Comparison of Water Dilution Effects on Spark-Ignition Engine Performance and Emissions using Hydrous Fuel Blends and Discrete Water Injection

Modern water injection systems typically deliver water separately from the primary fuel system using a discrete injector either through the intake port or directly to the cylinder. Recently, however, water dilution strategies using fully hydrous fuel systems have been receiving increased attention. Hydrous fuels are water and liquid fuel blends that are fully mixed prior to delivery to the combustion system. Removing water from naturally hydrous fuels such as ethanol requires large amounts of energy; consequently, it is possible to combine water injection with more economical production by leaving some amount of water in the fuel. This paper compares experimentally the water dilution effects on the combustion and emissions characteristics and overall engine performance when delivering the water through either a hydrous fuel blend or discrete port water injection.

A 2.4L 4-cylinder NA GDI engine was used in experimental testing. The engine was controlled using an aftermarket ECU interfaced with OEM components and a laboratory-grade wide-band oxygen sensor for equivalence ratio quantification and feedback. The results indicated that for brake measurements the type of water addition affects combustion sufficiently enough to be measured and quantified. ISFC reduction ranged between 0.5 and 2% for water injection and 0.5 and 3% for hydrous fuel. Combustion stability tended to be not strongly affected or degraded by water addition. Combustion analysis demonstrated retarded combustion timings and reduced peak pressures of up to 8.5% for all water dilution cases with the largest reductions at the highest speed and load points. Emissions effects showed mixed results that depended on both speed and type of water addition.