Pedro Teixeira Lacava

Pulsating combustion characteristics of a spray flame in a Rijke tube with two different atomizers

Pulsating spray combustion in a Rijke tube was characterized. A specially designed Y-type atomizer and a commercially available solid-cone atomizer were used. Both were characterized in terms of spray Sauter mean diameter using a phase Doppler particle analyser. The operating regions for which acoustic oscillations were excited in the Rijke tube were identified. These regions are characterized by atomizing air, fuel and combustion air flow rates, atomizer position in the tube, and spray mean droplet diameters. With the Y-type atomizer, oscillations did not have a defined structure, and the pressure amplitudes varied without control. Pulsations were generated only in fuel-rich combustion. With the solid-cone atomizer, operating regions for which acoustic oscillations occurred in the combustor were also identified. In this case, pulsations were generated at near-stoichiometric combustion. Sound pressure amplitudes for the oscillating cases, though present, were much more difficult to control and of lower magnitude than in similar studies related to the pulsating combustion of solid (coal, wood, agricultural residue) and gaseous (propane, natural gas, acetylene) fuels in Rijke combustors.

Experimental Evaluation of Low Pressure-Swirl Atomizer Applied Engineering Design Procedure

In a pressure-swirl atomizer a swirling motion is imparted to the fuel leading it, under the action of centrifugal forces, to spread out in the shape of a hollow cone as soon as it leaves the exit orifice. This kind of atomizer is used in gas turbines and liquid-propellant rockets. The need to minimize the combustor length usually leads to spray angles around 90 deg. The present work presents a procedure to design and verify the experimental behavior for low pressure-swirl atomizers. This atomization condition is especially important, for example, in the case of gas turbine operation under idle regime. The Sauter mean diameter and the spray-cone angle are evaluated and made to fit the calculated atomizer dimensions. The Sauter mean diameter is obtained through the use of a model originally developed for fan-spray atomizers and extended for pressure-swirl atomizers. A pressure-swirl atomizer was manufactured following this design procedure. The discharge coefficient, the spray-cone angle, and the Sauter mean diameter were evaluated experimentally and compared with the theory used to design the atomizer displaying a good matching. The spray Sauter mean diameter was measured with a laser scattering system.

NOx and CO emissions and soot presence in partially premixed acoustically excited flames

AbstractThe pulsating combustion process has attracted interest in current research because its application in energy generation can offer several advantages, such as fuel economy, reduced pollutants formation, increased rate of convective heat transfer and reduced investment, when compared with other new techniques of combustion. An experimental study has been conducted with the objective of investigating the effects of combustion driven acoustic oscillations in the emission rates of combustion gases, especially carbon monoxide and nitrogen oxides, and soot presence in partial premixed flames in confined partially premixed liquefied petroleum gas flames. The results basically showed that a more uniform fuel/air mixture due to the presence of an acoustic field increases the NOx emissions in operations close to stoichiometric equivalence ratios and the frequency is the most important parameter. Carbon monoxide and soot reduced significantly.

Experimental aspects of partially premixed pulsating combustion

The pulsating combustion process has won interest in current research due to indications that its application in energy generation can offer several advantages, such as: fuel economy, reduced pollutants formation, increased rate of convective heat transfer and reduced investment, when compared with conventional techniques. An experimental study has been conducted with the objective of investigating the effects of combustion driven acoustic oscillations in the emission rates of combustion gases, especially carbon monoxide and nitrogen oxides. The experiments were conducted in a water-jacketed 1-m long by 25-cm internal diameter stainless steel vertical tube. The combustor operated with liquefied petroleum gas (LPG) in both oscillatory and non oscillatory conditions, under the same input conditions. Part of the reactant mixture was excited acoustically, before the burner exit, by a speaker positioned strategically. The burner was aligned with the chamber longitudinal axis and positioned at its bottom. The experiments were conducted for 0.16 g/s of LPG burning in stoichiometric equivalence ratio. The main conclusions were: a) the pulsating combustion process produces more uniform fuel/air profile than the non pulsating process, b) close to stoichiometric equivalence ratio the pulsating combustion process generates higher rates of NOx; c) the frequency has a strong influence in NOx emission, but the pressure amplitude has a weak influence; d) the presence of the acoustic field may change drastically the combustion gas emissions in diffusion flames, but in pre-mixed flames the influence is not as strong.

