Water Recovery from Gasoline Engine Exhaust for Water Injection

Water injection (WI) can improve gasoline engine performance and efficiency, and on-board water recovery technology could eliminate the need for customers to refill an on-board water reservoir. In this regard, the technical feasibility of exhaust water recovery (EWR) is described in this paper. Water injection testing was conducted at a full load condition (5000 rpm/18.1 bar BMEP) and a high load condition (3000 rpm/14.0 bar BMEP) on a turbocharged gasoline direction injection (GTDI) engine. Water recovery testing was conducted both after the exhaust gas recirculation (EGR) cooler and after the charge air cooler (CAC) at a high load (3000 rpm/14.0 bar BMEP), as well as a part load (2080 rpm/6.8 bar BMEP) condition, at temperatures ca. 10-15 °C below the dew point of the flow stream. Three types of water separation designs were tested: a passive cyclone separator (CS), a passive membrane separator (MEM), and an active separator (AS). Water injection and recovery amount was also simulated on three different drive cycles: FTP, WLTP and US06. The results showed that using water injection at full load reduced fuel enrichment requirements and reduced knock, yielding a 13% fuel economy improvement. Engine testing at high load condition showed that WI had a negligible effect on three-way catalyst (TWC) conversion efficiency under stoichiometric conditions. EWR was shown to be effective both post EGR cooler and post CAC. The CS and AS showed better performance than the MEM separator for water recovery. With the CS, up to ~100% condensate separation efficiency was achieved with very low pressure drop (~1 kPa). All the condensate samples collected with low sulfur fuel showed near neutral pH levels (6.5-8.5). From the appearance of the condensate samples, MEM-collected water had better quality than the CS and AS collected water. Water collected after the CAC showed better quality and lower pH than that collected downstream of the EGR cooler. Water recovered from post-TWC EGR showed better quality and higher pH than that collected from pre-TWC EGR. Water injection and collection simulations on three different drive cycles using GT-Drive showed that more water could be collected than was required for injection on FTP and WLTP drive cycles, while 40~70% of required water for injection could be collected on the US06 cycle.