Using Petroleum and Biomass-Derived Fuels in Duel-fuel Diesel Engines - Novel Combustion Concepts for Sustainable Energy Development - page 262

95% 98.5%

Fig. 19 HO 2 mass fraction contours at different crank angles for the 95 and 98.5 % syngas cases.
Black lines indicate ϕ contour ( ϕ = 0.16 - 3)

indicate signi flame propagation for the 98.5 % syngas case compared

to the 95 % syngas, since the gaseous equivalence ratios for the two cases are 0.7
and 0.17 (Table 3 ). In fact for the latter case, the

cantly faster fl

°
ATDC due to ultra lean conditions, and due to decreasing temperature and pressure
during the expansion stroke. Furthermore, the comparison of HO 2 contours for the
97 % methane (Fig. 17 ) and 98.5 % syngas cases indicates signi

fl flame gets extinguished at about 4

ame
propagation in syngas-air mixture than that in methane-air mixture. However, as
indicated in Table 3 , the thermal ef

cantly faster fl

ciency is noticeably lower for 98.5 % syngas
compared to that for 97 % methane. This is further discussed in the next section.
In summary, for certain operating conditions, the combustion process in syngas-
based dual-fuel engine may become nearly spontaneous, which can possibly lead to
knocking.

4.4 Dual-fuel Engine Performance and Emissions

Two of the performance parameters, i.e., IMEP and engine ef ciency computed

from pressure pro les (p-v diagram), are listed in Table 3 for all the ve cases. At

low load, the IMEP and engine ef ciency are lower for the dual-fuel (90 % methane

and 95 % syngas) cases compared to the single-fuel case, although they are slightly
higher for syngas compared to those for methane. The loss of performance at low