Influence of injection strategy in a high-efficiency hydrogen direct injection engine 2011-01-2001

Energy security and climate change are two of the main drivers for development of sustainable and renewable transportation solutions. Entities around the globe have been working on strategic plans to reduce energy consumption and curb greenhouse gas emissions. In this context hydrogen is frequently mentioned as the fuel and energy carrier of the future. The U.S. Department of Energy's (DOE's) FreedomCAR and Vehicle Technologies (FCVT) Program has identified hydrogen-powered internal combustion engine (ICE) vehicles as an important mid-term technology on the path to a large-scale hydrogen economy. DOE has set challenging goals for hydrogen internal combustion engines including 45% peak brake thermal efficiency (BTE).

This paper summarizes recent research engine test results employing hydrogen direct injection with different injection strategies. A dedicated research engine optimized for lean hydrogen operation with a compression ratio of 12.9:1 was built and fast-acting Piezo injectors are used for the test sequence. Turbocharged high-load conditions are analyzed at several engine speeds to provide a full spectrum of relevant engine results for achieving peak efficiencies. Three injector nozzle designs are experimentally tested for their ability to meet the 45% efficiency target and their implication on engine-out NO_X emissions. Complimentary to experimental work 3-D CFD simulation is employed to analyze the mixture formation process and predict the ability of newly designed nozzles to provide favorable charge stratification.

The result of this integrated approach is a combustion system that is capable of achieving high engine efficiencies while minimizing the NO_X emissions penalty. Peak indicated efficiencies of 46-47% were reached at full load conditions translating into peak brake thermal efficiencies of approx. 45%. At the same time engine-out NO_X emissions below 200 ppm could be maintained with certain operating conditions reaching NO_X levels below 100 ppm.