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
ival
en
ce R
atio
“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 …