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.

Elements Of Electromagnetics
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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.
Transcribed Image Text: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.
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