1. Vehicle Fuel Usage Learning Objectives :
To understand what fuel consumption is
To understand the factors which affect fuel consumption
To consider the environmental impact of electric cars

2. Fuel Consumption
Fuel consumption indicates how efficiently a car uses fuel. We aim for better consumption to reduce cost & pollution
Two common measures :
UK / US “Miles per gallon” [higher = better]
Continental Europe “Litres / 100km” [lower= better]
Usually quoted for different driving conditions : Urban, Cruising, combined

3. Types of fuel
Currently, most cars use one of two types of fuel : Diesel and Petrol. Both are fossil fuels. In general diesel gives better fuel consumption: Consider a new Ford Fiesta with a 1.4 litre engine (mpg)
Urban
Extra Urban
Combined
Petrol
37.7
61.4
49.6
Diesel
53.3
80.7
67.3

4. Questions
What happens to the resistive forces, (air resistance and friction) at greater speeds?
How does kinetic energy increase with speed?
Where does this “extra” energy come from?

5. Factors Affecting Consumption
Work against Resistive Forces
When driving at high speed the engine must do work against air resistance and friction. Air resistance increases dramatically with speed.
Ultimately this limits the top speed of cars
It can be improved by streamlining

6. Factors Affecting Consumption
Increase in kinetic energy
As speed increases the Kinetic energy increases dramatically, (Ek = ½mv2)
This “extra energy” has to come from burning fuel more quickly

7. Factors Affecting Consumption
Driving style
Fast, harsh driving with rapid acceleration and heavy braking increases consumption
Slower, steady driving with less braking reduces consumption

8. Factors Affecting Consumption
Road Conditions
Driving up hill etc is doing additional work against gravity and so will use more fuel.

9. Electric Cars
Much is said about the use of electric cars to reduce pollution.
At the point of use (i.e. Driving the car) an electric car appear to produce no pollution
However, how was the electricity made?

10. Electric Cars
If the electricity has been made using a renewable source such as photo voltaic cells (solar) then it is fair to say that electric cars are pollution free.
However if the electricity was generated using fossil fuels (nearly all currently) then pollution is still produced