Effects of Engine Operating Parameters on near Stoichiometric Diesel Combustion Characteristics 2007-01-0121

Stoichiometric combustion could enable a three-way catalyst to be used for treating NOx emissions of diesel engines, which is one of the most difficult species for diesel engines to meet future emission regulations. Previous study by Lee et al. [1] showed that diesel engines can operate with stoichiometric combustion successfully with only a minor impact on fuel consumption. Low NOx emission levels were another advantage of stoichiometric operation according to that study.

In this study, the characteristics of stoichiometric diesel combustion were evaluated experimentally to improve fuel economy as well as exhaust emissions The effects of fuel injection pressure, boost pressure, swirl, intake air temperature, combustion regime (injection timing), and engine load (fuel mass injected) were assessed under stoichiometric conditions. The results showed that increased boost pressure and injection pressure improved the indicated specific fuel consumption (ISFC) and high swirl increases fuel consumption while intake air temperature, combustion regime, and engine load do not have significant effect on fuel consumption. The advantage of high injection pressure and boost pressure (air density) indicates that air entrainment is the most important process leading to an improved equivalence ratio distribution under stoichiometric operation, as well as for lean diesel operation.

Soot emissions under stoichiometric operation were significantly affected by the engine load and combustion regime, while the other operating parameters had only minor effects on the emissions. Boost pressure and engine load were the most dominant factors for NOx generation under stoichiometric operation and the intake air temperature and combustion regime had a relatively minor effect, while injection pressure and swirl did not have significant effects.