The proposed project aims at designing, manufacturing and building of a demonstrator for a new engine concept.
    The new concept replaces the usual turbine of a classical turboengine by a number of Pulse Detonation Combustors (PDC) placed on a disk that rotates under the tangential impulse provided by the exhaust jet of the PDC. The rotating disk is coupled, through a shaft, to the compressor that is placed upstream of the PDC in order to raise its inlet pressure. Two solutions will be considered for the engine propulsion: a propeller, coupled, via a gearbox, to the PDC shaft, or by using the reactive thrust of the PDC exhaust jet, directed at an optimal angle. The PDC inlet with be equipped with aerodynamic valves that control the air entrance into the PDC, thus allowing a significant increase in the detonation frequency, allowing for noise reduction and reduced dimensions.
    The demonstrator, consisting of a single, fixed, PDC equipped with a fuel injection and ignition system designed for the requirements of the engine concept, will be tested on an experimental facility in order to demonstrate the PDC capability to provide enough power to meet the requirements of the compressor, with sufficient reserve for powering to propel the host aircraft. The project also proposes the design and numerical simulation of the engine compressor, adapted to the requirements of the new engine, most importantly the high vibration load
and oscillatory back pressure under which the compressor operates.
    A last objective of the project is to provide a full definition of the engine constructive solution and a numerical simulation of the flow through the engine that will allow the estimation of the engine performances. The new emerging technology is expected to provide a significant increase in the engine's thermodynamic cycle maximum temperature and efficiency, a drastic reduction in its weight and specific fuel consumption, and a decrease of greenhouse gas emissions.

CONCEPT DESCRIPTION

Main idea:  replacement of gas turbine by simpler system
Advantages:
Reduction in engine weight;
Removal of cycle maximum temperature limitation
Reduction of engine complexity: more reliability, lower costs, shorter manufacturing time
Reduction of engine size, particularly length
Operating principle:
Multiple rotating pulsed detonating combustors
Tangential exhaust of combustor flue gases to rotate entire combustor assembly;

Remaining energy used to power aircraft, by:
- Propeller (turboprop),
- Re-axialization of flow exhaust nozzle (turbojet)
- Controlled direction of combustor exhaust
    * tangential velocity component drives compressor and rotating combustor assembly 
    * axial component provides thrust by means of exhaust nozzle

  

FUEL SYSTEM DIAGRAM

 - Fuel enters through channel 4 into stuffing box 11;
- From here, enters rotor through circular channel 14;
- Enters combustors through electronically controlled
  injectors through channels 6 and pipes 7
- Pressure signal transmitted through circular channel 8
  to pressure transducer 10 that controls injectors
- Sealing of circular fuel channel and pressure channel ensured by stuffing box 11,
placed between bearing casing 1 and rotor;
- Stuffing box guided by slide bars preventing its rotation with respect to casing 1,
while allowing axial movement;
- Sealing pressure force provided by two conical springs by means of graphite rings 13

IGNITION SYSTEM

- Induction coil mounted on the rotor above exit of channels;
- Coil, as well as the fuel injectors, controlled by means of mobile brush contacts

STATE OF THE ART

Detonation process studied intensely in the last century;
First observed in gaseous fuels by Bertolet in 1881, later, Chapman and Jouguet discovered that detonation products propagate at sonic speed relative to the detonation wave.
One of the first detonation theories was the one-dimensional, detonation wave propagation theory of Chapman – Jouguet in 1905 - 1906
Interest increased significantly with the first steps towards supersonic flight, in the mid-XX century
Various thermodynamic cycles aiming at modeling the detonation powered engine were developed: Humphrey cycle, ZDN (Zeldovich–von Neumann–Doring) cycle Fickett-Jacobs cycle.
During the space race, in the ’70, new types of detonation based thrusters were studied.
Over the last decade, the number of theoretical, experimental and numerical studies increased significantly.
The practical application of detonation waves in propulsion system dates back to the 1940s but the complexity of the problem delayed the first successful demonstrator flight to as late as 2008 (DARPA's Blackswift).
The demonstration flight was, however, at low speed, and the project was soon cancelled.
During this time, a significant number of constructive solutions and approaches has been proposed, however none completely successful, only as far as prototypes.

