TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 40 BIOGAS-GASOLINE HYBRID ENGINE ĐỘNG CƠ SỬ DỤNG PHỐI HỢP NHIÊN LIỆU BIOGAS -XĂNG BUI VAN GA - LE MINH TIEN TRUONG LE BICH TRAM TRAN HAU LUONG Da Nang University ABSTRACT A biogas-gasoline hybrid engine converted from a 2HP spark ignition engine is used in the study. The engine is supplied by gasoline at starting and idling regimes. Full power of the engine is given by biogas combustion. Engine speed is controlled automatically by a double regulator which activates the biogas valve and mixture valve simultaneously. The relationship between the motions of the two valves has been proposed. The engine consumes about 1m 3 biogas to produce 1kWh electricity and reduce 1kg CO 2 emission in the atmosphere. CO and HC emission amount is reduced by more than 60% when the engine runs on biogas in comparison with gasoline case. The new concept of double regulator allows a good stabilization of output voltage of the generator. The voltage fluctuation is less than 5% of the normal output voltage value. TÓM TẮT Thí nghiệm sử dụng động cơ phối hợp nhiên liệu biogas-xăng được cải tạo từ động cơ đánh lửa cưỡng bức 2HP. Khi khởi động và chạy không tải, động cơ sử dụng xăng. Khi kéo tải động cơ chuyển sang sử dụng biogas. Tốc độ động cơ được khống chế một cách tự động nhờ bộ điều tốc hai chức năng, tác động đồng thời lên van tiết lưu biogas và van hỗn hợp. Mối quan hệ chuyển động của hai van này đã được thiết lập. Động cơ tiêu thụ khoảng 1m 3 biogas khi sản xuất được 1kWh điện và góp phần giảm được 1kg CO 2 thải vào khí quyển. Mức độ phát thải CO và HC cũng giảm hơn 60% khi động cơ chạy bằng biogas so với khi chạy bằng xăng. Bộ điều tốc hai chức năng cho phép ổn định tốt tần số điện của máy phát. Điện áp đầu ra của máy phát chỉ dao động khoảng 5% giá trị điện áp định mức. 1. Introduction Energy is one of the world’s most critical issues in the 21 st century. As fossil fuel resource is depleting rapidly, energy security has become more sensitive in international affairs. Continuing increase in crude oil price in recent years (over 145USD/barrel in July 2008) poses threads to the stability of the world’s economy, particularly the economies in developing countries. On the other hand, air pollution caused by burning fossil fuels (coal, oil, and natural gas ) have caused impacts on human beings and the environment for decades. Combustion product contains pollutants that are very harmful to human health such as carbon monoxide (CO), hydrocarbons (HCs), nitrogen oxides TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 41 (NO x ), sulfur oxide (SO 2 ), soot etc. Especially carbon dioxide (CO 2 ), the main product of combustion, is a green house effect gas that significantly contributes to global warming. A lot of international efforts and initiatives has been made to reduce greenhouse effect gas emissions for controlling the phenomenon of climate change. ASEAN member countries have commitments to implementation of Kyoto Protocol under UN Framework Convention on Climate Change and are already making steps towards emission reductions, particularly through Clean Development Mechanism. The utilization of sustainable and renewable energy is apparently an effective measure to achieve CO 2 emission reduction targets and combat with the global warming. Research on using of renewable energy as an alternative source of energy has captured attention of scientists for decades, especially since the world’s oil crisis in 1973. Biogas, a neutralizing CO 2 fuel, has double interest: energy saving and environment protection. Biogas is a product of decomposing organic substances in anaerobic conditions. Organic substances can often be plants (trees, straws etc.) or animals (animal wastes, by-products from food processing…), and wastes from breeding. CO 2 generated by burning biogas will be absorbed by new plants; therefore, CO 2 amount in atmosphere will be balanced. There are two main sources of biogas produced: one from biogas digesters (tanks) and