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Estimation of Elemental Composition of Diesel Fuel Containing Biodiesel
Abstract:
Carbon, hydrogen and oxygen are major elements in vehicle fuels. Knowledge of fuels elemental composition is helpful in addressing its performance characteristics. Carbon, hydrogen and oxygen composition is an important parameter in engine calibration affecting vehicle performance, emissions and fuel economy.
Biodiesel, a fuel comprised of mono-alkyl esters of long-chain fatty acids also known as Fatty Acid Methyl Esters(FAME), derived from vegetable oils or animal fats, has become an important commercial marketplace automotive fuel in the United States (US) and around the world over last few years. FAME biodiesels have many chemical and physical property differences compared to conventional petroleum based diesel fuels. Also, the properties of biodiesel vary based on the feedstock chosen for biodiesel production. One of the key differences between petroleum diesel fuels and biodiesel is the oxygen content. Typical oxygen content in pure biodiesel (B100) is about 11 weight % while conventional ultra-low sulfur petroleum diesel fuel has negligible oxygen content. High oxygen content of biodiesel impacts its characteristics compared to petroleum diesel.
A previous paper (SAE2013-01-1139) discussed the change in energy content of diesel fuel containing biodiesel primarily due to its high oxygen content and the estimation of net heating values from common fuel properties. This paper is a continuation of the previous study and will discuss the estimation of elemental composition of biodiesel blended diesel fuels from common fuel properties. While the carbon, hydrogen, and nitrogen contents can be measured by combustion of the fuel in a tube and then quantifying the combustion products as described in ASTM D5291 or E191, the test is time-consuming and expensive. The repeatability of the method is also marginally satisfactory.
It is generally satisfactory and more convenient to estimate the elemental composition from other commonly-measured fuel properties. Several standardized empirical methods have been developed in the past for estimating the hydrogen content of hydrocarbon fuels. However, the addition of oxygenated biodiesel fuel to diesel has become very common in many countries, and most of the estimation methods developed for hydrocarbon fuels do not provide accurate results for biodiesel blends, especially blends containing more than about 5 volume-percent biodiesel.
This paper summarizes compositional data from recently collected retail samples from US market place, as well as laboratory blends containing different concentrations of biodiesels made from various types of biodiesels representing the most common feedstock.
The compositional data obtained by different standardized test methods is compared and discussed. New empirical methods and equations are proposed for diesel containing biodiesel blends.