The objective of this project was to study and manufacture a Wasted Heat Regeneration System (WHRS).
The WHRS is composed of :
- a heat exchanger, to be tested within the exhaust gas nozzle of a turbo shaft engine
- a hot air piston engine, to be tested with an artificial electric hot source
The heat exchanger is an air / air type directly installed in the gas turbine exhaust nozzle.
In the final application, it withdrew the heat from the exhaust gases and heated up the “hot loop” pressurised air flow coming from and going to the piston engine.
During this prototype phase, the air flow was supplied to the heat exchanger by an artificial air compressor in order to evaluate the heat transfer obtained by this heat exchanger.
The heat exchanger had to respect strong environment constraints due to its integration in a turbine exhaust nozzle. It should not have a major impact on the architecture of the turbine or on the exhaust gas flow.
The hot air piston engine was a mono-cylinder reciprocating piston engine rotating up to 7.500 rpm if necessary at the end of test (6000 rpm max speed during the main part of the tests), fed by external air through classical admission and exhaust system, and getting its power from the artificial electric hot loop.
The design of the engine was optimised in terms of internal frictions in order to maximize the work produced by the WHRS.
This was achieved by using the correct materials and surface treatments, and by the design of an engine equipped with unconventional valves.
The hot temperatures provided by the hot source required the use of low thermal expansion coefficient materials for the components in order to ensure the correct fitting of components and avoid seizure of the system.
Our consortium realised the following tasks:
- Detailed study and manufacturing of 2 heat exchangers
- Study of the base engine components (piston / rod / crankshaft / cylinder block)
- Performance test on partial cylinder head components in terms of permeability and friction-sealing compromise
- Partial redesign of cylinder head depending on partial tests results + process/material integration
- Manufacturing of one hot air piston engine
- Study and manufacturing of a bench (adaptation of an existing engine test rig) for the piston engine with the electric artificial hot source
- First verification of the piston engine performance and mini-endurance test (approx. 50h).
The reduction of CO2 emissions and consumption is a permanent concern of major actors in the transportation sector. Many technologies have thus been developed to improve the performance of engines. In recent years a constantly increasing number of work and patent deals with the recovery of heat losses in the exhaust. These losses represent about 30% of the energy produced by the engine.
WHEXPERS project used an innovative WHR solution (Waste Heat Recovery), based a new thermodynamic cycle combining Ericsson Cycle and major patented improvements. The proposed thermodynamic cycle is particularly innovative since it uses a high-performance heat exchanger associated with a hot air machine that performs both compression and expansion.
This technology used an open cycle. It meant that the working fluid is air that is taken and released to the atmosphere. In fact, it is not necessary to cool it down, as it is the case for a closed cycle such as Stirling or Rankine. The exhaust gases pass through a heat exchanger to warm the fresh admission air that is compressed by the hot air machine that also carries out the expansion and generates mechanical energy. This energy is directly sent to the engine, which allows high conversion efficiency and limits the cost compared to a system of electricity generation.
The objective of the WHEXPERS project was to study and manufacture the systems and components necessary to run a proof of concept of a recovery system (composed of a hot air engine and a heat exchanger) of the energy spread in the nozzle of a small shaft turbine (helicopter engine) based on this technology. The project also includes the test of this system in order to estimate its performances.
The hot air piston engine is a mono-cylinder piston engine rotating up to 7.500 rpm fed by external air through classical admission and exhaust system, and getting its power from the artificial electric hot loop.
The heat exchanger has to respect strong environment constraints due to its integration in a turbine exhaust nozzle. It should not have a major impact on the architecture of the turbine or on the exhaust gas flow.
A new design optimization for the prototype was necessary to design parts and components that could be manufactured with a huge work of product/process study with providers at reasonable cost (material, process etc.).
Regarding the heat exchanger, its dimensioning and its integration in the helicopter gas turbine exhaust flow has required an adaptation of thermodynamic and mechanical sizing tooling to improve its capacity on the heat exchanger behaviour simulation to obtain a real product by taking into account all the requirements and conditions of use.
Tests on some main components of the engine has made it possible to optimise permeability and frictions functionality as well as product/process studies allowed to manufacture a prototype.
Nevertheless, the tests on the complete engine showed a failure of the distribution system that requires a new design with the associated costs that made impossible to achieve the objective to demonstrate the potential performances of the system.