the other from the organic substance fermentation under anaerobic conditions in landfills. Biogas contains mainly CH 4 (50-70%) and CO 2 (25-50%) and other impurities such as H 2 S. If biogas is refined from impurities, we will have a fuel with the same properties as natural gas. Developed countries such as USA, France, Germany, Denmark etc use biogas from landfills to generate electricity. In developing countries, biogas production technology for household use has become popular, particularly in India, China and ASEAN countries. In the meantime, developing countries has also piloted or employed technologies of utilizing biogas form landfills for power generation. Over the past ten years, energy from biogas has become widely used in Viet Nam. Biogas production processes have been improved to achieve higher efficiency. Traditional biogas tanks (digesters) built with bricks and concrete often corroded by acids, which causes gas leakage problems. Recently, super durable composite biogas tanks to overcome such problems have been manufactured. This new type of digesters made of composite material is resistant to acid corrosion, and thus can avoid gas leakage. Especially with composite tank, it requires lesser time for installations. This kind of tanks is welcomed by many farmers thanks to its higher effectiveness. Else where in Viet Nam, biogas production technologies have been well developed. Many projects supported by international funds has significantly contribute to success of biogas applications across the country. In 2006, a collaboration project on biogas production between Viet Nam and Netherlands was awarded the Environment Prize of the United Nations. TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 42 Today, the utilization of energy from biogas has helped in dealing with major issues related to environment protection and energy use in rural areas where more than 80% Vietnamese population live. At present, biogas is used mostly for cooking. Direct combustion is the simplest method of biogas energy utilization. However, the growing demand for household energy further pushes up the development of biogas utilization in producing power for working machines used in argo-based industries such as pumps, mills, regrigerators. Development and applications of technologies to use biogas as a fuel for small power internal combustion engines will make an important contribution to meeting the demand for power, raising income and protecting local environment in rural areas of Viet Nam. In the previous works, we have presented the results of our research on spark ignition fueled by biogas [10]. The biogas-diesel dual fuel engine has been also presented by our recent paper [11]. This work will focus specially on a new concept of fuel supplying system to biogas-gasoline hybrid engine. 2. Theoretical modeling The combustion of hydrocarbon in general can be expressed by the following model: HH 2 1 2  ; 22 H 2 1 OHOH  OO 2 1 2  ; COOHHCO 222  NN 2 1 2  ; NOHN 2 1 OH 222  222 OH2OH2  The combustion product is assymed in thermodynamique equilibrum state. The application of the model in combustion chamber of engine requires law of flame propagation. We suppose that the flame front is spheric and it is deformed due to the combustion chamber wall. The two-zone model [3] has been applied here to calculate the combustion in combustion chamber. The mixture and the combustion product are separated by flame front. The thermodynamic state of fluid in combustion chamber is represented by following equation system: Fig. 1: Cross section of the 2HP engine TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 43           p m vp vm T T QV c c p     ;         mm m T R V p p V ;         pp p T R V p p V The calculation is applied to a 2HP engine whose compression ratio is 7.6 (fig. 1). The bore and the stroke of the engine are respectively 51mm and 42mm. Figure 2 shows comparison of variation of combustion pressure in cylinder when the egine is fueled by gasoline and by biogas. With