NO_x Reduction from Biodiesel Fuels

Abstract

The demand for energy around the world is increasing, specifically the demand for petroleum-based energy. Appeasing this growing energy demand without irreparably damaging the environment is of primary concern. With rising fuel prices and environmental concerns, alternative fuels could satisfy the need for renewable energy with low environmental impact. Some of the more popular alternative fuels for new vehicles are ethanol, hydrogen, and biodiesel. Although gasoline engines are expected to be replaced by hydrogen-powered fuel cells, compression-ignition engines, the diesel engines, are expected to remain in use for high-power applications because of limitations of hydrogen-storage densities. The viable environmental friendly alternative fuel for compression-ignition engines is methyl esters (commonly known as biodiesel), which is derived from vegetable oils or animal fats. Using biodiesel instead of conventional diesel fuel reduces emissions such as the overall life cycle of carbon dioxide (CO2), particulate matter, carbon monoxide, sulfur oxides (SOx), volatile organic compounds (VOCs), and unburned hydrocarbons significantly. However, biodiesel increases nitrogen oxides (NO x ) emissions, mostly NO and NO2, which are considered as zone A hazardous compounds. This paper reviews the kinetics of NO x formation in relation to thermal, prompt, and fuel NO x formation processes and critically reviews the techniques that have been attempted to reduce NO x emissions from mechanisms to effectively reduce the NO x formation with biodiesel fuel.

Water injection effects on the performance and emission characteristics of a CI engine operating with biodiesel

“…In addition, the catalytic convertors work best at a stoichiometric air-fuel ratio about 14.1:1. Most of the diesel engines tend to run lean which makes the catalytic converter less effective in reducing NOx emission [21].…”

“…In the EGR system, the heat of combustion from the fuel is used to heat the exhaust gas. The exhaust gas is essentially inert and therefore does not react in the combustion chamber and only absorbs heat [4]. Even though, the EGR has a potential of reducing NOx up to 50%, it has an inherent drawback of increasing the PM emissions [2,19,20].…”

“…However, to make hydrogen use commercially viable, there are many technical challenges that need to be addressed for example complexity in hydrogen production, requirement of special infrastructure for its storage, and high fuel cell production costs. Inspite of research advances on, hydrogen powered fuel cells, and diesel engines are expected to remain in use for high-power applications such as rail road locomotives, ships and over land transport trucks [4]. For these applications the biodiesel fuel appears to be a viable alternative to fossil fuel as its properties match favourably with fossil fuel and there are only few technical challenges that need to be overcome when used in compressionignition diesel engines [4].…”

“…Inspite of research advances on, hydrogen powered fuel cells, and diesel engines are expected to remain in use for high-power applications such as rail road locomotives, ships and over land transport trucks [4]. For these applications the biodiesel fuel appears to be a viable alternative to fossil fuel as its properties match favourably with fossil fuel and there are only few technical challenges that need to be overcome when used in compressionignition diesel engines [4]. Biodiesel is one of the renewable energy sources, which consists of short chain (methyl or ethyl) esters, produced from vegetable-based oils by transesterification.…”

“…This regulatory requirement has resulted in major research and development works being undertaken to reduce NOx emissions. Different methods have been used to reduce the NOx emission successfully from compression-ignition engine; some of these are exhaust gas recirculation (EGR), catalytic converter (post combustion method) and water injections/emulsion [4]. The working principles and the advantages and disadvantages of these methods are summarised below.…”