Development of Plasma Assisted Ignition for Wave Rotor Combustion Turbine

2019-08-15T19:09:54Z (GMT) by Ravichandra R. Jagannath
Gas turbines are important for power generation and aircraft engines. Over thepast century, there has been improvements in components of the gas turbine such ascompressors, turbines and nozzles, but very little progress has been made in combustor technology. The combustion still occurs at constant pressure and the only changes made are in terms of its design and mixing of fuel and air streams. These design changes have only allowed minimal improvements in gas turbine efficiency. To achievea substantative improvement in efficiency, it is required to make a technology change such as the introduction of constant volume combustion.

In this work, one such constant volume combustion device in the form of wave rotor combustion is studied and further developed for use in gas turbines. Wave rotors are periodic-flow devices that provide dynamic pressure exchange and efficient energy transfer through internal pressure waves generated due to fast opening and closing of ports. In addition, there is also confined high speed turbulent deflagration. If the blades are curved, then the flow undergoes angular momentum change from inlet to outlet, generating shaft work. This will allow maximum extraction of work potential from the wave rotor. In addition, an attempt is made to check the applicability of plasma assisted ignition for wave rotors.

A computational tool is developed to understand physics of non-axial channelwave rotors. The governing equations are formulated in one dimension through a passage average approach. Shaft work is estimated using conservation of angular momentum and enrgy to verify the working of numerical model. The model shows increase in shaft work with increase in blade curvature, but as the angle is increased, the possibility of ignititing the reacting mixture becomes difficult since it is hard tomove the mixture towards the ignition port.

An alternate ignition source using plasma discharges is investigated through experiments. Two experiments are developed, one to make ultrafast measurements of plasma properties such as gas heating and lifetime of electronically excited molecules, and a second experiment to understand ignition characteristics of a pin to ring electrode configuration. The experiments show that excited nitrogen which reacts with molecular oxygen to form atomic oxygen is short lived and forms oxygen atoms extremely rapidly. This rapid formation of oxygen atoms assists in fast ignition. The ignition experiment with pin to pin electrode showed that even though there is fast ignition, the propagation speed does not change significantly with pulse repetition frequency. Ignition with pin to ring electrode showed fast ignition and increase inflame speed with pulse repetition frequency. Results show that plasma discharge can be used as an ignition source for wave rotors but will need further investigation.

The development of computational tool and plasma discharge experiments has provided a solid base for future efforts in wave rotor combustion and design of full scale non-axial wave rotor combustor experiment.