In this regard, dual fuel combustion has received renewed
interest due to its adaptability for alternative fuels and due to its
excellent performance and ultra-low emissions compared to conventional
diesel combustion. Dual fuel combustion is an approach
that utilizes a high cetane number fuel such as diesel, biodiesel to
ignite a low cetane number fuel such as alcohol [9]. Separate fuels
direct injection [10], dual fuel injector [11] and fumigation [12] are
used for diesel methanol dual fuel (DMDF) operation. However, the
use of two separate fuels injection system is more complicated
because it involves significant engine modifications as the methanol
injector is placed at the top of combustion chamber. Using only
one injector to inject two fuels in an engine is only reported by the
system developed by Westport Corp., called HPDI [11]. In this
regard, fumigation is favored currently, because it requires a minimum
of modification to the engine since methanol injectors is
placed at the intake manifold. However methanol fumigation is
unfavorable for cold start and low load operation. Based on the
method of fumigation, Yao et al. [13,14] developed a diesel/methanol
compound combustion (DMCC) system. Under DMCC mode, at
cold start and low speed conditions, the engine operates on diesel
alone to ensure cold starting capability and to avoid aldehydes production
under these conditions. At medium to high loads, the
engine operates on diesel methanol dual fuel (DMDF) mode, of
which methanol is fumigated into intake manifold and the homogeneous
air/methanol mixture is ignited by the diesel directly
injected [14]. The advantage of DMCC system is that there is no
cold start difficulty when the engine operates at dual fuel mode.
Furthermore, in case of lacking methanol fuel supply, this engine
still runs according to the diesel cycle by switching from dual fuel
mode to neat diesel mode [15]. Unlike natural gas dual fuel engine,
there is no simultaneous reduction of air supply [16]. Hence, the
compression pressure and the mean effective pressure of the
engine are not decreased and even boosted with methanol
fumigation.
In this regard, dual fuel combustion has received renewedinterest due to its adaptability for alternative fuels and due to itsexcellent performance and ultra-low emissions compared to conventionaldiesel combustion. Dual fuel combustion is an approachthat utilizes a high cetane number fuel such as diesel, biodiesel toignite a low cetane number fuel such as alcohol [9]. Separate fuelsdirect injection [10], dual fuel injector [11] and fumigation [12] areused for diesel methanol dual fuel (DMDF) operation. However, theuse of two separate fuels injection system is more complicatedbecause it involves significant engine modifications as the methanolinjector is placed at the top of combustion chamber. Using onlyone injector to inject two fuels in an engine is only reported by thesystem developed by Westport Corp., called HPDI [11]. In thisregard, fumigation is favored currently, because it requires a minimumof modification to the engine since methanol injectors isplaced at the intake manifold. However methanol fumigation isunfavorable for cold start and low load operation. Based on themethod of fumigation, Yao et al. [13,14] developed a diesel/methanolcompound combustion (DMCC) system. Under DMCC mode, atcold start and low speed conditions, the engine operates on dieselalone to ensure cold starting capability and to avoid aldehydes productionunder these conditions. At medium to high loads, theengine operates on diesel methanol dual fuel (DMDF) mode, ofwhich methanol is fumigated into intake manifold and the homogeneousair/methanol mixture is ignited by the diesel directlyinjected [14]. The advantage of DMCC system is that there is nocold start difficulty when the engine operates at dual fuel mode.Furthermore, in case of lacking methanol fuel supply, this enginestill runs according to the diesel cycle by switching from dual fuelmode to neat diesel mode [15]. Unlike natural gas dual fuel engine,there is no simultaneous reduction of air supply [16]. Hence, thecompression pressure and the mean effective pressure of theengine are not decreased and even boosted with methanolfumigation.
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