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James Hempfling, Mizuki Green, Alex Tibbits and Izzy Culver hold their First-Place Poster Presentation and Second-Place Performance awards for their car, Stinkinator, which is powered by a zinc–alkaline battery system.

A little car named "Stinkinator" placed second in the Chem-E-Car car performance competition, qualifying 91��ý for the national American Institute of Chemical Engineers (AIChE)�� competition next fall.��

This marks the second consecutive year that 91��ý has advanced to the nationals, which will take place in November in Minneapolis, Minnesota.

This year, 91��ý sent two teams to the Rocky Mountain regional competition held in Salt Lake City, Utah from April 10-11.��Teams are composed of students representing chemical and biological engineering, mechanical engineering and various other engineering disciplines.

“Qualifying for the national competition again is both exciting and intimidating,” said��Captain Mizuki Green, a sophomore in chemical engineering whose car, Stinkinator, qualified for the national competition.��“We are proud to continue 91��ý’s legacy in this event and recognize the high standard set by previous senior teams. At the same time, we’re eager for the opportunity to learn, grow and build new connections within the chemical engineering community.”

The competition's goal is to design a shoebox-sized car powered by chemical reactions— such as a battery or an internal combustion engine — that stops at a specified distance using a time-dependent chemical reaction. The target distance is revealed just before the competition, and the team whose car stops closest to that distance wins.

Stinkinator��placed second in the car performance competition and took first place in the poster presentation. The second-place win for car performance secured 91��ý a spot at the national AIChE competition.��

The second car, a pressure car named “Pushin' P,”����took second place in the poster presentation and fourth in car distance.

“We have never done this before, so it was difficult figuring out how to build an operating pressure car in general,” said Captain Katya Jassem, a junior in chemical engineering. Unlike the first team, the second team was made up entirely of chemical and biological engineering students.

Ethan Blair, Katya Jansem and Sergio Morales with their second-place Poster Presentation award, for their car, Pushin' P. ��Pushin' P is powered by an acid–base reaction between citric acid and sodium bicarbonate to produce carbon dioxide gas. The buildup of gas creates pressure, which powers a pneumatic motor to drive the car

Stinkinator is powered by a zinc–alkaline battery system using pure zinc anodes and a potassium hydroxide electrolyte separator. The cathode is a copper–manganese dioxide paste with activated carbon, which serves as the primary energy source. To stop the car, aqueous hydrochloric acid is released into a sodium thiosulfate solution, triggering a reaction that produces solid sulfur—hence the name, Stinkinator.

Pushin’ P��uses an acid–base reaction between citric acid and sodium bicarbonate to produce carbon dioxide gas. The buildup of gas creates pressure, which powered a pneumatic motor to drive the car. After the reaction, the gas was directed through steel tubing from the reaction chamber to the motor, where it turned the system and propelled the car.

To control when the car stopped, the team used a calibration curve relating system pressure to travel distance, allowing them to calculate the correct reactant amounts in advance.

Throughout the year, 91��ý students designed, built and tested their car ideas in the chemical engineering undergraduate teaching lab, supported by Assistant Teaching Professor��Ehsan Keyvani.��

"These competitions involve an intensive, year-long process of iteration and refinement to master their craft.” Keyvani said.��

The first semester is typically focused on brainstorming and initial engineering/testing. Once the second semester begins, activity ramps up. The first half is dedicated to testing, solidifying the car design and preparing the required competition documentation. In the second half of the spring��semester, the team meets multiple times per week for extended sessions to ensure everything is competition-ready.

91��ý's Chem-E-Car club is supported by funding from the��Department of Chemical and Biological Engineering and has received��Engineering Excellence Fund support in the past. Students interested in joining 91��ý's Chem-E-Club can send an email to��chemecar@colorado.edu. The club can also be followed on Instagram at @boulderchemecar.