Abstract
The great reduction in future diesel engine emission limits, especially PM and NOx, forces one to develop means to comply with the more stringent legislation. Despite the new promising diesel aftertreatment and sophisticated injection system developments, the task to maintain stringent regulations appears to be great. This fact has encouraged automotive researchers to look for other options to help control diesel emissions. One such option is to control diesel exhaust emissions through fuel modification because it would affect both new and old engines. In the year 2005, the EURO IV fuel specification came into effect and the requirements for the diesel fuel properties have become even more stringent. In this way, the potential of diesel fuel for emissions reduction has already been to a large extent exploited and the most emissions-sensitive fuel parameters can nowadays be changed in a narrow range only. The shortfall in NOx and PM emissions control in diesel engines is, however, so great that more drastic fuel changes will be needed. One of the most promising fuel modifications for exhaust emissions control seems to be oxygenated additives.
The objective of the study described in this paper was to analyze under transient conditions the influence of synthetic oxygenated additives, which are compatible with diesel fuel and commercially available at reasonable prices. Support for this research project was provided by the Polish State Committee for Scientific Research from research funds 2005-2007. The research was carried out in the laboratories of the BOSMAL Automotive R&D Centre and Poznan University of Technology. The tests were conducted on a passenger car equipped with a direct injection (Common Rail) turbocharged engine, representing the latest technology in production at the start of the research program (mid-2005). The New European Driving Cycle (NEDC) was selected as a representative test for this study. Six synthetic oxygenated additives were tested. Each of them was evaluated at a concentration of 5% v/v in the same base diesel fuel. Due to a different oxygen content and a different density of the oxygenated additives, the individual oxygenated fuels differed between themselves with the oxygen content which varied from 1.17 to 2.16 % m/m. The base diesel fuel was the diesel fuel of the Euro V class with a sulphur content lower than 10 ppm.
The main findings followed from research described in this paper are:
- Synthetic diesel oxygenated additives are effective at a low concentration of 5% v/v.
- Synthetic diesel oxygenated additives reduce significantly CO, HC and PM emissions, however, this effect is connected with slightly increased NOx emissions.
- PM emissions reduction is generally dependent on the oxygen content in fuel, whereas CO and HC emissions reduction depends also on the molecular structure of the oxygenate.
- Oxygenated diesel fuels produce a favourable shift in PM/NOx trade-off.
Keywords:diesel, exhaust emissions, diesel fuel, fuel additives, synthetic oxygenates