Problem 3. A tractor-trailer rig has a frontal area of A = 102 ft² and drag coefficient CD = 0.9. The ratio of rolling resistance to vehicle weight is CR = FR/W = (6 lbf)/(1000 lbf). The specific fuel consumption (defined as mass of fuel consumed divided by power, or thrust, produced times the time period) for the diesel engine is SFC= mƒ/(P▲t) = 0.34 lbm/(hp hr) and the drivetrain efficiency is na = 92%. The density of diesel fuel is pf = 6.9 lbm/gal. (a) Estimate the fuel economy, FE, for a rig traveling at a speed of U = 55 mph with a weight of W = 72,000 lbs. (b) For a fairing system that reduces the aerodynamic drag by 15%, estimate the improved fuel economy, FE faired. (c) Calculate the annual fuel savings, FS, for a rig that travels 120,000 miles per year. (d) Plot FE and FEƒ faired versus speed, U, assuming SFC and nd are constant.
Problem 3. A tractor-trailer rig has a frontal area of A = 102 ft² and drag coefficient CD = 0.9. The ratio of rolling resistance to vehicle weight is CR = FR/W = (6 lbf)/(1000 lbf). The specific fuel consumption (defined as mass of fuel consumed divided by power, or thrust, produced times the time period) for the diesel engine is SFC= mƒ/(P▲t) = 0.34 lbm/(hp hr) and the drivetrain efficiency is na = 92%. The density of diesel fuel is pf = 6.9 lbm/gal. (a) Estimate the fuel economy, FE, for a rig traveling at a speed of U = 55 mph with a weight of W = 72,000 lbs. (b) For a fairing system that reduces the aerodynamic drag by 15%, estimate the improved fuel economy, FE faired. (c) Calculate the annual fuel savings, FS, for a rig that travels 120,000 miles per year. (d) Plot FE and FEƒ faired versus speed, U, assuming SFC and nd are constant.
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
Publisher:Kreith, Frank; Manglik, Raj M.
Chapter5: Analysis Of Convection Heat Transfer
Section: Chapter Questions
Problem 5.26P
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