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 NOX 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 NOX 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 NOX emissions below 200 ppm could be maintained with
certain operating conditions reaching NOX levels below 100
ppm.
