Page 219 - Biofuels Refining and Performance

202 Chapter Seven

If blends are used, some minor modifications in the engine are required,
as listed below:
1. The carburetor jet should be increased to increase the flow 1.56 times
that of petrol.
2. The float has to be weighted down to correct levels due to higher spe-
cific gravity.
3. The air inlet should be modified to get less air as blends require less
air for complete combustion than petrol.
4. Specific arrangement of heating the carburetor and intake manifold
should be provided as lower vapor pressure of alcohol makes the
starting difficult below 70 C.

7.6 Performance of Engine Using Ethanol
The effect of speed on power output, brake specific fuel consumption (BSFC),
and thermal efficiency of an engine using ethanol is compared with gaso-
line engine, is shown in Figs. 7.2 through 7.5.
The observations are listed below:
1. The power output of the ethanol engine is higher, compared to a gaso-
line engine at all speeds.
2. The BSFC is improved with an ethanol engine, compared to a petrol
engine.
3. The maximum thermal efficiency of an ethanol engine is higher than
that of a petrol engine. The efficiency curve of an ethanol engine is
flat for a wide range of speeds, which indicates that the partial-load
efficiency is much better, compared with a petrol engine.
4. The engine torque is considerably higher for ethanol as compared to
a petrol engine.

0.8

Power (kW) 0.6 Petrol Ethanol R c = 10.2

0.4

R = 8.2
c
0.2

Figure 7.2 Effect of speed on power
0 at different compression ratios.
1000 3000 5000 7000 9000
Speed (rpm)