A PRAGMATIC APPROACH TO REDUCING

THE CO2 FOOTPRINT OF THE INTERNAL

COMBUSTION ENGINE

SYNERGISTICALLY INTEGRATING ADVANCED SPARK

IGNITION ENGINES AND FUTURE FUELS

Paul Najt

General Motors Global R&D

THE CO2 CHALLENGE

THE CO2 CHALLENGE

Source: EPA US Light-Duty Automotive Technology, Carbon

Dioxide Emissions and Fuel Economy Trends: 1975 Through 2014

Meeting future CO2 regulations while delivering vehicles that customers want

and can afford ……

MY

2014 V

ehic

les M

eeting C

O2 R

eg

<5% MY2014 vehicles in

the US meet MY2025

CO2 and all make use of

are advanced powertrains

…. will require the synergistic

integration of fuels and engine technologies

THE ENGINE CHALLENGE

To maximize engine efficiency we must focus on minimizing loss

mechanisms and maximizing work recovery …

Aggressively downsize to reduce parasitic losses

o Key enablers are advanced boost systems and increased knock

tolerance – more knock resistant fuels

Migrate to compression ratios between 13 & 14 to maximize work

extraction without incurring major parasitic losses

o Key enablers are variable valve actuation and increased knock

tolerance – more knock resistant fuels

Migrate to high levels of charge dilution to minimize heat losses and

maximize work extraction

o Key enablers are increased EGR tolerance and Lean, Low

Temperature Combustion – more reactive fuels

Maintaining modest peak pressure levels to avoid incurring major

parasitic losses

o Key enablers are homogeneous stoichiometric operation at WOT with

rated speed above 6000rpm

200

220

240

260

280

300

320

340

360

380

400

0 10 20 30 40 50 60 70 80 90 100

BS

FC

(g

/kW

-hr)

Torque (Nm)

1.4L Prod. Turbo

2.0L Prod. Nat. Asp.

Downsizing

THE ENGINE CHALLENGE

Downsizing is critical to enhancing vehicle level fuel economy and thus fuels that

maximize resistance to knock are critical -- enabling increased compression ratios and

more advanced combustion phasings at high loads – to maximizing the benefits

Engines scaled to 120kW

(equivalent vehicle level performance)

200

220

240

260

280

300

320

340

360

380

400

0 10 20 30 40 50 60 70 80 90 100

BS

FC

(g

/kW

-hr)

Torque (Nm)

1.4L Prod. Turbo

2.0L Prod. Nat. Asp.

1.35L G-LTC EngineDownsizing

Lean, Low

Temp Comb

THE ENGINE CHALLENGE

High levels of charge dilution and lean, low temperature combustion at low loads are

critical to enhancing vehicle level fuel economy and thus fuels with good low load

reactivity are critical – but, not at the expense of full load performance

Engines scaled to 120kW

(equivalent vehicle level performance)

200

220

240

260

280

300

320

340

360

380

400

0 10 20 30 40 50 60 70 80 90 100

BS

FC

(g

/kW

-hr)

Torque (Nm)

1.4L Prod. Turbo

2.0L Prod. Nat. Asp.

2.1L Delphi GDCI

1.35L G-LTC Engine

Upsizing

THE ENGINE CHALLENGE

At equal performance, GDCI-like engines that operate lean, LTC at full load degrade

specific output and vehicle level fuel economy --- to maximize fuel economy it is critical

to synergistically blend aggressive downsizing (stoichiometric operation at full power)

with lean, low temperature combustion at part load

GDCI Data SAE 2015-01-0834

Engines scaled to 120kW

(equivalent vehicle level performance)

GDCI Engine

THE FUELS CHALLENGE

To maximize SI Engine potential the fuel should have high knock

resistance at high loads and good reactivity at low loads, the fuel

should have the following properties

High knock resistance with high sensitivity

o High RON and High Sensitivity

Low variability across the marketplace

o RON, Sensitivity, T90, ………

Near-zero sulfur, < 10 ppm

Good low temperature catalyst reactivity

Low propensity to soot

We don’t need a new fuels, we need an improved gasoline with

high RON, high Sensitivity and low variability

THE FUELS CHALLENGE – SENSITIVITY

Ignitio

n D

ela

y

1/Temperature

Typical Low

Sensitivity Fuel

(e.g. 100 PRF)

Typical High

Sensitivity Fuel

(e.g. Ethanol)

Increasing Sensitivity

Increasing Reactivity

Compression Ignition

Increasing Sensitivity

Decreasing Reactivity

Knock Resistance

Sensitivity = RON-MON

High sensitivity fuels are relatively stable at low temperatures,

but react rapidly at high temperatures.

High

RON

Low

MON

Higher Temperature

More

Reactive

THE FUELS CHALLENGE – OCTANE INDEX

Octane Index (OI = RON – K*Sensitivity) is a good measure of fuel

performance when “K” is adjusted to the engine/combustion mode

“K” characterizes the temperature, pressure trajectory associated with a

specific engine/combustion mode

Gasoline

Spark

Ignition

(conventional)

Knock Resistance – high pressure, low

temperature condition

K is negative – Sensitivity increases

Octane Index and “degrades reactivity”

Gasoline

Low Temp

Combustion

(e.g. HCCI)

Compression Ignition – low pressure,

high temperature condition

K is positive – Sensitivity decreases

Octane Index and “increases reactivity”

THE FUELS CHALLENGE – KNOCK RESISTANCE

For high load SI Engine Knock Resistance a K value of -1 reflects

modern, high boost SI engine/combustion performance

Reference: Sarah Remmert et. al., Fuel Effects in a downsized, Highly

Boosted direct Injection Spark Ignition Engine, 23rd Aachen Colloquium

Automobile and Engine Technology 2014.

THE FUELS CHALLENGE – COMPRESSION IGNITION

y = 1.3116x - 93.045R2 = 0.9586

0

2

4

6

8

10

12

14

16

18

20

72 74 76 78 80 82 84 86

CA

50 @

NV

O =

130

Gasolines B&Ternary

Octane Index (K = 2)

For Lean, Low Temperature Compression Ignition a K value of 2

accurately predicts engine/combustion performance

THE FUELS CHALLENGEThe ideal fuel is a high RON, high Sensitivity alternative to regular grade gasoline

for both near-term Boosted SI Engines and long-term LTC/HCCI Engines

Need to minimize the impact of low sensitivity paraffinic fuels

THE PRAGMATIC APPROACH

The ideal engine synergistically integrates aggressive downsize boosting with

lean, low temperature combustion

The ideal engine builds on the downsize boosting mega-trend, operating with

homogeneous, stoichiometric combustion at high loads to maximize specific

output and minimize parasitic losses

The ideal engine introduces lean, low temperature combustion at low loads to

maximize vehicle level fuel economy by reducing heat losses and maximizing

work extraction

The ideal engine needs a fuel that has excellent knock resistance at high loads

and good autoignition reactivity at low loads

The ideal fuel has High RON, High Sensitivity and low variability to support the

synergistic integration of downsizing and lean, low temperature combustion

We do not need radical changes, we need to continue building on

existing engine trends and developing a better gasoline!