Effect of Air-fuel Ratio on the Combustion Characteristics of Syngas (H2:CO) in Directinjection Spark-ignition Engine

Transcription

1 Universit Malaysia Pahang From the SelectedWorks of Ftwi Yohaness Hagos June, 2014 Effect of Air-fuel Ratio on the Combustion Characteristics of Syngas (H2:CO) in Directinjection Spark-ignition Engine Ftwi Yohaness Hagos A. Rahsid Abd Aziz, Universiti Teknologi PETRONAS Shaharin A. Sulaiman, Universiti Teknologi PETRONAS Available at:

2 Available online at ScienceDirect Energy Procedia 61 (2014 ) The 6 th International Conference on Applied Energy ICAE2014 Effect of Air-fuel Ratio on the Combustion Characteristics of Syngas (H 2 :CO) in Direct-injection Spark-ignition Engine Ftwi Yohaness Hagos a, *, A. Rashid A. Aziz b,c, Shaharin A. Sulaiman c a Faculty of Mechanical Engineering, Universiti Malaysia Pahang,Pekan, 26600,Pehang, Malaysia b Centre for Automotive Research and Electric Mobility, Universiti Teknologi PETRONAS, Seri Iskandar, 31750, Perak, Malaysia c Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Seri Iskandar, 31750, Perak, Malaysia Abstract This paper presents experimental results of the effect of air-fuel ratio on the combustion characteristics of a directinjection spark-ignition engine fuelled with a syngas of H 2 /CO composition of equal molar ratio. The engine was operated at fully open throttle and the start of fuel injection (SOI) was set at 180 o before top dead center (BTDC). The spark advance was set to the minimum advance for a maximum brake torque. The experiment was conducted at lean mixture conditions with engine speed ranging from 1500 to 2400 rev/min. The results show that syngas operated under wider operation excess air ratio (λ) as compared to CNG at the same engine speed. The minimum ignition advance for maximum brake torque and combustion duration were observed to increase with an increase in λ. The effect of air-fuel ratio was more visible on the initial stage of the combustion at lower speeds while it is visible on the rapid burning stage at higher speeds. Moreover, the combustion duration was increased with an increase in engine speed The The Authors. Authors. Published Published by Elsevier by Elsevier Ltd. This Ltd. is an open access article under the CC BY-NC-ND license ( Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the Organizing Committee of ICAE2014 Syngas; direct-injection; spark-ignition; combustion; air-fuel ratio 1. Introduction Syngas is believed to be a transition fuel from the carbon based economy to hydrogen based economy in the transportation sector [1]. It has moderate laminar flame speed, higher self-ignition temperature and its production is cheaper than fossil fuels and technologically mature. The objective of the current study is to investigate the effect of air-fuel ratio on the combustion characteristic of syngas in direct-injection (DI) * Corresponding author. Tel.: ; fax: address: ftwi@yahoo.com The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Organizing Committee of ICAE2014 doi: /j.egypro

3 2568 Ftwi Yohaness Hagos et al. / Energy Procedia 61 ( 2014 ) spark-ignition engine (SI). Syngas produced from gasification of biomass lacks consistency in the percentage composition of constituent gases. There are varieties of syngas products stated in literatures. Besides, the product of gasification requires a complex cleaning process to completely remove tar and other solid materials. In this research, fueling a DI SI gas engine is adapted with an imitated syngas. The syngas produced from gasification is mainly dependent on the gasifying agent used in the process. A low calorific value syngas (producer gas) of H 2, CO, CH 4, CO 2 and N 2 of varied proportion as constituent gases are generated if air is used. If steam or oxygen is used instead of air, a medium calorific value syngas with H 2, CO and CH 4 of varied proportions as constituent gases are produced. In the current study, the fuel selected is representative of the family of H 2 /CO syngas with a calorific value of MJ/Nm 3. This family of syngas was under investigation for its laminar flame velocity [2-4] and for its combustion and knock characteristics in carbureted SI engine [5, 6]. The H 2 /CO ratio can be controlled depending on the requirement of the end-use [7, 8]. 50% H 2 : 50% CO (H 2 /CO ratio of 1.0) syngas can be produced by a steam gasification of coal [7]. The ignition advance, mass fraction burn (MFB), flame development, rapid burning and overall combustion angles were investigated with the variation of an airfuel ratio of the charge. Flame development angle is the interval from the spark discharge up to 10% cylinder charge burn while the rapid-burning angle is the interval from 10% to 90% cylinder charge burn. The overall combustion angle is entirety of these two angles. 2. Methods 2.1. Equipment The study was conducted in a four-stroke, single cylinder, direct-injection spark-ignition research engine setup with a compression ratio of 14:1 similar to the engine setup used by Hagos [9] which gives the facility s schematic diagram and specifications. The engine was optimized for natural gas application. No alteration to the engine was made in this experiment except for the incorporation of syngas fueling through a double fuel line injector holder. In the current study, investigation of the combustion characteristics of syngas by monitoring the in-cylinder pressure data with the help of pressure sensor was employed. Piezoelectric pressure transducer was used to collect the pressure data. Pressure reading of up to 100 power cycles was recorded for a single run. Details of the mathematical models used in the analysis of the combustion characteristics from the pressure-crank angle reading can be found from Hagos [9]. The engine was operated at fully open throttle and the start of fuel injection (SOI) was set at 180 o before top dead center (BTDC). The experiment was conducted at lean mixture conditions with engine speed ranging from 1500 to 2400 rev/min Fuel Used Table 1. Supplied Syngas Composition Component Volume % Hydrogen 50 Carbon Monoxide 50 Table 2. Physicochemical properties of Syngas Component Syngas (calculated) Density at 0 o C and 1 atm (Kg/m 3 ) 0.67 Lower calorific value (MJ/Kg) Molecular weight 15 The syngas used in this study has fuel composition stated in Table 1 and its physicochemical properties indicated in Table 2. It was supplied by Mox Linde gases pressurized at 160 bar. The compressed natural

