The Texas Department of Transportation (TxDOT) began using an emulsified diesel fuel in July 2002. They initiated a simultaneous study of the effectiveness of this fuel in comparison to 2D on-road diesel fuel, which they use in both their on-road and off-road equipment. The study also incorporated analyses for the fleet operated by the Associated General Contractors (AGC) in the Houston area. Some members of AGC use 2D off-road diesel fuel in their equipment. The study included comparisons of fuel economy and emissions for the emulsified fuel relative to the conventional diesel fuels.
Cycles that are known to be representative of the typical operations for TxDOT and AGC equipment were required for use in this study. Four test cycles were developed from data logged on equipment during normal service: 1) the TxDOT Telescoping Boom Excavator Cycle, 2) the AGC Wheeled Loader Cycle, 3) the TxDOT Single-Axle Dump Truck Cycle, and 4) the TxDOT Tandem-Axle Dump Truck Cycle.
As is conventional for heavy-duty engines, the first two of these cycles are specified in terms of percent torque and percent engine speed versus time for engine dynamometer testing. The latter two cycles are specified in terms of vehicle speed versus time for chassis dynamometer testing. Due to the torque loss associated with the water in the emulsified fuel, there was concern that conventional means for comparing the two fuels would result in less work performed by the engine over the cycle when operating on the emulsified fuel.
The inadequacies of traditional speed versus time test cycles, when applied to heavy-duty vehicles where power-to-weight ratio can change greatly, have been recognized for some time. Speed versus distance test routes have been developed using icons as simple driver instructions, using free accelerations in a traditional speed versus time environment, and using sequences of distanced-based phases. For this study, a route technique was developed for testing the dump trucks. The route technique assures equal distances traveled for each micro-trip and for the overall cycle independent of the fuel. For engine dynamometer testing, the same command cycle was used to assure the same work was requested over the cycle independent of the fuel.