International Journal of Mechanical Engineering and Technology (IJMET) Volume 7, Issue 6, November December 2016, pp.105 113, Article ID: IJMET_07_06_011 Available online at http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=7&itype=6 Journal Impact Factor (2016): 9.2286 (Calculated by GISI) www.jifactor.com ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication COMBUSTION STUDY AND EMISSION CHARACTERISTICS OF BLENDS OF DIESEL AND HYTHANE FOR GAS TURBINE ENGINES C. Ajay Sekar Executive, LuK India Pvt Ltd., Schaeffler Group, Hosur, Tamilnadu, India ABSTRACT In the present study, the feasibility of use of blends of hythane (hydrogen enriched natural gas) and diesel for gas turbines engines are studied. The study has been carried out for different proportions of hythane and diesel blends using a computational approach. To understand the combustion characteristics of these blends, the total pressure and temperature distribution in combustion chamber are studied which will help in understanding heat release rate during combustion process while the emission characteristics of these blends are studied using NOx, Soot, CO concentrations after combustion. These results are then compared with emission characteristics of diesel. which is also obtained from fluent, to check on the feasibility of use of such blends as an alternative fuel for gas turbines. Key words: Hythane and diesel blends, combustion study, fluent, emission characteristics, gas turbine combustion chamber. Cite this Article: C. Ajay Sekar, Combustion Study and Emission Characteristics of Blends of Diesel and Hythane for Gas Turbine Engines. International Journal of Mechanical Engineering and Technology, 7(6), 2016, pp. 105 113. http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=7&itype=6 1. INTRODUCTION Combustion is process by which a fuel with help of oxidizer is burned to produce gaseous products along with certain by products and large amount of heat. This heat released depends on calorific value of fuel. Combustion can be characterized as complete and incomplete combustion. In former type of combustion, the products of combustion are oxides of hydrocarbons being burnt without any particulate matter while in latter type, particulate matter and smoke is formed in addition to products of combustion. The incomplete combustion process can be avoided by proper design of combustion chambers. By controlling the mass of fuel and mass of oxidizer, the process of combustion in an internal combustion engine can be carefully controlled to release required amount of heat and avoid the emission of harmful exhaust gases and other particulate particles. 2. NEED FOR THE STUDY The degree of combustion in an internal combustion engine plays a vital role in determining the performance of the engine. The need of the hour is also to determine fuels alternative to conventional fuels http://www.iaeme.com/ijmet/index.asp 105
C. Ajay Sekar such as diesel and petrol as conventional fuels are causing large amount of pollution problems. To add to this constraint, the sources of these conventional fuels are also dwindling day by day and would soon become extinct in coming years. Thus, a considerable amount of research work has been done on determining performance of engines using different alternative fuels such as biogas, biodiesel, ethanol etc. Several amounts of literatures have also been published on using blends of different alternative fuels. The blends of hythane and diesel add a new dimension to this category. 3. LITERATURE REVIEW Ganaraju Srinivasa Sharma et al studied the use of producer gas in gas turbine combustion chamber using non-pre-mixed model in ANSYS fluent. The results thus obtained are compared with that of methane. The results obtained showed that producer gas has a higher energy density than that of methane and it can be used as an alternative fuel for gas turbines. Ibrahim Ozsari et al modelled turbulent non-pre-mixed combustion chamber for three different fuels with and without the use of radiation models. The study was performed using fuels methane, ethane and propane. The study reveals that the temperature contours for all three fuels obtained with radiation model were lower as compared to that without the use of radiation model. Thus, the study reveals that radiation is an important parameter to be considered for heat transfer during combustion study of a gas turbine engine. P. Sravan Kumar et al investigated velocity profiles, species concentration and temperature distribution within combustion chamber of gas turbine using methane as a fuel using computational approach. P. Sarvan et al showed that proper mixing of fuel and oxidizer is obtained using methane as fuel due to high values of turbulent intensity and high mass fraction values of NO. Further mass fraction of water