Effect of swirl on the performance and combustion of a biogas fuelled spark ignition engine

• Tests were conducted on a biogas fuelled SI engine with normal and masked valve.
• Improvement in brake power and brake thermal efficiency with masked valve.
• Lean misfire limit is extended with enhanced swirl from 0.68 to 0.65.
• Enhanced swirl decreases HC level from1530 ppm to 1340 ppm and increases NO emission from 2250 ppm to 3440 ppm.
• The reduction in ignition delay and higher heat release rate with enhanced swirl.

The influence of swirl on the performance, emissions and combustion in a constant speed Spark Ignition (SI) engine was studied experimentally. A single cylinder diesel engine was modified to operate as a biogas operated spark ignition engine. The engine was operated at 1500 rpm at throttle opening of 25% and 100% at various equivalence ratios. The tests covered a range of equivalence ratios from rich to lean operating limits and also at an optimum compression ratio of 13:1 with normal and masked intake valve to enhance swirl. The spark timing was set to MBT (Minimum advance for Best Torque). It was found that masked valve configuration enhanced the power output and brake thermal efficiency at full throttle. The lean limit of combustion also got extended. Heat release rates indicated enhanced combustion rates with masked valve, which are mainly responsible for the improvement in thermal efficiency. NO level increased with masked valve as compared to normal configuration. The spark timings were to be retarded by about 6 °CA and 4 °CA when compared to normal configuration at 25% and 100% throttle respectively.