4 Ftwi Yohaness Hagos et al. / Energy Procedia 61 ( 2014 ) gas (CNG) used in this test was obtained from local NGV stations pressurized in a bottle with 200 bar. The lower heating value is in the range of MJ/Kg. Engine warming up and stabilization operation was done with CNG fuelling as imitated pre-mixed syngas cost was much higher. Fuel switch over was done once the engine attained stable operation. Since a common injector was used, the engine remained to operate with syngas for more than 5 minutes before formal reading was taken. This precondition was to avoid fuel contamination. 3. Results and Discussions The engine operation was restricted at λ= due to limitations associated to injector pulse width at lower λ and engine stability during lean operation at the lower end. The maximum IMEP was observed to be 9.08 bars at 2400 rev/min with λ=1.5. The lean limit of CNG fuelled in the same engine was reported to be in the range of λ = 1.6 to 1.8 depending on the degree of stratification [10]. However, syngas was shown to present a wider operational λ range as compared to CNG in the lean operation side. Fig 1 shows the variation of ignition advance in crank angle degree (CAD) with λ for different engine speeds. The result indicates that the optimum ignition timing was advanced with an increase in λ for all engine speeds. Similar trend of the ignition advance with increase λ was reported for natural gas-hydrogen mixture combustion [11]. The increase in ignition advance can be attributed to the decrease in burning velocity as the mixture gets leaner. Fig 1 Optimum ignition timing versus λ at different speeds and at 180 o CA BTDC a) b) Fig 2 MFB versus crank angle for different λ and at 180 o BTDC at a)1500 rev/min b) 2100 rev/min The combustion phenomenon could be further discussed with the cumulative heat release curve or mass fraction burn (MFB), flame development, rapid burning stage and overall combustion durations

