Numerical Simulation of Marine Diesel Engine Combustion and Emissions Using Intake Air Humidification at the Different Injection Timing

ABSTRACT

The computational fluid dynamics (CFD) model was established for the marine diesel engine. The effects of intake air humidification (IAH) and the start of injection (SOI) timing on cylinder pressure and temperature were studied; the influence rules and mechanisms of NO_x and soot formation were analyzed. The results show that under the water-fuel mass ratio of 0.2 (WR0.2), the IAH contributed to the combustion reaction process, and the peak cylinder pressure increase slightly. As the IAH rate increases, the combustion reaction process was suppressed, and the cylinder pressure and temperature were both decreased. When the IAH rate was at WR2.0, the peak pressure dropped by 3.4% compared with it at the non-humidification (WR0). The concentration of OH groups, O, H and N radicals decreased with the IAH rate increase, especially that the concentration of N radical decline was most apparent. The NO_x emissions decreased by 78% at WR2.0, but the soot emissions increased by the decrease of the oxygen concentration in the high-temperature zone. It was found that the cylinder pressure and average temperature increased with the increasing of the SOI, but the rising range of peak average temperature decreased. When the SOI was at 12°CA BTDC, the indicated mean effective pressure is the same as with the WR0. Affected by the cylinder temperature and oxygen concentration, both the rising range of NO_x and the descent range of soot decreased. Due to the IAH, the oxygen concentration and temperature limited the rate of rapid oxidation of soot.

KEYWORDS:

• Intake air humidification
• NO_x
• soot
• the start of injection

Acknowledgments

The authors thank the financial support are as follows:

Natural Science Foundation Committee of China (No.51709163);

Shanghai Sailing Program (No.17YF1407400).

Additional information

Funding

This work was supported by the Natural Science Foundation Committee of China [No.51709163]; Shanghai Sailing Program [No.17YF1407400].