was also found to decrease towards the outlet indicating large amount of heat released during combustion process of methane. K.R Patil et al used hythane (HCNG-hydrogen enriched CNG) as feasible fuel in automotive engine. The study further showed that HCNG engines are better than CNG fuels from fuel consumption and power output standpoints of view. The study also shows that addition of hydrogen reduces emission of CO emissions by 40%-50% and increases the brake power output of engine by 5%. Thus, the study shows that addition of hydrogen to CNG has many advantages and hints its use as possible fuel in future for IC engines. Ajay V. Kolhe et al investigated-on use of diesel and pongammiapinnata biodiesel blends in compression ignition engines using CFD code fluent in bowl in piston type combustion chamber. The pressure at maximum load was used to obtain heat release rate for diesel and biodiesel blends. Comparisons were then made between experimental and modelled heat release rate for biodiesel blend which showed good agreement. Plots of temperature and velocity at maximum load were also plotted to obtain. The study shows the feasibility of use of bio-diesel blend as a possible fuel in compression ignition type engine. György Bicsák et al studied different combustion models and wall thermal boundary conditions to identify their effect on combustion performance and found that non-premixed combustion model was most accurate to understand combustion phenomena in a combustion chamber of a gas turbine as results obtained using this combustion model showed minimum error deviation from experimental results. Yasin Karago z et al studied the effect of addition of natural gas to diesel on performance, emission and combustion characteristics of compression ignition engine. The study showed that brake thermal efficiency of engine decrease upon increasing the percentage of natural gas in natural gas diesel blend. The study attributed this to the inefficient combustion of gas air mixture along with a lower burning rate and lower frame propagation speed. http://www.iaeme.com/ijmet/index.asp 106
Combustion Study and Emission Characteristics of Blends of Diesel and Hythane for Gas Turbine Engines 4. COMPUTATIONAL MODEL A can type annular combustion chamber is chosen for analysis in this study. The 3-dimensional model required for cfd fluent is modelled using Creo and Ansys design modeler module. The model is imported in IGES format into ANSYS for further modifications to be done. The mesh is generated using tetrahedral type element with fine element size. The operating parameters of combustion chamber for solving the model using fluent combustion code is given in table 1. The turbulence model K-ε with standard wall functions is used and to account for radiation heat transfer P1 model is used. Inlet diffusion option in fluent is also enabled to mimic real conditions of fuel spray. The study is conducted for different proportions of hythane and diesel blends: - 20:80 (HCNG: Diesel), 40:60 (HCNG: Diesel) and vice versa. The study considers 5% of hydrogen to be present in hythane for all compositions of diesel and HCNG blends. Figure 1 Meshed model of can type combustion chamber Figure 2 Model imported in fluent with boundary conditions Table 1 Operating parameters of gas turbine combustion chamber Operating parameters Conditions Mass flow rate of fuel (kg/s) 0.0297 Mass flow rate of oxidizer (kg/s) 0.4606 Velocity of fuel through injector (m/s) 24.3 Temperature of fuel at inlet (K) 338 Pressure of fuel at inlet (Pa) 1000e5 Ambient temperature (K) 298 Ambient pressure (Pa) 101325 Lower Calorific value of HCN (KJ/kg) 47170 Lower Calorific value of diesel (KJ/kg) 48000 http://www.iaeme.com/ijmet/index.asp 107
C. Ajay Sekar 5. RESULTS AND DISCUSSIONS 5.1. Combustion Study The combustion phenomena for different proportions of hythane and diesel blends is studied using total pressure and total temperature profiles obtained from fluent. Figures 3 and 4 below shows the total pressure and total temperature distribution for blends of hythane and diesel. The pressure distribution in combustion chamber was found to increase upon addition of hydrogen enriched natural gas to air/fuel mixture. A similar situation can be observed for temperature profiles on combustion chamber upon addition of hythane to fuel mixture. This can be attributed to the fact that the heat release rate increases on addition of hythane to air/gas mixture since hythane comprises of primarily methane. Although high temperatures are obtained during combustion process inside the chamber, the overall steady state temperature of combustion chamber increases with increasing concentration of hythane in gas/fuel mixture. Similar is the case for total pressure distribution. Although the total temperature and pressure contours is obtained for different proportions of hythane and diesel blends, the contours for only selected proportion of diesel and hythane is shown below due to space constraints. The maximum temperature obtained for 20 % diesel and 80 % hythane was found to be 2280K while the maximum temperature obtained for vice versa combination was found to be 2260K. Figure 3 (a) Total pressure distribution for 40% diesel and 60% hythane proportion Figure 3 (b) Total pressure distribution for 60% diesel and 40% hythane proportion http://www.iaeme.com/ijmet/index.asp 108
