Dependence of Fuel Economy on Speed for Heavy Duty Vehicles

Abstract

Arecommendation has been made that vehicles should travel at certain speeds in order to reduce their fuel consumption because gasoline and diesel are currently very expensive in many countries and that there might be the menace of fuel shortages in the near future in some parts of the world. The  ecommendation is basedon the fact that on the road the fuel economy of a vehicle increases while travelling at cruise speed without acceleration, as it is shown in this paper. Some of the vehicles on the road are the heavy duty vehicles which transport people, food, medicine, minerals, gasoline, diesel and many other goods to keep the economy of any country running. The vast majority of the heavy duty vehicles on the road in the world still moves with diesel engines. In this paper it is demonstrated, for the cases examined, that the fuel economy of vehicles depend, on several factors which include the load transported, the acceleration to reach the cruise speed, the engine, the gearbox, the wheels, the final drive, the maximum driving speed and the slope of the roads. The reduction of fossil fuels consumption in road transportation also reduces the emision of carbon dioxide to the atmosphere, a greenhouse gas which contributes to global climate change. For the cases studied the carbon dioxide emissions are also calculated. The savings in fuel consumption in dollars of driving at the best constant speeds and the reduction in the environmental cost caused by less emissions of carbon dioxide is presented. The calculations in this paper have been carried out using UAM mero, a computer program developed at the Mexican Universidad Autónoma Metropolitana. The results are presented for three heavy duty vehicles with 455 HP, 350 HP and 200 HP diesel engines moving in two parts of a driving cycle used for the United States of America Environmental Protection Agency and the National Highway Transportation and Safety Agency to certify compliance of heavy duty vehicles to the fuel economy and carbon dioxide emissions regulations in that country.