Water injection strategies to control gas temperatures in hydrogen–air internal combustion engines

The work explores different water injection strategies to be used to control the temperature of gases across the intake, combustion, and exhaust systems of a modeled high-boost and high-compression-ratio, turbocharged, direct injection, and jet ignition hydrogen internal combustion engine. Working lean of stoichiometry with λ = 2, the engine delivers peak brake efficiency η approaching 48% and peak BMEP close to 30 bar. Intake ports water injection (IPWI), direct water injection (DWI), and exhaust manifold water injection (EMWI) are studied. Water mass flow rates up to ~ 0.4–0.5 times the hydrogen mass flow rate are considered. IPWI is effective at reducing the air temperature in the intake port, and then the temperature of the charge within the cylinder of ~ 40 K. EMWI does not affect in-cylinder temperatures, but it is more effective at reducing the temperature of the exhaust gases at the inlet of the turbine, achieving up to ~ 100 K reductions. DWI does not affect the inlet port temperature but may be effective at reducing the in-cylinder temperatures the same as IPWI, or the temperature to the turbine the same as EMWI. At the adopted water mass flow rates, the three strategies have small effects on η and BMEP. Looking at these strategies from the design perspective rather than the gas temperature control perspective, IPWI remains the preferred strategy to use water, permitting higher boost pressure and compression ratios. Better results for DWI may be found working with higher in-cylinder temperatures working closer to stoichiometry and adopting super-turbocharging to collect the work from oversized turbines above the compressors' work to the crankshaft.