Available online at www.sciencedirect.com ScienceDirect Energy Procedia 52 (2014 ) 659 665 2013 International Conference on Alternative Energy in Developing Countries and Emerging Economies Effects of CH 4, H 2 and CO 2 Mixtures on SI Gas Engine S. Chuayboon a, *, S. Prasertsan a, T. Theppaya a, K. Maliwan a and P. Prasertsan b a Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand b Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand Abstract Performance of a four-stroke spark ignition gas engine operated on mixtures of CH 4, H 2 and CO 2 was studied. Experiments were carried out at a constant engine speed of 2,000 rpm and throttle opening of 14% with various equivalence ratios. The results showed that the highest brake power output of 12.5 kw and 35% thermal efficiency were achieved when operated with the mixture of 69.70% CH 4, 9.95% H 2 and 20.45% CO 2 and the equivalence ratios between 1.0 and 0.82. 2014 2013 Elsevier Published Ltd. This by is Elsevier an open access Ltd. article Selection under the and/or CC BY-NC-ND peer-review license under responsibility of the Research (http://creativecommons.org/licenses/by-nc-nd/3.0/). Center in Energy and Environment, Thaksin University. Selection and peer-review under responsibility of the Organizing Committee of 2013 AEDCEE Keywords:Hydrogen; Methane; Carbon dioxide; Biohythane; SI engine 1. Introduction As a country lacking of fossil resource and the pressing need to be responsible for global warming, Thailand is supporting biogas production to become more self-reliance on energy. Biogas is expected to represent 0.24% of total renewable energy used in Thailand by 2021 [1]. At present, Ministry of Energy has already subsidized the biogas installation of 49 MW in total. It is planned to increase to 97 MW by 2022. In order to attract biogas investment, the Government provides an adder of 0.50 Baht for one kwh electricity produced from biomass or biogas. Industrial-scale biogas can be produced from municipality waste and agro-industry waste such as wastes from palm oil mills, tapioca mill, slaughter house and other food processing factories [2]. Biogas * Corresponding author. Tel.: +6-674-287-035; fax: +6-674-558-830. E-mail address: sriratpsu@gmail.com. 1876-6102 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Organizing Committee of 2013 AEDCEE doi:10.1016/j.egypro.2014.07.122
660 S. Chuayboon et al. / Energy Procedia 52 ( 2014 ) 659 665 consists of approximately 60% methane (CH 4 ) and the rest is mostly 40% of carbon dioxide (CO 2 ) [3]. Unless CO 2 removal is applied, biogas has an exceptionally low energy density. Consequently, its flame speed is 25 cm/s while the corresponding figure for methane is 34 cm/s [4]. Hydrogen is an excellent additive to natural gas for vehicle (i.e. CNG which is mainly CH 4 ), which is known as hythane [5]. The properties of hydrogen and methane are shown in Table 1. Hydrogen is able to burn at an equivalence ratio of 0.1 lower than in comparison to 0.53 for methane. Hydrogen has lower mass-basis heating value (LHV) of 119,930 kj/kg, which is twice of that of methane [6]. However due to its substantially low density, hydrogen is 3-times lower in volumetric lower heating value than that of methane. Table 1. Fuel properties of hydrogen and methane [6]. Types of fuel Hydrogen (H 2) Methane (CH 4) Equivalence ratio ignition lower limit in NTP air 0.10 0.53 Mass lower heating value (kj/kg) 119,930 50,020 Density of gas at NTP (kg/m 3 ) 0.083764 0.65119 Volumetric lower heating value at NTP (kj/m 3 ) 10,046 32,573 Stoichiometric air-to-fuel ratio (kg/kg) 34.20 17.19 Volumetric fraction of fuel in air, = 1 at NTP (kj/m 3 ) 0.290 0.095 Volumetric lower heating value in air, = 1 at NTP (kj/m 3 ) 2913 3088 Burning speed in NTP air (cm/s) 265-325 37-45 % thermal energy radiated from ame to surroundings 17-25 23-33 Molar carbon to hydrogen ratio 0 0.25 Quenching distance in NTP air (cm) 0.064 0.203 Flame temperature in air (K) 2318 2148 With the potential of hydrogen and biogas production in a 2-stage reactor, additional energy from H 2 can be obtained. Recently, a project aiming for biohythane production from palm oil mill effluent (POME) was commenced [7]. A study on the performance of a gas engine with mixtures of H 2, CH 4 and CO 2 was carried out to gain understanding of the effect of CO 2 in biohythane, which is reported in this paper. 2. Experimental setup 2.1. Fuel supply In this study, mixtures of CH 4, H 2 and CO 2 gas that represents biohythane gas were used to run the engine. In reality, biogas contains impurities, such as H 2 S and NH 3, but these components were not included in the present study due to their negligible effect on the engine performance. The experiments were conducted to represent the CO 2 removal of 10%, 20%, 30%, 40%, 50% and 60%, which was achieved by adjusting the 3 gas flow rates as shown in Table 2. Methane used in this experiment was obtained from CNG bought from a gas station in HatYai, Songkhla. The CNG composition was certified by the NG separation plant in Chana district. Its composition is shown Table 3.
