Question

TASK:

Each of the following generators is going to supply a load of 10kw at a power factor of 0.8 (If AC, if DC 1) for 24hrs, each of them will run at 3000rpm. Both diesel and petrol have energy values of 45MJ/kg but the efficiency of petrol engines is 25% whilst the efficiency of diesel engines is 45%. Calculate the fuel burn rate in kg/hour and the efficiency of each. Use the burn rate to calculate the cost of fuel and add that to the daily hire rate to get a total cost of the generator for 24hrs and hence say which would be the most suited to the job.

Answer 1

Energy consumed by each generators per second = 10 KJ/s   (watt=J/s)

Energy consumed per hour = 10 K * 60 *60 = 36000 K J = 36 M J / hour

Energy output of Petrol engine per kg = (25/100) * 45 M J/Kg = 11.25 MJ/Kg

Energy output of Diesel engine per kg = (45/100) * 45 M J/kg = 20.25 MJ/kg

Fuel burn rate (Petrol) = Energy consumed in a hour/ Energy output of Petrol engine per kg = 3.2 Kg /hour

Fuel burn rate (Diesel) = Energy consumed in a hour/ Energy output of diesel engine per kg = 1.78 Kg/hour

Cost estimation :

**Petrol**

Density of Petrol = 0.832 Kg /L

Volume of 1 Kg petrol = 1.2 Liters

Cost per Liter petrol = 80.89 Indian rupees(INR)/L

Cost per kg of petrol = 97.22 INR

Cost per hour for operating using petrol = 311.11 INR / hour

Cost for operating 24 hrs using petrol = 7466.76 INR

**Diesel**

Density of Petrol = 0.77 Kg /L

Volume of 1 Kg petrol = 1.298 Liters

Cost per Liter petrol = 76.54 Indian rupees(INR)/L

Cost per kg of petrol = 99.4 INR

Cost per hour for operating using petrol = 176.93 INR / hour

Cost for operating 24 hrs using petrol = 4246.47 INR

Diesel engine has lesser cost of operation in comparison to petrol engine. Hence it would be most suited for the job.