Executive Summary : | In recent times, laser initiation of combustion of atomized fuel-air mixture has become an active area of research in the field of aircraft gas turbine engines. The technique essentially involves creating a non-resonant air breakdown in a fuel-air mixture by focusing a laser beam into a volume of around 3 mm³ thereby igniting the mixture. The conventional spark plugs have a limited peak power output of around 100 W [1]. It is, however, a well-known fact that increase of peak output power ignites fuel more effectively and the combustion also becomes more effective and complete. This is especially true in cases where the flow residence time in the engine is of the same order as the summation of ignition and kernel development times (e.g. engines for high speed flows (SCRAMJET)), engines generating power with a lean fuel-air mixture, and those requiring ignition at low temperature [2]. A method to increase the peak output power of the spark is to use pulsed power, where the energy is stored over a relatively long period (~20 ms) but discharged quickly (~ 1 ns). The pulsed plugs could discharge over 1000 kW of power. The high peak power in case of pulsed spark plug results in 60% faster growth of the flame kernel than the conventional iridium tipped spark plug [3]. This phenomenon outperforms the conventional spark plug for a lean fuel-air combination in engines. The laser ignition is a variant of pulsed ignition. However, the laser initiation of atomized fuel-air mixtures is found to be a tricky job. The main issue reported so far is the amount of energy to be deposited and its duration. It is observed that despite having high laser pulse energy (~50 mJ), an atomized ethyl alcohol-air mixture fails to ignite with certainty by the technique [4]. It is important to mention here is that the conventional sparks deposit around 4-5 mJ of energy for the ignition purpose. It is also reported that, subsequent to the laser induced breakdown, a significant amount of the absorbed energy by the medium is carried away by a blast wave which appears post breakdown around the energy deposition zone. In recent times, it is reported [5] that the lifetime of the hot core zone around the focal point is important for successful ignition of the atomized fuel-air mixture. If the core loses its heat quickly, the chances of successful ignition is also less. The present proposal would focus on increasing the lifetime of the core by utilizing two successive laser pulses. A successful identification of the actual cause of ignition failure by the technique and then its implementation would result in a new technology. The aerospace gas turbine combustor technology would benefit tremendously by this in terms of low emission of pollutants, successful high altitude relight of aero engines, and possible improved design of modern gas turbine combustors. |
Co-PI: | Dr. Shivakiran BN Bhaktha Indian Institute Of Technology Kharagpur, West Bengal,Kharagpur,West Bengal,Paschim Medinipur-721302, Dr. Kalyan Prasad Sinhamahapatra Indian Institute Of Technology,Department Of Aerospace Engineering Iit Kharagpur,West Bengal,Paschim Medinipur-721302 |