In order to achieve the targets for hydrogen engines set by the U.S. Department of Energy (DOE) - a brake thermal efficiency of 45% and nitrogen oxide (NOx) emissions below 0.07 g/mi - while maintaining the same power density as comparable gasoline engines, researchers need to investigate advanced mixture formation and combustion strategies for hydrogen internal combustion engines.
Hydrogen direct injection is a very promising approach to meeting DOE targets; however, there are several challenges to be overcome in order to establish this technology as a viable pathway toward a sustainable hydrogen infrastructure.
This paper describes the use of endoscopic imaging as a diagnostic tool that allows further insight into the processes that occur during hydrogen combustion. It also addresses recent progress in the development of advanced direct-injected hydrogen internal combustion engine concepts.
Our paper characterizes the hydrogen combustion behavior in a single-cylinder research engine and provides an analysis of the results of hydrogen direct-injection operation. Unlike conventional combustion analysis, which employs pressure traces and derived information (e.g., rate of heat release), the combustion characterization in this study was done by using an ultraviolet (UV)-transmitting endoscope in combination with an intensified charge-coupled device (ICCD) camera. By using this technique, we were able to obtain a two-dimensional optical signature of hydrogen combustion, even at high engine speeds and loads. Analysis of the optical information allowed us to draw conclusions about the mixture homogeneity and possible stratification effects for different injection strategies.
Finally, the paper provides a discussion of the effects of start-of-injection and injector nozzle designs on engine efficiency and emissions during hydrogen direct injection and evaluates the pros and cons of the endoscopic technique.