S. Chuayboon et al. / Energy Procedia 52 ( 2014 ) 659 665 661 Table 2. Mixture of gases representing various percentage of CO 2 removal. Composition number Simulated % of CO 2 removal Gas composition (%) by volume Total lower heating value (MJ/kg) CO 2 CH 4 H 2 1 0 39.12 53.34 7.54 35.65 2 10 36.64 55.51 7.85 37.10 3 20 33.95 57.87 8.18 38.67 4 30 31.02 60.43 8.54 40.39 5 40 27.82 63.23 8.94 42.26 6 50 24.31 66.31 9.37 44.31 7 60 20.44 69.70 9.85 46.58 Table 3. Composition of natural gas (gas station in Hat Yai, Songkhla). Gas composition (%) by volume Methane CH 4 73.836 Ethane C 2H 6 4.146 Propane C 3H 8 1.938 Isobutane i-c 4H 10 0.548 n-butane n-c 4H 10 0.384 Isopentane i-c 5H 12 0.174 n-pentane n-c 5H 12 0.104 Hexanes C 6H 14 0.229 Carbon dioxide CO 2 17.149 Nitrogen N 2 1.492 Specific gravity, (SG.) 0.791 Water H 2O (Lb/MM scf) 0.17 The engine was fuelled by the 3 gasses via 3 mass flow controllers (Aalborg, GFC 67). The engine was directly coupled to a dynamometer for load control at a predetermined speed of 2,000 rpm. The accuracies of the instrumentation are listed in Table 4. Table 4. Accuracies of measurements. 2.2. Gas engine Measurements Accuracy Temperature ±0.3 0 C Speed ±1 rpm Lambda 0.500-2.000 res. 0.001 CNG (flow rate) ±1.5% full scale H 2 (flow rate) ±1.5% full scale CO 2 (flow rate) ±1.5% full scale The experiments were carried out on a 1.5-L, four-stroke, four-cylinder, spark ignition engine modified for gas fuel. The specifications of the engine are given in Table 5 and a schematic diagram of the experimental setup is shown in Fig. 1. The modification included fuel air mixer and fuel supply line. For safety concern, an anti-backfire valve was installed at the engine intake line. In addition, pressure regulators were equipped for each gas cylinder to keep the supply gasses at a constant pressure of 2.5 bars.
662 S. Chuayboon et al. / Energy Procedia 52 ( 2014 ) 659 665 Table 5. Specifications of the gas engine. Engine type Vertical water-cooled spark-ignition engine Bore 78.7 mm Stroke 77 mm Displacement 1,500 cc Engine speed 2,000 rpm Maximum power (original) 75 kw/5,600 rpm Compression ratio 10.5:1 Maximum torque (original) 138 nm /4,400rpm 9 10 6 7 5 4 11 8 Air 13 3 2 1 12 17 14 15 16 Fig. 1. Schematic diagram of the experimental setup. Number Equipment/ instrument Number Equipment/ instrument 1 H 2 Tank 10 CH 4 Valve 2 CH 4 Tank (CNG) 11 CO 2 Valve 3 CO 2 Tank 12 Gas mixer 4 H 2 Pressure regulator 13 Air Flow meter 5 Flame arrester 14 Engine 6 H 2 Flow meter 15 Dynamometer 7 CH 4 Flow meter 16 Engine control panel 8 CO 2 Flow meter 17 Gas analyzer 9 H 2 Valve
S. Chuayboon et al. / Energy Procedia 52 ( 2014 ) 659 665 663 2.3. Experimental methods The fuel gas in the gas mixture was fed to the injector, mixed with air and entered intake port. The amount of fuel and excessive air ratios were controlled by an electronically controlled unit (ECU). The spark timing of the engine was set to 13 degree before top dead center [8]. All tests were conducted at a constant throttle of 14% opening and a fixed engine speed of 2,000 rpm. Excess air ratios were varied from stoichiometry to lean operational limit. The results were analyzed for the optimum operating conditions (i.e. maximum power output). 3. Results and discussion Engine performance at difference equivalence ratios Brake power output with respect to the equivalence ratio is shown in Fig 2. The maximum break power was achieved at stoichiometric mixture (equivalence ratio = 1.00). The more LHV gas (i.e. more CO 2 removal), the more output was obtained. The 60% removal of CO 2 gave output of 22.5% higher than that of without CO 2 removal. At low equivalence ratios, the output tended to drop sharply to 7-9 kw. The lean limit was indicated by the misfire observed at an equivalence ratio of 0.7 and no CO 2 removal. The brake power output increased by the increase of H 2 concentration which can be explained by its effect in enhancing flame speed and propagation. 13 12 Speed 2000 rpm Ignition timing 13 deg btdc Throttle 14 % Brake Power (kw) 11 10 9 0% of CO 2 reduction 10% of CO 2 reduction 8 20% of CO 2 reduction 30% of CO 2 reduction 40% of CO 2 reduction 7 50% of CO 2 reduction 60% of CO 2 reduction 6.65.70.75.80.85.90.95 1.00 1.05 Equivalence Ratio Fig. 2. Variation of brake power output with equivalence ratio.
