Environmental Performance of Diesel Fuels Containing Oxygenated Additive Packages

Abstract

The application of oxygenated additives seems to be one of more promising modifications of diesel fuels in order to decrease exhaust emissions. The authors have so far tested many oxygenates, from different chemical families, but as sole fuel components. Generally speaking, these oxygenates produced favorable but different changes in exhaust emissions. The objective of this study was to investigate whether the positive effect on emissions could be maximized by the application of packages of multiple oxygenated compounds. Four different oxygenated additive packages were tested. Each package contained a combination of 2 synthetic oxygenates, which represented different chemical groups, namely: glycol ethers, maleates and carbonates. The packages were evaluated as fuel additives at a concentration of 10 % v/v in a Euro 5 diesel fuel. The New European Driving Cycle (NEDC) was selected as a representative test for this study. All the oxygenate packages were additionally tested using the US Federal Test Procedure 75 (FTP-75). This cycle was carried out in order to determine the influence of cycle conditions on oxygenated fuels’ effectiveness as regards reductions in exhaust emissions. The tests were conducted on a Euro 4 passenger car equipped with a direct injection (common rail) turbocharged diesel engine. During the tests, mass emissions of CO, HC, NO_x, PM and CO₂ were measured. The influence of individual oxygenates on CO, NO_x and PM emissions is roughly additive when these oxygenates are applied together (i.e. as a package of additives). There is no such regularity for HC emissions. The research showed that the application of oxygenated additives generally produces a significant reduction in PM emissions and a slight increase in NO_x emissions. An increase in CO and HC emissions was observed when maleates and carbonates were used as sole oxygenates. This increase was significantly lower when the oxygenates mentioned above were applied in a package with glycol ethers. The influence of oxygenated additive packages was different over the NEDC and FTP-75 cycles. Generally, the packages produced more favorable changes in exhaust emissions over the FTP-75 cycle, which is more transient and dynamic (stronger accelerations). The reduction in PM emissions was higher over the FTP-75 cycle. In the case of NO_x emissions, these were higher by a factor of dozen or so for oxygenated fuels than for neat diesel fuel over the NEDC, whereas over the FTP-75 they was slightly lower for oxygenated fuels than for diesel fuel. In the case of CO and HC emissions, such a clear-cut relationship between the type of driving cycle and emissions changes was not observed. Regardless of test conditions, no significant influence of oxygenated additive packages on CO₂ emissions was noted. The application of oxygenated diesel fuels containing packages of oxygenated compounds caused a significant reduction in PM and a small change in NO_x emissions, so it produced favorable changes in the PM/NO_x emissions trade-off. Favorable changes in PM/NO_x emissions produced by the application of oxygenated additive packages were, however, comparable to these achieved with use of the most effective individual oxygenates.

F2012-B01-045