Using Petroleum and Biomass-Derived Fuels in Duel-fuel Diesel Engines - Novel Combustion Concepts for Sustainable Energy Development - page 260

90% 97%

2°

4°

7°

9°

Fig. 17 HO 2 mass fraction contours at different crank angles for the 90 and 97 % methane cases.
Black lines indicate contours. Red line in these figures shows the fl flame propagation

ϕ

HRR pro le corresponding to diffusion combustion can be constructed based on

this observation and the overall HRR pro le. This is also shown in Fig. 16 b. The

diffusion combustion is estimated to occur between 0

° and 60 ° ATDC, during

which time CO 2 (cf. Fig. 16 a) and H 2 O attain their peak values.
As stated earlier, the methane pro les (Fig. 12 ) indicate the extinction of lean

combustion zone for the 90 % methane case. This is further con rmed by analyzing

the HO 2 contours presented in Fig. 17 for the two dual-fuel cases. For both cases, the
contours at 2

flame in the piston
bowl. For the 90 % methane case, however, the HO 2 contours at 7

° ATDC indicate the presence of a lean propagating fl

° and 9 ° ATDC

indicate that the fl flame is extinguished due to ultra lean conditions, with ϕ ≈ 0.05 - 0.1

ahead of the flame, and due to the fact that pressure and temperature decrease during

the expansion stroke. In contrast, the contours for the 97 % case indicate a lean
propagating

fl

0.5. Consequently, most of methane gets consumed
through lean premixed combustion for this case, while a signi

fl flame with

ϕ ≈

cant amount of

methane remains unreacted for the 90%case. This is further con rmed by themethane

pro les discussed earlier in the context of Fig. 12 . Note that a small amount of methane

remains unreacted for the 97 % case, but it is mostly con ned to the crevice and

boundary layer regions. These regions also contribute to UHC and CO emissions.