emulsion ratio, the ignition timing and peak pressure were
similar to those of the pure diesel, but the ignition timing and the
peak pressure variation ranges were greater than pure diesel. It
means that O2-doped intake air can advance in-cylinder ignition
timing, accelerate combustion speed and slightly increase the
maximum pressure whether under both low-load and high-load
conditions. Engine fueled with water emulsified diesel fuel can
reduce combustion temperature and prolong the ignition delay,
the higher the water emulsification ratio, the longer the ignition
delays. The ignition timing can be controlled within a certain
range by adjusting intake oxygen concentration and water
emulsification ratio.
3.5. The effect of water emulsion ratio and oxygen-enriched on NO
emission-BSFC distribution zone
From the previous discussions, it can be found that in the entire
range of 21%e24% intake oxygen concentration and 0%e30% water
emulsion ratio, there must be optimized combination of the water
emulsification ratio and intake oxygen concentration, which can
improve the Smoke-NO trade-off and also ensure the BSFC not
exceeding 5% of the original engine.
As shown in Fig. 3, by applying either water emulsion diesel fuel
or oxygen-enriched intake air, the smoke emission can be reduced
both lower than that of the original engine. Therefore, all the
combinations between 21% and 24% intake oxygen concentration
and 0%e30% water emulsion ratio can be classified as low smoke
emission zone. Overlapping Figs. 5 and 7 and removing the areas of
high BSFC (red area) and high NO emission (blue area) in the map of
combination of intake oxygen concentration and water emulsion
ratio, as shown in Fig. 11, the lower smoke-NO emission can be
realized in green area with BSFC not exceeding 5% of the original. In
Fig. 11a, at the work condition of 2000 rpm and 180 Nm torque, the
green areawas about 0%e20% water emulsion ratio and 21%e21.5%
intake oxygen concentration. And in Fig. 11b, at the operating
condition of 2000 rpm and 100% fuel throttle, the green area was
about 10%e15% water emulsion ratio and 10%e15% intake oxygen
concentration. In these ranges of water emulsion ratio combined
with intake oxygen concentration, the NO-Smoke emission can be
reduced to much lower than that of the original engine without
serious penalty in BSFC. From Fig. 11a and b, it also can be found
that the scopes of low smoke emission and low NO-BSFC areas in