You probably remember those tiny pinewood derby cars from scouts or the CO2 dragsters in middle school shop class. They were fast. Terrifyingly fast for a piece of balsa wood on a string. You’d pop the seal on a small pressurized canister, and whoosh—the thing cleared twenty meters before you could even blink. It makes you wonder why we’re currently obsessed with massive lithium batteries that weigh a thousand pounds when we could just use compressed gas.
But scale changes everything.
Current CO2 powered car designs aren't just bigger versions of those hobby shop toys. They represent a weird, niche corner of pneumatic engineering that struggles to break into the mainstream. It's a physics problem. While liquid CO2 is incredibly energy-dense when stored under high pressure, the hardware needed to turn that pressure into reliable torque for a two-ton SUV is, frankly, a nightmare.
The engineering reality of pneumatic propulsion
Let’s be real for a second. When people talk about "CO2 cars," they are usually talking about one of two things: either using the gas as a propellant in a pneumatic motor or using a "closed-loop" supercritical CO2 system.
The first version is simple. You have a tank. It’s filled with liquid or high-pressure gaseous carbon dioxide. You release that gas into a piston engine or a turbine. The expansion of the gas pushes the piston. It’s basically a steam engine, but instead of burning coal to boil water, you’re using the "stored cold" and pressure of the CO2.
The problem? Freezing.
Physics is a jerk. When a gas expands rapidly—like when it leaves a pressurized tank to move a car—it loses temperature. Rapidly. This is the Joule-Thomson effect. In many CO2 powered car designs, the engine block literally turns into a block of ice within minutes of operation. To fix this, you need a heat exchanger to pull warmth from the ambient air, which adds weight, complexity, and reduces efficiency.
Guy Negre, the late French engineer and founder of MDI (Moteur Développement International), spent decades trying to solve this with compressed air. While he focused on air, the principles apply to CO2. His designs used "active heat" chambers to prevent the freezing issue. But even with his brilliant packaging, the range was always the "gotcha." You can only squeeze so much gas into a tank before the tank itself becomes a bomb.
Why CO2 is actually a better "spring" than air
Carbon dioxide has a weird property that makes it cooler than regular compressed air for energy storage: it liquefies at relatively low pressures. At room temperature, CO2 turns into a liquid at about 56 bars of pressure.
Why does that matter?
Because you can fit way more liquid in a tank than gas. It acts like a chemical spring.
In a typical CO2 powered vehicle design, the tank holds liquid CO2. As you draw gas off the top, some of the liquid boils off to replace it, keeping the pressure relatively constant until the tank is almost empty. This is a huge advantage over compressed air, where the pressure drops steadily as you drive, making the car slower and slower.
Wait.
There's a catch. There's always a catch.
To get that liquid to turn into gas fast enough to drive at highway speeds, you need a massive amount of heat. If you’re driving in a cold climate, your car basically becomes a refrigerator that’s trying to freeze itself solid. It’s an uphill battle against thermodynamics.
Real world attempts and the supercritical CO2 loop
If we move away from the "hobbyist" dragster style, we get into the heavy-duty stuff. Companies like Echogen Power Systems have been looking at supercritical CO2 (sCO2) for years.
What is supercritical CO2? It’s a state where the gas is held at a temperature and pressure where it acts like both a gas and a liquid.
In these designs, the CO2 isn't "exhausted" out of a tailpipe. It stays in a closed loop. A heat source (like a concentrated solar array or even a small nuclear reactor) heats the CO2, it expands through a turbine to create power, and then it's cooled back down.
- It’s incredibly efficient.
- The turbines can be 10x smaller than steam turbines.
- It doesn't corrode parts like water does.
But for a passenger car? It’s overkill. You’d need a miniature power plant under your hood. Most CO2 powered car designs that actually work on the road are hybrid systems. They use the CO2 expansion to assist a small internal combustion engine, or they use it as a regenerative braking system. Instead of charging a battery when you hit the brakes, you compress CO2 back into a storage tank.
It’s clever. It’s also expensive.
The sustainability paradox
We have to talk about the elephant in the room. Carbon dioxide is the bad guy in the climate change narrative.
So, is a CO2 car eco-friendly?
Honestly, it depends on where you get the gas. If you are "mining" CO2 from the atmosphere—what we call Direct Air Capture (DAC)—then the car is carbon neutral. You’re just borrowing the CO2, using it to move, and then letting it go (or keeping it in a loop).
If you’re using CO2 captured from an industrial smokestack, you’re basically giving that carbon one last "job" before it hits the atmosphere.
But here is the kicker: the energy required to compress and liquefy CO2 is immense. If you use coal power to compress CO2 for your "green" car, you’ve just moved the tailpipe to the power plant. You'd be better off just driving an EV.
What most people get wrong about the safety
People freak out about high-pressure tanks. They imagine a fender bender turning into a rocket launch.
In reality, modern carbon-fiber-wrapped tanks are incredibly tough. In many ways, they are safer than a tank of flammable gasoline or a lithium battery that can undergo thermal runaway. If a CO2 tank fails, it’s a "physical" explosion (pressure release), not a chemical fire.
The real danger is actually asphyxiation.
If you have a massive leak in a closed garage, the CO2 displaces the oxygen. You can’t smell it. You can’t see it. You just get sleepy and... well, that's it. Any viable CO2 powered car designs for the consumer market would need sophisticated leak detection and ventilation systems that most DIY builders forget to include.
The niche where CO2 actually wins
Where does this actually make sense? Indoor environments.
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Think forklifts in food-processing plants or tugs in underground mines. You can’t have diesel fumes there. Batteries are heavy and take hours to charge. A CO2 or compressed air system can be "refueled" in three minutes.
The University of South Australia actually developed a "liquid nitrogen" car years ago, which operates on almost identical principles to CO2. They found that for short-range, high-torque applications, cryogenic/pneumatic systems are surprisingly robust. They don't degrade over thousands of cycles like batteries do. You can charge and discharge a gas tank a million times and it stays exactly the same.
Actionable insights for the curious
If you’re looking into CO2 powered car designs as a hobbyist or an engineer, stop thinking about it as a primary fuel. It’s a terrible primary fuel for long distances.
Instead, look at it as a "Power Take Off" (PTO) or a secondary storage medium.
- Focus on the heat exchange: The secret to a working CO2 motor isn't the pressure; it's how fast you can get heat into the gas. Use a copper-finned heat exchanger and consider a water-glycol loop if you're building a prototype.
- Standardize your fittings: Most DIY failures happen at the valves. Use CGA-320 standard fittings for CO2. Don't try to "rig" air compressor parts; CO2 pressures can spike wildly with temperature changes, and cheap brass fittings will shear off.
- Weight vs. Pressure: A steel tank is too heavy for a car. Look into Type 3 or Type 4 cylinders (aluminum or plastic liners wrapped in carbon fiber). They are expensive but essential for a decent power-to-weight ratio.
- Safety first: Always, always install a burst disc. If your car sits in the sun on a 100-degree day, the pressure inside that tank will climb. Without a burst disc, the tank becomes a literal bomb. With one, it just makes a very loud noise and empties itself safely.
The "dream" of the CO2 car isn't about replacing the Tesla. It's about finding a mechanical, battery-free way to store energy that doesn't rely on mining rare-earth metals in questionable conditions. It’s a niche tech, a bit clunky, and physically demanding, but it’s one of the few ways to move a vehicle using nothing but a "spring" made of gas.