Eco: On-Board Distillation System for Reduced HC Emissions and Improved Fuel Economy

A new on-board destillation system to reduce start-up emissions of unburned hydrocarbons was developed at the University of Texas.

The on-board distillation system (OBDS) extracts high-volatility components from gasoline and stores them for exclusive during start-up and warming. New tests show that OBDS reduced cranking fuel requirements by 70%, enabled a 57% decrease in catalyst light-off time, cut the emissions of regulated hydrocarbons (NMOG) by 81%, and delivered an apparent 1% increase in fuel economy. The team reports on its work in a paper in Environmental Science & Technology.

In modern vehicles, 60-95% of all HC emissions occur during the first 90 seconds after a cold start.

The primary reasons for this are twofold: low/unknown fuel volatility and poor catalytic converter efficiency. The relatively low volatility of gasoline (10-30% vaporizes upon injection at 20° C) requires the injection of considerably more fuel (typically 8-15 times) than the stoichiometric amount in order to generate a reliably ignitable fuel/air mixture.

Furthermore, the volatility of the fuel is not known a priori by the engine controller (the powertrain control module, PCM), so the PCM is often calibrated to command fueling rates based upon the expectation of the worst-case volatility fuel. This results in an air/fuel mixture that is overly fuel-rich for most starting conditions and a large amount of liquid fuel that will enter the combustion chamber during the first several cycles. Much of the excess fuel exits the engine unburned or only partially combusted.

A conventional three-way catalytic converter will not reach “light-off” temperature (corresponding to 50% HC conversion efficiency) for 30-40 s or more during the FTP drive cycle. Ironically, the period of highest engine-out HC emissions coincides with the period of lowest catalyst efficiency, making the combination of low fuel volatility with poor catalysis the primary cause of high HC emissions during the cold-start and warm-up period.

(This is also a design consideration for plug-in hybrids, as the longer periods of all-electric drive could be accompanied by more engine cold-start events during the day.)

The OBDS originally was designed to address the cold-start problems inherent in E85-fueled vehicles. The OBDS separated the most volatile fractions of gasoline fr

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Source: Green Car Congress

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