Project Initium - Liquid Rocket Engine

Initium was a project I started and led in my last semester at Pitt and then continued work on post-graduation with the rest of the engineering student team. This project had the goal of designing, manufacturing, and testing Pitt's first ever student-developed liquid rocket engine using isopropanol and nitrous oxide as a fuel and oxidizer, respectively. The engine system was succesfully cold flow and hot fire tested in April 2026. A major resource for guidance and design philosophy for this project was Half-Cat Rocketry and their publically available designs.

On this project, I served as the Chief Fluid Systems & Operations Engineer and one of three primary Lead Engineers on a team of eight other students. In my role, I was responsible for: 

1. Designing and assembling a floating-piston style propellant tank to safely store and feed the IPA and N2O propellants at pressures up to 1,000 psi.

2. Engineering a piping system to remotely fill the N2O tank and feed the propellants to the injector assembly at an expected flow rate of 0.5 lb/s and pressures exceeding 800 psi.

3. Sensor device selection to reliably gather critical pressure and temperature data within the propellant tank, piping system, and injector manifold.

4. Safe operating procedures for safely testing the engine system while minimizing risks associated with high-pressure systems.

Videos

Piping System Design Overview

The above P&ID was created in AutoCAD, and it shows the as-built version of the piping and instrumentation system.

The system incorporates three main safety devices to prevent over-pressurization when the fluid system is active. The main system is the static vent on the N2O-side of the tank, which allows the system to fill with liquid and, more importantly, vent off pressure even in the event of a power or communication failure. Additionally, there are two pressure relief valves set to 1,200 psi that can independently vent either propellant in the event of a high-pressure event.

In addition to safety, electronic devices were sourced and installed in the propellant tank and piping system for system monitoring and remote control. On the Initium system, four pressure sensors and one temperature sensor (RTD) are are installed in the tank and piping to analyze tank pressures, feed pressures, and pressure drops accross the system. Additionally, every ball valve is servo-actuated to allow for remote control of the entire feed system, which minimizes the amount of time that a person must spend near pressurized equipment. 

The system also incorporates many passive instruments to maximize reliability and performance when in operation. Both propellant feed lines contain a Y-strainer to prevent debris from clogging the sensitive injector orifices. Past the strainers, the check valves on the fill and feed lines prevent back-flow and keep fluid flowing in one direction. Finally, flexible braided hoses are utilized for vibration-resistance and quick connection points during assembly. 

The 3D modelling and assembly for Initium was done primarily in a collaborative OnShape project space. On this system, I laid out the fluid system hardware in the test stand assembly to gauge system layouts, dimensions, and possible constraints or red flags prior to physical construction. The image above shows the final 3D assembly of the engine fluid system from which the physical Initium system was based on. 

Tank Hardware Design Overview

Initium's propellant tank stores the fuel and oxidizer inside a single structure built from a 3-inch Sch. 40 aluminum pipe. Inside the tank is an aluminum floating piston, which separates the two propellants to create a stacked-tank configuration. 

The floating-piston design employed by the tank was selected to utilize the self-pressurizing properties of nitrous oxide. At a temperature of 70°F, N2O has a saturation pressure of 760 psi. This high pressure serves as the driving force for fluid delivery, and the internal floating piston is used to pressurize the IPA and N2O liquid. 

This tank configuration removes the need for an external pressure source, such as an inert gas or pump. However, this also creates the risk of the propellants mixing inside the tank before reaching the combustion chamber, which could be an explosion hazard. Careful calculations and testing were performed on the o-ring glands for the floaitng piston to ensure that a proper dynamic seal was achieved as the piston was pushed upward.

The tank successfully held pressure during two engine tests at a peak pressure of 900 psi for 40 seconds. Post-test analysis revealed there were no leaks on any sealed interface, and all the hardware remained structurally sound and ready for re-use.

Although the propellant tank wall was able to be purchased as an off-the-shelf part, each bulkhead was custom designed and machined out of aluminum for this project. 

Each bulkhead has three o-ring glands as a critical redundancy to ensure no propellants leak out of the tank from the end bulkheads or mix by leaking past the floating piston. Every o-ring gland in this tank is sized to house a -232 Buna-N o-ring with 15% compression.

The two ends of the tank (IPA and N2O bulkheads) are retained using eight radial 1/4"-20 bolts. These bolts pass through clearance holes in the tank wall and thread into the bulkhead body to contain them inside the tanks. Assuming a working pressure of 800 psi inside the tank, these radial bolts provided a factor of safety of 3.2. 

The IPA bulkhead (left image) contains two threaded NPT ports, one for the discharge/pressure relief piping and one for a pressure sensor. 

The floating piston (center image) is a hollow puck structure that separates the two propellants and transfers the N2O pressure to the IPA. The N2O-facing side of the piston is hollowed out to provide create an ullage space for N2O vapor to compress, which reduces the risk of hydraulic lock and over-pressurization.

The N2O bulkhead (right image) is the most complex with four threaded NPT ports for the filling/feeding piping, pressure sensor & pressure relief piping, RTD temperature sensor probe, and 0.025" orifice static vent structure. 

As mentioned above, the static vent structure serves two primary functions. The main function is to allow the propellant tank to fill with N2O liquid from the supply bottle. Because N2O has a very high vapor pressure, simply connecting the supply bottle to the propellant tank would cause the propellant tank to become pressurized with N2O vapor and prevent liquid flow once the pressure is equalized. The static vent utilizes an internal dip tube to vent vapor from the N2O headspace so the volume may be replaced with liquid. A 0.025" orifice is used to control the venting rate of the vapor and thus the inlet flow rate of the liquid. 

The second purpose of the vent is to provide a constant flow path for N2O pressure relief. If the electronics that cotrol valve actuation were to fail due to power or commucation loss, the staic vent ensures that the system pressure can be safely relieved passively. 

Assembly Images