IACSIT International Journal of Engineering and Technology, Vol. 7, No. 2, April 2015 Analysis of Combustion Efficiency for Turbofan Engine Combustor Using MATLAB Yasin Şöhret, Önder Turan, and T. Hikmet Karakoç When we check open literature, we can see familiar studies Abstract—The thermal efficiency of an aircraft turbofan however, no similar study could be found. Many researchers engine is related to combustion efficiency.It is net output thrust studied emission measurement and combustion efficiency power to total input fuel energy of the combustor.However, net determination methods from gas turbine engines heretofore. heat effects on thermal efficiency and net heat is related to In Poland, some researchers studied the development of combustion efficiency.Furthermore, specifying combustion efficiency has a key role inestimating emission indices. In this special probes for the measurement of emissions from study, the combustion efficiency of a turbofan engine combustor aircraft engines [7]. In this study, researchers examined the is analyzed by MATLAB. In the program codes,the basic measurement of different parameters, one is exhaust gas combustion equilibrium is analyzed for carbon, hydrogen, emissions. Kaminaga and other researchers analyzed exhaust oxygen, nitrogen, sulfur, carbon dioxide, carbon monoxide, emissions in their study [8]. In this, emissions data was hydrocarbon, nitrogen oxide, nitric oxide and water.As a analyzed and variation of different parameters was handled. conclusion, researchers examinethe relationship between combustion efficiency and exhaust gas emissions. At NASA Lewis Research Center, researchers examined the performance of a modular turbojet combustion chamber [9]. Index Terms—Combustion efficiency, turbofan engine, Within the scope of this study, mathematical models are used emissions, sustainable aviation, environment. to explain the relationship between exhaust gas emissions and combustion efficiency. This method is similar to the mathematical model explained in our study. In another I. INTRODUCTION research carried out by NASA, the effect of two different At the present time, emission values are seen as important fuels on exhaust emissions in an aircraft engine combustor criteria for the investigation of environmental effects. are investigated [10]. The performance parameters and Emission data measured from aircraft engines are compared emissions variations of the combustor are examined with regulations and improvements are sustained [1]-[3]. according to Jet A and diesel fuels. Pourmovahedet al. Another emphasis of emission values is to obtain an opinion studied a jet engine. In this research the researchers examined about combustion in the combustion chamber. As known, the engine performances and performance parameters at various ingredients of exhaust gases provide ideas about combustion pressures, temperatures and fuel flow. Additionally, proximity to stoichiometric combustion. efficiencies for each component of the engine were Thermodynamically, the thermal efficiency of a thermal calculated and measured, this measurement data and system is net output energy ratio to total input energy [4]. If calculation results were then compared and examined by the we apply this to an aircraft engine we can express thermal researchers. As a result of this study, researchers proved the efficiency of an engine as the ratio of net output work to performance characteristics of the engine [11]. In another combustion heat value. However, net heat produced by study, researchers examined emissions variations of a gas combustion effects on thermal efficiency directly and net turbine engine [12]. Lebedevet et al., modeled a gas turbine heat is related to combustion efficiency. That is, the thermal combustor on CFD and analyzed emission variations on CFD. efficiency of an aircraft engine is also related to combustion These results are also validated by an experimental efficiency. combustor using methane and kerosene as fuel. As a result of At this moment in time, developing more efficient aircraft this experimental study, researchers estimated the increase of engines that consume less fuel is a key objective. In this inlet temperature, decreases CO and UHC emissions. context, determining combustion efficiency experimentally Erbogosoet et al., examined an industrial gas turbine with a can contribute to these improvements [5], [6]. Determining thermodynamically approach and analyzed CO, UHC, NOx combustion efficiency experimentally is used to compare emissions [13]. In this study, researchers measured the results with design efficiency. Comparing these values can different emissions data from the gas turbine and explained show us the