Key words: Biogas, internal combustion engines, combustion, CHP

Third International Conference on Applied Energy - 16-18 May 2011 - Perugia, Italy Omid Razbani, Nima Mirzamohammad, Mohsen Assadi Theoretical and Exp...
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Third International Conference on Applied Energy - 16-18 May 2011 - Perugia, Italy Omid Razbani, Nima Mirzamohammad, Mohsen Assadi Theoretical and Experimental investigation of biogas fueled technologies: Literature review and road map for internal combustion engines pages nn-mm

Literature review and road map for using biogas in internal combustion engines Authors (Omid Razbani, Nima Mirzamohammad, Mohsen Assadi) Authors’ affiliation (University of Stavanger, Department of Mechanical and Structural Engineering and Materials Science) Mailing address (University of Stavanger N-4036 Stavanger, Norway)

Abstract Using biogas in internal combustion engines started from 1940s and till now a lot of progress has been made to cope with biogas specifications. Here through detailed literature review, the challenges such as lower flame speed (compared to natural gas) and biogas impurities are studied; combustion characteristics of biogas in reciprocating engines are investigated. Solutions and lessons learnt such as advancing spark timing, increasing compression ratio, changing the bearing and piston materials and pre-chamber ignition systems are presented. Some ideas on further research work, such as simplification of controller systems, data driven model development and component and performance degradation survey are presented at conclusion. Key words: Biogas, internal combustion engines, combustion, CHP Introduction Biogas found its way from developing countries to developed countries. In 2008 the biogas production in Europe exceeded 7.5 million tonnes of oil equivalent. Germany is, in this respect, a leading country in Europe with 4500 biogas plants and 1650 MW installed electric power in 2009 and is expanding for more capacity[1]. Norway started lately but has a growing trend in biogas production. Table 1, shows biogas production history for Norway. “Utilizing biogas in the engines (when compared to fossil fuels) avoids any additional greenhouse gas emission. Due to organic nature of the components of biogas, burning it in a gas engine for power generation emits the same amount of CO2 into the atmosphere as was originally absorbed during the process of photosynthesis in the natural CO2 cycle”[2]. To illuminate technological as well as techno-economical concerns regarding the best way of power generation from biogas, a research project funded by the Research Council of Norway has been established to address the today’s challenges of the different technologies. In this project internal combustion engines, gas turbines and fuel cells will be studied theoretically and experimentally to identify existing limitations and investigate possible solutions. The energy conversion technologies used in this study are developed for natural gas, but during the project they will be operated by both natural gas and biogas. Experiments will be carried out to generate data to develop and train an Artificial Neural Network (ANN) model for monitoring purposes and at the same time to validate the theoretical results. Availability and economical viability of three conversion technologies will be investigated at a comparative basis. Performance and component degradations also will be considered and maintenance cost and lifetime will be established for each technology. In this first paper it is tried to investigate previous works on using biogas in internal combustion engines and find the road map for further development. Omid Razbani: [email protected], +4751875682

Third International Conference on Applied Energy - 16-18 May 2011 - Perugia, Italy

Table 1 - biogas production trend in Norway[3] 70

1000 tonnes

60

Biogas production

50 40 30 20 10 0 2003 2004 2005 2006 2007 2008

History The origin of biogas is traced back to the Persians. They discovered that organic matter such as rotting vegetables gave of a flammable gas that could be used for other purposes. Marco Polo has mentioned the use of covered sewage tanks in China. This is believed to go back to 2,000– 3,000 years ago in ancient China. In modern times, the first sewage plant was built in Bombay in 1859; an idea that was brought to the UK in 1895, when produced wood gas from wood and later coal was used to light street lamps. The use of biogas in internal combustion engines dated back to Second World War when thousands of vehicles ran by sewage gas in Europe. “In 1942-44, garbage collection trucks with diesel engines were operated using purified and compressed sewer gas in Zurich, Switzerland”[1]. “Around 1955 the importance of biogas was significantly reduced, as biogas was not profitable any longer due to an excess of oil. The price of fuel oil was very low and almost all biogas plants were shut down”[4]. In 1980s after energy crisis biogas became important again in internal combustion engines to produce electricity. In 1981 an effort has been made to use biogas in a converted diesel engine to SI engine by D. J. Hickson[5]. He experienced 35% less power compared to diesel and 40% less compared to gasoline fuel. In that year another research was done by S. Neyeloff and W. W. Cunkel. They used a CFR engine and ran it with simulated biogas in different compression ratios. They reached to compression ratio of 15:1 for optimal solution[6]. The lower heating value, corrosive composition and difficulties in transportation of the fuel were main challenges for biogas. In 1983, R.H. Thring concluded that biogas would be attractive just where it is close to production site and he suggested converting gaseous fuels like biogas or natural gas to liquid fuels such as methanol or gasoline[5]. JENBACHER WERKE AG introduced a total energy plant which was able to burn lean gas to produce electricity and heat in 1985[7]. They were able to control the air fuel ratio to put more fuel into the cylinder but they needed to modify the cylinder head for bigger inlet valve. A.G. Wunsche did not define the gas composition but they experienced lower methane number for the gas they used to fuel the engine. Then to prevent knocking they used knock detection sensor and retarded the ignition when it detects knock. The lower power output was still an unsolved issue. Caterpillar another big engine manufacturer tried to operate a spark ignition engine with landfill gas in 1987[8]. They developed the engine on site to tackle the biogas problems.