Combustion Study and Emission Characteristics of Blends of Diesel and Hythane for Gas Turbine Engines Figure 4 (a) Total temperature distribution for 80% diesel and 20% hythane proportion Figure 4 (b) Total temperature distribution for 20% diesel and 80% hythane proportion 5.2. Emission Characteristics 5.2.1. NOx Concentration NOx is one of harmful by products of combustion formed by presence of nitrogen in air/gas mixture during process of incomplete combustion. The NOx mass fraction concentrationn is obtained for different proportions of hythane and diesel blends. The NOx concentration for 40% diesel and 60% hythane and that of only diesel are shown in figures 5 and 6 respectively. A graph is plotted between proportion of hythane and diesel blend and maximum mass fraction of NOx species which is shown in figure 7 below. Figure 7 shows that with an increase in proportion of hythane in air and fuel mixture the mass fraction of NOx decreases rapidly. Thus, with addition of 80% of hythane to diesel, the NOx concentration in exhaust gas is reduced by 26%. http://www.iaeme.com/ijmet/index.asp 109
C. Ajay Sekar Figure 5 NOx mass fraction for 40% diesel and 60% hythane proportion Figure 6 NOx mass fraction for only diesel as fuel Figure 7 NOx mass fraction Vs proportions of diesel and hythane blends http://www.iaeme.com/ijmet/index.asp 110
Combustion Study and Emission Characteristics of Blends of Diesel and Hythane for Gas Turbine Engines 5.2.2. CO Concentration Carbon monoxide is a product of incomplete combustion. The figure below shows mass fraction of carbon monoxide for 20% hythane and 80% diesel. As graph in figure 9 indicates, there occurs an increase in CO emission on increasing hythane proportion and begins to decrease on addition of 80% hythane to diesel fuel. The increase in CO concentration is because fuel mixture gets trapped in crevices in engine and hence the flame must propagate through this charge to initiate combustion. At certain regions, the mixture is lean in nature to maintain the flame accumulation resulting an increase in incomplete combustion. These results are also parallel with literature by Yasin Karago z et al whose study also suggests that the CO emissions increase with addition of natural gas to diesel blend. However, CO mass concentrations were found to be 7.6% lower when compared with use of diesel fuel only. Figure 8 CO mass fraction for 80% diesel and 20% hythane proportion Figure 9 CO Mass fraction Vs proportions of diesel and hythane blends 5.2.3. Soot Concentration Soot is unburnt carbon particles that are released in exhaust gases due to ineffective combustion. Figure 11 shows mass fraction of soot for different proportions of hythane and diesel blends. As suggested earlier the soot concentration increase with addition of hythane to diesel mixture as hydrocarbons gets stuck at crevices of engine thus preventing propagation of flame resilting an increase in emission of hydrocarbons. Figure 10 below shows soot mass fraction of 20% diesel and 80% hythane blend. http://www.iaeme.com/ijmet/index.asp 111
C. Ajay Sekar Figure 10 Soot mass fraction for 20% diesel and 80% hythane proportion 6. CONCLUSION Figure 11 Soot mass fraction Vs proportions of diesel and hythane blends The study shows that hythane mixed with diesel as a possible alternative fuel for compression ignition type engines. This is also justified by fact that hythane and diesel blends have lower NOx, Co and soot concentrations as compared with that of diesel alone. However, the use of hythane and diesel blends as fuel requires certain modifications to be performed on engine systems such as on ignition systems and combustion chamber to achieve even better results which in turn will require an in-depth study of combustion phenomena of hythane and diesel blends by conducting trial experiments at different conditions. REFERENCE [1] Yasin Karago z, Tarkan Sandalc, Umit O Koylu, Ahmet Selim Dalkılıc and Somchai Wongwises, Effect of the use of natural gas diesel fuel mixture on performance, emissions, and combustion characteristics of a compression ignition engine, Advances in Mechanical Engineering 2016, Vol. 8(4) 1 13. http://www.iaeme.com/ijmet/index.asp 112
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