Facilitation of HCCI combustion of biogas at moderate compression ratios by application of fuel reforming and inlet air heating

The HCCI shows large benefits in NOx emissions and fuel economy, but is difficult to achieve and control in engines with moderate compression ratios when natural gas and particularly biogas are used as fuel. It has been shown in literature that the addition of hydrogen translates into the lowering of the auto-ignition temperature during the combustion stroke. A major efforts is being devoted to developing further the fuel reforming technology which facilitates the auto-ignition of hydrocarbon fuels in Homogeneous Charge Compression Ignition engines. The fuel used in this study was simulated biogas which contained 67% CH4 and 33% CO2 by volume. Investigations were made into HCCI feasibility using inlet heating alone, HCCI feasibility using inlet heating and addition of simulated reformed fuel, feasibility of H2 production using fuel reforming and a full closed loop test including on-line H2 production. All HCCI results were compared to spark ignition baseline results. HCCI combustion for biogas shows significant improvement in NOx emissions and efficiency over SI combustion. However, it is difficult to achieve with biogas and was only stable with both reformed fuel addition and intensive inlet heating.