Obviously there are two major things that make a car energy to use. (others effects are not much)
- Accelerate the Car.
- maintain the velocity.
1- for the first how much you increase the speed then break, you will waste more energy.
Driving in a fix Speed is More Economy
the energy required for a car to increase its speed can be calculated with this formula:
Energy [Joules] = 0.5 * mass[kg] * ( velocity[meter/second] )^2
two drivers drive a route with average 108 km/h
driver A accelerate a car to 108 km/h you will need 450 Kj.
0.5 * 1000 * (30)^2 = 450 Kj
driver B would accelerate the car 3 times then breaks. would required 3 times energy for acceleration.
Only Including above Would only correct for In Vacuum Driving.
so there are other rules for an terrestrial vehicle
more energy consuming is maintaining the velocity for this to happen,
the consequence of Forces implies to car should be zero.
the car engine should resist with two major forces:
Providing this forces requires Engine Energy :
Energy = Force X Distance
The Friction can be calculated using this formula:
friction force = support force * friction coefficient
supporting force will be increasing by Mass, Earth Gravitational Acceleration, additional force on top of the vehicle.
friction coefficient is related with Wheels width and materials and their deformation.
(which Gearing and speed has no effect on them)
Note: just driving with in very high speed formula 1 car will increase on top force significantly.
so driving with 10km/h and 20km/h has same force.
20km/h would require twice power (joule/second) but will end in half of the time.
so: they are equal in friction resistance energy consumption.
but about Air Drag Resistance Conditions Are Different.
Air Drag Force is related to Shape, Cars Cross sectional Area, Air Velocity.
The Velocity is our interest. which depends on Wind and Car Speed.
V = Car Speed - (Wind Speed X Cosine(Wind Angle) )
But Force has Cubic Relation with The Speed means:
make speed twice, needs eight time Power, and we will end our journey in half the time, this results in Four Times Energy Consumption for Air Drag Resistance.
Driving Slower Would Significantly Reduce Fuel Consumption
its get more significant in high speeds (80+ km/h) which 80% of fuel consumption is for air drag resistance and 20% is for friction resistance.
This Rules would be perfectly correct for an electric car.
But a Mechanical Car has to Consume Fuel in 4-stroke Engine to make its power,
it needs perfect burning and perfect engine breath.
if RPM is low, Engine cannot Breath its required Oxygen (closed throttle) and raw Fuel releases in smoke.
if RPM is high, Engine cannot Breath its required Oxygen (imperfect burnt) and Carbon-monoxide releases in smoke.
The Above Conditions Are Relative (in both we have raw fuel and carbon-monoxide)
The Economy-Friendly Would be The Maximum Torque RPM (my car is 2800 RPM)
Driving in Maximum Torque RPM Would Result in Fuel Perfect Burning
for example i have calculated my efficient maximum torque RPM in each gears as follow:
gear & speed relation :
1(20 km/h),2(40 km/h),3(60 km/h),4(90 km/h),5(110 km/h)
Note: IN CVT Cars we dont have just a few steps, and
Every speed after RPM Reach its Point Would be Fuel-Perfect-Burning.
The Above Rule is True For Injector Based Car, Which ECU Controls The Fuel Flow.
For Old Cars, There is One-State Gasoline Flow Screw. in Those Cars,
Gears Mostly For Setting Torque And Driving In Higher Gears Is More Fuel-Efficient.
In Carbrator Cars, Driving in High Gears Are More Fuel Efficient
in Injector based Cars Its More Fuel Efficient to Drive In Maximum Torque,
Not Like Old-Cars Which Driving In High Gears Were More Fuel Efficient.
PS: my car is Saipa Pride (injector)
PS: Its Based on My Researches, Internet Searches, Intellectual Toughs, and Calculations. If Some one Thinks I am Wrong, Please Let me Know.
PS: I used to Drive my car in Higher Gear Strategy before, But After Switching to Maximum Torque RPM Strategy, it seems to give me more millage (10% more).
for 30 Liter of gasoline it was like 500Km, now it seems like 550km.