Joonsik Hwang

Spray and combustion of waste cooking oil biodiesel in a compression-ignition engine

An experimental study was carried out to compare the spray and combustion characteristics of waste cooking oil biodiesel with those of conventional diesel in a common-rail direct-injection compression-ignition engine. The indicated mean effective pressure of approximately 0.7 MPa was tested under an engine speed of 800 r/min. The fuels were injected at an injection timing of −5 crank angle degree after top dead center with injection pressures of 80 and 160 MPa. The experiments were performed to investigate the combustion and emission characteristics in a metal engine, while spray and combustion flame characteristics in an optical engine. The morphological and compositional features of particulate matter were also analyzed by using transmission electron microscopy and thermogravimetric analysis. The direct imaging of the spray indicated a longer injection delay for waste cooking oil biodiesel. However, it exhibited longer liquid penetration length and narrower spray angle than diesel as the spray developed. Waste cooking oil biodiesel combustion showed a longer ignition delay with a slightly lower peak of in-cylinder pressure and heat release rate than diesel due to the deteriorated atomization and evaporation of fuel spray. In terms of emission, waste cooking oil biodiesel showed benefits in reduction of carbon monoxide, unburned hydrocarbon and particulate matter emissions. The particulate matter from waste cooking oil biodiesel was composed of smaller primary particles and more volatile organic fraction than diesel soot. The combustion flame imaging verified the retarded combustion phase of waste cooking oil biodiesel. Waste cooking oil biodiesel combustion showed lower flame luminosity accompanied by shorter visible flame duration, at both injection pressures. The flame spatial fluctuation and flame nonhomogeneity were also lower for waste cooking oil biodiesel.

Particulate morphology of waste cooking oil biodiesel and diesel in a heavy duty diesel engine

The effect of biodiesel produced from waste cooking oil (WCO) on the particulate matters (PM) of a direct injection (DI) diesel engine was experimentally investigated and compared with commercial diesel fuel. Soot agglomerates were collected with a thermophoretic sampling device installed in the exhaust pipe of the engine. The morphology of soot particles was analyzed using high resolution transmission electron microscopy (TEM). The elemental and thermogravimetric analysis (TGA) were also conducted to study chemical composition of soot particles. Based on the TEM images, it was revealed that the soot derived from WCO biodiesel has a highly graphitic shell-core arrangement compared to diesel soot. The mean size was measured from averaging 400 primary particles for WCO biodiesel and diesel respectively. The values for WCO biodiesel indicated 19.9 nm which was smaller than diesel’s 23.7 nm. From the TGA results, WCO biodiesel showed faster oxidation process. While the oxidation of soot particles from diesel continued until 660°C, WCO biodiesel soot oxidation terminated at 560°C. Elemental analysis results showed that the diesel soot was mainly composed of carbon and hydrogen. On the other hand, WCO biodiesel soot contained high amount of oxygen species.

Biodiesel Soot Characteristics

Diesel engines are widely utilized as a power source in various applications, such as passenger and commercial vehicles, electricity generation, marine transportation, and construction equipment. Despite several advantages for instance, low operating cost, high durability, and high power-to-weight ratio, diesel engines have the inherent disadvantage of high NOx and soot emissions. In terms of environmental concerns, oxygenated fuels such as biodiesel have been considered as a promising alternative fuel for diesel engines. It is well known that the oxygen content of biodiesel suppresses the formation of soot precursors in diffusion flames. Many researchers are now trying to examine the soot formation with biodiesels. In this chapter, the effect of biodiesel on soot particles in compression ignition engines is discussed. The morphological characteristics of soot particles were analyzed with transmission electron microscope (TEM). The chemical composition was determined by the elemental analysis (EA) and thermogravimetric analysis (TGA). From the previous studies, it emerged that soot particles from biodiesel were composed of smaller primary particles compared to those in case of diesel. The nano-structure analysis of biodiesel soot particles showed that biodiesel origin soot is preferable for oxidation due to its unstable graphene structure. On the other hand, biodiesel soot particles were composed of lesser carbonaceous materials. They contained lower carbon-containing species but higher hydrogen, oxygen, and nitrogen in the soot.