Page 230 - Biofuels Refining and Performance

Ethanol and Methanol as Fuels in Internal Combustion Engines 213

7.8.6 Formaldehyde emission
The major problem with methanol is high levels of formaldehyde emis-
sion, which is negligible with conventional fuels. Formaldehyde emis-
sion levels with and without an electric heater are shown in Fig. 7.13.
The level with an electric heater is considerably lower compared with
its absence.
The performance characteristics compared with petrol engine are
considered as brake thermal efficiency versus air fuel (A:F) ratio, the
effect of speed power output and specific heat consumption. In addi-
tion, the performance characteristics also include the effect of A:F
ratio on exhaust emission. The effects of A:F ratio and speed on brake
power are shown in Figs. 7.14a and 14b. Another important charac-
teristic is the effect of speed on volumetric efficiency, which is shown
in Figs. 7.15 and 7.16.
Both alcohols, as well as their blends, are studied as alternative fuels
for IC engines. The power can be increased from 6 to 10% with alcohols
, which
or their blends. The use of a leaner mixture provides more O 2
reduces the emission. Because of the high heat of vaporization of these
fuels compared to petrol, greater cooling of the inlet mixture occurs,
which gives higher thermal efficiency, less specific heat consumption,
and smooth operation. At higher speeds, the specific heat consumption
is lower than that of petrol. Methanol dissociates in the engine cylinder
forming H . This H gas helps the mixture to burn quickly and increases
2
2
the burning velocity, which brings about complete combustion and
makes a leaner mixture more combustible. In a petrol engine, misfiring

30 Formaldehyde emission
with electric heater
Formaldehyde emission
without electric heater
Formaldehyde (mg/s) 20

10

0

0 2 4 6 8 10
Time after engine start (min)
Figure 7.13 Performance of methanol as an IC engine fuel.