What is Swiss-Roll Combustor Technology?
The Swiss-Roll combustor is a burner core surrounded by a spiral heat exchanger (Figure 1 Left). The concept was first proposed by Professor Weinberg in 1974[1]. The cold reactants travel into the center reaction zone through a spiral inlet channel. After the exothermic reaction, the hot products travel out through the adjacent spiral outlet channel. The heat from the products is exchanged to the cold reactants via the spiral heat exchanger. The reuse of products’ thermal energy recirculated back into reactants results in an excess enthalpy process that raises the temperature above the classically defined adiabatic temperature, as shown in Figure 1 Right. Such conditions enable self-sustained combustion in either ultra-lean or ultra-rich conditions that are beyond the flammability limits without heat recirculation.
Figure 1. Left: Schematic of Swiss-roll combustor. Right: Illustration showing how super-adiabatic combustion temperatures can be achieved.
Many studies have demonstrated the Swiss-Roll’s superior performance in heat recirculation and its effect on promoting internal reactions [2]. Specifically, it has been shown effective at extending the flammability of a variety of fuels and enabling the achievement of equilibrium state concentrations i.e. fully complete combustion.
WHICH FEATURES MAKE THE SWISS-ROLL COMBUSTOR EXTREMELY THERMALLY EFFICIENT?
- A large internal heat transfer to external heat loss area ratio enables highly efficient heat exchange in a very confined volume
- The curvature of the channel creates a centrifugal instability (Dean vortices) that further enhances heat transfer
- The reaction zone, which has the largest potential for heat loss, is surrounded by the spiral heat exchanger so most of the heat loss from the reaction can be recovered
- Long inlet channels with elevated temperatures provide a long residence time that may significantly reduce the formation of non-equilibrium state products
Figure 2. Three dimension CFD modeling. Left: Boundary conditions. Right: Mesh file.
ACT has been developing Swiss-Roll-related technologies together with Professor Paul Ronney at the University of Southern California (USC). Extensive experimental work and detailed CFD-based modeling (Figure 2) has been performed to understand the effect of heat recuperation on the chemical reaction. A fuel reformer and incinerator are currently being developed. Unique material requirements drive innovation in fabrication methods including high-temperature brazing (Figure 3 Right) and 3D printing of metal reactors (Figure 3 Left). Novel additive manufacturing methods for advanced ultra-high temperature materials are currently under development.
Figure 3. Different fabrication methods of Swiss-roll combustor developed at ACT. Left: 3D printing (stainless-steel). Right: Braze (Inconel).
WHERE CAN SWISS-ROLL TECHNOLOGY BE USED?
The unique, highly efficient operation and extension of flammability make Swiss-Roll combustors an excellent solution for a multitude of thermal processes, some of which include:
- Self-powered incineration of harmful VOC and other fuel fumes that normally would not combust due to too small a concentration
- Ultra-efficient combustion process with near 100% fuel destruction
- Stabilization of intermittent combustion processes thanks to the substantial thermal mass of the solid
- Efficient radiant heat source stemming from super-adiabatic temperatures and enhances gas-solid thermal coupling
- Autothermal fuel reforming uses energy within the fuel itself to drive the process
LEARN MORE
[1] Lloyd, S. and Weinberg, F., “A Burner for Mixtures of Very Low Heat Content,” Nature, 251, 47-49 (1974).
[2] Jones, A., Lloyd, S., and Weinberg, F., “Combustion in Heat Exchangers,” Proceedings of the Royal Society of London Section A, 360, 97-115 (1978).
[3] Chen, C. and Ronney, P., “Three-dimensional Effects in Counterflow Heat-recirculating Combustors,” Proceedings of the Combustion Institute, 33, 3285-3291 (2011).
