. MEC were measured in the range of 0.6-0.85 in terms of burnt equivalence ratio, Øburnt, which were comparable to the coal samples. The measured Kst (25-60 bar m/s) and turbulent flame speeds (~1.3 m/s) were lower than for coal, which was a reflection of the lower calorific value. These results showed that these crop residues are technically feasible power plant fuels to burn alongside coal or as a renewable biofuel on their own

Combustion of Pulverized Biomass Crop Residues and Their Explosion Characteristics

Two Pakistani crop residues bagasse (B) and wheat straw (WS), both with high ash content, were milled to <63µm and the ISO 1 m3 explosion equipment was used to investigate flame propagation in the dispersed cloud of pulverised biomass. Their turbulent flame speed was measured and the Kst (dP/dtmaxV1/3) and comparison was made with two pulverised coal samples. Minimum Explosion Concentration (MEC) values for B and WS were, in terms of the burnt dust mass equivalence ratio (Ø) 0.2Ø to 0.3Ø , which was leaner than for the coal samples. These MEC were lower than had previously been determined using the Hartmann explosion tube, and this was considered to be due to the 10 kJ ignition energy in the 1 m3 equipment and 4J spark energy in the Hartmann explosion tube, which extended the lean limit in the 1 m3 equipment. Peak turbulent flame speeds were 3.8 m/s for B and 3.0 m/s for WS compared with 3.5–5.2 m/s for the two coal samples. The peak Kst was 103 bar m/s for bagasse and 80 bar m/s for wheat straw and the two coal samples had peak Kst of 78 and 120 bar m/s. Overall the agricultural biomass and coal samples had a similar range of reactivity. Thus these agricultural crop residues are a viable renewable fuel for co-firing with coal or as 100% biofuel operation of steam power plants

The role of virtual photons in nanoscale photonics

The fundamental theory of processes and properties associated with nanoscale photonics should properly account for the quantum nature of both the matter and the radiation field. A familiar example is the Casimir force, whose significant role in nanoelectromechanical systems is widely recognised; the correct representation invokes the creation of short-lived virtual photons from the vacuum. In fact, there is an extensive range of nanophotonic interactions in which virtual photon exchange plays a vital role, mediating the coupling between particles. This review surveys recent theory and applications, also exhibiting novel insights into key electrodynamic mechanisms. Examples are numerous and include: laser-induced inter-particle forces known as optical binding; non-parametric frequency-conversion processes especially in rare-earth doped materials; light-harvesting polymer materials that involve electronic energy transfer between their constituent chromophores. An assessment of these and the latest prospective applications concludes with a view on future directions of research