Article révisé par les pairs
Résumé : The filtration of condensable tars is a necessary step before biomass syngas can be used in spark ignition engines. In small scale gasifiers, this step represents one third of the investment cost and create several issues of maintenance. Since tar related problems occur primarily due to tar condensation, an alternative system is being developed where a Homogeneous Charge Compression Ignition (HCCI) engine is operated at intake temperatures above the tar dew point, thereby eliminating the need for tar filtration. Based on a conservative estimate of tar dew points, HCCI combustion has been studied at an intake temperature of 250°C. This paper presents a comprehensive study of the first HCCI engine operated with syngas. In particular, it addresses a control technique based on Exhaust Gas Recirculation (EGR). Simulated biomass syngas and simulated EGR were used on a 500cc mono-cylinder HCCI engine operated at 1000 RPM. The effects of charge dilution, thermal and kinetic damping as a consequence of EGR and the consequential combustion control have been discussed. In addition to being an effective control, the use of EGR decreases the Maximum Pressure Rise Rate and allows increasing the upper limit of the Indicated Mean Effective Pressure from 2.8 bar at EGR=0% to up to 3.5 bar at EGR=25%, a rise of about 25%.