Michael S. Graboski

Combustion of fat and vegetable oil derived fuels in diesel engines

In this article, the status of fat and oil derived diesel fuels with respect to fuel properties, engine performance, and emissions is reviewed. The fuels considered are primarily the methyl esters of fatty acids derived from a variety of vegetable oils and animal fats, and referred to as biodiesel. The major obstacle to widespread use of biodiesel is the high cost relative to petroleum. Economics of biodiesel production are discussed, and it is concluded that the price of the feedstock fat or oil is the major factor determining biodiesel price.Biodiesel is completely miscible with petroleum diesel fuel, and is generally tested as a blend. The use of biodiesel in neat or blended form has no effect on the energy based engine fuel economy. The lubricity of these fuels is superior to conventional diesel, and this property is imparted to blends at levels above 20 vol%. Emissions of PM can be reduced dramatically through use of biodiesel in engines that are not high lube oil emitters. Emissions of NOx increase significantly for both neat and blended fuels in both two- and four-stroke engines. The increase may be lower in newer, lower NOx emitting four-strokes, but additional data are needed to confirm this conclusion. A discussion of available data on unregulated air toxins is presented, and it is concluded that definitive studies have yet to be performed in this area. A detailed discussion of important biodiesel properties and recommendations for future research is presented. Among the most important recommendations is the need for all future studies to employ biodiesel of well-known composition and purity, and to report detailed analyses. The purity levels necessary for achieving adequate engine endurance, compatibility with coatings and elastomers, cold flow properties, stability, and emissions performance must be better defined.

Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus

This report presents the findings from a study of the life cycle inventories (LCIs) for petroleum diesel and biodiesel. An LCI is a comprehensive quantification of all the energy and environmental flows associated with a product from “cradle to grave.” It provides information on raw materials extracted from the environment; energy resources consumed; air, water, and solid waste emissions generated.

Deactivation of PdO–Al2O3 oxidation catalyst in lean-burn natural gas engine exhaust: aged catalyst characterization and studies of poisoning by H2O and SO2

A palladium oxide on alumina oxidation catalyst was employed to remove combustible pollutants from the exhaust of a spark-ignited, lean-burn natural gas engine. Rapid deactivation was seen for the oxidation of methane and ethane. Characterization results are consistent with sulfur as the primary source of catalyst activity loss. In microreactor studies, deactivation of the engine aged catalysts was only apparent if water was present in the feed stream. In dry feed gas, the activity of fresh and engine aged samples was the same. SO2 in dry gas was shown to cause both inhibition and deactivation for methane oxidation. This deactivation is partly reversible at 733 K and completely reversible at 793 K. Water inhibits the rate of methane oxidation and causes some permanent activity loss. Activity studies at 733 and 793 K indicate that activity loss is greater when both water and SO2 are present. Sulfur oxide groups on the surface increase both the amount of water sorbed and the water desorption temperature in TPD experiments. It is proposed that water and SO2 compete for adsorption sites on the alumina surface. Enhanced activity loss in the presence of both poisons is attributed to enhanced water inhibition and spillover of sorbed SO2 and SO3 species from alumina to the PdO surface.

Diesel and CNG Transit Bus Emissions Characterization By Two Chassis Dynamometer Laboratories: Results and Issues

Emissions of six 32 passenger transit buses were characterized using one of the West Virginia University (WVU) Transportable Heavy Duty Emissions Testing Laboratories, and the fixed base chassis dynamometer at the Colorado Institute for Fuels and High Altitude Engine Research (CIFHAER). Three of the buses were powered with 1997 ISB 5.9 liter Cummins diesel engines, and three were powered with the 1997 5.9 liter Cummins natural gas (NG) counterpart. The NG engines were LEV certified. Objectives were to contrast the emissions performance of the diesel and NG units, and to compare results from the two laboratories. Both laboratories found that oxides of nitrogen and particulate matter (PM) emissions were substantially lower for the natural gas buses than for the diesel buses. It was observed that by varying the rapidity of pedal movement during accelerations in the Central Business District cycle (CBD), CO and PM emissions from the diesel buses could be varied by a factor of three or more. The driving styles may be characterized as aggressive and non-aggressive, but both styles followed the CBD speed command acceptably. PM emissions were far higher for the aggressive driving style. For the NG fueled vehicles driving style had a similar, although smaller, effect on NO{sub x}. It is evident that driver habits may cause substantial deviation in emissions for the CBD cycle. When the CO emissions are used as a surrogate for driver aggression, a regression analysis shows that NO{sub x} and PM emissions from the two laboratories agree closely for equivalent driving style. Implications of driver habit for emissions inventories and regulations are briefly considered.

