Rocket Engine Nozzle Design Study — Engineering_▢✕
FileEditViewGoFavoritesHelp
UpAddress:C:\Projects\hardware\rocket-nozzle-research
Drawing NZL-002 · Entry 02 · Jul 2024 – May 2025

Rocket Engine Nozzle Design Study

Propulsion · Independent Research
Complete

An independent research paper ("Optimizing Small-Scale Rocket Engine Performance") comparing three classic nozzle geometries — conical, bell, and aerospike — to find which best suits small-scale commercial engines, a corner of propulsion that's usually overlooked in favor of large orbital launchers.

The gap

  • Most nozzle research targets large orbital engines; small-scale propulsion is comparatively unexplored and often just a scaled-down large design.
  • That ignores the thermodynamic, fluid-dynamic, and geometric constraints that change at small scale — where nozzle geometry matters even more.

Method

  • A physical test rig wasn't approved by the school research board, so I moved to a simulation-based approach for a controlled, repeatable environment.
  • Built 3D CAD models of each geometry (throat and exit dimensions), then ran them in the HalfCat Simulator across consistent chamber conditions.
  • Ran each configuration multiple times and normalized results to reduce run-to-run computational variance.

Findings

  • The bell nozzle led on performance — 79% efficiency and 297 lbf peak thrust — thanks to better flow attachment and fuller gas expansion, but showed noticeable thrust oscillations early in the burn.
  • The aerospike was the most stable (near-zero oscillation) at 60% efficiency and 221 lbf, but its manufacturing complexity works against commercial use.
  • The conical nozzle was steady and simple at 61% efficiency and 191 lbf.
  • Specific impulse rose with expansion ratio only up to a point — an optimal band around 8:1–12:1 for small engines at atmospheric conditions, beyond which gains don't justify the added complexity.

Conclusion

  • For most small-scale commercial applications — short-to-moderate burns where thrust matters — the bell nozzle is the best all-around choice: strong efficiency and thrust, and easy to manufacture.
  • The broader takeaway: small engines should be designed for small-scale use from the start, weighing stability and manufacturability, not just chasing maximum theoretical performance.

Results

MetricConicalBellAerospike
Mass flow (kg/s)0.7010.8440.861
Exit Mach0.600.950.81
Exit temp (K)160018301740
Exit velocity (m/s)230325275
Efficiency61%79%60%
Peak thrust (lbf)191297221

Simulated performance by geometry (HalfCat)

Specifications

Geometries:Conical · Bell · Aerospike
Simulation:HalfCat Simulator + Fusion 360 CAD
Best overall:Bell — 79% eff., 297 lbf
Optimal expansion ratio:≈ 8:1 – 12:1
Paper length:~4,700 words
Type:Independent research
Tools:HalfCatSimFluid DynamicsThrust Modeling

Figures

Bell nozzle — CAD model
Fig. 1 — Bell nozzle — CAD model
Conical nozzle — CAD model
Fig. 2 — Conical nozzle — CAD model
Aerospike nozzle — CAD model
Fig. 3 — Aerospike nozzle — CAD model
Bell — thrust curve (297 lbf peak, early oscillations)
Fig. 4 — Bell — thrust curve (297 lbf peak, early oscillations)
Conical — thrust curve (191 lbf, steady)
Fig. 5 — Conical — thrust curve (191 lbf, steady)
Aerospike — thrust curve (221 lbf, most stable)
Fig. 6 — Aerospike — thrust curve (221 lbf, most stable)

Attachments

Full research paperOpen ↗

Complete write-up with literature review, method, and analysis (DOCX download).

Complete · Independent Researcher, scale Sub-scalePropulsion