VOL. 11, NO. 2, JANUARY 2016 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences © 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 912 THE EFFECT OF CO2 FRACTION ON THE FLAME STABILITY OF BIOGAS PREMIXED FLAME Mega Nur Sasongko and Widya Wijayanti Mechanical Engineering, University of Brawijaya Jalan Mayjend Haryono Malang, East Java, Indonesia E-Mail: megasasongko@ub.ac.id ABSTRACT This study aimed to determine the effect of CO2 on flame structure and stability of premixed flames biogas using counterflow flame configuration. In this research, the CO2 fraction in Biogas was varied from 0% to 50%. The total mass flow of gas flowed from both combustion nozzle was varied within 6 L / min and 8 L / min. The burning behavior of biogas counterflow flames were photographed by digital camera. Besides, the stability limit of counterflow diffusion flame was characterized by the minimum oxygen concentration at extinction. The results showed that the CO2 content in the biogas affect the characteristics of premixed flame, especially the change of a blue flame to blue flame with lower luminosity when increasing CO2 concentration. On the other hand, the variation in the oxygen concentration has more significant effect on the dimension of the premixed flame compared to the effects of the CO2 content in the biogas. The flash back phenomena exist in the counterflow premixed flame when the equivalence ratio of reactant closes to 1. It means that the biogas combustion is recommended to be done in the equivalence ratio close to 1 in order to obtain the best combustion performance. The results also showed that the highest concentration of oxygen minimum to keep the biogas premixed flame remained stable occurred in the percentage of CO2 in the biogas is 30%. This result could be explained based on the composition of unburned CH4 and CO2 gas in the combustion process. Keywords: biogas, premixed flame, CO2 fraction, counterflow configuration, flame stability. INTRODUCTION Nowadays, the utilization of Biogas as one of the potential fuel for fossil fuel replacement is gaining increased public attention. Biogas is cheap and renewable energy source because it is produced from organic waste like garbage, food scraps, manure and industrial waste. The main composition of Biogas is commonly methane (CH4) and CO2, with small amount of other substances such as hydrogen sulphide, moisture and siloxanes. The presence of CO2 in the biogas (ranges from 30 % to 60 %) have many negative effect in combustion processes. For instance, it will significantly reduce the heating value of combustion. The present of CO2 will be dropped the calorific value of fuel results in the lowering combustion energy generated from the combustion process [1-2]. Moreover, CO2 has a high specific heat so that some of the heat of combustion will be absorbed by these substances. Negative effect due to the presence of CO2 in the biogas cannot be avoided. Therefore, the application of biogas directly in energy conversion machines still need comprehensive review on the characteristics of the biogas combustion process in more detail. A next challenge is to find new methods in the combustion process that can minimize the effect of CO2 on the performance of combustion. Porpathan [3] investigated performance of spark combustion engine using biogas as a fuel. His research showed that CO2 on the Biogas affected the engine performance. The engine will significantly improve its performance when the CO2 content reduced 41% to 20%. Besides, the level of emissions of hydrocarbons HC and NO reduced with decreasing the CO2 content. The application of Biogas as a fuel on the diesel engine also have the same tendency. The thermal efficiency of diesel engine reduced with increasing the concentration CO2 in the Biogas [4]. However, the application of biogas in diesel engine operating on HCCI mode showed more promising results. The thermal efficiency of diesel engines in HCCI mode using biogas fuel approached the same value with the efficiency of fossil fuel diesel engines. This study presents an experimental investigation of the premixed combustion of Biogas. Counterflow premixed flame configuration is used as a method to investigate more detail the effect of CO2 on the burning behaviour and the flame stability limit of Biogas. Counterflow configuration technique is one of a convenience configuration to study the combustion model. The phenomenon of one-dimensional counterflow flame configuration is very suitable for studying the structure of the flame due to the influence of the type of content of the fuel, the mass flow (AFR) and the characteristics of the fuel reactant fuel and oxidizer [5,6,7]. This study is expected to provide a new improvement of biogas combustion model in practical application EXPERIMENTAL METHOD Figure-1 shows the counterflow burner configuration used in this research. The burner consists of two concentric double cylinders were mounted opposite each other. In the premixed flame experiment, the fuel and oxidizer have been mixed before it reaches the flame front. Accordingly, CH4 and CO2 gases as a main component of