Principle of the technology
The heat2power proprietary concept is based on requirements that we have identified as mandatory in the environment of automotive mass production. Study of more than 40 different waste heat regeneration technologies led us to develop this concept because all other concepts had inconveniences or even unacceptable properties. The main characteristics of an automotive WHR should in our opinion be :
- Operate within the waste heat temperature range of the ICE's exhaust gases
- Compact, therefore have a high specific power (kW/l)
- Lightweight, therefore have a high specific power (kW/kg)
- Best possible efficiency level in all working points, especially at part load for every day driving
- Easy to adapt in an industrial equipment (maintain existing production tools, no dangerous materials)
- Easy to adopt (no hazardous materials, chemicals)
- Comply with regulations (no hazardous materials, chemicals)
- Free of particular maintenance
- Cost effective (industry target is to be at less than 25 Euro per percent of fuel economy)
- Use conventional technology (for low barriers to industrialisation)
- The torque level should be fully controllable for following the drivers request for torque. (accelerator pedal)
We have indeed come up with a system that combines all these requirements. We are therefore convinced that it has a strong market potential. We had previously also investigated alternative systems currently in the market or being developed and found their main inconveniences :
- Rankine Cycle (steam engine) - piston blow-by contaminates lubrication oil and generates lubrication problems. Piston sealing remains an issue, especially with time. For vehicles that often run short distances the oil does not get hot enough to evacuate the water it contains. The oil gets thick and the lubrication system of the engine fails.
- Organic Rankine Cycle - uses liquids that should not leak to the environment with respect to global warming, piston blow-by dilutes in sump oil - just like diesel engines that have too strong lining wetting - and deteriorates lubrication properties. Typical liquids are either highly flammable (butane, pentane, hexane) or in a family of liquids that will be forbidden for vehicle air-conditionings as of 2010 in Europe. We therefore see no future for ORC, even though its efficiency improvement can be very good.
- Thermo-electricity - For many years still very expensive and with limited regeneration capacity. It would cost several thousands of Euros to significantly improve engine efficiency. This can be acceptable for Formula 1 race cars but not for road cars.
- Stirling Cycle - Too heavy and bulky and the vehicles are not structurally conceived to adopt such a system. Furthermore, the efficiency drops strongly above 2200 RPM and is negligible at 3000 RPM.
- All Turbo-compounds - We believe that turbo-compounding is a good solution for engines that stay in a small RPM-load point most of the time (motorway hauling of trucks for example) but for every day driving this would give a too small efficiency improvement due to the limited efficiency at part load.
- Electric turbo-compound - If significant fuel savings are looked for it means that there are several kilowatts generated by this system. The normal electric requirements of a car are actually quite low and excess electric power should be consumed by the vehicle. This requires additional and expensive electric equipment if vehicle is not a hybrid.
When we understood that the inconveniences of the existing technologies would really be big hurdles for the industrialisation of a WHR system in the automotive industry we focussed on system simplicity and low cost. Not for optimal thermal transfer properties. This is why we based our system on air. Though it is not the best working medium for thermodynamic cycles, its abundance in nature, its compatibility with the lubrication system and known behaviour in engines are true advantages. What we have come up with is discussed below.
Introduction to the heat2power concept
In our quest for better fuel efficiency we have decided to let others work on the improvement of the combustion. However when studying the total power flows in an engine we judged that there was some potential of reduction of waste heat power flow. In parallel we worked out several ideas and did a technology survey on Waste Heat Recovery (see the Benchmark section on this website). Our experience in the automotive industry gave us the conviction that a system should have a low level of required investment to be industrialized. Otherwise bringing the system to the market would be most difficult, even if fuel consumption reduction is important.
The heat2power system is based on the use of one or more cylinders for the regeneration of waste heat. These cylinders can be in replacement of the combustion cylinders inside an existing engine or as an add-on module that is connected to the engine by means of a gear set or a belt drive. Also is it possible to have no mechanical linkage between combustion engine and regeneration unit in case the power from the regeneration unit is taken off electrically. In general for low cost of installation and development we recommend OEMs to use an add-on system. In that way the original engine remains basically unchanged.
The thermal power is extracted from the exhaust of the internal combustion engine by means of a heat exchanger. This is a gas-gas heat exchanger operating at high temperatures: up to about 950°C. Basically the heat2power system works like most other thermodynamic cycles : intake and compress a gas, then heat it up and finally let it expand. The difference between an ICE and the heat2power system is that the heat input is not by combustion inside the cylinder but by heat exchange external to the cylinder.
After the expansion stroke the air is released at low temperatures (250-300°C instead of 600-950°C). This can also be considered as an advantage for military vehicle that require a low thermal profile.
The heat exchanger in the exhaust is placed after the catalyst (gasoline vehicles) or after the particle filter (diesel vehicles). In such manner the exhaust gas after treatment remains unaffected and the combustion engine does not need its tuning to be done all over again. However we recommend applying thermal insulation of the exhaust manifold and the first part of the exhaust and catalyst/DPF so that a maximum amount of heat is available for the regeneration process.
The layout of an add-in system and the associated power flows are represented in figure 1:
The regeneration device is made of :
- one or more [ piston - cylinder & rod ] group,
- with 4 valves per cylinder, driven by standard camshafts (excluded specific cams design),
- 1 air / air heat exchanger,
- 1 dedicated boosting turbocharger
Any fuel used in the combustion process of the "combustion cylinders" that generates heat is compatible with heat2power.
The heat2power system is a machine that works with heat only. It does not need any fuel. It can therefore also be applied in the fields of solar energy and geothermal energy as an alternative to the Stirling engine as well. The heat2power engine works with 5 (4) strokes (3 (2) strokes is possible), has the same RPM limitation as the IC engine, and operates with a good efficiency and with relatively high specific power.
More information will be made available soon. Feel free to contact us for more details.
Once we have established a confidentiality agreement between heat2power and your company we can transmit to you a more complete document. This explains in detail the following topics:
- Waste heat power flow of an IC engine
- Introduction to the heat2power concept
- The heat2power thermodynamic cycle
- The heat2power engine warm-up process
- How the pressure increases in the heat exchanger
- Limit and convergence for the heat exchanger pressure
- Theoretical P-alpha and P-V diagrams with a converged system
- Major steps of the heat2power cycle (with a converged HAC pressure)
- Theoretical heat2power efficiency principle
- The heat2power hybrid engine configurations
- The heat2power machine in a simulation model
- Description of the 1D modeling
- Geometry and dimensions
- Simulation results at 3000 RPM
- Real P-V diagram at 3000 RPM
- Temperatures and local working gas pressure inside the cylinder function of alpha
- Instantaneous flows vs sonic speed at the valve restriction function of alpha
- Performances and efficiencies simulated at 3000 RPM
- Thermal dispersion by element with current model : energy assessment
- Parameters that influence the heat2power efficiency and performances
- Extrapolation to other engine speeds and temperatures still at full load
- Part load functioning (decreased boost pressure)
- Heat exchanger and HAC specification for achieving such performances
- Performance predictions of the heat2power hybrid engine
- Potential heat2power’s performance improvements
- Various proposals for layouts in a road cars, race cars, trucks and powergeneration