Experimental investigation on the effects of nozzle-hole number on combustion and emission characteristics of ethanol/diesel dual-fuel engine

Since fuel reactivity stratification greatly influences the combustion process of dual-fuel engines and nozzle geometry directly affects the distribution of direct injected fuel, experiments were carried out to investigate the effects of nozzle-hole number on the combustion and emissions of dual-fuel engine. The experiments were performed on a single-cylinder diesel engine with port injection of ethanol and direct injection of diesel. There are four diesel injectors with 4, 5, 6 and 8 nozzle holes studied in this paper, while the total orifice areas and included spray angles of the injectors are kept the same. With reduced nozzle holes, the experimental results showed that both the in-cylinder peak pressure and PPRR (peak pressure rise rate) of ethanol/diesel dual-fuel combustion were decreased while with extended combustion durations. This is mainly because the number of high fuel reactivity regions was reduced with fewer diesel sprays, then the combustion of premixed ethanol was slowed down which consequently decreased the heat release rate. With reduced nozzle holes, the engine-out NOx emissions were decreased, and soot emissions were slightly increased while still maintained at quite low level. The UHC and CO emissions were slightly increased with reduced nozzle holes which resulted in lower combustion efficiency. However, the influences of nozzle-hole number on dual-fuel combustion were gradually decreased with advanced injection, which was mainly because of the enhanced diesel/air mixing. The experimental results indicated that dual-fuel combustion with reduced nozzle holes could achieve moderate heat release with lower PPRR.