Using Petroleum and Biomass-Derived Fuels in Duel-fuel Diesel Engines - Novel Combustion Concepts for Sustainable Energy Development - page 263

load can be attributed to the incomplete combustion of gaseous fuel as discussed
earlier. Thus, the use of gaseous fuels at low loads may adversely affect the engine
performance and would require the optimization of other parameters, such as EGR
and injection timing for the liquid fuel. In contrast, at high load (97 % methane and
98.5 % syngas), both methane and syngas are almost completely consumed through
lean premixed combustion. Consequently for methane, the engine performance can
be maintained or even enhanced with dual-fuel operation. However, for 98.5 %
syngas, once the mixture is ignited, it is followed by nearly spontaneous com-
bustion, with the result that the CA50 is

− 0.4 ° ATDC for this case. Consequently,

the work output, IMEP, and engine ef cantly reduced with syngas

compared to those with methane and with single fuel (n-heptane).
The effect of gaseous fuel on dual-fuel engine emissions is summarized in
Table 3 , which lists the speci

ciency are signi

c soot, NO x , UHC, and CO emission values (mg/

kwh) for the five cases at EVO (exhaust valve opening at 116 ° ATDC). Results

indicate that with dual-fuel operation, the soot emission is signi cantly reduced at

all loads, while the NO x emission is increased. Moreover, the reduction in soot
becomes more pronounced with syngas compared to that with methane at both low
and high loads. In contrast, there is greater increase in NO x emission with syngas
than that with methane. The UHC emission is essentially eliminated with dual-fuel
operation using syngas. However, the UHC and CO emission can signi cantly

increase with methane at low load due to its incomplete combustion.

5 Summary and Conclusions

There is worldwide interest in developing renewable energy sources in a sustainable
manner. Syngas and biogas offer signi cant potential in this context. These fuels

can be produced from a variety of feedstock using different conversion methods and
offer great flexibility with regard to their utilization in transportation and power

generation systems. This chapter provides an overview of research dealing with the
combustion and emissions of these fuels, both as stand-alone fuels or by blending
with petroleum fuels. Conversion methods for producing these fuels from different
biomass sources are also brie

fl

y reviewed.
There are notable differences between the combustion characteristics of these
two fuels and those of hydrocarbon fuels. While the syngas composition can vary
widely, it generally has lower heating value, lower density, higher mass diffusivity,
higher

fl

flammability limits. Its combustion leads to almost
zero soot emission, although NO x emission may be a concern depending upon its
composition and operating temperatures. Similarly, biogas has lower heating value
compared to hydrocarbon fuels, and its ignition and combustion characteristics can
vary noticeably depending upon its composition. While there have been few studies
focusing directly on biogas combustion, there is extensive literature on methane
combustion, including ignition, extinction,

fl flame speeds, and wider fl

flame speeds, cel-
lular instabilities, and emissions. Results from many of these studies can be readily

fl flammability limits, fl