Influence of water injection on performance and emissions of a direct-injection hydrogen research engine

The application of hydrogen (H2) as an internal combustion (IC) engine fuel has been under investigation for several decades. The favorable physical properties of hydrogen make it an excellent alternative fuel for IC engines and hence it is widely regarded as the energy carrier of the future. Direct injection of hydrogen allows optimizing this potential as it provides multiple degrees of freedom to influence the in-cylinder combustion processes and consequently engine efficiency and exhaust emissions. At certain operating conditions the stratification associated with hydrogen direct injection (DI) leads to an efficiency improvement. However, it also results in higher emissions levels. This paper examines the effects of combining an advanced direct injection strategy with water injection for efficiency benefits and emissions reduction of a hydrogen fuelled DI spark ignition (SI) engine. Results from experimental investigations at various levels of water injection on engine efficiency, combustion duration and stability as well as NOx emissions are discussed. The results show that water injection into the intake manifold results in a decrease in the NOx emissions up to nearly 55% at a marginal loss in efficiency. © 2008 SAE International