No abstract

Biodiesel is an oxygenated diesel fuel made from vegetable oils and animal fats by conversion of the triglyceride fats to esters via transesterification. In this study we examined biodiesels produced from a variety of real-world feedstocks as well as pure (technical grade) fatty acid methyl and ethyl esters for emissions performance in a heavy-duty truck engine. The objective was to understand the impact of biodiesel chemical structure, specifically fatty acid chain length and number of double bonds, on emissions of NOx and particulate matter (PM). A group of seven biodiesels produced from real-world feedstocks and 14 produced from pure fatty acids were tested in a heavy-duty truck engine using the U.S. heavy-duty federal test procedure (transient test). It was found that the molecular structure of biodiesel can have a substantial impact on emissions. The properties of density, cetane number, and iodine number were found to be highly correlated with one another. For neat biodiesels, PM emissions were essentially constant at about 0.07 g/bhp-h for all biodiesels as long as density was less than 0.89 g/cm3 or cetane number was greater than about 45. NOx emissions increased with increasing fuel density or decreasing fuel cetane number. Increasing the number of double bonds, quantified as iodine number, correlated with increasing emissions of NOx. Thus the increased NOx observed for some fuels cannot be explained by the NOx/PM tradeoff and is therefore not driven by thermal NO formation. For fully saturated fatty acid chains the NOx emission increased with decreasing chain length for tests using 18, 16, and 12 carbon chain molecules. Additionally, there was no significant difference in NOx or PM emissions for the methyl and ethyl esters of identical fatty acids.

q John Sheehan, who initiated and organized this whole effort at the start, provided detailed process modeling for the soybean crushing and biodiesel production technologies.q K. Shaine Tyson, NREL Project Manager for DOE's Biodiesel Program, provided overview and management for the work (and, more importantly, shared her insights based her experience conducting a life cycle study for ethanol).

This is a three part thesis regarding the regulated emissions from in-use heavy duty diesel vehicles. The first part of the thesis involves the collection and analysis of emissions from 21 vehicles. Emissions of particulate matter (PM), nitrogen oxides (NO x ), carbon monoxide (CO), total hydrocarbon (THC) and PM sulfate fraction were measured as well as smoke opacity. The vehicles were tested on three different driving cycles. This study found that when emissions were converted to a g/gallon basis, the effect of driving cycle was eliminated for NO x and reduced for PM. Sulfate comprised less than 1% of the emitted PM. Smoke opacity was not well correlated with mass emissions of any of the regulated pollutants. Multivariate regression analysis indicated that in-use NO x emissions did not decrease for this fleet during the years 1986 to 1995 while engine certification standards dropped sharply during that time. A review of all inuse emissions data in the scientific literature supported this result. The review also showed that PM emissions were widely variable among vehicles certified under identical standards. The variability was attributed to environmental factors, inertial weight, test cycle, driver variability and vehicle condition, but the relative importance of these factors could not be determined based on previously collected data. The wide variability in PM emissions within model years and the uniformity of NOx results despite the change in engine standards showed that engine certification was not an accurate tool to predict and iv control emissions from vehicles. To better understand the relationship between engine and chassis test results, a computer model was developed that estimates engine speed and load from vehicle speed. Using this model it was possible to detect the use of electronic controls which operate the engine in a different mode during engine testing and other more typical types of operation. The model also showed that the engine certification test generated consistently less PM than the vehicle tests when the model was used to put the engine and chassis emissions on a consistent basis. A good correlation was found between rate of HP increase integrated over the test cycle and PM emissions for both the chassis and engine tests. The engine test procedure includes engine behaviors that cannot be duplicated in in-use operation, and appears to favor lower rates of acceleration than typical chassis operation. The model also showed how small changes in vehicle speeds (+/-2 mph) due to driver variability can lead to a doubling of load on the engine.v

The Soave modification of the Redlich-Kwong equation of state is shown to work well for the estimation of the vapor-liquid equilibrium behavior of a wide variety of technically important hydrocarbon mixtures. The American Petroleum Institute's Technical Data Book-Petroleum Refining recently adopted a modified Soave procedure for vapor-liquid equilibria calculations. It is the purpose here to present the finished form of the correlation for treating mixtures of hydrocarbons of importance to the natural gas and petroleum refining industries. The complete correlation is fully generalized, requiring only the readily available characterization parameters to make equilibrium calculations. The utility of the correlation is demonstrated by equilibria predictions for binary and multicomponent defined and undefined hydrocarbon systems.