Carbon Buster: A Novel Prototype to Reduce Carbon Emissions from Exhaust Systems.

Carbon dioxide emissions from combustion engines are a major contributor to climate change and ocean acidification. Although electric vehicles are becoming more common, most transportation still relies on fossil fuels. Since this transition will take time, technologies that reduce emissions from existing engines could help bridge this gap.

My interest in CO2 capture began from learning a common chemistry demonstration in which blowing air through limewater turns the clear solution milky (Fig. 1). This occurs because carbon dioxide reacts with calcium hydroxide in limewater to form calcium carbonate, a solid compound that removes CO2 from the gas.

I applied this reaction to design an initial prototype called the Carbon Buster that used two large chambers (Fig. 2). In that system, exhaust gas first bubbled through limewater and then passed through a second chamber containing soda lime pellets, reducing CO2 concentration by up to 98.7%. While highly effective, the system was bulky and impractical for real world use.

So I redesigned the Carbon Buster to a smaller and more practical form that could attach directly to an exhaust pipe (Fig. 3). Instead of bubbling gas through a liquid chamber, the new design uses foam soaked in limewater eliminating the need for a liquid chamber (Fig. 4). I explored different filter combinations and foam materials to determine the most effective configuration for reducing CO2. This project investigates whether the more compact prototype combining the physical properties of foam and chemical absorption of limewater can meaningfully reduce CO2 emissions.

The prototype was created using a 3D modeling application (Shapr3D) and printed using a 3D printer with PETG filament. The prototype contains two main detachable parts: the exhaust pipe adaptor and the filter chamber (Fig. 5). The adaptor can be easily switched to fit a different exhaust pipe dimension. The filter chamber contains two smaller chambers that can be filled with different materials. The different chamber combinations and materials tested are summarized in Figure 6.

Limewater was prepared by dissolving food grade calcium hydroxide in distilled water until a saturated solution formed (Fig. 7). Foam was selected because it provides a large internal surface area that allows gas to interact with liquids or reactive materials while remaining lightweight and compact. Initially, a medium density foam commonly used in aquarium filtration systems (Seapora Filter Floss) was used. To evaluate whether foam material influenced CO2 capture efficiency, a high density kitchen sponge foam and a low density activated carbon aquarium filter foam (Fluval Carbon Foam) were compared.

Carbon dioxide gas was generated using a SodaStream CO2 canister connected to plastic tubing and a metal exhaust pipe to simulate engine exhaust flow (Fig. 8). CO2 concentration at the prototype outlet was measured using a Vernier Go Direct CO2 gas sensor connected to Graphical Analysis software, which reports concentrations in parts per million (ppm). A sensor holder was 3D printed to ensure the sensor remained at the same distance and position for every measurement.

For each configuration, one-, two-, and three-second bursts of CO2 were released and the outlet CO2 concentration was recorded. The results from the three bursts were averaged to determine the final value for each configuration.

The results showed that both chamber configuration and foam material significantly affected CO2 reduction. With no filter installed, the CO2 concentration of one-, two-, and three-second bursts was measured as baseline comparison (Table 1). Using a single layer of dry aquarium filter foam produced an average CO2 reduction of approximately 31%. Adding a second layer of dry foam increased the reduction slightly to about 34%. This modest reduction likely occurred due to airflow restriction rather than chemical absorption. When the foam was soaked in distilled water, the reduction increased to approximately 42%. This suggests that some carbon dioxide dissolved in the water before leaving the chamber. When the foam was soaked in limewater, the reduction increased further to about 45% for one foam layer and 53% for two limewater soaked foam layers. Adding more layers of limewater soaked foam progressively increased CO2 reduction. This increase confirms that the chemical reaction between carbon dioxide and calcium hydroxide removed additional CO2 from the gas stream.

Soda lime pellets placed in the chamber alone produced an average reduction of approximately 66%. When limewater-soaked foam was combined with soda lime pellets, the reduction measured was approximately 64%. The highest reduction during this phase of testing occurred when three limewater soaked foam layers were combined with soda lime pellets, producing approximately 71% CO2 reduction (Graph 1).

Additional experiments were then conducted to investigate whether foam material affected performance (Table 2). Kitchen sponge foam produced approximately 50% reduction when dry and about 45% when soaked in limewater. Activated carbon aquarium filter foam performed better, producing about 55% reduction when used alone. When this foam was soaked in limewater, the reduction increased to approximately 76%.

The highest reduction measured during the material comparison experiments occurred when two limewater soaked activated carbon foams were used together, producing approximately 84% CO2 reduction (Graph 2). These findings indicate that both chemical absorption and foam material structure play an important role in carbon capture efficiency.

My results show that the redesigned Carbon Buster can significantly reduce CO2 concentration. While the earlier large two chamber system achieved up to 98.7% CO2 reduction, the new compact design achieved reductions of up to 84% depending on the materials used. This decrease in efficiency is expected because the new chambers are smaller and the gas does not bubble through liquid for as long as in the original design. However, the compact system provides an important advantage because it is small enough to attach directly to an exhaust pipe.

The results also revealed an important design insight. Foam material selection had a major influence on performance. Activated carbon filter foam significantly improved carbon capture efficiency when combined with limewater. The highly porous structure likely increases internal surface area and improves gas contact with the reactive solution.

Another important observation involved soda lime pellets. Soda lime reacts with carbon dioxide in a three step chemical reaction. Although they improved CO2 capture, the reaction between soda lime and carbon dioxide is exothermic and generates heat. During testing, the outer surface of the soda lime chamber reached approximately 43°C. Heat generation could affect safety, durability, and long term performance.

Overall, these results suggest that compact carbon capture using limewater soaked activated carbon foam may provide an efficient and practical approach to reducing carbon emissions at the exhaust source.

Future work will focus on improving durability, safety, and real-world performance. Using metal instead of plastic will help the device withstand high exhaust temperatures and continuous vibration.

The durability of foam materials must also be evaluated, as they may dry out, degrade, or lose effectiveness over time.

Another key area is engine performance, since adding a filter could increase back pressure and affect efficiency.

Safety testing is also critical to ensure that carbon monoxide and other harmful gases do not enter the vehicle cabin.

I would like to thank my parents for their support as well as ordering and purchasing the materials I needed for my project. I would also like to thank QRSTF for all their support leading up to the CWSF.

Intergovernmental Panel on Climate Change. (2023). Climate change 2023: Synthesis report. https://www.ipcc.ch/report/ar6/syr/

International Energy Agency. (2024). Carbon capture, utilisation and storage. https://www.iea.org/energy-system/carbon-capture-utilisation-and-storage

Marsh, H., & Rodríguez-Reinoso, F. (2006). Activated carbon. Elsevier. https://www.sciencedirect.com/book/monograph/9780080444635/activated-carbon

Royal Society of Chemistry. (n.d.). Test the gas. https://edu.rsc.org/in-search-of-more-solutions/test-the-gas/608.article

U.S. Environmental Protection Agency. (2024). Transportation air pollution and climate change. https://www.epa.gov/transportation-air-pollution-and-climate-change