664 S. Chuayboon et al. / Energy Procedia 52 ( 2014 ) 659 665 Figure 3 shows thermal efficiency at various equivalence ratios. Thermal efficiency increased with the removal of CO 2. The maximum 35% thermal efficiency was achieved at slightly lean condition (the equivalence ratio of 0.82). At this optimum equivalence ratio, the efficiency was quite sensitive to fuel quality. The highest and the lowest figures were 35% and 27%, respectively. At equivalence ratio of 1.03 the efficiency drastically dropped to 18%, especially when CO 2 removal was not applied. Brake Thermal efficiency (%) 38 36 34 32 30 28 26 24 22 20 Speed 2000 rpm Ignition timing 13 deg btdc Throttle 14 % 0% of CO 2 reduction 10% of CO 2 reduction 20% of CO 2 reduction 30% of CO 2 reduction 40% of CO 2 reduction 50% of CO 18 2 reduction 60% of CO 2 reduction 16.65.70.75.80.85.90.95 1.00 1.05 Equivalence Ratio Fig. 3. Variation of brake thermal efficiency with equivalence ratio. The specific fuel consumption (kg/kw.hr) is illustrated in Figure 4. The specific fuel consumption increased at the extreme equivalence ratios of 0.7 and 1.03 due to incomplete combustion. Because of differences in fuel quality the SFC depends on the percentage of CO 2 removal. Fuel with high quality resulted in lower SFC, which was reflected by the high efficiency as shown previously in Figure 3. Specific Fuel Consumption, SFC (kg/kw.hr).40.35.30.25.20 Speed 2000 rpm Ignition timing 13 deg btdc Throttle 14 % 0% of CO 2 reduction 10% of CO 2 reduction 20% of CO 2 reduction 30% of CO 2 reduction 40% of CO 2 reduction 50% of CO 2 reduction 60% of CO 2 reduction.15.65.70.75.80.85.90.95 1.00 1.05 Equivalence Ratio Fig. 4. Variation of specific fuel consumption with equivalence ratio.
S. Chuayboon et al. / Energy Procedia 52 ( 2014 ) 659 665 665 4. Conclusions The effects of CH 4, H 2 and CO 2 mixtures on an SI gas engine were determined. The results are summarized as follows: There is an improvement in brake power output and thermal efficiency with the removal of carbon dioxide from biohythane fuel. The highest power output was 12.5 kw, which was 27.5 % higher than that of without CO 2 removal (9.8 kw). While the maximum output was obtained at the stoichiometric condition, the maximum thermal efficiency was achieved at slightly lean condition (equivalence ratio = 0.82). Rich mixture and low quality fuel (no CO 2 removal) resulted in high specific fuel consumption. The lowest SFC tended to coincide with the highest efficiency condition. Acknowledgements The authors wish to thank the Agricultural Research Development Agency and the Prince of Songkla University for the financial support to this work. References [1] Energy Policy and Planning Office (EPPO), "http://www.eppo.go.th/index-t.html," 2013. [2] P. Noparat, P. Prasertsan, and S. O-Thong, "Potential for using enriched cultures and thermotolerant bacterial isolates for production of biohydrogen from oil palm sap and microbial community analysis," International Journal of Hydrogen Energy, vol. 37, pp. 16412-16420. [3] E. Porpatham, A. Ramesh, and B. Nagalingam, "Effect of hydrogen addition on the performance of a biogas fuelled spark ignition engine," International Journal of Hydrogen Energy, vol. 32, pp. 2057-2065, 2007. [4] A. R. E. Porpatham, B. Nagalingam, "Investigation on the effect of concentration of methane in biogas when used as a fuel for a spark ignition engine," fuel, 2007. [5] N. Kahraman, B. keper, S. O. Akansu, and K. Aydin, "Investigation of combustion characteristics and emissions in a sparkignition engine fuelled with natural gas-hydrogen blends," International Journal of Hydrogen Energy, vol. 34, pp. 1026-1034, 2009. [6] C. G. Bauer and T. W. Forest, "Effect of hydrogen addition on the performance of methane-fueled vehicles. Part I: Effect on S.I. engine performance," International Journal of Hydrogen Energy, vol. 26, pp. 55-70, 2001. [7] M. Suwansaard, W. Choorit, J. H. Zeilstra-Ryalls, and P. Prasertsan, "Isolation of anoxygenic photosynthetic bacteria from Songkhla Lake for use in a two-staged biohydrogen production process from palm oil mill effluent," International Journal of Hydrogen Energy, vol. 34, pp. 7523-7529, 2009. [8] K. Lee, T. Kim, H. Cha, S. Song, and K. M. Chun, "Generating efficiency and NOx emissions of a gas engine generator fueled with a biogas-hydrogen blend and using an exhaust gas recirculation system," International Journal of Hydrogen Energy, vol. 35, pp. 5723-5730.