Case Study

This case study highlights how the previously mentioned concepts of combustion-driven actuators (CDAs) can be applied in order to power a pump. This is done by using the expansion of the combustion chamber in order to squeeze an adjacent pump chamber. Soft pumping has the advantage of conveying liquid without the need of any bearings. Due to the physical separation of combustion and pump chamber, fluids containing solid fragments (i.e. sand or stones) can be transported without any severe internal pump abrasion.

Combustion-driven Soft Pump

Figures and videos are taken from Schumacher et al.

The figure on the right shows the design of a pump chamber with an adjacent combustion chamber, as mentioned in the above paragraph. Schumacher et al. analyzed the following behaviors of the designed pump:

  • Expulsion rate at different fill levels (0 cm to 80 cm)
  • Thermo stability of the soft pump at different ignition frequencies
  • Surface damage upon combustion
  • Pumping under deformational stress

This design lasted for 10,000 combustion cycles. Schumacher et al. were able to show that pumping was still possible even though the pump was exposed to severe mechanical deformation (see the video below for more details). The overall energy efficiency was determined to be 0.03%, which is not acceptable for practical applications. Nevertheless, this design is not optimized in terms of geometry (only a single wall is used) and material behavior (part of the energy is lost due to deformation of the outer wall). 

Fabric Reinforced Soft Pump

Figures and Videos are taken from Loepfe et al.

The above pump did not have any optimization in terms of geometry. Too much energy was being lost due to deformation of the outer wall (the energy supplied by the combustion process was going towards deforming the outer wall instead of driving the fluid). So the resulting designs attempted to account for this by using a fabric reinforced outer wall to increase outer wall expansion stiffness. Loepfe et al. analyzed the following parameters:

  • Impact of fabric reinforcement and outer wall thickness on pump rate
  • Impact of air/methane-ratio on pump rate
  • Impact of methane flow rate and ignition frequency on pump rate
  • Exhaust gas tracking at different ignition frequencies     

This pump design lasted for over 30,000 combustion cycles and pumped up to 13 m (this corresponds to a pressure of 1.3 bar). Flow rates were determined and go up to 250 mL/min with an energy efficiency of 0.05%.

As shown here, combustion-driven actuators can be used to create usable soft pumps. This may have important implications in terms of actuation of other soft actuators like those found in this toolkit (i.e. PneuNets).