1) You are responsible for selecting automobiles that will beused in your company’s fleet and have been asked to determine theenergy consumption of the described vehicles for each of thedriving processes described below. The vehicles have the followingcombined wind drag and rolling friction force during averageoperation conditions. The relationship for this force is Ff =(0.214m + 5.63) where, m=vehicle mass and Ff is the combined windand rolling friction forces in N. Note the numerical parameter haveunits associated with them.
One automobile is an all-wheel drive hybrid vehicle with a massof 1450 Kg and it is powered by a storage battery- motorcombination that provides electricity to four wheel mountedmotors/generators. It does not have plug in capabilities at thistime. The batteries in the hybrid configuration are charged usingan internal combustion engine-electrical generator combination atthe end of the driving cycle or by regenerative braking. Thebattery in this problem has sufficient energy storage to accomplishthe given driving cycle and it is used to keep account of theenergy used in each driving process. For the purpose of thisproblem the battery is initially fully charged. Determine thechange in the chemical energy of the battery for each describedprocess for the hybrid vehicle. The efficiency of the batterycharging process is 90% when it is charged from the engine. Theefficiency of the regenerative braking mechanism is 85% and isdefined as the energy provided to the battery divided by thebraking energy needed to reduce the speed of the automobile. Thebattery charging process is included in the regenerative brakingefficiency. The battery discharge efficiency is 90%. The batteryefficiencies are defined as the energy provided by the batterydivided by the change in the chemical energy of the battery duringthe discharge and the reciprocal of this parameter for the chargingphase. The hybrid regeneration braking system can operate down to avelocity of 10 Km/hr when the standard friction brakes are applied.All processes can be considered to be isothermal. The efficiency ofthe engine-generator system is 34% for the hybrid vehicle. Thesecond automobile has a mass of 1200 Kg, has the same all wheelmotor drive configuration and is powered by a conventional internalcombustion engine with a generator that has an efficiency of 31%.This efficiency is for the engine-generator combination. In thisconfiguration there is no regenerative braking mechanism and nobattery.The different driving cycles are composed of the followingindividual processes.
a) The vehicle accelerates from a stop to a speed of 50 km/hr atconstant elevation. This acceleration takes place over a distanceof 75 m. This applies to both the hybrid and nonhybrid vehicle.
b) The vehicle stops from a velocity of 50 km/hr at a constantdeceleration rate. During regenerative braking the distancedtraveled is 67 m and during frictional braking the distancedtraveled is 15 m. This process is also at constant elevation. Forthe nonhybrid vehicle the braking distance is 78 m.
c) A hill climb with an elevation change of 150 m at an angle of12 degrees and a constant velocity of 50 km/hr. The drag workshould be included in this calculation.
d) Calculate the power from the power device, either the batteryor the internal combustion engine vehicle, required during the hillclimb described in part (c).
e) A hill descent with an elevation change of 150 m at an angleof 1 degrees and a constant velocity of 50 km/hr. The drag workshould be included in this calculation.
f) Energy consumed per km during a level driving distance.
2.1) Determine the chemical energy change in the battery (in thehybrid vehicle) or fuel consumed (nonhybrid vehicle) and thethermal energy (heat) added to the environment (heat flow) for a),b), c), e) and f) of the above driving processes.
2.2) Using the above results and the given information, considertwo driving cycles that your company uses. The first is composed of51 start and stops, 5 hill climbs and descents and a level,constant velocity component of 21 km. The second driving cycle iscomposed of one start stop, one hill climb and descent and 310 kmof level, constant velocity driving. The first driving cycle isused twice as often as the second.
2.3) Based on your calculations, write a recommendation forpurchasing the type of vehicles. The company plans to purchase fourvehicles. The heating value of gasoline is 32.0 MJ/L. The cost ofgasoline is $1.75/liter. The recommendation is to the ChiefFinancial Officer of the company who has an MBA and a publicrelations background. To do this problem it will help if you drawyour system and identifying the energy property changes and theenergy interactions at the boundaries. In some cases, you may needa sub system analysis to identify the energy interaction,especially the heat flows associated with the inefficiencies of thesystem. Also, there is no external energy input until the end ofthe driving cycle for the hybrid vehicle, all the driving processesare supplied by the battery. For the nonhybrid vehicle, there is anexternal energy input from the fuel supplied to the engine fordriving process. It will also help if you view this problem as asimulation analysis of fuel consumed by each type of vehicle overeach driving cycle. The problem has been sub divided intoindividual processes that make up the driving cycle.
