One way to reduce the NO_X Emission of biodiesels: The increase of cetane number

ABSTRACT

Compared to conventional diesel fuels, biodiesels normally have lower smoke and particulate matter, while higher nitrogen oxides (NO_X) emissions. In our study, an attempt was made to reduce the NO_X emissions of biodiesels by increasing the cetane numbers (CNs). Three kinds of biodiesels with extremely high CNs (70.1, 76.9, 80.9, respectively) were developed. Their main physical and chemical properties were tested. With a two-cylinder direct injection diesel engine, their emission performances were experimentally investigated. The results indicate that, CN, freezing point, as well as viscosity of biodiesels are linearly increased with the increase of carbon number. The NO_X emission for biodiesels with high CNs is lower than that of conventional diesel fuels. High CN promotes smoke formation as well while lower smoke emissions are still obtained for biodiesels when certain oxygen contents are present. That is, the smoke/NO_X tradeoff is broken. Besides, as fuel CN is elevated, NO_X for biodiesels decreases but smoke and carbon monoxide emissions are increased.

KEYWORDS:

• Biodiesel
• cetane number
• oxygen content
• NO_X
• smoke

Funding

This project was granted financial support from the China Natural Science Foundation (No. 50976125).

Nomenclature

CN	=	Cetane Number
NOX	=	Nitrogen oxides
CO	=	Carbon monoxide
HC	=	Unburned hydrocarbon