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), P-50-G(50) (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 P-50-G(50). There is a small benefit to BSFC under a low water-fuel mass ratio (Rwf). 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, P-50-G(50) and PFI, respectively. As WI timing (tWI) postpones to around -30 degrees 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 (Pmax) and combustion phasing is less affected by WI temperature (TWI) compared to the effects of Rwf 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.

Automated summary

Global warming is closely related to CO2 emissions, and OFC technology is promising to help reduce CO2 emissions. This study investigates the effects of WI strategies on OFC characteristics in dual-injection SI engines, showing that appropriate WI strategies are beneficial to OFC combustion, but the benefit in fuel economy is limited.