Potential for Improving Short-Trip Fuel Economy by Fuel Formulation

An experimental investigation was undertaken to determine the influence of fuel characteristics on fuel economy penalty incurred in short trips and in operating vehicles at other than normal ambient temperatures. The overall objective of the project was to determine the potential benefits of fuel reformulation to minimize fuel economy penalty associated with cold-start, warm-up operation.

Two vehicles, fueled with gasoline and natural gas, were operated from cold start in a chassis dynamometer facility maintained at 20° and 90° F ambient temperatures. Results indicate 15% less energy consumed in a 5-mile trip achieved by changes in choke schedule and mixture stoichiometry which were made possible by use of the gaseous fuel.

A data treatment system was devised to allow differentiation of economy penalty due to “friction” from that due to enrichment/choking. The friction penalty, when expressed in terms of distance, appears to be nearly independent of vehicle or engine size and is about three times greater at 20° F than at 90° F.