Idle Emissions from Heavy-Duty Diesel and Natural Gas Vehicles at High Altitude

ABSTRACT Idle emissions of total hydrocarbon (THC), CO, NOx, and particulate matter (PM) were measured from 24 heavy-duty diesel-fueled (12 trucks and 12 buses) and 4 heavy-duty compressed natural gas (CNG)-fueled vehicles. The volatile organic fraction (VOF) of PM and aldehyde emissions were also measured for many of the diesel vehicles. Experiments were conducted at 1609 m above sea level using a full exhaust flow dilution tunnel method identical to that used for heavy-duty engine Federal Test Procedure (FTP) testing. Diesel trucks averaged 0.170 g/min THC, 1.183 g/min CO, 1.416 g/min NOx, and 0.030 g/min PM. Diesel buses averaged 0.137 g/min THC, 1.326 g/min CO, 2.015 g/min NOx, and 0.048 g/min PM. Results are compared to idle emission factors from the MOBILE5 and PART5 inventory models. The models significantly (45-75%) overestimate emissions of THC and CO in comparison with results measured from the fleet of vehicles examined in this study. Measured NOx emissions were significantly higher (30-100%) than model predictions. For the pre-1999 (pre-consent decree) truck engines examined in this study, idle NOx emissions increased with Health and Environment; June 30, 1999 (available from the authors).

Development and commercialization of oxygenated diesel fuels from waste vegetable oils

Abstract Vegetable oils and animal fats (triglycerides) were the first liquid fuels used in the rise of civilization, and now again are a potential source of alternate diesel fuel. They are 20 times as viscous as diesel fuel, however, and so form carbon deposits on diesel cylinders and injectors. They are also typically

Effect of Humidity on Heavy-Duty Transient Emissions from Diesel and Natural Gas Engines at High Altitude

3–

A mathematical model of a ramp forced hot-wire thermal conductivity instrument

5/gallon, and so are too expensive to compete economically with diesel today. A number of solutions have been proposed for these problems, including transesterification, dilution, pyrolysis and microemulsification. The viscosity can be lowered by transesterification of the triglycerides with methanol or ethanol to form fatty acid esters. This cleaves the fat molecule and removes the glycerine, yielding a viscosity comparable to that of diesel. The heat of combustion is 95% of that for conventional diesel (on a volume basis). They have a Cetane number of 50–80 (compared to 42 for diesel). The cost of the fuel can be reduced by using waste vegetable cooking oils. There are 350 million gallons of waste vegetable oil produced annually in the U.S.A., and various quantities available in other countries. We have developed a process for making the esters from waste vegetable oils and we call the fuel “M-Diesel”. The oil is reacted with sodium hydroxide dissolved in methanol. A sufficient quantity of alkali is used to neutralize the fatty acids in the waste oil plus 0.3% excess. A batch of 300 gallons was made for testing. We have tested the fuel in a Denver public bus and find power comparable to that of diesel. A 30% blend with diesel reduced smoke opacity to 60% of that from diesel, while neat M-Diesel reduced the opacity to 26% of that of diesel. Tests of 10 and 20% mixtures are now underway.

The Production of Synthesis Gas from Methane, Coal and Biomass

Abstract The Code of Federal Regulations (CFR 40 Part 86 Subpart N) defines a universal humidity correction for NOx emissions from heavy–duty diesel and alternative fueled engines measured by the heavy–duty transient test. This testing procedure and humidity correction apply to any heavy–duty engine subject to regulation of particulate matter emissions, including spark ignited engines. This correction has been evaluated for a 1988 Detroit Diesel Series 60 engine and a 1995 Cummins B5.9G natural gas engine. The correction at high altitude for the diesel engine is in excellent agreement with the correction published in the Code of Federal Regulations. In addition, humidity is found to affect particulate matter in agreement with the Engine Manufacturers Association correction factor. This suggests that these results, acquired at high altitude, are generally applicable to all altitudes. CO emissions are also correlated with humidity. Emission traces show that humidity affects NOx uniformly for the diesel engi...

A new transient vertical hot-wire thermal conductivity instrument for fluids utilising a ramp power input

Abstract The fundamental model and model corrections for the absolute determination of fluid thermal conductivity using a transient hot-wire technique were studied. Analytical solutions for three heat generation functions (Dirac, step and ramp) are presented. The ramp heat generation function is shown to offer several advantages over the step function, which is currently used by experimenters. Expressions for the corrections to the idealized model of a ramp forced system are presented for: heat capacity effect, truncation error, nonuniform wire radius, bounded media, Knudsen effects, axial conduction, free convection and radiation.