CO emission of the producer gas engine was found to be higher
than the diesel engine for all loads and speeds, shown in Fig. 8.
Higher CO in the exhaust was due to insufficient oxygen for combustion.
CO emission from the producer gas engine was slightly
reduced with increasing load and speed, while CO from diesel
engine was stable when loads were in a range of 60–100%.
Reduction of CO emission at high load was due to more complete
combustion. Minimum CO emission of 0.34% and 0.01% were
achieved at full load. However, in comparison with gasoline operation,
CO emission of the producer gas engine was significantly less
than that from gasoline operation in a range of 2–6% [22]. Hydrocarbon
emissions of both engines were obtained in the range of
3.5–10 ppm and 3–8.5 ppm respectively, shown in Fig. 9. The average
HC of the producer gas engine was marginally higher than diesel
engine. The HC emissions of both engine was decreased with
increased engine loads and speeds. This may be due to efficiency
loss at low loads and incomplete combustion in the engine. However,
comparison against gasoline engine, the HC emissions of
the producer gas engine was lower, which HC emissions from gasoline
engine of about 330 ppm was reported [22]. Smoke density of
the producer gas engine was observed to be lower than the diesel
engine, shown in Fig. 9. Smoke density of the producer gas engine
started at 80–100% of load. The smoke density of the producer gas
engine was achieved 0–2%, while 1.5–12% for diesel engine was
recorded (see Fig. 10).