Third International Conference on Applied Energy - 16-18 May 2011 - Perugia, Italy Afterwards the engine was run on a real landfill site. N. C. Macari reported excessive wear after 400 hours and as a result shorter lubricating oil life. One study on Volkswagen cars has been done in Brazil to compare the performance of biogas fueled with Alcohol fueled cars in 1992. Ignition timing, mixture distribution and emissions were studied and different vehicle parameters such as maximum vehicle speed, acceleration and maximum engine speed are presented in tables[9]. While it was easier to convert SI engines to biogas, dual fuel engines showed some benefits. After 1990s diesel engines were converted to dual fuel biogas engines[10][11]. V. Deri and G. Mancini converted a diesel engine to dual fuel and experienced more stable combustion in lean mixture because of using diesel pilot to ignite the mixture. However the control strategy for separate control of the air-gas mixture and pilot fuel became too complex[10]. Growing interest for using biogas in internal combustion engines demanded more detail investigation of the combustion process. In 1992 G. A. Karim and I. Wierzba from university of Calgary carried out a valuable research on thermodynamic and kinetic characteristics of methane-air combustion in presence of carbon dioxide[12]. G. A. Karim continued to publish more papers regarding the biogas combustion phenomenon in internal combustion engines[13] [14]. To improve combustion limitations of biogas such as lower flame speed and flammability limit, K. Tanoue et al investigated hydrogen addition to lean methane mixture[15]. The idea of hydrogen addition to natural gas was studied before to enhance natural gas combustion in internal combustion engines[13]. After detail studies and clarifying biogas combustion in internal combustion engines by scientists, it was engineer’s task to find a solution to extend the limits. G. P. Mueller reported that in Caterpillar Inc., they were successfully developed a SI engine for landfill gas application without any power loss using pre-chamber combustion concept[16]. Table 1 shows that they were able to reach to the same power but bsfc (brake specific fuel consumption) was increased around 4%. Prechamber concept to improve biogas combustion in SI engines is studied in detail by A. Roubaud and D. Favrat in 2005[17]. They showed that it is possible to reach to higher output and efficiency with biogas fuel comparing to natural gas engines while the emission remains at low levels. Table 2- G3606 engine performance results[16]

Lower Heating Value (MJ/m3) Power (bkW) Speed (rpm) Bmep (kPa) Bsfc (MJ/bkW-h) Exhaust port Temp (°C) Air/Fuel (vol. /vol.) Excess Air Ratio (λ) Ignition Timing (btdc) Exhaust Emission (g/bhp-hr) NOx CO THC

Simulated Pipeline Landfill gas Natural Gas 18.26 34.46 1185 1185 900 900 1240 1240 9.79 9.39 561 510 8.9 21.0 1.73 2.18 15.5 19.0 0.78 1.62 3.2

0.75 1.45 4.0

Apart from John K. S. Wong who studied the effect of biogas on engine emission [18] no other important work was carried out until 1998 when J. Huang and R. J. Crookes established a set up and measured emissions for different biogas composition on a research engine[19].

Third International Conference on Applied Energy - 16-18 May 2011 - Perugia, Italy Further research is done which was focused on different biogas composition effects on engine application[20] and[21]. Biogas Anaerobic biogas is result of decomposition of organic material by microorganisms in a humid environment and in the absence of oxygen. It mainly consists of methane and carbon dioxide but it also contains other elements. Table 2 shows the typical composition of biogas. This composition can vary in different plants and even can change in a certain plant regarding the condition of the digester. Amount of long hydrocarbon chain materials in the digester, exposure time, substrate, liquid content, temperature, pressure and more parameters can affect the bioreactor processes and change the methane content of resulting biogas. Hydrogen sulfide content depends on the process and waste type. Without any reduction measure, the concentration can easily exceed 0.2% by volume. Variation of H2S content in the biogas in the course of the day is unexplainable (see Figure 1). With special types of waste such as poultry or when a high amount of co-substrate is used, ammonia concentration may exceed 1mg/m3. “Concentrations up to 150 mg/m3 have been reported”[4]. Siloxanes are used in cosmetics, detergents and building materials and then they can enter to biogas reactors and carried over into the biogas. These compounds can form SiO2 which is an abrasive material. Table 3 - biogas composition and qualities[4] Gas composites/ features

Formula

Units

Biogas

Methane

CH4

% by vol.

Sewage gas 65-75

Carbon dioxide

CO2

% by vol.

20-35

25-55

25-30

Carbon monoxide

CO

% by vol.