A numerical investigation of lean operation characteristics of spark ignition gas engine fueled with biogas and added hydrogen under various boost pressures

The lean burn capability of spark ignition engines fueled with biogas was investigated using cycle simulation and Latin hypercube sampling. Dominant variables were CO2 contents, boost pressure, spark timing, relative AF ratio, and H2 contents. Optimum boost pressures were optimized for various biogas compositions and relative AF ratios through maximum brake torque timing (MBT) optimization. Optimized boost pressures were relatively lower under a given turbocharger performance, thus causing a decrease in the mass fraction of fuel burnt. To enhance lean burn capability, effects of H2 addition were also studied under low boost pressure. By adding H2, the mass fraction of fuel burned could be enhanced. Furthermore, H2 could increase the range of spark timing. By advancing spark timing by adding H2, the mass fraction of fuel burned could be remarkably increased, leading to enhancement of lean burn capability.