The cost of fuel for commercial trucks is second only to labor in the total vehicle operating costs. Therefore, technologies that reduce fuel consumption can have a significant impact on the bottom line for both trucking fleets and owner/operators. Quantifying the fuel savings associated with different technologies, however, is complicated by many factors, and short-term testing often cannot adequately quantify small changes in fuel consumption that, over time, can add up to substantial cost savings on a vehicle. For example, fuel economy gains of less than one percent may not be reliably measurable using fuel tests, and variable environmental and use factors can cast some doubt on the appropriateness of short-term testing. Nonetheless, with today's fuel prices, each percent improvement in fuel economy for heavy duty trucks results in annual savings of about $335 per vehicle in fuel costs, based on 100,000 miles (160,000 km) annual vehicle mileage, 6.5 mpg (36.2 L/100km) fuel economy and a fuel price of $2.20/gallon. It is therefore quite worthwhile to identify technologies that can provide even modest fuel savings and to quantify the gains.
As an alternative to conducting fuel tests, fuel savings can be quantified through detailed simulation of a vehicle's performance using a physics-based model that incorporates performance maps of the drivetrain components and all other elements of the vehicle responsible for energy losses. This paper describes the development of a model for heavy-duty trucks using AVL-CRUISE software. This model can be used to predict fuel consumption when a vehicle is operated following any specified driving cycle, and the fuel savings potential of specific technologies can be evaluated when the energy loss characteristics of the technology are available. Results of testing are presented that were used to validate the model results. Instantaneous fuel flow measurements during various driving cycles show excellent agreement with the model predictions.
The effect of tire rolling resistance on vehicle fuel consumption was investigated using the model developed. Based on these results, fuel savings of 1.40 to 1.62 L/100km can be expected per kg/T reduction in the average rolling resistance coefficient for this vehicle, depending on the cycle evaluated. This equates to fuel savings of 600 to 690 gallons of diesel for each 100,000 miles driven, times the reduction in the coefficient of rolling resistance expressed in kg/ton.