연료 액적의 레이저가열이 연료？공기 혼합물, 연소 및NOx 매출에 미치는 영향에 관한 이론적 고찰
Theoretical Considerations on the Effect of Laser Heating of a Fuel Droplet on Fuel/Air Mixing, Combustion and NOx Emission
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본 연구에서는 NOx 생성의 열적 생성기구를 구명하기 위하여 연료증기와 공기 혼합물을 자연발화온도까지 예열시켜 액적화 하는 2가지 이론적 모델을 비교․분석하였다. 즉 첫 번째 모델은 액적이 높은 레이저 에너지의 흡수에 의해 발생되는 폭발증기로 되는 것이고, 두 번째 모델은 액적의 증기와 불꽃이 비폭발성에 의하여 채택되어진 경우이다. 수학적 모델의 결과는 액적이 고에너지인 레이저 흡수에 의해 발생된 폭발증기가 연료증기의 비균일 분포를 일으키며, 미세연료의 대부분이 외곽에 농축되어 있음을 알 수 있었으며, 이 경우 NOx 의 발생량은 매우 낮은 연소온도와 연료혼합공기의 낮은 비율로 인하여 감소하였다. 또한 비폭발 모델인 경우는 많은 량의 NOx 를 발생시키며, 경유의 경우 폭발조건을 만족하는 에너지는 3.4 μm 의 파장을 갖는 IR 레이저의 경우 15 W 이었다.
Abstract
Two theoretical models of combustion of a single fuel droplet of finite size in air, preheated to the temperature of autoignition of fuel-vapour / air mixture, were modelled. Thermal mechanism of NOx formation was considered. In the first model the droplet underwent an explosive vaporization caused by the absorption of energy from a high-energy laser beam. In the second model a non-explosive vaporization of droplet and burning was adopted. This work was to compare the NOx production rates by the aforementioned two models. From the results of mathematical modelling, it suggests that the explosive vaporization of the droplet caused by the absorption of energy from a high-energy laser beam lead to non-uniform distribution of the fuel vapour and most of the mass of the fuel vapour concentrated in the outer shell of the exploded droplet. In this case nitrogen oxides were not produced because of the very low fuel/air ratio and low flame temperature. The second model resulted in substantial production of nitrogen oxides. The 15 W IR laser operating at 3.4 μm wavelength can provide the power flux required to satisfy the explosion conditions.
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