Fuels in Transportation - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 20

Table 2.8 Quality criteria of conventional and synthetic fuels in the combustion process

Designation Diesel fuel

from the refinery

Synthetic
fuel

Advantages and disadvantages

Sulfur content
ppm

10-5,000 0 Low local SO 2 emissions and particles

Easier handling in the exhaust gas
after treatment system

Cetane number 40-55 75-80 Low CO, HC, NO and NO 2 emissions

Low noise emission levels and smooth
acceleration
Enhanced technical efficiency in the
engine driving characteristics

Density
gcm -3
((lb ft -3 )

0.82-0.86
(51.2-53.7)

0.78
(48.7)

Slightly increased consumption
on volume basis
Less particle emissions

Heating value
MJ kg -1

ca. 43
(18.46 9 10 3 )

ca. 44
(18.89 9 10 3 )

Slightly smaller consumption on mass basis
Fewer CO 2 emissions per kilometer

(BTU lb -1 )

cryogenic tank at a temperature of -253C(-423F). [ 19 ]. Preventing leaks in the
fuel tank is still an unsolved problem. The innovative storage of hydrogen in metal
hydrides or in special carbon modifications is possible, but is rarely used except in
submarines [ 20 ].

2.2.5 Synthetic Fuels

Synthetic fuels can be produced from natural gas with the Gas to Liquid (GTL)
and from coal with the Coal to Liquid (CTL) technology. The final product is
identical in both cases. The convertibility of the products between natural gas and
charcoal is ensured. With the CTL or GTL technologies the base materials are
converted into water-gas (H 2 and CO) and later into gasoline and diesel fuel
through the use of catalysts with the help of Fischer-Tropsch synthesis. The
by-products are liquefied gas and liquid paraffin.
Table 2.8 shows the most important differences in the quality criteria between
conventional and synthetic fuels in the combustion process [ 21 ].
This technology is mostly used in South Africa. Synthetic fuels are generally
colorless and burn cleanly, have a high Cetane number, and are almost sulfur free [ 22 ].

2.2.6 Biogenic Fuels

Biogenic fuel, i.e., bio-organic fuel is the name of any plant or animal substances
that can be used in combustion engines. They can support not only the fuel
production, but also aid the market position of agriculture worldwide, since they
increase the income and the employment opportunities of farmers. The aim is to