Partially Premixed Combustion (PPC) is a combustion concept which aims to provide combustion with low smoke and NOx with high thermal efficiency. Extending the ignition delay to enhance the premixing, avoiding spray-driven combustion and controlling the combustion temperature at an optimum level through use of suitable lambda and EGR levels have been recognized as key factors to achieve such a combustion. Fuels with high ignitability resistance have been proven to be a useful to extend the ignition delay. In this work pure ethanol has been used as a PPC fuel.
The objective of this research was initially to investigate the required operating conditions for PPC with ethanol. Additionally, a sensitivity analysis was performed to understand how the required parameters for ethanol PPC such as lambda, EGR rate, injection pressure and inlet temperature influence the combustion in terms of controllability, stability, emissions (i.e. HC, CO, NOx and Soot) and combustion and thermodynamic efficiency.
Investigations have been performed experimentally on a single cylinder heavy duty engine where each of the parameters swept one at time. The results showed that the combustion is not sensitive to changes in injection pressure but the adjustments in lambda, EGR and inlet temperature should be controlled very carefully as there are clear limitations for each of these parameters. These limitations are highlighted and presented in this study. Engine-out soot emissions showed to be detectable only once the global lambda is very low (1.25 or lower) with very high EGR rates.