Kinetics Parameters Evaluation of Paraffin-Based Fuel

In recent years, Hybrid Propulsion is turning into a significant alternative to Liquid and Solid Propulsion Systems, it presents attractive features and good balance between performance and environmental impact. Thus, paraffin based propellant grains are indicated as a substitute for hydroxyl-terminated polybutadiene (HTPB), the actual solid propellant fuel grain. Despite being a well-known material, scarce data on the relation of activation energy (Ea) and molecular weight (WCxHy) of paraffin is available. In this work, the kinetic parameters (activation energy and pre-exponential factor) of microcrystalline 140/145°F paraffin have been raised through Thermo Gravimetric Analysis in conjunction with the Arrhenius kinetic mechanism, according to ASTM-E1461 and the dependence of molecular weight with melting point from Etessam and Sawyer approach. The 140/145°F paraffin activation energy calculated in this study was compared with different activation energy from alkanes and substances used as fuel in the propulsion systems field. The analysis indicated that the microcrystalline 140/145°F paraffin, manufactured by Petrobras, presents activation energy of 224 KJ.mol−1 and pre-exponential factor of 5.48×1022 min−1. Ignition was achieved with a 50 W pyrotechnic igniter. The firing test with 140/145°F paraffin fuel and gaseous oxygen (GOX) mass flux of 130 Kg.s−1 m−2 at pressure above 0.80 MPa, was easily sustained.Copyright

The influence of the flame structure on the combustion oscillations in a cylindrical chamber

An experimental study has been conducted with the objective of investigating the effects of the flame structure in the combustion oscillation conditions into a laboratorial scale cylindrical chamber. The experiments were conducted in a water-jacketed 1-m long by 25-cm internal diameter stainless steel vertical tube. The combustor operated with liquefied petroleum gas (LPG) in both oscillatory and non oscillatory conditions, under the same input conditions. Part of the reactant mixture was excited acoustically, before the burner exit, by a speaker positioned strategically. The burner was aligned with the chamber longitudinal axis and positioned at its bottom. The experiments were conducted for 0.16 g/s of LPG burning in stoichiometric equivalence ratio. To analyze the flame structure the image tomographic reconstruction process were used, and the resultant images were associated to the oscillatory conditions (frequency and amplitude) into the combustion chamber. The main conclusions were: 1) when the flame premixed condition increase, for example 60% of the total air flow rate is premixed with LPG, the region of intense energy released is close to burner exit and strong amplitudes of oscillation (close to 50 mbar) were obtained into the chamber; 2) for long flames, predominantly diffusive flames, just weak amplitudes were detected, in the spite of the speaker exiting the premixed flow; 3) when the energy is released distributed through the combustion chamber, the long flame acts like a baffle.

Theoretical analysis of aqueous residues incineration with oxygen enriched flames

The use of oxygen to enrich the oxidizer can be an attractive alternate to increase incineration rates of a combustion chamber originally designed to operate with air. For a certain fuel flow rate, if some incineration parameters are held constant (as combustion chamber temperature, turbulence level, and residence time), an increase of incineration rates becomes possible with injection of oxygen. This work presents a theoretical evaluation of combustion air enrichment in a combustion chamber designed to incinerate aqueous residues using methane as fuel and air as oxidizer. Detailed chemistry was employed to predict pollutants formation. The overall process was investigated using the PSR routine from the CHEMKIN library.

