Truck & Off-Highway Engineering - December 2024 - 13

POWERTRAIN FEATURE
" We've significantly lowered NOx
more than any other program or
engine that's out there. "
- Ryan Williams, Southwest Research Institute
One of the advantages of the SuperTurbo is that the turbo compounding boost over
the full cycle of the engine cancels out the parasitic losses from the supercharger.
SuperTurbo provided one of its combination supercharger/
turbocharger units for the demonstrator truck.
to redesign things and rethink things for DI. "
The aggressive timeline for the project was a major
limitation. " We wanted to take available hardware and
we had a very short timeframe, about 18 months from
start to finish, " Williams said. " So we didn't have time
to go fully redesign the cylinder head to consider DI. "
Sporadic spark
As is the case with any prototype vehicle, there were a
few stumbling blocks along the way to making the
SwRI demonstrator work as intended. One of those
challenges was on the ignition side. " We started with
the natural gas version of the X15 engine because it
already had a spark plug, which is beneficial for hydrogen.
But the rest of the ignition system is fairly unique
for this engine, " Williams said.
" Usually, when you're burning a hydrocarbon fuel,
you end up with a lot of charged ions that are the byproducts
of combustion and they sit there in the gap of
the plug. So even after your spark is extinguished, you
have these ions in there and you'll still have some flow
of current through the gap. But with hydrogen combustion,
we don't get that, " he explained. " It's a very abrupt
end. So rather than a gradual bleed down of the charge
on the coil, we have some residual charge that stayed
there. And then when we come around to the next
combustion cycle, the pressure drops and we're adding
TRUCK & OFF-HIGHWAY ENGINEERING
new fuel and the dielectric properties of the hydrogen.
" Once those ions get into your spark gap, they're ideal for initiating
another spark because we've got that residual charge on the coil, "
Williams continued. " So we would get these random spark events
during intake when the valve is open. It showed up as a misfire and it
was really baffling to us because the engine would just stumble and
be misfiring. But the reason that it's misfiring is because you've consumed
all the fuel that was meant to go into the cylinder while it was
still in the intake manifold. "
The solution to the issue came from previous research that SwRI
had conducted 20 years ago. " We looked at just about everything we
could on the engine itself, " he said. " And we ended up going back
and finding a paper that was written by SwRI around 2003 that talked
about this exact phenomenon.
" What was happening is called 'ghost spark,' which is when you
get random spark plug discharges that you didn't plan for, " he explained.
" To solve the issue, we tapped one of our consortium members
(SEM) who provided a capacitive discharge ignition system.
That system charges and full discharges on every cycle, which therefore
eliminated our issue with residual charging when using traditional
inductive coils. "
The future is now
More than any time in the last century, investment in alternative propulsion
systems is producing results that can be put into use today.
While there will always be growing pains, the collective that came
together to create SwRI's H2 demonstrator have shown that the
knowledge and tools exist to make this technology both commercially
and economically viable.
December 2024 13
BOTH IMAGES: SUPERTURBO
Truck & Off-Highway Engineering - December 2024

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