How a CO2 Cartridge Powers a Dragster

A CO2 cartridge powers a dragster by venting high-pressure carbon dioxide through a small rear nozzle, producing a backward jet that pushes the car forward in accordance with Newton’s third law. In typical school competitions, a starter pin pierces the sealed cartridge; liquid CO2 inside flashes into gas and rushes out for a few tenths of a second, delivering a sharp burst of thrust that accelerates the car rapidly before it mostly coasts to the finish.

What Exactly Is in the Cartridge?

A CO2 cartridge is a small steel canister, commonly 8 grams for educational dragsters, prefilled with liquefied carbon dioxide under its own vapor pressure. At room temperature, internal pressure is roughly 5–6.5 MPa (about 700–950 psi), rising with temperature and falling with cold. Because the CO2 is stored as a liquid with a gas headspace, the cartridge can deliver a high mass flow nearly immediately after it is opened.

From Piercing to Propulsion: The Launch Sequence

The launch follows a repeatable sequence that turns stored pressure into forward motion. Below is the step-by-step process as it typically occurs on regulated tracks.

1. Arming: The dragster is placed on the track and tethered (often via a monofilament line through guide eyelets) to keep it straight.
2. Piercing: The starting gate drives a sharp pin into the cartridge’s thin seal at the nozzle end.
3. Flash expansion: Liquid CO2 near the puncture flashes to gas, dropping temperature rapidly (Joule–Thomson cooling) and sustaining high internal pressure.
4. Jet formation: Gas accelerates out of the small orifice; if the pressure ratio is high enough, flow “chokes” to sonic speed at the throat, creating a high-velocity plume.
5. Thrust: The rearward jet imparts an equal and opposite reaction, pushing the dragster forward. Peak thrust occurs early when pressure is highest.
6. Decay and coast: As CO2 mass is expelled and temperature falls, pressure and thrust decline. After roughly 0.2–0.5 seconds, the cartridge is effectively empty and the car coasts, with speed limited by aerodynamic drag and rolling resistance.

Together, these steps create a short, intense impulse that delivers most of the run’s acceleration in the first few meters, after which the vehicle’s design efficiency determines how much speed it can retain.

The Physics Under the Hood

The cartridge produces thrust by ejecting mass: thrust ≈ (mass flow rate) × (exhaust velocity), plus a small pressure term at the exit. The nozzle or orifice determines how quickly gas can leave; with sufficient upstream pressure, the flow chokes and reaches Mach 1 at the throat, then expands to supersonic speeds outside. Because pressure in a CO2 cartridge depends on temperature, warmer cartridges start with higher pressure and can deliver greater mass flow, while cooling during discharge reduces pressure in real time. The result is a short, high-power pulse rather than a sustained push.

Key Equations in Plain Language

The thrust can be approximated by F ≈ m_dot × v_e + (p_e − p_a) × A_e, where m_dot is the mass flow, v_e is exhaust speed, p_e is exhaust pressure at the nozzle, p_a is ambient pressure, and A_e is nozzle exit area. Vehicle acceleration is then a = F / m, opposed by rolling resistance and aerodynamic drag (which grows roughly with the square of speed).

What Determines How Fast the Car Goes?

Several design choices and conditions govern the time from start to finish. The list below summarizes the major factors that control performance.

• Total mass: Lower mass increases acceleration (a = F/m), but rules typically impose minimum body masses for safety and fairness.
• Nozzle/orifice quality: A round, burr-free nozzle preserves flow; too-small orifices restrict mass flow, too-large ones waste pressure and shorten burn too quickly.
• Alignment and tracking: Straight axles, true wheels, and low toe/camber minimize scrub; clean guide eyelets reduce tether friction.
• Rolling resistance: Smooth, concentric wheels, low-friction bearings/bushings, and proper axle fit reduce losses.
• Aerodynamics: Streamlined shapes with minimal frontal area, smooth finishes, and clean transitions lower CdA and help sustain top speed during the coast phase.
• Center of mass and stability: Proper weight distribution reduces fishtailing and parasitic yaw that add drag.
• Ambient conditions: Warmer cartridges (within safety limits) start at higher pressure; higher altitude slightly reduces air drag but also lowers back pressure at the nozzle.
• Manufacturing precision: Symmetry, surface finish, and dimensional accuracy help ensure repeatable, low-loss runs.

Optimizing these elements focuses the cartridge’s brief energy delivery into forward motion, trading early acceleration against minimal losses during the coast.

