Effect of Engine Operating Conditions on Spark-Ignition Engine PAH Emissions

It is established that spark ignition (SI) engines are a contributor to polycyclic aromatic hydrocarbons (PAH) in the atmosphere. Studies have shown that the PAH emissions from SI engines are dependent on fuel chemistry. In addition, a few previous studies have shown that the PAH emissions are also dependent on operating conditions. Those studies however, did not involve a wide range of operating conditions such as spark timing, engine speed and compression ratio. This paper presents experimental results of PAH emissions from a single cylinder SI engine (Ricardo E6 engine) at various operating conditions employing contemporary PAH sampling and analysis techniques. Results show that PAH emissions increase with increasing equivalence ratio, spark advance, increase in engine load and with increase in compression ratio. With the engine speed, however, the PAH emissions show a sharp decrease and then a slight increase in the emissions as the speed is increased. The results have also revealed that PAH and particulate matter (PM) emissions have similar trends at all of the engine operating conditions considered in the present study. This supports earlier findings that PAH and PM emissions are closely related to each other.