biogas containing 80% CH 4 , the maximal combustion pressure is about 10% lower than that of gasoline case. Figure 3 presents the variation of pressure in combustion chamber with different concentration of CH 4 in biogas fuel. The result shows that the maximal pressure increases 10% when the CH 4 in biogas changes from 60% (crude biogas) to 80% (purified biogas). When CH 4 concentration is higher than 60%, biogas can be applied directly to engine. In some biogas digester, CH 4 concentration is lower than that value. In this case, the combustion in low load regime is very poor and it is very difficult to start up the engine directly by biogas. Thus biogas-gasoline hybrid engine is the best way to solve the problem. 3. Experimental set up and results Our the research on different biogas sites shows that the engine consumes approximatively 1m 3 biogas to produce 1kWh electricity. The continuous operation time of generator depends on capacity of biogas production of the installation. Most of biogas degesters in our countries actually use wastes of animals, particularly that of pigs in farms. The daily time of continuous operation of generator in function of pigs number is shown in the table 1. The use of biogas as a fuel for engines requires firstly treatment of produced gas to remove 0 5 10 15 20 25 -200 -160 -120 -80 -40 0 40 80 120 160 200 () p(bar) 80% CH4 70% CH4 60% CH4 0 5 10 15 20 25 -200 -160 -120 -80 -40 0 40 80 120 160 200 () p(bar) 80% CH4 70% CH4 60% CH4 Fig.3: Effect of biogas quality on combustion pressure 0 5 10 15 20 25 -200 -160 -120 -80 -40 0 40 80 120 160 200 () p(bar) Gasoline Biogas 0 5 10 15 20 25 -200 -160 -120 -80 -40 0 40 80 120 160 200 () p(bar) Gasoline Biogas Fig. 2: Comparison of combustion pressure given by gasoline and biogas fuels TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 44 impurities (known as biogas filtration), of which H 2 S and CO 2 are major substances. Figure 4 presents the picture of an experimental compact biogas filtration system. - H 2 S removal process: To remove H 2 S from biogas stream, simple method of adsorption by iron oxides is employed [1], [2]. In preparation of iron oxides as adsorbent, ion scraps are pre-treated by oxidization to form the coated iron oxides layer. The formed iron oxides are the mixture of FeO, Fe 2 O 3 , Fe 3 O 4 . Pre-treated iron scraps are mixed up with wooden scraps and sawdust in the ratio 1:1 and then loaded into an adsorption vessel. With the diameter of 0.2m and height of 1.5m, a PVC vessel is capable of containing 8 kg adsorbing material and processing 0,86 m 3 biogass per hour. Averaged pressure loss through the H 2 S removal column is about 0.3mbar during operation [6]. - CO2 scrubber: Liquids with increased solubility for CO 2 are typically chosen over water in CO 2 scrubbing process, but the principal advantages of water as an absorbent are its Fig. 4: Compact H 2 S-CO 2 filtration system Table 1: Daily time of continuous operation of generator in function of pigs number in farm Output power (kW) Number of pigs 20 50 100 150 200 300 400 500 1 3 8 16 24 2 1,5 4 8 12 16 24 3 1 2,5 5 8 10 16 21 4 2 4 6 8 12 16 20 5 3 5 6 9,5 12 16 6 4 5 8 10 13 7 3,5 4,5 7 9 11 8 3 4 6 8 10 9 3,5 5,5 7 9 10 3 4,5 6,5 8 11 4,3 6 7 12 4 5,2 6,5 13 3,5 5 6 14 4,5 5,5 15 4 5 Tăng tải Giảm tải Cần điều khiển từ bộ điều tốc Gas vào 1 2 3 4 5 Fig. 5: Principle of power control of biogas/gasoline hybrid engine TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 45 availability and low cost. Absorption of acid gas by water produces slight corrosive solutions that can be harmful to equipment if not controlled. CO 2 and water countercurrent contact with each other in a scrubber. A neutral material layer consisting of brickbats, woodchips and gravels as a packed column is fitted into the scrubber by a perforated plastic sheet to intensify the gas-water contact. In our experiment, the scrubber operates at biogas flow rate of 0.86 m 3 /h, CO 2 concentration at inlet is 36.47%, and 19.22% at outlet