Microturbines - Fluid Flow, Combustion, CFD
Some of the common challenges in designing reliable microturbine are listed below, as noted by other experienced microturbine manufacturing and R&D companies.
● and sustaining a flame is difficult at small scales. As the size of the combustion chamber decreases, the walls of the chamber draw heat away from the flame more quickly than than it can be produced by the burning of the fuel. You can demonstrate this phenomenon by trying to get a flame to pass through a piece of metal window screen held horizontally over a lighter. You will observe that the flame stops at the plane of the screen; the wire in the screen dissipates the heat of the flame, preventing it from passing through. This effect was used with great success in the creation of safety lamps for miners.
● Keeping moving parts cool is also difficult at small scales. All parts in and around the combution chamber become very hot as the turbine operates; any oils used for lubrication are quickly burned off. Bearing life tends to be short under these circumstances.
● Precise fabrication of small-scale parts is always a challenge! The microturbine runs at 40-70,000 rpm; all rotating parts must be balanced to avoid catastrophe.
Gas turbine thermal efficiency to a large extent depends on losses resulting from flow leakage, thermal losses and friction. These losses become more dominant when down-scaling a gas turbine in size and power, due to blade tip clearance and volume-surface ratio scale effects. Moreover, when decreasing size (lower Reynolds number) viscous friction losses become larger in conventional turbo machinery. As a result, there is a fundamental limitation to efficiency of micro turbines with a conventional configuration.
Typical Specs for Microturbine:
Nominal mass flow: 20 g/s Pressure ratio: 3.0, Turbine: 5083 W , Net mechanical output: 1180 W
T-s polytropic efficiency: Compressor: 66 %, Turbine: 78 % Turbine inlet temperature: 1200 K
Cycle efficiency Without recuperation: 11 %, With recuperation: 20 %
Links to links
Articles, Notes, Pictures etc
CFD Study of Microturbine combustor...
CPL.USC.edu/eschuste/turbine.htm Submicro 2.25” Jet (USC Combustion Physics Lab Microcombustion)
Aerospaceweb.org... The term "jet engine" is often used as a generic name for a variety of engines, including the turbojet, turbofan, turboprop, and ramjet.
20 years of micro turbo jet engines - RCuniverse.com
Plans how to build Microturbine
The KJ-66 micro turbine jet engine is by far one of the most popular micro jet models built today. It is a relatively affordable and simple design with great performance. Some people have built versions of this engine using an automotive oil filter for the outer casing and internal filter basket for the combustion chamber. Plans $5.
The ETV microturbine will operate on RQL (Rich-Quench-Lean) principles and will have the unique property of achieving optimum efficiency at two operating points. This “dual mode” property will provide a number of degrees of freedom when matching the microturbine to various drive cycles and vehicle categories.
Books and Magazines
The history of North American small gas turbine aircraft engines By Richard A. Leyes, William A. Fleming
Vortechonline.com General Resources, Books
Wiseowlmagazines : Flying Models
RMcybernetics.com/projects/DIY_Devices/diy.htm DIY Propulsion Projects
RC Airplane World
RC Model Airplanes
RC Plane Talk
hMiniature Liquid-Fueled Turbojet Engine - 5782079
Ultra Micro Gas Turbine -
Microturbine Power Generating System - Allied Signals
Gas turbine Simulation Program GSP
Mentor.com/... CFD simulation of turbomachinery
Links to MicroTurbines Resources
List of past and present aircraft engine manufacturers. (from Wikipedia)