The Outlook for Transport Fuels and GCI (Gasoline Compression

Ignition) Engines

Gautam Kalghatgi

Saudi Aramco

Outline of the talk

• Outlook for Transport Fuels

• Gasoline Compression Ignition (GCI)

• Fuel properties and GCI

• Possible long-term fuels scenario

World Transport Energy

• Transport is essentially driven by liquid fuels – high energy density, ease of transport and storage, extensive infrastructure

• ~95% of transport energy supplied by petroleum

• Demand in 2035 around 35% higher compared to today – mostly because of growth in non-OECD countries

• Even in 2040, ~90% of transport energy from petroleum

• Plenty of oil will be available

U.S. EIA (Energy Information Admin.)

ExxonMobil 2012 Energy Outlook, WEC

BP energy Outlook 2030, Jan 2012, IEA

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Current Fuels for IC Engines

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Gasoline

Diesel

Gasoline and diesel are complex mixtures of hydrocarbons –

Primary fuel property is the autoignition quality – Gasolines are

resistant to autoignition to avoid knock (measured by octane

numbers, RON and MON)

Diesel fuels are prone to autoignition (measured by Cetane

Number)

Diesel fuels are also heavier and less volatile

• Jet fuel is the other important transport fuel

• Naphtha is the product from the first distillation of crude

Transport Energy Demand Increase Skewed Heavily

Towards Commercial Sector • Passenger Car Sector – a) future average car will be smaller/lighter

and drive fewer miles compared to today b) larger scope for

efficiency improvements e.g. hybridisation

• Very significant investments in refineries will be needed on

current technology trajectory

• Significant number of future CI engines (especially heavy

duty) will have to move from conventional diesel fuel to

alternatives such as natural gas, GTL, light fractions

WEC, World Energy

Council. Freeway

Scenario.

ExxonMobil 2012

Energy Outlook ….

Engine Development Trends and

Gasoline Compression Ignition (GCI)

• Engine Development Trends

SI Engines : Improve fuel economy – downsizing and

turbocharging.

• Knock and fuel anti-knock quality become important –

high RON/low MON fuels.

• Cost increase if high performance is to be maintained

CI Engines: Reduce soot and NOx.

• High engine/after-treatment cost with existing diesel fuel

• Efficiency might be compromised

Hybridization:

• Cost increase

• Effective in low-duty urban cycles. Currently possible on

small vehicles

• Very difficult to implement on heavy-duty commercial

transport

High efficiency, low emissions and affordable

Premixed Compression Ignition (PCI)

• NOx can be controlled by EGR

which brings down combustion

temperature

• Increasing EGR reduces soot

oxidation and increases engine-out

soot

• Soot formation should be avoided

• Soot and NOx emissions standards getting more stringent

• Final fuel injection must be completed sufficiently before

combustion starts to avoid soot-forming equivalence ratios – Φ

< 2. Premixed Compression Ignition, PCI

• Advanced diesel engines are expensive and complicated

because they are trying to achieve PCI while using

conventional diesel fuel (DCN > 40)

PCI much easier with fuels with high ignition delay

i.e. “Gasoline” CI (GCI)

Equ

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ce R

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“Premixed-enough” CI

• Fuel/air must not be fully pre-mixed unlike in HCCI

• Allows in-cycle control over combustion phasing

• At low loads, with high ignition delay fuels, combustion occurs

by auto-ignition in lean packets – zero smoke, low NOx and low

noise but high HC and CO

• Low injection pressures help . Perhaps larger hole size.

• At high loads, multiple injection strategies help alleviate high

pressure-rise rates and noise

With GCI, efficiency at least as good as with diesel, much lower

injection pressures needed and after-treatment focus shifts to HC

and CO control rather than NOx and soot control

Ideal fuel is “low-quality” gasoline

Fuel Properties and Gasoline

Compression Ignition (GCI)

Fuel Effects – volatility, composition, ignition delay

Fuel Aromatic Isooct

n-

hep tolu density

RON MON DCN % vol vol% vol% vol% g/cc

PRF 84 84 84 0 84 16 0.682

TRF 84 84.5 74.5 65 0 35 65 0.785

TRF 82 82.1 78.1 26 50 24 26 0.723

n-Hept 0 0 55 0 0 100 0 0.632

ULG 72 72.9 68.4 19 0.715

ULG 78 78.5 73 23 0.726

ULG 84 84.1 78 26.5 0.736

ULG 91 90.7 81.8 29.8 0.731

D4 22.5 75.3 0.865

D1 56 25.2 0.833

B.P.s of n-hept, isooctane, toluene – 98 C, 99 C 110 C

SAE 2009-01-1964, SAE 2010-01-0607, THIESEL 2010, IJER (2011) vol

12(5), p452.

Volatility/ Ignition Delay

If two fuels match

for combustion

phasing, they have

similar NOx, CO,

smoke and to some

extent HC emissions

for PCI

Fuel D4 with 75% aromatics gives very low smoke like TRF 84 and

91 RON gasoline with very different volatility

Combustion phasing and fuel Octane Index 1200 RPM, 4 bar IMEP, 650 bar inj, 1.1 bar intake, no EGR, CA50 = 11 CAD

OI = (1- K) RON + KMON If two fuels have the same RON and MON, they will have the same

OI and hence the same combustion phasing.