of biogas stream. CO 2 removal efficiency reaches 47.30%. Pressure drop through the packed column is about 5mbar [6]. - Biogas supplying system for biogas-gasoline hybrid engine The principle of filling of biogas- gasoline hybrid engine is presented on figure 5. The main gasoline injector closed. The gasoline system supplies only the idling injector. Biogas is supplied to the engine via the flow control valve (Fig. 6). The regulator has double action. It commands simultaneously biogas valve and mixture valve. At starting up and idling regime, the engine is fueled by gasoline. When the load is increased, the butterfly mixture valve is opened, vacuum at idling injector is decreased so that gasoline injection is stopped while biogas valve is opened gradually: the engine turns to run on biogas. With this system, the engine can be started easily and it can be stable at idling regime particularly with poor CH 4 biogas fuel. The ratio of displacement of conic needle of biogas valve l and rotation of mixture butterfly valve  is calculated via the relationship (fig. 7): B m m B 2 2 vo . p p C C1 2 ltgdd 4 sinSS                          Where S o , S v are respectively areas of admission hose and that of butterfly valve plate;  is equivalent ratio of the mixture; C is stoechiometric mass ratio between biogas and air;  m and  B are respectively densities of mixture and biogas; p m and p B are respectively upstream-downstream pressure differences of mixture valve 50 45 110 15 18 M13x1,5 35 10 M18 M13x1,5 25 7 M10 32 1,5 3 3 38 7 3 9 lỗ 1 2 lỗ 3 Fig. 6: Design of biogas control valve   l d Mixture Biogas S v S o Regulator Air Fig. 7: Relationship between motion of mixture valve and biogas control valve TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 46 and of biogas valve; d is diameter of biogas valve; is angle of needle. The diameter of injector is calculated approximately in function of biogas consumption. According to our experiments, the relationship between biogas flow, supplying pressure and injector diameter can be given by following expression: pd.KQ 2  Where Q: Biogas flow (m 3 /s) d: Diameter of injector (m) p: Biogas pressure in storage bag (N/m 2 ) K: Constant The result of our research shows that the constant K=0,45. The generator supplies to a load panel constituted by 500W electric bulbs (fig. 8a and fig. 8b). The result is shown on figure 9. After starting up, the engine runs in idling regime with indicated output voltage of the generator is about 40 volts. By increasing of acceleration spring tension, output voltage 220 volts is obtained. The engine turns now to run on biogas. When we switch on or switch off the 500W bulbs, the fluctuation of voltage is less than 5% normal voltage. It satisfies the requirement of electricity production quality. The emission level of the engine was also compared in cases the engine fueled with gasoline and with biogas. The pollution measured results in the two cases are shown in figure 10. Measurements were carried out in the variant load modes. Results showed a very small amount of pollutant concentration in exhaust gas when engine runs on biogas (about 0,07% of CO and 30ppm of HC) in the critical regimes making a great reduction of 78% for CO and 60% for HC in comparison with gasoline case . - Economy and environment impacts The engine consumes about 1m 3 of biogas to produce 1kWh of electricity. The 1kW generator engine consumes 5 liters of gasoline in 10 hours. If it runs 10h/day on biogas, the 0 50 100 150 200 250 0 50 100 150 200 Idling, gasoline Loading, biogas Switch on 500W Switch off 500W t(s) U(V) Fig. 9: Output voltage variation in function of load regime Fig. 8: Load testing of biogas/gasoline hybrid engine TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 47 owner can save 2 millions VND/month or 24 millions VND/year. If we use 10,000 similar biogas engine groups, we can save 240 billion VND per year. CO 2 emission of combustion gasoline fuel is 2.31kg/liter. The above 1kW generator gasoline engine runs 10h/day emits 11.55kg CO 2 per day or 3.5 tons CO 2 per year. Thus the production of 1kWh electricity by biogas will contribute to the reduction of 1kg CO 2 emission. So, if the engine runs on biogas, we can reduce CO 2 emission about 3.5 ton per year. If we use 10.000 similar biogas engine groups, we can reduce 35.000 tons of CO 2 emission per year. This is a considerable contribution to global warming mitigation. 