Micro Gas Turbine

The CIMJET is a Micro Gas Turbine concept. It is intended that each part is made from ceramic by Ceramic Injection Moulding (CIM). However, ceramic has a low fracture toughness and ceramic blades have a history of failure at stress concentrations.

It took three years unconventional research to develop a gas turbine design methodology that respects the required aerodynamic design constraints to produce a ceramic blade design that exhibits no stress concentrations under a combined gas bending load and a tensile load. The SAP-Blade design does not use any fillets and presents an inherent minimum weight for the design load case.

The research started in 2014 on the geometric configuration of the extreme high power density ceramic injection moulded microgas turbine. 

Historical research shows that over the last 60 years of design, research and manufacture of ceramic gas turbine blades, there is a stress level above which fast fracture occurs in the blades. Traditional circular fillet enlargement does not reduce the stress concentration sufficient enough for long term-high temperature survival. Also, larger fillets interfere with optimum aerodynamics and add weight to the rotating mass.

Extensive research produced a promising solution for a gas turbine blade that is subject to a combined tensile and gas bending load. The gas turbine blade above was designed from first principles using a SAP methodology for the design of the total ceramic blade of 25mm height uncooled at a service temperature of over 1500°C.

The attribute of this methodology are shown in the photos below:

• The CIMJET blade has no stress concentrations (tested by photoelasticity)
• The stress distribution in the CIMJET blade are in inverse to the "traditional blade stress distribution" where normally high stress regions are located towards the base of the blade
• The CIMJET blade does not contain fillets
• The CIMJET has no aerodynamic losses due to fillet intrusion as there are no fillets
• The CIMJET blade in the above photo, is subject to a combined loading
• The CIMJET aerodynamics have not been compromised
• Designed with reference to mean radius design methodology and a h/d conforms with that laid out in Rogers & Cohen
• The SAP methodology produces a minimum weight design as a function of the combined loading