Investigation of Supercharging Strategies for PFI Hydrogen Engines 2010-01-0582
Hydrogen-fueled internal combustion engines (H₂ICEs) are an
affordable, practical and efficient technology to introduce the use
of hydrogen as an energy carrier. They are practical as they offer
fuel flexibility, furthermore the specific properties of hydrogen
(wide flammability limits, high flame speeds) enable a dedicated
H₂ICE to reach high efficiencies, bettering hydrocarbon-fueled ICEs
and approaching fuel cell efficiencies.
The easiest way to introduce H₂ICE vehicles is through
converting engines to bi-fuel operation by mounting a port fuel
injection (PFI) system for hydrogen. However, for naturally
aspirated engines this implies a large power penalty due to loss in
volumetric efficiency and occurrence of abnormal combustion.
The present paper reports measurements on a single-cylinder
hydrogen PFI engine equipped with an exhaust gas recirculation
(EGR) system and a supercharging set-up. The measurements were
aimed at increasing the power output to gasoline engine levels or
higher, while maximizing efficiency and minimizing emissions. Two
strategies were tested: one using stoichiometric mixtures, with or
without EGR, where a three-way catalyst (TWC) was relied upon for
aftertreatment of oxides of nitrogen (NOX); and a second one
using lean mixtures limiting engine-out NOX emissions so that
aftertreatment was not needed.
Test results are reported for varying supercharging pressure and
engine speed; it is shown that both strategies allow power outputs
exceeding gasoline levels. The brake thermal efficiencies for both
strategies are compared, to derive the best operating strategy as a
function of torque demand and engine speed. It can be concluded
that the lean burn supercharged strategy is best overall.