Indice

1. Hybrid propulsion
   
2. Development of numerical models
   
3. Test facility
4. Hybrid Propulsion Group
   

CISAS propulsion group is deep involved in chemical propulsion study, especially hybrid engines. The aim is to build a solid numerical model to predict the performance of a hybrid rocket for civil and scientific applications as quick launchers or suborbital vehicle propulsion systems. Furthermore this technology is useful for fine throttable engines, adopted in space maneuvers (landing on Mars).
At the same time an intense experimental test campaign is carried out to verify real functioning of various rocket configurations.

1. Hybrid propulsion

Hybrid motors combine elements from both liquid and solid propulsion systems. Gaseous or liquid oxidizer - generally liquid oxygen (LOX) or nitrous oxide (NOX) - is stored in a tank, and a hollow fuel grain - generally plastic or rubber - lines the combustion chamber. The liquid oxidizer used is either stored at room temperature or at cryogenic temperatures in a storage tank. Feeding of the liquid into the combustor is accomplished by pressurized gas, gas generator or pump. To start motor operation, an ignition device is needed. Ignition can also be achieved through the use of a hypergolic mixture.
After full combustion is accomplished, the motor burns until the oxidizer flow is halted. When the flow of oxidizer stops, the motor shuts down.
A source of ignition is applied to the fuel grain, vaporizes some of the fuel, and the oxidizer is injected into the chamber. At about 1000 degrees, the 36% oxygen (by molecular weight) in NOX is released to combust with the fuel vapour in a thin boundary layer above the fuel grain. This creates both gases and more heat, which in turn continues to vaporize the fuel grain. The oxidizer flow can be increased or decreased for throttling, and, if the ignition system is re-usable and onboard, the motor can be stopped and re-started in flight.

 

Main activities
Theoretical - Numerical	Thruster structural lumped model
	Oxidizer discharge numerical model
Experimental	“Cold tests”: oxidizer discharge and injector tests
	Development of innovative ignition methods
	“Hot tests”: hybrid rocket full operative tests
	Tests on new hybrid engine configurations / fuels
	Development of high level measurement systems

Link al file “HYBRID ROCKET NUMERICAL MODEL.pdf”



In the first hot firing experimental campaign a subscale hybrid engine has been tested in various configurations. This choice has been made to achieve reliability of the entire facility, to verify sensors and data acquisition, for the electronic control tuning and the engine performance validation.
The activity started concerning a full scale designed hybrid motor, resulting in a multi-port configuration, and to test a scaled one, which corresponded to only one port of that version.

The test stand facility and other dedicated devices can adapt to various types of hybrid rockets, single-port and multi-port configurations, subscale and full scale, with a maximum thrust of 2000 N and 20 lit of storable oxidizer.
During the operative phases the following measurements can be acquired:

• vapor and liquid phase oxidant temperature and pressure (thermocouples and pressure gauges)
• temperature and pressure before injection
• temperature and pressure in pre-combustion chamber (after injection)
• temperature and pressure in post-combustion chamber
• acoustic investigation of engine functioning (microphone)
• weight of oxidizer tank and combustion chamber
• developed thrust
• grain weight and thickness before and after the test (to achieve regression rate mean value).

These data is real-time acquired in automatic (triggered) manner by a dedicated data acquisition system (see Errore. L'origine riferimento non è stata trovata.), and stored after a computer elaboration.

Furthermore, the facility is provided with an electronic control system, which permits to control the operative phases both in manual and in automatic mode.

Test stand facility completely assembled.

Nominal configuration of the engine provided the following performance:

Besides the nominal configuration, also other versions of the motor have been tested: they are described in the following table.

Test #	Definition	Description	Measurement (on combustion chamber)
1	No post-combustion chamber	Nominal config. without post-combustion chamber	Ignition pressure and temperature, thrust
2	Pre-combustion chamber	Nominal config. with pre-combustion chamber	Pre and post-combustion chamber pressure and temperature, thrust
3	High/Low Gox	Nominal Gox ± (value)	Post-combustion chamber pressure and temperature, thrust
4	Different O/F	Nominal grain length ± (X)mm	Post-combustion chamber pressure and temperature, thrust
5	Different fuels	Nylon, polyethylene, wax	Post-combustion chamber pressure and temperature, thrust
6	Different port config.	Triangular port, 4 circular ports, 3 circular helicon ports	Post-combustion chamber pressure and temperature, thrust

Configurations can also be “mixed” together, to create further configurations (ex: a 4 circular port grain configuration with high value of Gox or with different fuel material).

Particular of the combustion chamber.

Scheme of the hydraulic circuit.

CISAS propulsion group is already developing a new test stand for the hybrid rocket test facility, and a full scale hybrid engine will be tested very soon. Expected performance is:

Measurements will be also improved:

• oxidizer mass flow rate during engine functioning
• fine regression rate acquisition (X-ray sensor).

Experimental test facility
The experimental tests are conducted in a new facility, which has been set up by the hybrid propulsion group. It is organized in several specific areas:

• test room: it contains the test bench for the rocket and sensors;
• monitoring room: main room for data acquisition and remote control of the entire engine functioning;
• work-room: room for engine assembling and components tooling
• stockroom: room for stocking non operative materials and components (tanks, hardware, etc.)

Plant of the hybrid rocket facility at CISAS.

In the test room the test bench has been designed to allocate a wide range of combustion chambers and oxidizer tanks, with an easy and fast set-up changing.
At the external side of the test room a dedicated silencer system has been set up for the acoustic emission reduction of exhaust gases. This assures a low acoustic pollution even with high total impulse engines.

Particular of the test room in the hybrid rocket facility at CISAS.

Inner side of the monitoring room of the hybrid rocket facility at CISAS.

Mail Daniele Pavarin : daniele.pavarin@unipd.it
• Alberto Bettella
• Federico Moretto
• Stefano Giacometti
• Marta Lazzarin
• Nicolas Bellomo