4. Conclusions  Biogas is great potential energy in the rural areas of Vietnam. The use of this kind of energy will be an important contribution to resolving of energy-environment problem of the country.  Biogas-gasoline hybrid fuel supplying system is an appropriate way to apply poor biogas on spark ignition engine.  For producing 1kWh electricity, the biogas-gasoline hybrid engine consumes about 1m3 of biogas and it contributes to the reduction of 1kg CO2emission.  Double action regulator can provide good stabilization of engine speed. Output voltage fluctuation of generator is less than 5% of normal voltage Acknowledgement: The present research is partially funded by the National Fundamental Scientific Research Program. REFERENCES [1] Hydrogen sulfide removal from anaerobic digester gas. Agricultural Wastes, Volume 11, Issue 3, 1984, Pages 167-179. Figure 10: Comparison HC and CO concentration in exhaust gas of the 2HP biogas-gasoline hybrid engine fueled by gasoline and by biogas 0 70 140 210 280 0 200 400 600 800 1000 Power(W) HC(ppm) 200 400 600 800 1000 0 2 4 6 8 10 0 Power(W) CO(%) TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 48 [2] Biogas Utilization Handbook, published by the Environment, Health and Safety Division, Georgia Tech Research Institute, Atlanta, Georgia, 1988. [3] BUI VAN GA, TRAN VAN NAM, LE VAN TUY: Numerical code for combustion calculation in spark ignition engines. Journal of Science and Technology, No 36+37/2002, pp. 131-137 [4] BUI VAN GA: Combustion: Modeling and experiment. Proceedings of Conference on 25th Anniversary of Mechanic Institute, pp. 38-44, Hanoi, 8-9 April 2004 [5] BUI VAN GA, NGO VAN LANH, NGO KIM PHUNG, VENET CEDERIC: Testing of biogas on motorcycle engine. Review Science and Technology, The University of Danang, No.1(18), pp. 1-5, 2007 [6] BUI VAN GA, NGO VAN LANH, NGO KIM PHUNG: Purification of biogas for fueling internal combustion engine. Review Science and Technology, The University of Danang, No 4-2007 [7] BUI VAN GA, TRAN VAN NAM: Combustion of LPG-Air Lean Mixture: A solution for pollution reduction of motorcycles in Vietnam. The 6 th General Seminar of the Core University Program “Environmental Science and Technology for sustainability of Asia, Kumamoto, Japan, 2-4 October 2006, pp. 361-367 [8] BUI VAN GA: Patent 5940 “LPG/gasoline conversion kit for motorcycles" National Office of Intellectual Property, 2006. [9] NHAN HONG QUANG: bi-fueled reciprocating engines - an effectively solution for renewable energy utility and environmental protection in the vietnamese rural areas.Journal of Science and Development N o 127-2007, pp. 30-37, 2007 [10] BUIVANGA, TRUONG LE BICH TRAM, TRUONG HOANG THIEN, LE MINH TIEN: Biogas Supplying System for Small Power Engine. National Conference on Fluid Mechanics, Hue, 21-23 July, 2007 [11] BUI VAN GA, LE MINH TIEN, NGUYEN VAN DONG, NGUYEN VAN ANH: Biogas Supplying System for Biogas/Diesel Dual-Fuel Engine. Review Science and Technology, The University of Danang, No 3-2008 . nghiệm sử dụng động cơ phối hợp nhiên liệu biogas- xăng được cải tạo từ động cơ đánh lửa cưỡng bức 2HP. Khi khởi động và chạy không tải, động cơ sử dụng xăng. Khi kéo tải động cơ chuyển sang sử dụng. TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ, ĐẠI HỌC ĐÀ NẴNG - SỐ 3(26).2008 40 BIOGAS- GASOLINE HYBRID ENGINE ĐỘNG CƠ SỬ DỤNG PHỐI HỢP NHIÊN LIỆU BIOGAS -XĂNG BUI VAN GA - LE MINH. động cơ chuyển sang sử dụng biogas. Tốc độ động cơ được khống chế một cách tự động nhờ bộ điều tốc hai chức năng, tác động đồng thời lên van tiết lưu biogas và van hỗn hợp. Mối quan hệ chuyển động