Paraffinic versus Olefinic Refinery Streams: An Engine Exhaust Emissions Investigation

To gain a better understanding of the exhaust emissions impact of olefins in a low aromatic, full boiling range gasoline, an evaluation of the before and after catalyst emissions of three highly olefinic refinery streams and three highly paraffinic refinery streams, blended 50/50 in motor alkylate, was conducted using a 3.1 L GM engine. The test fuels were also selected to consider the effects of volatility in addition to olefin concentration. The fuels were evaluated under three steady state engine operating conditions.

The results of the tests indicate essentially only small differences in the before and after catalyst total hydrocarbons (THC) between the pairs of highly olefinic streams and the highly paraffinic streams at relatively the same volatility level, for two of the test conditions (2400RPM-light and moderate/heavy loads. The ozone forming potentials (OFP) for these fuels, across all three speed and load conditions, also show relatively small differences. Furthermore, the results show that in general, even with large volatility differences (T50 range of 140 - 185 °F), only small differences are seen in engine out THC across the fuel set olefin range (3 - 57%). The OFP of the highly olefinic fuels did increase at the wide open throttle, high speed condition where very little catalytic oxidation took place. A low volatility olefinic stream (polymer gasoline) generated higher THC and OFP at all conditions. Mathematical modeling and artificial intelligence techniques were employed to investigate the relationship of individual fuel species and bulk fuel properties on the character of the exhaust effluent.