Turbojet engine

System Design

An automotive turbocharger provides the fundamental compressor and turbine stages to make a simple gas turbine, but normally depends on an engine for exhaust energy and pressurized oil. Converting one into a self-sustaining jet engine required developing both a combustion system and loop to direct gas flow from the combustion chamber to the turbine.

During operation, ambient air enters the turbocharger compressor and is directed into the combustion chamber. Propane is introduced and burned inside a perforated flame tube, raising the temperature of the flow before it enters the turbine. The turbine extracts enough energy from the exhaust stream to drive the compressor through the turbocharger shaft.

Once the turbine produces sufficient power to maintain compressor speed without assistance from the starter, the engine reaches self-sustaining operation.

The complete system consists of:

• Automotive turbocharger compressor and turbine

• Custom combustion chamber and flame tube

• Propane fuel system

• Independent oil reservoir, pump, filtration, and cooling loop

• Battery powered high voltage ignition system

• Electric ducted fan starting system

• Welded structural test stand integrating all subsystems

Combustor Design

The combustor was designed around the airflow requirements of the selected turbocharger using the JetSpecs combustor-sizing calculator as an initial reference. I designed a custom stainless-steel outer casing and perforated flame tube to stage airflow through the primary combustion, secondary mixing, and dilution zones. This staged arrangement helps maintain a stable propane flame while progressively mixing in compressor air and reducing gas temperature before the turbine inlet.

Lubrication and Cooling

Because the turbocharger normally relies on an automotive engine for pressurized oil, I built an independent closed-loop lubrication system with an oil reservoir, electric pump, filter, and cooling system. The system continuously supplies and cools oil through the turbocharger center housing to lubricate the high-speed bearings and manage heat transferred from the turbine.

Ignition System

I built a self-contained electric ignition system powered from the test-stand battery. A buck converter connected to the 12v main battery supplies 5v to a compact high-voltage generator module, powering a spark plug connected inside the combustion chamber

Starting System

A 22 V electric ducted fan was used to force air through the compressor and initially spool the turbocharger. Once sufficient airflow was established, propane and ignition were introduced until turbine output accelerated the compressor enough for the engine to transition to self-sustaining operation.

Combustor Fabrication

The combustor was fabricated primarily from stainless steel, using a modified fire-extinguisher body for the outer casing and a custom flame tube rolled from sheet. The flame tube was perforated according to the calculated airflow distribution and TIG welded into its final geometry. Working with thin stainless required careful control of weld heat iwhile maintaining alignment between the combustor, injector, and turbine inlet.

Machining

Custom flanges and mounting components were CNC machined from steel and stainless steel. Because the available mill had limited rigidity and spindle power, machining required conservative toolpaths and iterative adjustment of feeds, speeds, and depth of cut to reliably produce the required parts.

Test Stand and Integration

I fabricated a welded steel test stand to integrate the turbocharger, combustor, oil system, ignition electronics, battery, fuel hardware, and starter into a single portable assembly. Layout was driven by the need to keep fuel lines, wiring, and temperature-sensitive components separated from the combustor and turbine while maintaining access for testing and maintenance.

Testing

Testing required coordinating starter airflow, propane flow, ignition, and lubrication while progressively increasing turbine output. After iterative adjustment of the startup sequence and fuel delivery, the engine successfully reached self sustaining operation, allowing the electric starter to be removed while the turbocharger continued running independently.