MAP | CALMAIL |
Combustion Modeling Lab at UC Berkeley

Current Research

Microwave-Assisted Combustion


Ben Wolk, Tiernan Casey, Daniel Pineda (CML)

Dan Murphy (CPL)

In conjuction with Imagineering, Inc.


Introduction

Microwave-assisted combustion has shown the potential to:

  • Enhance early heat release rates
  • Extend the ignitability range of fuel-air mixtures
  • Facilitate ignition in high-pressure mixtures

Plasma-assisted combustion research, which investigates combustion enhancement through electromagnetic interactions in gases, has the potential to bring new ignition technologies to market. Generation or enhancement of plasma in a combustion environment through the use of microwaves (MW), radio frequency waves (RF), dielectric barrier discharges (DBD), nanosecond discharges, and other electric discharges has been shown to improve ignition characteristics and flame speeds under a variety of conditions and is thus an active area of research.The current research at UC Berkeley examines the ability of a novel ignition technology, the microwave-assisted spark plug, to enhance early heat release and extend the ignitability limits of laminar methane-air flames.


Enhancement of flame development by microwave-assisted spark ignition in constant volume combustion chamber

Abstract: The enhancement of laminar flame development using microwave-assisted spark ignition has been investigated for methane-air mixtures at a range of initial pressures and equivalence ratios in a 1.45 liter constant volume combustion chamber. Microwave enhancement was evaluated on the basis of several parameters including flame development time (FDT) (time for 0%-10% of total net heat release), flame rise time (FRT) (time for 10%-90% of total net heat release), total net heat release, flame kernel growth rate, flame kernel size, and ignitability limit extension. Compared to a capacitive discharge spark, microwave-assisted spark ignition extended the lean and rich ignition limits at all pressures investigated (1.08-7.22 bar). The addition of microwaves to a capacitive discharge spark reduced FDT and increased the flame kernel size for all equivalence ratios tested and resulted in increases in the spatial flame speed for sufficiently lean flames. Flame enhancement is believed to be caused by (1) a non-thermal chemical kinetic enhancement from energy deposition to free electrons in the flame front and (2) induced flame wrinkling from excitation of flame (plasma) instability. The enhancement of flame development by microwaves diminishes as the initial pressure of the mixture increases, with negligible flame enhancement observed above 3 bar.


CV Flame SimulationKiva3V+CHEMKIN simluation of stoichiometric methane-air flame in constant volume chamber.
Image of FlameFlame developing after microwave-assisted ignition in constant volume chamber.


Schlieren Images, phi = 0.75Schlieren images taken at 1200 fps for spark-ignited and microwave-assisted ignition modes.