AIChE's annual Chem-E-Car Competition® engages college students in designing and constructing a car powered by a chemical energy source, that will safely carry a specified load over a given distance and stop.
The competition, which involves multiple regional competitions and a final competition at the Annual Student conference, increases awareness of the chemical engineering discipline among the public, industry leaders, educators, and other students.
The NTUA team was given the opportunity to participate in the 2016 Chem-E-car Competition thanks to an initiative taken by the Greek-American Chemical Engineers led by Professor Greg Stephanopoulos, MIT and Professor Christos Georgakis, Tufts University.
The car is an electrically propelled vehicle (EPV). Braking is controlled by the rate of a separate chemical reaction, since according to the competition rules, no mechanical breaking method is allowed.
A homemade zinc-air battery powers an electric motor driving the rear axle. The car can run for a specific time and thus, a specific distance, given by the kinetics of a chemical reaction which produces foam with a known and controllable rate. The travel time is determined the produced foam volume.
Power source: The power source is a Zn-Air battery. Oxygen is collected from the atmosphere with an air electrode, made by hot pressing a mixture of LDPE (Low Density Poly-Ethylene), activated carbon, graphite and manganese dioxide. The zinc electrode is zinc sheet metal. Electricity is generated through the reaction:
using KOH as the electrolyte. The electrolyte is contained within a sponge which is in contact with both the electrodes. Multiple cells are used to achieve the necessary voltage to move the motor.
Stopping mechanism: The stopping mechanism is based on a foam created and disrupting a laser beam which is pointed from one side of the cylinder to the other. The reaction used is:
The reaction is catalyzed using potassium iodide, and kitchen soap is used to trap the produced oxygen and create a foam. Given the distance and the speed of the vehicle, the time that the car has to move is calculated. Using experimental diagrams (foam height as a function of time), the height the foam will reach in the time the vehicle must move can be calculated. A laser and photoresistor are placed at that height. Two laser pointers are used and two photoresistors that detect each beam. When the first beam is interrupted by the foam the car starts moving. When the second beam is interrupted the car stops. This process is moderated by an Arduino Due microcontroller.