Course: BFM 202 Biodiesel Production

Lecture

Diesel Fuel
Credits
BFM 202 Biodiesel Production Unit 2 Lecture has been adapted from "ENGY 131 Unit 2 Commentary: The Diesel Engine" by Southeastern Illinois College.

ENGY 131 Biodiesel Production course content by Southeastern Illinois College is licensed under a Creative Commons Attribution 3.0 Unported License. Except where indicated otherwise.

Diesel Fuel

Energy Content refers to the heat of combustion. Historically, both
vegetable-based and petroleum-based were pursued as liquid fuel.
How did petroleum gain wider acceptance? During the original refinement
of crude oil into gasoline, there was a heavy by-product that was considered
waste. Dr. Craig Freudenrich provides an excellent description of diesel
distillate in the four-page article, "How Oil Refining Works.” (©  HowStuffWorks, Inc)

The energy content of petroleum-based diesel and biodiesel cannot be
defined in general terms. Why? There are too many variables that affect
the heating value of diesel fuel, including: where the petroleum crude
comes from, which refinery is used, and the time of year it's manufactured.
Diesel fuel with lower energy content per liter causes engines to
produce less peak power. This is important to note since petroleum-based
fuels with a higher percentage of aromatics have higher energy per liter
even though aromatics contain lower heating values per kilogram. The
higher aromatic density more than compensates for the lower energy
content per weight since diesel fuel is metered into the engine by volume.
An engine under partial load conditions may be able to meet the demand
for power but a greater volume of fuel is used, thereby increasing NOx
emissions from increased fuel usage.

Aromatics

Aromatic hydrocarbons are stable chemical structures present in diesel
fuel at levels of about 25-35%. In diesel fuel they provide greater
energy per gallon/liter, however they also emit a higher concentration of
of NOx and particulate matter. In addition, they have a lower cetane number,
explained later in this lecture.

Biodiesel does not contain aromatics.

Carbon monoxide and hydrocarbon  emissions are lower for diesel engines
as compared to gasoline engines, making it easier to comply with regulations.
However, NOx and particulates are still problematic. Increased reductions
of both took effect in 2010. Although biodiesel fuels contain no aromatics,
they do contain varying levels of methyl esters. Unsaturated esters have
lower energy content by weight, but have more energy per volume.
On a weight basis, the energy content of soy biodiesel is 12.5% less
than No. 2 diesel fuel, 37.2 MJ/kg to 42.6 MJ/kg, respectively. Biodiesel,
being more dense than petroleum-based diesel fuel, has an
energy content that is only 8% less per gallon, 32.9 MJ/L vs. 36.0 MJ/L.
Depending upon the feedstock, other measurements indicate that
biodiesel's power loss could be less due to its higher viscosity. The
reason is because increased viscosity decreases the amount of fuel
leaking by plungers in the fuel injection system allowing that fuel to
be ignited.
There are indications that the efficiency of converting fuel to power is
the same for biodiesel and petroleum-based diesel. The Brake Specific
Fuel Consumption (BSFC) test divides the fuel flow rate by the engine
output power and is a standard used by manufacturers of diesel engines
to describe fuel economy. This test indicates that fuel economy is actually
12.5% higher for biodiesel. A variety of exhaust after-treatments are being
used to eliminate emissions voiding biodiesel's advantages.

In the 1990s, the California Air Resources Board adopted

standards limiting the aromatic content of diesel fuels sold in

California to 10%.

California later altered that standard for to a higher aromatic content if
fuel manufacturers proved their fuels produced lower or equivalent
emissions to that of the low-aromatic diesel fuel.