Pressure gain combustion by shock-flame interaction
- Pressure gain combustion (text version)
Compuer aided design (CAD) model (left) and photo (right) of the pressure gain combustion test facility installed within the TFMRC at University of Sussex.
Weak shockwaves at 250 Hz are injected into the combustion chamber which is running steadily otherwise. Unsteady pressure transducers show that as the shockwaves get stronger the combustion efficiency rises.” Professor Martin G. Rose
Professor of Mechanical Engineering
In steady flow gas turbines the total pressure across the combustion chamber can typically fall by about 5%. This signifies a considerable reduction in thermal efficiency of the engine. It is well known that isochoric (constant volume) combustion could lead to a significant increase in thermal efficiency. However, the difficulty is that isochoric combustion must occur under unsteady conditions, while gas turbines are steady flow devices.
The worlds first gas turbines (Holzwarth 1920’s) used constant volume combustion chambers with valves to fill and empty them. In TFMRC we are addressing a different possibility using shock waves which can cause acceleration of the combustion process by the Richtmayer–Meshkov instability. The non uniform density associated with combustion interacts with the pressure rise of the shock creating strong vorticity. Flow structures (funnels) form whihc increase the flame area rapidly. The increased heat release causes a rapid pressure rise. Borisov has demonstrated that a weak shock wave (Mach = 1.1) can accelerate the combustion right up to detonation.
We have modified our Dart combustion rig by introducing a series of shockwaves. A solenoid valve connected to a pressure vessel at 6 bar is used to create a chain of shockwaves at 250 Hz. So far, we have demonstrated the acceleration of combustion and found that as the shockwaves get stronger the combustion efficiency increases.