Effect of syngas composition on combustion and exhaust emission characteristics in a dual-fuel engine operated in PREMIER combustion mode
Researchers at Okayama University (Japan) found that conventional combustion in a pilot-ignited, supercharged duel-fuel engine powered with different types of syngas at various equivalence ratios can be transformed into combustion with two-stage heat release. These researchers have investigated this mode of combustion—PREmixed Mixture Ignition in the End-gas Region (PREMIER)—in previous studies with natural gas.
PREMIER combustion begins as premixed flame propagation. Because of mixture autoignition in the end-gas region ahead of the propagating flame front, a transition occurs resulting in a rapid increase in the heat release rate.
It was determined that the mass of fuel burned during the second stage affected the rate of maximum pressure rise. As the fuel mass fraction burned during the second stage increased, the rate of maximum pressure rise also increased, with a gradual decrease in the delay between the first increase in the heat release rate following pilot fuel injection and the point when the transition to the second stage occurred. The H2 and CO2 content of syngas affected the engine performance and emissions.
Increased H2 content led to higher combustion temperatures and efficiency, lower CO and HC emissions, but higher NOx emissions. Increased CO2 content influenced performance and emissions only when it reached a certain level. In the most recent studies, the mean combustion temperature, indicated thermal efficiency, and NOx emissions decreased only when the CO2 content of the syngas increased to 34%.
PREMIER combustion did not have a major effect on engine cycle-to-cycle variation, they found. The coefficient of variation of the indicated mean effective pressure (COVIMEP) was less than 4% for all types of fuel at various equivalence ratios, indicating that the combustion was within the stability range for engine operation.
The researchers are presenting a paper on PREMIER at the upcoming 2011 JSAE/SAE International Powertrains, Fuels & Lubricants meeting in Kyoto at the end of this month.
Ulugbek Azimov, Eiji Tomita, Nobuyuki Kawahara, Yuji Harada (2011) Effect of syngas composition on combustion and exhaust emission characteristics in a pilot-ignited dual-fuel engine operated in PREMIER combustion mode. International Journal of Hydrogen Energy, In Press doi: 10.1016/j.ijhydene.2011.04.192
Ulugbek Azimov, Eiji Tomita, Yuji Harada, Nobuyuki Kawahara (2011) PREMIER (Premixed Mixture Ignition in the End-gas Region) combustion in a natural gas dual-fuel CI engine: Operating range and exhaust emissions. International Journal of Engine Research in press.