Name:_________________
Period:_________________
Fuel Cell Car Lab: Determining fuel efficiency of the car
Objectives:
1. Students will calculate average speed and fuel efficiency of the fuel cell car
Background:
With oil prices hitting new records almost daily and the price of gas climbing as well, fuel
efficiency is of as much importance to our wallets as to the environment. Increasing fuel efficiency is
one way to reduce the amount of fossil fuels that we use. The reasoning is simple: the farther you
can travel on a gallon of fuel, the less fuel you will need.
One way to conserve gasoline even further is to use an alternative fuel such as hydrogen
instead of gasoline. Currently, life-size cars that run on hydrogen are too expensive (all we can afford
are the small models we use in class!). But as technology improves and the costs come down, we
may be filling up our tanks with hydrogen just as we currently fill up with gasoline or diesel.
Hydrogen is not a source of energy, but it is a molecule that stores energy. This means that
the way that we produce hydrogen is important in calculating whether its use decreases our use of
fossil fuels. Consider the following cases:
1) Hydrogen is produced by electrolysis using electricity from coal-fueled power plants (Note:
coal is a fossil fuel).
2) Hydrogen is produced from natural gas by chemical conversion (Note: natural gas is a fossil
fuel).
3) Hydrogen is produced from photosynthetic organisms growing in a bioreactor.
Of the three cases above, only #3 actually decreases the amount of fossil fuels we use. Cases
#1 and #2 use fossil fuels to make the hydrogen. In case #3, the hydrogen is made by the power of
the sun, just as our crops grow from the energy of sunlight.
In this exercise you will measure the fuel efficiency of the model hydrogen fuel cell car. In
gasoline burning cars, fuel efficiency is expressed as the average number of miles the car can travel
on a gallon of gasoline. Since we like to use the metric system in science, we will first measure the
number of meters the car can travel on a mililiter of hydrogen. So that we can compare this number
to our own automobiles, we will then convert the number to miles per gallon (mpg).
You will need the following materials:
• Solar panel
• Electric Light (60-100 watt bulb)
• Car body with fuel cell
• Syringe with tubing nozzle
• Distilled water (Use only distilled water for experiments with the fuel cell. The water must be free of
all ions and salts or it can destroy the fuel cell. NEVER USE WATER FROM THE TAP OR BOTTLED
DRINKING WATER.)
• Masking tape
• Stop watch
• Meter stick
Setting up:
1. Set up the fuel cell car and fill up the tanks completely with hydrogen and oxygen as we learned in
the previous exercise. Do not connect the motor wires until you have set
up your test course (see the following step).
2. Set the wheels of the car as far to the side as they will go (but NOT so
they are touching the body of the car). Careful not to pick up the car by
the fuel cell, which might come loose. Instead carry the car from the
bottom.
3. Set up the test track. Make sure you have an open space on the floor
with several square meters of cleared space.
4. Mark the starting point with a small piece of masking tape.
5. You will need at least two people to do this experiment: One to count
the laps the car completes and operate the stop watch, and the other to
mark the far side of the circular path traveled by the car.
Diameter
Diameter
of
ofcircle
circle
circle
Path of car
Do the experiment:
6. Now plug in the motor wires to the fuel cell -- again: red wire to the red side of the car, black wire
to the bluish gray side. The car should begin to move when the second wire is attached.
7. Start the stop watch as soon as the car begins to move. The stopwatch operator should count the
number of laps completed by the car (every time the car crosses the starting point tape mark counts
as one lap).
8. Once the car has settled into a defined path, the another member of the group should mark the
far side of circular path with a second piece of tape.
9. Allow the car to travel until it stops and then stop the stop watch.
Speed and fuel efficiency calculations:
Number of laps completed: _____________
Total time for all laps:______________
Average time per lap:_____________ (Divide total time by # laps)
Diameter of circular car path (in meters):____________
Circumference of circular car path (multiply diameter by 3.14): ___________
Total distance traveled by car (multiply circumference by # laps):___________
What was the car’s average speed in meters per second? __________
Fuel efficiency of cars is commonly reported in miles / gallon. In the metric system, we would report
this value as kilometers / liter. We will first calculate the fuel efficience in km/L and then convert it to
miles/gallon to compare to life sized cars. Note, the hydrogen tanks holds 20 ml of hydrogen gas.
How many kilometers did the car travel? ____________
What is the tank volume in liters? ___________
Calculate the fuel efficiency in Km/L: _____________
Convert the distance the car traveled to miles (note: 1 km = 0.62 miles) _____________
Convert the fuel the car used to gallons (note: 1 L = 0.26 gallons) ____________
What is the fuel efficiency of the car in miles per gallon? ____________
Questions:
1. What is the approximate fuel efficiency of your car at home? _________________
2. How does the fuel efficiency of the fuel cell car compare? Is it higher or lower? Can you think of
any reasons why it is higher or lower?
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3. Convert the average speed of the car from m/s to miles per hour.