EXISTING CONSTRUCTIVE SOLUTIONS

 

EXPECTED PROGRESS

Fuel supply system
Needs to provide fuel in close correlation with the PDC operating frequency.
Continuous supply through the disk supporting the rotating PDCs.
The disk will also include the ignition system.
Has the advantage of providing sufficient space to premix the air and fuel.
To achieve vaporization and possibly preheating in the case of liquid fuels.
By monitoring the pressure inside the combustor, feedback signal can be provided to ensure the correct synchronization.
Initiation of detonation wave
Strongly dependent on the inlet conditions.
Use of very energetic spark, deflagration-to-detonation transition, or shock wave ignition.
Geometry of the PDE exit nozzle
To increase overall engine efficiency combustors must provide the highest possible impulse on a direction other than along the combustor axis, the optimal direction with respect to the engine performances and constructive solution, as well as the minimization of pressure losses due to the deflection of the flow have to be studied.
The addition of ejectors on the PDC nozzle should also be considered.
PDC flow path
Critical for the optimal detonation wave travel.
Stability and completeness of the supersonic combustion, strongly dependent on the combustor geometry, must also be optimized.
Of special interest is the production and emission of NOx. The high temperatures in the PDC favors the NOx production, while the very short residence time in the combustor will tend to decrease the effect, hence a quantitative approach will have to be used to determine NOx emissions.
Supersonic combustion models for finite rate kinetics numerical simulations, as well as the limitations of the existing models applied to detonations are still an open research topic.
Optimal compressor geometry
Rotation of the downstream combustor.
Discontinuous discharge of the combustor shroud.
A high frequency PDC will alleviate the problem, but the effect on compressor stability remains to be assessed.
Furthermore, since the combustion process is supersonic, the need to decelerate the flow upstream of the combustor disappears.
Therefore, the presence of the compressor stator vanes may no longer be required, thus reducing the pressure losses during the passage between the rotating and fixed blading.
The noise generated
The effect of opposite phase pairs of PDCs and the optimal interference of the resulting sound waves needs to be investigated.
Also, the presence of detonation waves inside PDCs raises questions on the vibration levels of the new engine, which need further evaluation, understanding and solution finding.
Optimal fuel selection
To allow the reliable initiation of the detonation wave, is also an open research field.
Most of the research studies carried out up to the present focus on gaseous fuels.
Experimental studies conducted on PDCs using liquid fuels (kerosene) have been reported in recent years.
The main problems when considering liquid fuels for PDC are the increased difficulty to initiate the detonation and the required very high mixing velocity of the air and fuel to be supplied to the combustor.
The specific fuel consumption
Lower than in the case of a PJE.
By reducing the overall engine weight, optimizing the supersonic combustion process, and maximizing the engine power, the overall fuel consumption can be further minimize.
Novel materials
Able to withstand the high temperatures in the PDC, together with the mechanical solicitations (mainly centrifugal load and vibrations) to bring the engine concept from a breakthrough technology to a market ready product.

PROJECT OBJECTIVES

- Given the complexity of the task, and the limited resources, the its scope is limited and does not try to tackle all the problems raised by the new engine concept.
- Instead, the main goal of the project is to prove the functionality and feasibility of the concept, opening the road towards developing a mature technology over the next 50 years.
- The most important result expected from the proposed project is to demonstrate, both numerically and experimentally, that the power provided by the rotating PDCs can provide the energy to accelerate the compressor to the speed required for its design performance, with sufficient excess energy to power up the aircraft.
- A second achievement is expected to be the practical realization of a high frequency, self supporting ignition PDC.
Combustor inlet will be valve free, and the solution selected to control the inlet must be proven to prevent the detonation wave to propagate upstream. A high frequency PDC is expected to be compact, both in diameter and in length, allowing significant reduction in engine dimensions and weight.
- The constant volume cycle is of higher efficiency than the classical Brayton cycle. Due to the elimination of the classical engine turbine, the maximum temperature limitation will be removed, thus allowing an overall increase in the engine performance and efficiency. The project aims at demonstrating the increase in theoretical cycle efficiency.
- Finally, the project will provide an integrated solution for the proposed concept, validated through numerical simulation, and laying the foundation for building a demonstrator engine concept in the future.