CFD Design optimization to achieve self-sustaining combustion in a micro gas turbine

Project Overview

This project focused on a micro gas turbine engine designed to generate 50 kg of thrust. While the hardware was successfully assembled and could be spun up to 13,500 RPM using an external starter motor, the engine consistently failed to sustain combustion once the starter was disengaged. The RPM would quickly fall to 6,500 and then the engine would shut down entirely, clearly indicating a failure in transitioning to self-sustained combustion.

To solve this, we conducted a detailed CFD analysis across the compressor, combustion chamber and turbine. The goal was to understand the root cause of this failure and deliver a design that would sustain combustion above 11,000 RPM and reach the target 50 kg of thrust at full load.

The Challenge

The key issue was that the engine could not maintain enough internal energy to continue running autonomously. Initial observations suggested an imbalance between the work produced by the turbine and the work required by the compressor, particularly during mid-RPM ranges. Further, the original compressor design showed signs of stall at low RPMs and insufficient pressure ratios across the operating band.

The specific challenges included:

The compressor stalled at low speeds (notably at 18,000 RPM)
The pressure ratio of the original compressor was too low (only 2.1 at 50,000 RPM).
Fuel-air mixing and combustion stability were problematic
The net power output at critical RPM points was likely negative or insufficient.
The engine could not meet the condition for self-sustaining operation without continuous starter input.

A. Performance evaluation of existing design

We first simulated the engine's behaviour at three key RPM points, idle (18k), mid (50k) and max (85k):

At 50k RPM:

Compressor required 130 kW
Turbine produced 340 kW
Net power: +210 kW → Self-sustaining confirmed
Thrust achieved: 360 N

At 18k RPM:

Compressor required 7.5 kW
Turbine produced 16 kW
Net power: +8.5 kW → Barely self-sustaining
Thrust achieved: 105 N

At 85k RPM:

Compressor required 510 kW
Turbine produced 1050 kW
Net power: +540 kW
Thrust achieved: 596 N

While the turbine had sufficient capacity, the original compressor was the bottleneck, unable to support airflow or pressure at low and mid RPMs, particularly during transitional phases.

B. Redesign of the Compressor

To eliminate stall and improve pressure buildup, we completely redesigned the compressor geometry:
The new compressor increased the pressure ratio from 2.1 to 4.0 at 50,000 RPM
CFD results at low RPM (18k) showed stable flow characteristics with no signs of stall. Performance curves indicated much better airflow behaviour across a wider RPM band.
The tip velocity improved from 303 m/s in the old design to 456 m/s in the new design. Compressor maps showed a clear characteristic curve even at 18,000 RPM, which was absent before.

A micro gas turbine engine targeting 50 kg of thrust was successfully assembled, but it failed to transition to self-sustained combustion, shutting down after the external starter disengaged (RPM quickly dropped from 13,500 to 6,500). To solve this critical issue, a detailed CFD analysis of the compressor, combustion chamber and turbine was conducted. The project's goal was to identify the root cause of the failure and deliver a design capable of sustaining combustion above 11,000 RPM to ultimately achieve the 50kg thrust target at full load.

Results & Benefits

With the updated compressor, the engine now:

Achieves self-sustaining combustion above 11,000 RPM, even at 18,000 RPM idle.
Produces sufficient net power across all key RPM ranges to support autonomous operation.
Delivers 360 N of thrust at 50k RPM and 596 N at 85k RPM, confirming the ability to scale to the design goal of 50 kg of thrust.
Shows no stall characteristics, allowing reliable startup and ramp-up.
Supports subsonic nozzle operation with 95% efficiency, as verified through isentropic and actual exit velocity calculations.
Operates with validated compressor-turbine performance balance — no oversizing or underloading.

Conclusion

This project demonstrates how simulation-driven redesign can resolve combustion instability and performance bottlenecks in gas turbine engines. By addressing the mismatch between the turbine's power output and the compressor's pressure generation, we restored full functionality and met the engine's thrust target.

The redesigned compressor eliminated stall, improved pressure ratios, and enabled consistent airflow across RPM ranges. Most importantly, the engine now transitions seamlessly from assisted startup to self sustained operation, a critical milestone for any micro gas turbine.

This work sets the stage for further development, including thermal optimization and mechanical durability studies. The engine is now fully capable of moving into integrated testing and eventual deployment.

Testimonials

What Our Clients Says

I worked with Muhammad on a classic acoustic topic, trying to develop one project related to my bussiness. He rewied my work, that we shared, improved it, fixed bugs and errors and clearly explained his work. I apreciated the clarity of the workflow proposed and its implementation. He was available and present in spite of our time offset. Also, it was my first time

Serrena Allen

Founder & Co-Founder of Airvitalize

It was an absolute pleasure to work with Muhammad! He had excellent communication throughout the process, ensuring everything was clear and addressing any questions quickly. His understanding and flexibility made working together very easy. The work was delivered earlier than expected and of high quality. Would definitely recommend.

Elliot Tucker

Managing Member at Megachip Solutions LLC

Solvo Engineers did an excellent job on our CFD project for airflow optimization in a dust catcher device. They carefully analyzed the design, improved efficiency by addressing critical flow issues, and clearly explained every step of their process. Their expertise and responsiveness made collaboration very smooth and effective.