Page 223 - Biofuels Refining and Performance

206 Chapter Seven

Ethanol fumigation in diesel engines can play a major role in envi-
ronmental air pollution control, and ethanol is a viable alternative fuel
for diesel engines.
Ethanol is a very good SI engine fuel and a rather poor CI engine fuel.
Ethanol has a high octane rating of 90 and a low cetane rating of 8, and
will not self-ignite reasonably in most CI engines. Dehydrated ethanol
is fumigated into the air stream in the intake manifold of a 42-hp trac-
tor diesel engine to improve its self-ignition quality. The performance
of the engine under dual-fuel (diesel and fumigated ethanol) operation
is compared with diesel fuel operation at various speeds (800, 900, 1000,
1100 rpm), loads (0, 4, 8, 12, 16 kgf), and fumigation rates (0.00, 1.06,
1.45, 2.06 kg/h). Analysis of the results shows that ethanol fumigation
has the advantages of reduction in BSFC, NO x emission, and smoke level
and the disadvantage of slight reduction in brake thermal efficiency. The
fumigation rate of 1.06 kg/h (40% diesel substitution) is optimal for
good engine performance.
It has been concluded that ethanol is a viable alternative fuel for
and the smoke level sug-
diesel engines. A dramatic reduction in the NO x
gests that fumigation, as an emission control technique in diesel engines,
can play a vital role in environmental air pollution control on a farm.
In the dual-injection method, two injection systems are used, one for
diesel and the other for alcohol. This method can replace a large per-
centage of diesel fuel. In this method, air is sucked and compressed, and
then methanol is injected through a primary injector. To ignite this, a
small amount of diesel is injected through a pilot injector. The relative
injection timing of alcohol and diesel is an important aspect of the system.
As two injection systems are required, two injectors are required on the
cylinder head, which limits the application of this method to large-bore
engines. An additional pump, fuel tank, and fuel line are also required,
making the system more complicated. But this method replaces 60% of
diesel at a partial load and 90% at a full load, and provides higher ther-
mal efficiency.

7.7.1 Alcohol–diesel fuel solution
This method is the easiest but requires anhydrous ethanol, because
methanol has limited solubility. A maximum of 10% diesel can be sub-
stituted due to the lower solubility of methanol in diesel. No component
changes; only adjustments of injection timing and fuel volume delivery
are required to restore full power. Dodecanol is an effective surfactant
for methanol–diesel fuel blends. Straight-run gasoline is an economical
additive for ethanol–diesel blends.
Solubility of alcohols in diesel fuels is a function of (a) fuel tempera-
ture, (b) alcohol content, (c) water content, (d) specific gravity of diesel,