Combustion and Exhaust Emissions Characteristics of Pilot-Ignited Engine Fueled with Digester Gas
A gas engine is one of the candidates for local energy system for providing both power and heat. The system plays an important role from the viewpoint of increasing total thermal efficiency. Another viewpoint is saving fuels of limited resources. Recently, when solar and/or wind power systems increase in a small and smart grid, the power supply becomes unstable. Therefore, gas engines may be placed there to compensate to supply a constant power to consumers. Furthermore, the reduction of carbon dioxide is also very important issue for preventing the earth from global warming. In particular, biomass is considered to be one of the most prominent alternative fuels. The biomass contributes to establish sustainable society as renewable energy. There are a few kinds of utilization of biomass, that is, ethanol, biodiesel fuel and biogas. This study focuses on biogas to use in a gas engine. Biogas is practically produced as landfill gas (LFG) or digester gas. Biogas comprises primarily methane (CH4) and carbon dioxide (CO2). The ratio of methane is about 50 60%, so that heat value is about a half of natural gas. Therefore, the combustion strength is not so strong. However, low exhaust emissions of NOx is expected from the dilution effect of carbon dioxide and nitrogen. In this study, a four-stroke cycle, water-cooled, single-cylinder and dual-fuel test engine is prepared to investigate the combustion and exhaust emissions. This engine has a bore of 96mm and stroke of 108mm. The compression ratio was 17:1. Gaseous fuel is introduced from an intake port with super-charged condition. After the gaseous fuel is compressed, a small amount of gas oil is injected in the engine cylinder with common rail system. The injector was specially made to reduce the amount of gas oil as less as possible. The engine was operated at 1000 rpm. Injection timing and intake pressure were changed. Imitated gaseous fuel was used instead of the real biogas. Namely, methane was used as main fuel while carbon dioxide and nitrogen were used as dilution gases. Each gas was supplied to the intake port with mass flow controller from each gas cylinder. Lean burn was performed to reduce NOx. Rate of heat release was analyzed from the pressure history measured with a pressure transducer. Exhaust emissions of NOx, HC, CO and smoke were measured. The results obtained with biogas were compared to those with the natural gas, which includes a small amount of ethane, propane and n-butane besides methane. Main results were obtained as follows: (1) The engine operated stably with lean biogas ignited with a small amount of gas oil. Under the condition of higher intake pressure, higher thermal efficiency was obtained as well as higher indicated mean effective pressure. (2) Because the biogas includes carbon dioxide, the specific heat increases. The compressed temperature with biogas is lower than that of the natural gas. Therefore, the property of anti-knock of biogas is superior to that in the natural gas.
Eiji Tomita Nobuyuki Kawahara Yuta Sunada Morio Kondo
Okayama University,Japan Mitsui Engineering and Shipbuilding,Co.Ltd.,Japan
国际会议
上海
英文
1-9
2013-05-13（万方平台首次上网日期，不代表论文的发表时间）