Momentum - September 2020 - 16

TODAY'S
ENGINEERING

THE IC FUTURE POINTS TO MORE
DOWNSIZING, LEAN MIXTURES
Three engineers from the front lines of
advanced internal-combustion (IC) engine
development affirmed that despite the
industry's public promotion of a battery
electric future for light-vehicle propulsion,
committed research and development
continues for IC. They said work is focused
on incremental enhancement to IC
efficiency and reduction in greenhousegas emissions, including oxides of
nitrogen (NOx). 
The engineers participated in a recent
webinar as part of the WCX Digital
Summit, a series of video presentations,
speeches, and webinars replacing the inperson programming planned for SAE's
April WCX 2020 conference that was
transformed because of the COVID-19
outbreak.
This panel focused on technologies that
have potential for improving the efficiency
of IC engines, specifically downsized
boosted gasoline engines with dilutemixture combustion and four-stroke, sparkignited boosted engines. Also addressed
was the potential for tailoring IC engines
as the centerpiece for more-sophisticated
hybrid powertrains-all within a framework
of "reasonable cost/benefit."

DOWNSIZING GETS
AGGRESSIVE
The engine downsizing movement has
been underway for more than a decade,
but Jeremie Dernotte, propulsion-systems
research engineer at General Motors,
prefers "aggressively downsized" to
describe his team's unique "disruptive
engine platform:" a 3-cylinder with two
4-stroke "power cylinders" with a total
displacement of 1.1 L and compression
ratio of 13.5:1. There is also an expander
cylinder that displaces 1.33 L.
In the SAE technical paper, "Downsized
Boosted Gasoline Engine with Exhaust
Compound and Dilute Advanced
Combustion" (paper number 2020-010795) that details the GM engine, its
exhaust-energy recovery configuration
is explained: "The exhaust-compounding
16 September 2020

2009_TE_15_16.indd 2

Image credit: General Motors

Layout of a spark-ignited, compression-ignition, exhaust-energy-recovering engine envisioned by
GM engineers.

is the main distinction of this engine
architecture, with the presence of an
additional piston-expander cylinder
connected to the power cylinder
via insulated transfer passages. The
exhaust gas from the firing cylinders is
transferred during its exhaust stroke into
the expander cylinder while this piston is
going down (expander expansion), thus
performing an additional expansion to
recover the exhaust gas enthalpy into
mechanical work at the crankshaft.
"As such," the paper continues, "the
expander behaves like a two-stroke
engine, repeating its expansion stroke
and exhaust stroke, switching the work
recovery from one power cylinder to the
other after every revolution.  A clutched,
high-efficiency supercharger is engaged
to achieve peak power with homogenous
stoichiometric combustion."
Moreover, the engine employs a
sophisticated valve-timing arrangement
to provide positive valve overlap (PVO)
timing and negative valve overlap (NVO)
to optimize the exploitation of the
expander cylinder's energy. This also
facilitates the dilute low-temperature
combustion - in this case, spark-ignited
homogenous-charge compressionignition (HCCI) - from which the engine

derives much of its fuel-efficiency
gain, while also enabling conventional
stoichiometric operation when the engine
is under high-load demand.
In the WCX Digital Summit
presentation, Dernotte said the engine's
novel exhaust-energy recovery design
contributes as much as 10% of its overall
efficiency improvement. And its advanced
lean-burn combustion is claimed to
deliver a brake-specific fuel consumption
(BFSC) gain of up to 38% compared with
a normally aspirated conventional engine
with a similar power rating.
He added that the goal of the research
is to make lean-burn combustion
practical for a larger range of engines
and vehicles. Dernotte added that
although control of NOx emissions is
the perpetual challenge for engineers of
lean-burn engines, his GM team's current
concept has been developed with the
intent of complying with all foreseeable
U.S. emissions limits.

By Bill Visnic, editorial director, SAE Mobility Media

MOMENTUM

8/19/20 9:26 AM



Momentum - September 2020

Table of Contents for the Digital Edition of Momentum - September 2020

Momentum - September 2020
Don’t worry students, you got this!
Benefits U
Formula SAE pivot puts focus on adaptability
U Calgary is MVP of UAVs at SAE AeroConnect Challenge
Avoiding burns in the SAE Supermileage ‘trial by fire’
Air domination
Teams from India on rise at Formula Hybrid
After 21 tries, Michigan Tech snowmobile team finally sleds to victory in 2020
Team from U Michigan takes all 3 titles in re-imagined Baja SAE competitions
Briefs
COMVEC 2020 preview
The IC future points to more downsizing, lean mixtures
SAE 101: Scholarships
Dossier: María Fernanda Castillo of VIKUA
Networking helps keep your options open
Momentum - September 2020 - Momentum - September 2020
Momentum - September 2020 - Cover2
Momentum - September 2020 - 1
Momentum - September 2020 - Don’t worry students, you got this!
Momentum - September 2020 - Benefits U
Momentum - September 2020 - Formula SAE pivot puts focus on adaptability
Momentum - September 2020 - 5
Momentum - September 2020 - U Calgary is MVP of UAVs at SAE AeroConnect Challenge
Momentum - September 2020 - Avoiding burns in the SAE Supermileage ‘trial by fire’
Momentum - September 2020 - Air domination
Momentum - September 2020 - 9
Momentum - September 2020 - Teams from India on rise at Formula Hybrid
Momentum - September 2020 - After 21 tries, Michigan Tech snowmobile team finally sleds to victory in 2020
Momentum - September 2020 - Team from U Michigan takes all 3 titles in re-imagined Baja SAE competitions
Momentum - September 2020 - 13
Momentum - September 2020 - Briefs
Momentum - September 2020 - COMVEC 2020 preview
Momentum - September 2020 - The IC future points to more downsizing, lean mixtures
Momentum - September 2020 - SAE 101: Scholarships
Momentum - September 2020 - Dossier: María Fernanda Castillo of VIKUA
Momentum - September 2020 - 19
Momentum - September 2020 - Networking helps keep your options open
Momentum - September 2020 - Cover3
Momentum - September 2020 - Cover4
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