In combined heat and power plants operated with biomass syngas, the removal of condensible tars is a necessary but expensive step (up to one third of the installation and maintenance costs). This step is required because the syngas has to be cooled down to avoid knocking in the spark ignition engines traditionally used in such plants. To remove the tar condensation problem, we developed an alternative system based on an Homogeneous Charge Compression Ignition (HCCI) engine operated at intake temperatures above the tar dew point. To address the challenge of power derating of such engine setups, the current paper focuses on the application of Exhaust Gas Recirculation (EGR) as a control parameter that would indirectly allow the improvement of the engine performance. Based on a conservative estimate of tar dew points, HCCI combustion was studied at an intake temperature of 250 °C using synthetic biomass syngas and synthetic EGR on a mono-cylinder HCCI engine operated at 1000 RPM. The effects of charge dilution, thermal and kinetic damping due to the EGR gases were also analysed to understand their main effects. The use of EGR successfully increased the maximum achievable Indicated Mean Effective Pressure from 2.5 bar at EGR = 0% up to 3.3 bar at EGR = 25%, through damping the maximum pressure rise rate and allowing higher equivalence ratios.

在使用生物质合成气运行的联合热电厂中，去除可凝结的焦油是必要但昂贵的步骤（安装和维护成本的三分之一）。之所以需要这一步骤，是因为必须将合成气冷却下来，以避免爆震传统上用于此类工厂的火花点火发动机。为了消除焦油凝结问题，我们开发了一种基于均质充气压缩点火（HCCI）发动机的替代系统，该发动机在进气温度高于焦油露点的情况下运行。为了应对这种发动机装置的功率降低的挑战，当前的论文集中在排气再循环（EGR）作为控制参数的应用上，该参数将间接地改善发动机的性能。根据对柏油露点的保守估计，使用合成生物质合成气和合成EGR在以1000 RPM运行的单缸HCCI发动机上研究了HCCI燃烧在进气温度为250°C时的情况。还分析了由于EGR气体引起的电荷稀释，热阻尼和动态阻尼的影响，以了解其主要作用。通过抑制最大压力上升率并允许更高的当量比，EGR的使用成功地将最大可达到的最大指示平均有效压力从EGR = 0％时的2.5 bar提高到EGR = 25％时的3.3 bar。