Effects of Water Injection Strategies on Oxy-Fuel Combustion Characteristics of a Dual-Injection Spark Ignition Engine

Currently, global warming has been a serious issue, which is closely related to anthropogenic 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 (${\theta }_F$) is significantly prolonged, and the spark timing is obviously advanced. Combustion duration (${\theta }_C$) 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 ($R_{wf}$). However, with the further increase of $R_{wf}$ 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 ($t_{WI}$) postpones to around −30 °CA under the conditions of $R_{wf}$ ≥ 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 ($P_{max}$) and combustion phasing is less affected by WI temperature ($T_{WI}$) compared to the effects of $R_{wf}$ or $t_{WI}$. BSFC just has a small decline with the increase of $T_{WI}$ 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. View Full-Text