Page 225 - Biofuels Refining and Performance

208 Chapter Seven

The most effective ignition improvers are nitrogen-based compounds
which can aggravate exhaust emissions of NO . Ethylene glycol nitrates
x
have shown promising trends at 5% concentration.
Engines operating on cetane-enhanced alcohol need a few changes, e.g.,
Injection volume and timing must be adjusted to obtain optimum
performance.
A large pump, fuel lines, and injectors are required to satisfy total fuel
requirements of the engine for the desired output.
A lubricant (generally castor oil used so far) is required to be added
to alcohols using improvers.

7.8 Methanol as an Alternate Fuel
Methanol behaves much like petroleum, so it can be stored and shifted in
the same manner. It is a more flexible fuel than hydrocarbon fuels, per-
mitting wider variation from the ideal A:F ratio. It has relatively good lean
combustion characteristics compared to hydrocarbon fuels. Its wider
inflammability limits and higher flame speeds have shown higher ther-
mal efficiency and less exhaust emissions, compared with petrol engines.
Methanol can be used directly or mixed with gasoline. Tests have
shown improvements in fuel economy by 5–13%, decreases in CO emis-
sion by 14–70%, and reductions in exhaust temperature by 1–9%, with
varying methanol in petrol from 5 to 30%. Depending on the gasoline–
methanol mixture, some changes in fuel supply are essential. Simple
modifications to the carburetor or fuel injection can allow methanol to
replace petrol easily. Some important features of methanol as fuel are
listed below:

1. The specific fuel consumption with methanol as fuel is 50% less than
a petrol engine.
2. Exhaust CO and HC are decreased continuously with blends con-
taining higher percentage of methanol. But exhaust aldehyde con-
centration shows the opposite trend.
3. Like ethanol, methanol can also be used as a supplementary fuel in
heavy vehicles powered by CI engines with consequent savings in
diesel oil and reduced exhaust pollution. No undue wear of engine
components are encountered with methanol as a fuel, while engine
peak power improves and smoke density and NO concentration in
x
exhaust is reduced.
Phase separation, vapor lock, and low-temperature starting difficulties
are the problems associated with the use of methanol or its blends as