This experimental study investigated the effects of nanoparticles on evaporation rate of nanofluid fuel droplet based on kerosene liquid fuel in high pressure environment. The base liquid fuel was kerosene and aluminum (Al) nanoparticles with 70 nm diameter were selected. Evaporation behavior was recorded by high speed CCD camera and investigated by suspending the droplet on the silicon carbide (SiC) fiber with $100 \mu m$ diameter in high pressure chamber. Oleic acid was used as a surfactant to synthesize the stable nanofluid fuels and the effect of oleic acid, of course, was investigated for comparison. The concentrations of aluminum nanoparticles were 0.1 % and 1.0 % by mass fraction and the ambient pressure was increased from 0.1 MPa to 2.5 MPa. The temperature range was from $300^\circ C$ to $700^\circ C$. The evaporation rates of droplets were determined by interaction of diffusion coefficient and heat of vaporization of the droplet. In high pressure environment the diffusion coefficient controlled the evaporation and in high temperature environment the heat of vaporization controlled the droplet life time. Moreover, nanoparticles had negative effects for droplet evaporation in low temperature due to its higher thermal conductivity than that of liquid fuel. The nanoparticles absorbed most of heat energy so they played as a heat sink. However, in high temperature region ($500^\circ C$ - $700^\circ C$), the nanoparticles acted as a heat source rather than a heat sink so the nanofluid fuel droplets had higher evaporation rates than the pure kerosene droplets in all pressure ranges. Also, in high temperature region, 0.1 % and 1.0 % of aluminum-kerosene droplets showed different evaporation rates depending on the pressure. Distinct phenomenon of evaporation of nanofluid fuel droplet was a micro-explosion and it was observed at only atmospheric pressure environment.
고압환경에서 나노유체 연료 액적의 증발율에 나노입자가 미치는 영향을 알아보기 위해 실험적 연구가 진행되었다. 기본 액체연료로써 케로신이 사용되었고 지름 70나노미터의 알루미늄 나노입자가 사용되었다. 고속 카메라로 촬영된 액적의 변화를 통해 증발율이 계산되었다. 계면활성제로써 올레산이 사용되었고 알루미늄 나노입자의 농도는 무게비율 0.1%와 1.0%이 사용되었다. 압력은 0.1MPa에서 2.5MPa까지 증가시켰고 온도는 300도에서 700도까지 증가시켰다. 액적의 증발율은 증발열과 확산계수의 상호작용에 의해 결정되었다. 고압환경에서는 확산계수의 영향이 지배적이었지만 고온으로 갈 수록 증발열의 감소에 의한 증발율의 증가가 두드러졌다. 더욱이, 낮은 온도에서는 알루미늄 나노입자가 부정적 영향을 미쳤지만 고온으로 갈수록 나노입자들의 열원현상으로 인해 증발율을 더욱 증가시키는 역할을 하였다. 미소폭발 현상은 오직 대기압환경에서만 관측되었다.