Multi-Dimensional Engine Modeling Study of EGR, Fuel Pressure, Post-Injection and Compression Ratio for a Light Duty Diesel Engine

For copious levels of exhaust gas recirculation (EGR) (>30 %), oxides of nitrogen (NOx) emissions can be reduced from Euro V to Euro VI regulated levels at the expense of fuel economy and soot emissions. The Lifted-Flame Concept (LFC) has been demonstrated by several researchers to be successful in reducing NOx, while minimizing soot emissions and impact to fuel economy. By simultaneously applying increased EGR and fuel pressure the LFC extends the lift-off length of a diffusion flame and enhances fuel-air entrainment leading to improved fuel and oxygen utilization. When combined with advanced turbocharging and EGR systems the LFC applied to a modern light duty (LD) diesel engine can result in improved fuel economy and lower soot emissions and shows good potential for meeting low soot engine-out targets.In the proposed paper a computational study was conducted using a multi-dimensional engine model. A modified 3D CFD KIVA code with detailed chemistry solver was used to model the diesel fuel spray, droplet breakup, vaporization, mixing, auto-ignition and subsequent heat release and emissions. The model uses inputs from 1D Amesim electro-hydraulic solver to generate the rate of injection (ROI) profile to raise pressure of 1800 bar to 2500 bar as well as to include a simulated post-injection. A 1D model using GT-Power was developed and utilized to provide air system boundary conditions for the 3D CFD model. Post-processing optimization was conducted using Matlab to identify minimum fuel economy and soot emissions for the study of several parameters.The objective of the study was to demonstrate Euro VI emissions levels on a 3.2 L LD diesel engine without NOx aftertreatment and minimal impact to fuel economy using the lifted flame concept. The engine-out NOx emission level was targeted at 0.4 g/kWh and the soot levels were targeted at 0.2 g/kWh assuming diesel particulate filter would be used for after-treatment. The results of the computational study successfully demonstrate the potential of the lifted flame concept to meet Euro VI without the use of NOx aftertreatment technology.Copyright

Physical Property and Carbon Black Distribution Impact on Propulsion Efficiency of Paraffin-Based Fuel

In the last decade the hybrid propulsion has been considering as a viable alternative of chemical energy conversion stored in propellants into kinetic energy. This energy is applied in propulsive systems of manned platforms, maneuvering procedures and even in the repositioning process of micro satellites. It is a system of minimum environmental impact and lower cost than traditional systems based on liquid or solid propellants. Paraffin based grains are the hybrid solid fuels appointed as polymeric fuel substitute. The liquid layer formed on the burning surface ensures high regression rate when driven into the flame front. Paraffin grains allow row material recovery and reduce the risk of explosion in the presence of erosive burning. The structure of the grain and the control of the liquefying burning surface layer depend on the additives concentration, such as carbon black, which are added to the fuel matrix during the production process. In the solid propellant paraffin based grain a cylindrical center port developed during the centrifugation tends to concentrate carbon black in the outer region of the grain. During solidification 15% of shrinkage occurs and appears hardness gradient in the longitudinal and transverse directions. The influence of carbon black distribution and hardness gradient in paraffin based grain were evaluated in this work. The study suggests that multiple thin layers grain may generate burning surfaces with hardness and carbon black concentration almost constant. The ballistic properties and propulsion efficiency of a hybrid lab rocket scale with 150 N of thrust were evaluated in the pressure of 2.8 MPa with 140 Kg/(sm2) gaseous oxygen (GOX) mass flux, the results show up the nozzle operation and motor-propellant relationships.Copyright

Experimental aspects of soot presence in pulsating diffusion flame

The present paper shows experimental results about soot suppression on a laboratorial scale jet free diffusion flame of liquefied petroleum gas submitted to acoustic oscillations. The experiments were conducted to verify the influence of amplitude and frequency of oscillations in the regions of soot formation and suppression through the flame. To quantify the soot presence the laser induced incandescence was utilized. The results show combinations of frequency and amplitude of oscillation which the presence of soot is close to zero.