Then in PCI combustion, they will have comparable emissions (IJER,

2011, vol 12)

Hence a good surrogate for PCI is a toluene reference fuel with

the same RON and MON as the target fuel

13

“Optimum” Fuel

Optimum RON between 70 and 85. CN < 25 to see real

benefits. Low volatility not required if ignition delay is

high enough.

•Volatility will still play a role in mixing – wider volatility range

might be beneficial by enabling more stratification.

Won et al. (J Auto 2011, 2012) – [10% diesel + 90% gasoline]

allowed PCI operation over a wider speed/load range than a

gasoline of the same RON and MON

• Initially GCI will have to use available fuels either in RCCI or as

mixture of diesel and gasoline.

Gasoline Compression Ignition (GCI)

Efficiency High

Co

st

High Diesel

SI Engine GCI

Low injection Pressure,

CO/HC vs NOx/ Soot after-treatment

• GCI enables high efficiency, low emissions, low

cost engines using less processed fuels

• Opens up a path to mitigate expected demand

imbalance between light and heavy fuels.

“Low-quality”

Gasoline

“Low-quality” Gasoline – RON between 70 and 85, no strict volatility requirement

GCI – Developing fuel/engine systems

Use existing fuels and alter engines

• GDCI from Delphi - use market gasoline, re-design SI engine

(CR, injection system, combustion chamber...) to run in CI

mode. Significantly improved efficiency compared to SI

operation.

• RCCI – Use market gasoline and diesel fuel, re-design injection

strategy of diesel engine. Low NOx/ low soot and high

efficiency

• Use gasoline/diesel fuel mixtures in GDCI?

Essential enabling/transition technologies. But would not be

sustainable if we can get the benefits of GCI with less processed

fuels.

Use existing technology with less processed/enabling fuels

• SAE 2013-01-0267, Chang.et al (Saudi Aramco/FEV). Use

heavy naphtha with DCN of 38 (instead of 52+ DCN European

diesel) in a vehicle to achieve Euro 6 emissions targets without

compromising driveability and efficiency.

Also Lund

GCI – Improving the efficiency of a SI engine by running it in CI mode using naphtha

SAE 2012-01-0677, Chang et al. (Saudi Aramco)

• Single – cylinder DISI research engine with CR of 12. Maximum

fuel injection pressure of 150 bar

• Heavy naphtha ( ~60 RON/ 40 DCN) enabled the engine to be

run in CI mode at idle + 5 other steady state conditions covering

the FTP 75 cycle.

• 19% lower fuel consumption on FTP 75 cycle compared to

running the engine in SI mode on 91 RON gasoline.

• At low loads, fuel efficiency improvement is much larger (e.g.,

50% at idle)

We have now increased the CR to 14 and optimized the piston-

bowl shape. Using light naphtha (~66 RON), 26% lower fuel

consumption compared to running the engine in SI mode on 91

RON gasoline. (To be published)

Naphtha is an example of “less processed” fuel. It is the product in the boiling

range between 30ºC and 200ºC of the initial distillation of crude oil

Future CI engines should move away from using conventional diesel fuel

Engine High Eff,

affordable

Demand imbalance

Fuel Less

processed

GCI

• In the short term diesel engines

will continue to use diesel fuels –

OEMs have too much invested in

existing diesel technology (Could

countries like China where this is

not the case be more receptive to

GCI?)

• Development work needed – starting, optimisation of

injectors and injector strategy, transients, sufficient boost

pressures at high EGR levels, lower temperature

oxidation catalysts …

A Possible Long-term Fuels Scenario

~ 40% high efficiency SI engines – need high RON and low MON

fuels. Ethanol will play a role (May be methanol even?)

• ~ 60% GCI engines running on 70-85 RON, wide volatility range

fuel. Heavier oil fractions need to be cracked to bring them in the

diesel boiling range with much less upgrading required in terms of

octane.

• Common fuel components for both SI and CI engines – fuel

blending becomes more flexible

•Current bio-diesels with cetane in the 50s will have little

relevance

•Very high cetane of gas-to-liquids (GTL) diesel has no advantage

• During the transition, GCI will have to run with existing gasoline

and diesel fuels e.g. 10% diesel blends or RCCI. Both will use

90% gasoline and help mitigate the demand mismatch that is

expected otherwise.

Conclusions The best option for (long-term) future high-efficiency CI engines –

• Fuel- Low Octane (70-85 RON, DCN < ~22), no stringent

requirement on volatility. “Less processed” fuel. Will help

mitigate demand imbalance between diesel and gasoline that is

otherwise expected.

• Engine – Low injection pressures (< 500 bar), perhaps bigger

injector holes. After treatment focus on HC/CO control rather

than NOx and soot. A simpler and cheaper diesel engine

• In the short term diesel engines will continue to use diesel fuels

– OEMs have too much invested in existing diesel technology

(Could countries like China where this is not the case be more

receptive to GCI?)

• Development work needed – starting, optimisation of injectors

and injector strategy, transients, sufficient boost pressures at

high EGR levels, lower temperature oxidation catalysts …