In this study, the combustion characteristics of low calorific gas (LCG) fuels are investigated by numerical simulation. PREMIXED code is used to predict the flame structure and NO emission with two mechanisms, which are GRI 3.0 and USC II chemical reaction mechanisms for CH4 and LCG 8000 and LCG 6000, respectively. Also, elementary reactions related with production and destruction for OH radical are studied because OH radical is dominant for burning velocity and NO emission. As results, the production and the destruction of OH radical for CH4 and LCG 8000 using GRI 3.0 are dominated by reactions of No. 4, No. 2 and No. 3 and by No. 5, No. 3 and No. 7, respectively. For LCG 6000 using USC II, reactions of No. 3, No. 4 and No. 11 and of No. 7, No. 8 and No. 12 dominates to the production and the destruction, respectively. In addition, NO emissions for LCG gas fuel are generated by thermal NO because the flame temperatures are over 1800 K.

The stoichiometric gas from an advanced alkaline electrolysis process as developed by Yull Brown is called as HHO gas or Brown gas. By this process, two moles of H2 and 1mole of O2 gases are generated stoichiometrically in a wellpremixed state. Due to the fact that very clean fuel can be obtained relatively easily by the simple equipment of electrolysis, the research of this gas has been continuously performed, even though the criticism has been made by many researcher of this area. The main controversial argument is in that the use of high quality electrical energy is used again for the generation of another combustible fuel with less than 100% efficiency in its energy transform. In fact, since Brown gas exists in the state of a completely mixed state only with oxygen molecule, there is no time delay due to turbulent mixing occurring in practical combustion process. Therefore, the high reaction rate is likely to have a high chance of backfire. Further, since there is no inert material like nitrogen as in air, the flame temperature rises unnecessarily high. In order to prevent the backfire phenomenon, the increase of injection velocity of fuel nozzle causes the formation of very unstable long flame with good chance of flame lift-off. One of practical application methods, the co-combustion of Brown gas with other fuel like gasoline and LNG, etc has been reported in open literature in order not only to increase the combustion efficiency but also for the reduction of pollutant emission such as NOx. In order to control the negative aspect of flame characteristics of Brown gas, in this study, an novel method is employed by premixing Brown gas with water vapor and the co-combustion performance and characteristics has been studied numerically for a combustor operated for kiln drying method. To this end, a commercial code(STAR-CCM+7.06) has been employed with the program verification against operational data of kiln drying combustor and a parametric numerical calculation has been made with the change of the amount of water vapor in the fuel mixture of Brown gas and water vapor. The calculation results show that the combustion feature looks quite stable without showing any unstable flame feature like long thin flame and backfire. Further temperature and streamline contours with the amount of water vapor content look consistent and physically acceptable. This result suggests that the addition of water vapor in the Brown gas looks one of promising method for the use of Brown gas as clean fuel.

The coal gasification fuel is important to replace petroleum fuel. Also they have many benefits for reducing the air pollution. Measurements on the combustion characteristics of synthetic gas from coal gasification have been conducted as compared with LPG in constant volume combustion chamber. The fuel is low caloric synthetic gas containing carbon monoxide 30%, hydrogen 20%, carbon dioxide 5%, and nitrogen 45%. To elucidate the combustion characteristics of the coal gasification fuel, the combustion pressures, combustion durations, and pollutants(NOx, CO2, CO) are measured with equivalence ratios(ø), and initial pressures of fuel-air mixture in constant volume chamber. In the case of the coal gasification fuel, maximum combustion pressure and NOx concentration are lower rather than LPG fuel. However CO and CO2 emission concentration are similar to that of LPG fuel.