Effect of Various Diesel Injection Timings on Combustion and Emissions Characteristics as Different Compression Ratio and Bowl-shaped Pistons in a Heavy-duty Natural Gas/Diesel Dual-fuel Engine

The governing combustion regimes were slightly different between the neat diesel and dual-fuel combustion conditions. Neat diesel combustion was based on the auto-ignition of heterogeneous mixture of air and diesel fuel, whereas dual-fuel combustion mainly consisted of pre-mixed combustion and some local flame propagation. Therefore, the condition of the combustion chamber should be modified so as to adjust to the dual-fuel combustion instead of the neat diesel combustion. For this reason, dual-fuel combustion characteristics were investigated in this research under two different pistons(compression ratio and bowl shape together) as varying diesel injection timings. Under 1,200 rpm and low load condition, the diesel injection timing varied from TDC to advance limit(CoV of gIMEP < 5 %), which differed as natural gas fractions(60 % and 80 %).