Influence of port water injection on the combustion characteristics and exhaust emissions in a spark-ignition direct-injection engine 2020-01-0294
It is well known that spark-ignition direct-injection (SIDI) gasoline engines have a huge advantage in fuel economy due to their good anti-knock performance compared to port fuel injection engines. However, higher particle number (PN) emissions associated with fuel impingement make the SIDI engines have additional difficulties to meet the upcoming China VI emission standards. In this study, the port water injection (PWI) techniques on a 1.0-L turbocharged, three cylinder, SIDI engine were investigated. PWI strategies were optimized to quantify port water injection as a means of mitigating the knock and improving the combustion performance by sweeping water-fuel mass ratios and PWI timing at different operating conditions.
Measurements indicate that regardless of engine load, PWI induced a worsening of the maximum in-cylinder pressure (P-Max) and cycle-to-cycle variations (IMEPN-COV ) , which mainly due to the eﬀects of water dilution and slower burning velocities. But by the advance of spark timing with knock mitigation, we find that the improvement of combustion phasing finally makes it possible to eliminate fuel enrichment, which bring the potential advantages on the fuel consumption. For the exhaust emissions, the PN and NOx emissions show a decreasing trend with water-fuel mass ratios increased due to increasing heat capacity of the mixture. However, the THC emissions increases on an average of 20% over the non-water injection. The reason is may be that more unburned fuel-air mixture will enter the gaps in the combustion chamber due to the increase P-Max. In addition, with the increase of engine load, the fuel economy brought by PWI is more obvious, indicating that PWI is more suitable for high load conditions. Finally, the potential of low temperature and dilution combustion caused by PWI on the engine combustion characteristics and emissions performance were revealed.
Yadong Fan, Tianbao Wu, Xuesong Li, Min Xu, David Hung