Oxygenated fuel composition impact on heavy-duty diesel engine emissions

This paper reports on a study of a large number of blends of a low-sulfur EN-590 type diesel fuel respectively of a Swedish Class 1 fuel and of a synthetic diesel with different types of oxygenates. Oxygen mass fraction of the blends varied between 0 and 15%. For comparison, the fuel matrix was extended with non-oxygenated blends including a diesel/water emulsion. Tests were performed on a modern multi-cylinder HD DAF engine equipped with cooled EGR for enabling NO\dx levels between 2.0 and 3.5 g/kWh on EN-590 diesel fuel. Additional tests were done on a Volvo Euro-2 type HD engine with very low PM emission. Finally, for some blends, combustion progress and soot illumination was registered when tested on a single-cylinder research engine with optical access. The results confirm the importance of oxygen mass fraction of the fuel blend, but at the same time illustrate the effect of chemical structure: some oxygenates are twice as effective in reducing PM as other well-known oxygenates. In combination with conventional CI combustion with extended ignition delay, such fuel blends will produce extremely low PM levels without the necessity of very high amounts of EGR, suggesting a possible alternative pathway towards clean diesel combustion.