condition of a working engine and therefore a the variations of emissions by temperature and fuel flow. maintenance schedule can be constructed. If this procedure is Datta and Som examined the emission characteristics of a gas applied to a new engine design, at the end of tests, design turbine combustor at different pressures and swirl conditions faults can be detected. [14]. In this research, emissions variations, EGT and combustion efficiencies are measured and calculated for Manuscript received April 10, 2014; revised June 19, 2014. This work different workloads. Also a numerical model of liquid fuels was supported by the TUSAS Engine Inc. and is a development of work pray com bustioninagasturbinecombustor was developed by carried out on a collaborative project with Anadolu University. The authors are with Anadolu University, School of Graduate Sciences, researchers to analyze the influence of inlet swirl number and Airframe and Powerplant Maintenance Department, TR-26470, Eskisehir, combustion pressure on combustion and emission Turkey (e-mail: [email protected], [email protected], characteristics. [email protected]). DOI: 10.7763/IJET.2015.V7.772 86 IACSIT International Journal of Engineering and Technology, Vol. 7, No. 2, April 2015 Through this study, researchers examined relations Equations (4) through (15) are written according to direct between combustion efficiency and exhaust gas emissions. measurement data. For these equilibrium equations, analyzer Thus, the basic combustion equilibrium is analyzed and interferences and calculation correction coefficients are not related to emission indices. This analytical method is adapted taken into consideration. If we know analyzer interferences to Matlab programming language and researchers developed and calculation correction coefficients, the derived equations COMEFF (Combustion Efficiency) software to calculate are given below [8], [15]: combustion efficiency of any type of gas turbine engine by using emissions data. CO → → (14) NO C→ II. METHOD → (15) A. Mathematical Model To relate emission data to combustion efficiency, firstly NO → → (16) we need to analysis the basic combustion equilibrium in the combustion chamber. Equation (1) can be written for one CO → (17) mole of fuel and air [15] For Equations (14) through (17); “ Ca → b ” shows CHONS O N interference coefficient of a on the measurement of b. During emissions measurements, chemiluminescent analyzers can be CO H O CH used. These type of analyzers can measure the concentration →CO N O (1) of nitric oxide and nitrogen oxides. Theoretically, the concentration of nitrogen dioxide equals the difference H O CO C H between nitric oxide and nitrogen oxide. For these analyzers, NO NO SO converter efficiency is defined and is notated by “η”. If we continue derivations by implicating this converter efficiency, we can find this corrected equation [8], [15]: At Equation (1) A1 through A9 are the number of moles CO , N , O , H O, CO, C H , NO NO and SO . 2 2 2 2 x y 2 2 NO (18) By further derivations, the equations given below can be written for the equilibrium of carbon, hydrogen, oxygen, “ ” is defined as water content of the sample exhaust nitrogen, sulfur, carbon dioxide, carbon monoxide, hsd gases after dryer and calculated as given in Equation (19) hydrocarbon, nitrogen oxide, nitric oxide and water [15]: respectively [15]: (19) x (2) 2 42 (3) If we conflate derived equations as a matrix system, the solution can be simplified. After solving this equation set, the 2 2 2 2 emission indexes are calculated. The emission index of 2 2 (4) variable Z can be calculated as given in Equation (20) [15]: 2 2 (5) mass rate of 1000 mass rate of fuel (6) . 1000 (20) CO (7) Depending on this equation emission indexes can be CO (8) derived [15]: CH (9) .,. (21) ,,.⁄ NO (10) ... NO (11) (22) ,,.⁄ HO (12) “ ” connotes molecular weight of unburned For the equations given, “A” means total mole number of hydrocarbon gases in exhaust gases. Equation (23) is written products as shown at Equation (13): for carbon monoxide and unburned hydrocarbons respectively. (13) According to these equations, combustion efficiency can 87 IACSIT International Journal of Engineering and Technology, Vol. 7, No. 2, April 2015 be calculated as given below [15]: Fig. 1. A screen capture of COMEFF. The fuel properties necessary to run COMEFF. In this 100 1 10.109 (23) section, the user is required to input the characteristic properties of the fuel used for combustion in the gas turbine. In Equation (23), Hf denotes net heat of fuel. Equation 23 Another subsection is used to input the properties of exhaust is current for net heat of fuel as J/kg. gases. The user specifies the unburned