MAE PhD Defense – Libing Wang

Title: Experimental Investigation of Spray and Combustion of Gasoline Direct Injection under Different Ambient Conditions

Advisor: Dr. Tiegang Fang

Date and Time: Friday, March 22, 2019 at 10:00am

Location: EB3 – 3115

Abstract: Experimental investigation of spray and combustion of gasoline direct injection was carried out in a constant volume combustion chamber. Different ambient pressures, system temperatures, ambient gas compositions and spark conditions were used to create a multitude of environments for the spray and combustion from a hollow cone GDI injector.

Firstly, the flash boiling spray of an outwardly opening hollow cone GDI piezoelectric injector can cause the cone shaped spray to expand, both in-wards and outwards. The axisymmetric inward expansion of hollow cone spray would merge together and form a fast developing plume along the axis of the spray, and the transition point for the plume to appear is around 0.5 for Pa/Ps ratio. When Pa/Ps ratio is larger 0.5, the spray penetration is mostly determined by the initial spray momentum. When Pa/Ps ratio is smaller than 0.5, the flash boiling and spray plume front becomes the dominant factor affecting the spray penetration velocity. Under same conditions, ethanol has higher superheated degree comparing to isooctane, but much higher heat of vaporization. Less boiling is observed in ethanol spray, while ethanol penetration is longer in several cases.

For multi-component fuels, mixture 50/50 shows a good average data of isooctane and ethanol. Gasoline, due to its low initial boiling point and wide range of components, has the widest plume ratio distribution and smallest gradient. This gives us insight that adding low boiling point (preferably with low heat of vaporization) additive or component to high boiling point fuel, can facilitate flash boiling, fuel vaporization, and mixing.

Compression ignition (CI) and spark assisted compression ignition combustion (SACI) developments were investigated using PRF95 (high octane fuel) and PRF65 (low octane fuel). The cumulative heat release (CHR) decreases with the increase of ambient temperatures and decrease of oxygen levels. The peak heat release rate (HHR) first increases then decreases with the increase of the ambient temperature, For PRF95, the peak HRR appears at about 750K to 800K, while for PRF65 it is about 700K to 650K. The peak heat release rate timing always decreases with the increase of the ambient temperature or oxygen level. Under a low ambient temperature, the oxygen level plays a major role in affecting the peak heat release rate. Under lower oxygen levels, the flame becomes darker, the ignition delay becomes longer, and the combustion process takes more time to complete. Proper spark timing can help advance the peak HRR and shorten ignition delay, but this effect becomes minor when the temperature increases. The added spark has less effect on PRF65 than on PRF95.

Under flash boiling spark ignition condition, the flame appears with low luminosity and cloud-like shape. These cloud-like flame region is where the fuel is distributed well into the whole volume of the chamber. The peak pressure to initial pressure ratio can be more than 10 times under 0.2 bar. The more weight of added mass and higher peak temperature are major factors contributing to the very high peak pressure to initial pressure ratio under 0.2 bar. The flash boiling spark ignition combustion can lead to better distributed mixtures, lower flame temperature and less locally fuel rich spots, resulting in very clean combustion and greatly reduced particulate matter production, which is promising in pursuing lower emissions.

Biography: In 2007, Libing went to Xi’an Jiaotong Univeristy for undergraduate study. His major was power engineering and he developed great interest and enthusiastic in thermal science research and study. He graduated in 2011 and continued his Master study in Xi’an Jiaotong University, until 2014 when he decided to further pursue higher degree and study overseas.

In 2014, Libing started his PhD study in North Carolina State University under the supervision of Dr. Tiegang Fang. His research interest mainly lies in spray and combustion of different fuels (gasoline and diesel) under various ambient conditions. He conducted series of study with high pressure diesel spray and gasoline spray under low ambient pressure conditions.