By using low temperature gasification, many kinds of biomass materials can be transformed into a gaseous mixture. This gaseous mixture includes combustible and incombustible gases. If the concentration of an individual component could be controlled, there is a possibility of using the gaseous mixture to fuel the internal combustion engine and finally to generate electricity. Furthermore, the utilizing of biomass fuel as an energy resource of internal combustion engine leads to a decrease in the emission of CO2, NOX, SOX, and particulate matters into the atmosphere. The components of biogas vary with the reactants and the reaction conditions. However, they usually include hydrogen (H2), carbon monoxide (CO), CH4, carbon dioxide (CO2), nitrogen (N2), and some other hydrocarbons. Under many conditions, the main components of biogas are CH4 and H2, as well as incombustible component CO2. Some researchers have carried out experimental researches to introduce the design and construction of internally circulating fluidized-bed gasifier (ICFG), to investigate the feasibility of gasifying manure compost using ICFG, and to evaluate the effects of pressure balance, reaction temperature, and steam ratio on the performance of the gasifier. The temperature conditions of the experiments were between 600℃ and 700℃ The results showed that the concentration of the components varied much with the reaction conditions. Different fuel components led to a different influence on combustion. Hydrogen has a much faster combustion velocity than CH4. As a result, combustion happens quickly with the increase in hydrogen composition in the fuel mixture. Meanwhile, carbon dioxide is an inert gas. It could cause an extinguishing of the flame if the composition of CO2 is too high. However, it is very difficult to avoid carbon dioxide in biogas. Moreover, the presence of CO2 leads to less input energy in fuel mixtures. Therefore, the combustion temperature will decrease. As a result, NOx emission will decrease. Since the influences of hydrogen and carbon dioxide on combustion are different, and the presence of CO2 also has benefits on engine performance, it is necessary to find out the balance point between combustion and exhaust emissions of the internal combustion engine which is fueled with the mixture of hydrogen, CH4 and carbon dioxide. And the main objective of the work in this paper is to research the influence of fuel components on engine operation stability. The experimental researches of engine operation stability were carried out based on a small-sized spark ignition engine fueled with simulated biogas, which includes hydrogen, CH4, and carbon dioxide. The influences of equivalence ratio, H2 concentration and CO2 concentration on combustion stability were investigated under wide opening throttle valve (WOT) and maximum brake torque (MBT) conditions. The results showed that engine operation stability was strongly influenced by fuel composition. Under low H2 concentration conditions, CO2 concentration played a dominant effect on combustion stability, and its increasing could induce the increase in cyclic variation and the occurrence of partial burn. However, under high H2 concentration, the effect of CO2 concentration on combustion gradually weakened. By adjusting fuel composition, the operation stability of biogas engines can be improved.%为探明生物质燃气各组分相对含量对发动机工作稳定性的影响，在一台小型火花点火发动机上进行了生物质燃气发动机循环变动试验研究，着重分析了理论空燃比与实际空燃比的比值理论空燃比与实际空燃比的比值、H2含量（H2在CH4-H2中的体积分数）及CO2含量（CO2在CH4-H2-CO2中的体积分数）的变化对燃烧稳定性的影响。试验结果表明，燃料组分对燃烧稳定性有较大影响。在本试验中，当理论空燃比与实际空燃比的比值较小、燃料组分中H2含量较低时（如理论空燃比与实际空燃比的比值为0.4、H2的体积分数为25%及理论空燃比与实际空燃比的比值为0.6、H2的体积分数为17%），CO2含量对燃烧稳定性起支配作用，CO2含量的增加导致循环变动增加（上述工况的平均指示压力循环变动系数均超过了10%），在个别条件下导致部分燃烧。随着理论空燃比与实际空燃比的比值及 H2含量的增加，CO2含量对燃烧的影响作用逐渐减弱，当理论空燃比与实际空燃比的比值及H2含量达到一定程度时（理论空燃比与实际空燃比的比值为0.6、H2的体积分数为33%及50%，以及理论空燃比与实际空燃比的比值为0.8所对应的所有H2含量条件）CO2含量对燃烧的影响作用已不明显。通过改变燃料组分条件的方法，能够提高生物质燃气发动机的工作稳定性。该研究的成果对生物质燃气发动机燃烧稳定性、经济性及排放特性改善，以及生物质燃气发动机技术应用、推广均有重要指导意义。
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