Effects of water injection strategies on oxy-fuel combustion characteristics of a dual-injection spark ignition engine

Abstract

Currently, global warming has been a serious issue, which is closely related to anthro-pogenic emission of Greenhouse Gas (GHG) in the atmosphere, particularly Carbon Dioxide (CO2 ). To help achieve carbon neutrality by decreasing CO2 emissions, Oxy-Fuel Combustion (OFC) technology is becoming a hot topic in recent years. However, few findings have been reported about the implementation of OFC in dual-injection Spark Ignition (SI) engines. This work numerically explores the effects of Water Injection (WI) strategies on OFC characteristics in a practical dual-injection engine, including GDI (only using GDI), P50-G50 (50% PFI and 50% GDI) and PFI (only using PFI). The findings will help build a conceptual and theoretical foundation for the implementation of OFC technology in dual-injection SI engines, as well as exploring a solution to increase engine efficiency. The results show that compared to Conventional Air Combustion (CAC), there is a significant increase in BSFC under OFC. Ignition delay (θF ) is significantly prolonged, and the spark timing is obviously advanced. Combustion duration (θC ) of PFI is a bit shorter than that of GDI and P50-G50 . There is a small benefit to BSFC under a low water-fuel mass ratio (Rw f ). However, with the further increase of Rw f from 0.2 to 0.9, there is an increment of 4.29%, 3.6% and 3.77% in BSFC for GDI, P50-G50 and PFI, respectively. As WI timing (tWI ) postpones to around −30◦CA under the conditions of Rw f ≥ 0.8, BSFC has a sharp decrease of more than 6 g/kWh, and this decline is more evident under GDI injection strategy. The variation of maximum cylinder pressure (Pmax ) and combustion phasing is less affected by WI temperature (TWI ) compared to the effects of Rw f or tWI . BSFC just has a small decline with the increase of TWI from 298 K to 368 K regardless of the injection strategy. Consequently, appropriate WI strategies are beneficial to OFC combustion in a dual-injection SI engine, but the benefit in fuel economy is limited.