Typical Performance Numbers

With an 8 g CO2 cartridge, thrust is commonly on the order of a few newtons during the initial pulse, with expulsion lasting roughly 0.2–0.4 seconds depending on temperature and nozzle details. On a ~20–24 m track, well-built educational dragsters often finish in about 1.0–1.6 seconds, peaking around 20–35 m/s (45–78 mph) before drag and rolling resistance bleed speed.

Safety and Handling

CO2 systems store substantial pressure and get extremely cold as they discharge. The following practices help keep launches safe and consistent.

• Use only approved, undamaged cartridges; never heat, puncture, or modify a cartridge outside the sanctioned launcher.
• Wear eye protection and keep hands clear of the nozzle and starter pin.
• Allow cartridges to warm to room temperature naturally; do not warm with open flames, hot water, or heaters.
• Beware of frostbite risk from cold metal and exhaust; handle spent cartridges with care.
• Secure the track tether and ensure the run area is clear before launch.
• Recycle empty steel cartridges according to local guidelines; never attempt to refill single-use cartridges.

Following these steps minimizes risk while preserving fair, repeatable results across runs and teams.

Environmental and Practical Notes

Single-use steel cartridges are widely recyclable once empty. Because the CO2 originates from industrial sources, events often focus on material minimization and reusability in the car body and wheels. Consistent storage conditions and careful inspection of the nozzle and alignment before each run usually yield more improvement than “hot-rodding” the cartridge itself, which is prohibited in most rule sets.

Summary

A CO2 dragster accelerates when a starter pin pierces its cartridge, allowing high-pressure carbon dioxide to escape through a rear nozzle and create a powerful jet. That brief, high-thrust pulse is converted into forward speed, after which the car coasts while fighting aerodynamic and rolling losses. Smart design—low mass, clean alignment, efficient aerodynamics, and safe handling—turns the cartridge’s short-lived energy into a fast, consistent run down the track.

What does CO2 do in drag racing?

In drag racing, CO2 has two primary uses: it can be used to power educational miniature dragsters propelled by a CO2 cartridge, demonstrating principles of physics and engineering, or it can be used in high-performance turbo applications to provide a consistent, stable, and instant pressure source for the wastegate, which enables faster turbo spool and precise boost control. 
1. Educational CO2 Dragsters

• Propulsion: Opens in new tabThese small, wooden race cars are propelled by the rapid release of compressed CO2 gas from a cartridge that has been punctured by a launch mechanism. 
• Track System: Opens in new tabThey race on a typically 60-foot (18-meter) track, with a guide string or wire underneath the car to keep it moving in a straight line. 
• Learning Objectives: Opens in new tabCO2 dragsters are popular in educational settings to teach students about fundamental mechanical principles, including mass, force, acceleration, aerodynamics, Newton’s Third Law of Motion (action-reaction), and the effects of gas pressure. 

This video demonstrates how CO2 dragsters are powered and how they run on a track: 55sPitsco EducationYouTube · Mar 10, 2016
2. High-Performance Turbo Boost Control

• Wastegate Application: In high-performance, turbo-charged engines, a CO2 system provides a stable and regulated pressure source to control the engine’s wastegate. 
• Benefits:
  • Faster Spool: The instant, reliable CO2 pressure helps the turbocharger spool up faster by keeping the wastegate closed until it’s needed. 
  • Precise Boost Control: CO2 offers a more consistent and precise method for holding boost pressure compared to engine-based manifold pressure, leading to more repeatable performance and accurate boost target hitting. 
  • Reduced Stress: Faster spooling reduces stress and temperature on the transmission and torque converter. 
• How it Works: A high-pressure CO2 bottle inside the car provides regulated CO2 gas to the wastegate, giving the engine control system a much stronger and more responsive force to hold the wastegate closed, even when the engine is producing less pressure. 

You can watch this video to learn about CO2 boost control systems in drag racing vehicles: 56sHigh Performance AcademyYouTube · Jun 7, 2019

How does the CO2 cartridge demonstrate Newton’s third law?

A CO2 cartridge is inserted in the holder at one end of the crossbar and the spring loaded pin is used as a firing device. When the cartridge is punctured, the release of CO2 gas propels the crossbar around, simulating rocket flight and demonstrating that for every action there is an equal and opposite reaction.

How does a CO2 cartridge power the dragster?

CO2 dragsters are made of lightweight material usually balsawood or basswood. They are propelled down a track by compressed carbon dioxide gas. The CO2 cartridge is punctured so the compressed gas can rapidly leave the canister causing the dragster to move. The dragster is guided down the track by a fish line or wire.
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What makes a CO2 dragster go fast?

Simply put, the less weight your dragster has, the faster it will go. This is the most important factor that will figure into your design. Keep it light! Thrust: The gas escaping from the CO2 cartridge in the car.