نشریه سوخت و احتراق
سال دوم شماره 1 (پیاپی 3، بهار و تابستان 1388)

The stability behavior of jet non-premixed flame developing in a coflowing stream is studied experimentally, using city gas and propane as fuel gases. Effects of oxidant and fuel stream velocities and oxidant stream dilution have been studied. Two types of stability limits are observed. Blow-off of the rim-stabilized flame is the first stability limit. The second is the break-off or extinction of the turbulent portion of the flame at the transition point from laminar to turbulent flow. Oxidant and fuel streams are in environmental temperature. In dilution experiments, oxidant primary stream is oxygen as diluted with nitrogen or carbon dioxide. In the other experiments, oxidant is environmental air.

In this article, results of flame temperature measurements of a fire engulfed object are presented. The effects of nano particles at the time of flame spread, as well as the effect of such parameters as pool fire dimension, height from fuel surface, and fuel type on flame temperature are investigated. Multi-walled Carbon nanotubes were used as nano particles, and Kerosene as well as diesel oil were used as fuels. The results show that pool dimension is the most effective parameter for flame temperature rise. They also indicated that, altogether, presence of MWNT reduces flame temperature by 10-20%, while it increases the flame spread time of kerosene by 15-30% and that of diesel oil by 6-26%.

The paper presents a detailed solid oxide fuel cell (SOFC) model that is specifically developed for the performance evaluation of planar SOFC stacks in combined heat and power (CHP) systems. The developed model includes the mass, momentum, thermal and electrochemical analysis, as well as the kinetic models of hydrocarbon reactions. The electrochemical model includes a complete evaluation of ohmic, activation and diffusion polarisations. To increase the accuracy of the model; methane reforming and water-gas shift reactions, several layers of temperature, radiation heat transfer model and material temperature dependent property are also applied to the model. The model is also validated with available numerical and experimental data for a high temperature SOFC with internal reforming, showing the capacity to accurately predict its operating conditions. Finally, sensitivity analyses on fuel utilization factor and on air excess ratio are performed to investigate the effects of different key parameters.

This study investigates the effects of sulfur contents and Cetane number (CN) of diesel fuel on combustion, performance and exhaust emission characteristics of a direct injection (DI) diesel engine. The engine experiments were run at 8-modes steady-state emission test procedure (ECE-R96). To evaluate the influence of fuel properties on engine’s emissions and performance characteristics, seven different test fuels were prepared: three fuels with different sulfur contents in the ranges of 50 ppm, 500 ppm and 3500 ppm and four fuels with a different cetane number that changes from 47 to 57. Experimental results indicate that the sulfur level of the diesel fuel has a significant effect on all regulated emissions, especially on PM. Also, the obtained results for fuels with different cetane numbers show that NOx emissions are reduced and PM emissions are increased when cetane number increases.

In the present study, the use of biodiesel collected from waste vegetable oil in a CFR diesel and a direct injection M 8.1 diesel engine is studied. Experiments were carried out in wide ranges of engine load conditions to evaluate the engine ignition delay with waste vegetable oil and its blends on volume basis with ordinary No.2 diesel fuel. The engine under investigation operates at a fixed speed of 730 rpm, but at different loads, i.e. 25%, 50%, 75% and 100% of full loads. First, the cetane number for blended fuels was measured in a CFR diesel engine based on ASTM-D613 standard method, and ignition delay of blended fuels was calculated based on the cetane number using the relationship between the two. Experimental results revealed that by increasing the biodiesel percentage in the blend, the cetane number of the blended fuels increases, which then causes reduction of the ignition delay. Then, M 8.1 diesel engine was tested at 4 loads and constant engine speed conditions based on the ECE R-49 standard. Engine cylinder pressure data was measured, and the first and second derivatives of pressure curves were drawn to obtain the ignition delay on the basis of these curves. The results indicated that by increasing the biodiesel percentage, ignition delay of blended fuels decreases. Comparison of the results for both methods for ignition delay of the diesel engine confirmed that incresing biodiesel percentage in biodiesel/diesel blended fuels reduces the ignition delay. The decreasing trend of ignition delay for the complete range of engine load though increase in the biodiesel percentage in the fuel blend is an important advantage in diesel knock, NOx emission, engine parts wear reduction, and lengthening the effective life span of the engine.

In this study, the effect of several parameters such as feedstock location, fuel mass flow rate, fuel type and length of furnace inlet are studied. All of the measurements have been done in a laboratory furnace that has been designed and made specifically for this purpose. Carbon black concentration is measured using the weighted method. Measurements are obtained for four fuels: methane, propane, acetylene, and oil gas. The results show that carbon black yields for methane, propane and oil gas are similar, but such carbon black yield for acetylene is more than twice that of the other fuels. The results reveal that the effect of feedstock injection place strongly depends on furnace geometry. They also indicate that the maximum yield for all of the above mentioned fuels, except for acetylene, occur when feedstock fuel mass flow rate is 4 times that of pre-combustor fuel rates.