5 2570 Ftwi Yohaness Hagos et al. / Energy Procedia 61 ( 2014 ) depicted in Fig 2 and 3. Fig 2 (a) shows the MFB versus crank angle of different λ at an engine speed at 1500 rev/min. Similarly, the variation of MFB of 2100 rev/min is presented in Fig 2 (b). The overall combustion angle was shown to increase with an increase in λ at both speeds. This was attributed to the mixture energy density in the chamber. Higher energy density generated more heat leading to higher incylinder temperature and thereby fast combustion. The effect of change in air-fuel ratio on MFB was more evident at the initial stage of combustion at 1500 rev/min. However, at 2100 rev/min the effect of air-fuel ratio on MFB was visible on the rapid burning stage. This is due to an increase in turbulence as a result of increased speed. This would speed up the combustion rate mainly at the rapid burning stage. a) b) Fig 3 Combustion duration versus λ at 1500 and 2100 rev/min at 180 o CA BTDC a) Flame development and rapid burning stage durations b) Overall combustion duration As shown in Fig 3, the trend of flame development, rapid burning stage and overall combustion durations were shown to increase with an increase in λ in both engine speeds. The flame development, rapid burning stage (Fig 3 (a)) and overall combustion durations (Fig 3 (b)) are shown to be steeper at 2100 rev/min than at 1500 rev/min. Therefore, there was an increase in combustion duration with an increase in engine speed. This phenomena was also reported by Heywood [12]. This was attributed to the effect of engine speed on the mixture burning rate. Turbulence effect on the combustion increases with an increase in engine speed causing an increase in mixing rate. 4. Conclusions The effect of air-fuel ratio of the combustion characteristics of syngas (H 2 :CO) was investigated in a direct-injection spark-ignition engine. Combustion characteristics such as ignition advance, MFB and combustion durations as function of λ were investigated setting the start of injection at 180 o BTDC and the throttle position at wide open throttle. Syngas was observed to operate at wide air-fuel ratio, improving the lower end performance as compared to CNG. Air-fuel ratio and engine speed were observed to have influence on the MFB and the different stage combustion durations. Therefore, systematic optimization of the air-fuel ratio and engine speed is required for the best performance and emissions. The current study was limited to speed range of rev/min due to the cost of imitated syngas. Further study is required by expanding the speed range. Acknowledgements The authors would like to extend their sincere thanks to Center for Automotive and Electric Mobility (CAREM), Universiti Teknologi PETRONAS and PETRONAS Carigali Sdn Bhd for their financial and

6 Ftwi Yohaness Hagos et al. / Energy Procedia 61 ( 2014 ) material support. References [1] N. Z. Muradov and T. N. Veziroglu, " Green path from fossil-based to hydrogen economy: An overview of carbonneutral technologies," Int. J. Hydrogen Energy, vol. 33, pp , [2] N. Bouvet, C. Chauveau, I. Go kalp, and F. Halter, "Experimental Studies of the Fundamental Flame Speeds of Syngas (H 2/CO)/Air Mixtures," in Proceedings of the Combustion Institute, 2010, pp [3] H. J. Burbano, J. Pareja, and A. s. A. Amell, "Laminar Burning Velocities and Flame Stability Analysis of Syngas Mixtures at Sub-Atmospheric Pressures," Int. J. Hydrogen Energy, vol. 36, pp , [4] J. Natarajan and J. M. Seitzman, "Laminar Flame Properties of H 2/CO Mixtures," in Synthesis Gas Combustion: Fundamentals and Applications, T. Lieuwen, V. Yang, and R. Yetter, Eds., ed Boca Raton: Taylor and Francis Group, 2010, pp [5] A. S. Bika, "Synthesis Gas Use in Internal Combustion Engines," PhD, Faculty of Graduate School, University of Minnesota, Minnesota, [6] N. N. Mustafi, Y. C. Miraglia, R. R. Raine, P. K. Bansal, and S. T. Elder, "Spark-Ignition Engine Performance with Powergas Fuel (Mixture of CO/H 2): A Comparison with Gasoline and Natural Gas," Fuel, vol. 85, pp , [7] J. Wu, Y. Fang, Y. Wang, and D.-k. Zhan, "Combined Coal Gasification and Methane Reforming for Production of Syngas in a Fluidized-Bed Reactor," Energy Fuels, vol. 19, pp , [8] S. Ramani, J. D. Allison, and A. E. Keller, "Controlling syngas H 2:CO ratio by controlling hydrocarbon composition," United States of America Patent, [9] F. Y. Hagos, "Combustion, Performance and Emissions Characteristics of Imitated Syngases in Direct-injection Sparkigntion Engine," PhD, Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Seri Iskandar, Malaysia, [10] F. Y. Hagos, A. R. A. Aziz, S. A. Sulaiman, and Firmansyah, "Combustion Characteristics of Late Injected CNG in a Spark Ignition Engine under Lean Operating Condition," J. Applied Sci., vol. 12, pp , [11] Z. Huang, B. Liu, K. Zeng, Y. Huang, D. Jiang, X. Wang, et al., "Experimental Study on Engine Performance and Emissions for an Engine Fueled with Natural Gas-Hydrogne Mxitures," Energy Fuels, vol. 20, pp , [12] J. B. Heywood, Internal Combustion Engine Fundamentals. New York: McGraw Hill International, Biography Dr. Shaharin Anwar Sulaiman is an Associate Professor in Mechanical Engineering. He holds B.Sc, M.Sc and PhD in Mechanical Engineering from the USA and the UK. He had five years of experience as an M&E Engineer prior to joining the academics. His research interests include HVAC, combustion, and biomass energy.